CA2025713C - Pressure-tube type heavy-water moderated nuclear reactor - Google Patents
Pressure-tube type heavy-water moderated nuclear reactorInfo
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- CA2025713C CA2025713C CA002025713A CA2025713A CA2025713C CA 2025713 C CA2025713 C CA 2025713C CA 002025713 A CA002025713 A CA 002025713A CA 2025713 A CA2025713 A CA 2025713A CA 2025713 C CA2025713 C CA 2025713C
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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Abstract
A pressure tube type nuclear reactor arranged in such a manner that pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes disposed in a calandria tank which contains heavy water, wherein the pressure tubes are arranged so as to form an equilateral triangular lattice configuration and/or a member, which replaces heavy water positioned around the calandria tube, is positioned around the calandria tube. Therefore, the volume ratio of nuclear fuel to heavy water can be made a proper value with which the coolant void reactivity coefficient becomes closer to negative values so that the self-control performance of the pressure tube type nuclear reactor is improved.
Description
CA 0202~713 1998-02-11 .~
PRESSURE-TUBE TYPE HEAVY-WATER MODERATED NUCLEAR REACTOR
The present invention relates to a pressure tube type nuclear reactor which uses heavy water as the neutron moderator, and, more particularly, to an improvement in the reactivity coefficient which is a critical factor when controlling the operation of a nuclear reactor.
The structure of a conventional tube type nuclear reactor which uses heavy water as the neutron moderator and uses light water as the coolant will be described.
A plurality of calandria tubes are inserted into a calandria tank which contains heavy water. A
pressure tube is inserted into each of the calandria tubes, the pressure tube accommodating sealed nuclear fuel. As a result, nuclear reaction heat is supplied from the nuclear fuel to the light water which passes through the pressure tube and serves as the coolant.
Thus, heated light water is taken out as hot and high pressure steam. The pressure tubes for the pressure tube type nuclear reactor are, for example as disclosed in Japanese Patent Laid-Open No. 55-94190, disposed so as to form a square lattice configuration. In order to improve the control performance of the core of the nuclear reactor of the type described above, a variety of structures have been disclosed as follows:
(1) A structure disclosed in Japanese Patent Laid-Open No. 58-34386 and arranged in such a manner that the pressure tubes are, as the basic configuration, arranged so as to form a square lattice configuration.
The intervals between the lattices of the pressure tubes, in which both a control rod and instrumentation guide tubes are not provided, are narrowed.
PRESSURE-TUBE TYPE HEAVY-WATER MODERATED NUCLEAR REACTOR
The present invention relates to a pressure tube type nuclear reactor which uses heavy water as the neutron moderator, and, more particularly, to an improvement in the reactivity coefficient which is a critical factor when controlling the operation of a nuclear reactor.
The structure of a conventional tube type nuclear reactor which uses heavy water as the neutron moderator and uses light water as the coolant will be described.
A plurality of calandria tubes are inserted into a calandria tank which contains heavy water. A
pressure tube is inserted into each of the calandria tubes, the pressure tube accommodating sealed nuclear fuel. As a result, nuclear reaction heat is supplied from the nuclear fuel to the light water which passes through the pressure tube and serves as the coolant.
Thus, heated light water is taken out as hot and high pressure steam. The pressure tubes for the pressure tube type nuclear reactor are, for example as disclosed in Japanese Patent Laid-Open No. 55-94190, disposed so as to form a square lattice configuration. In order to improve the control performance of the core of the nuclear reactor of the type described above, a variety of structures have been disclosed as follows:
(1) A structure disclosed in Japanese Patent Laid-Open No. 58-34386 and arranged in such a manner that the pressure tubes are, as the basic configuration, arranged so as to form a square lattice configuration.
The intervals between the lattices of the pressure tubes, in which both a control rod and instrumentation guide tubes are not provided, are narrowed.
(2) A structure disclosed in Japanese Patent Laid-Open No. 49-103091 and arranged in such a manner that a carbon rod is disposed in the heavy water moderator in the calandria tube.
(3) A structure disclosed in Japanese Patent Laid-Open No. 61-26891 and arranged in such a manner that the pressure tubes and the heavy water tubes are alternately disposed.
(4) A structure disclosed in Japanese Patent Laid-Open No. 52-61697 and arranged in such a manner that a water sealing rod is inserted into the pressure tube.
(5) A structure disclosed in Japanese Patent Laid-Open No. 52-100073 and arranged in such a manner that the outer diameter of the calandria tube at the central portion of the core is arranged to be larger than that at other portions.
In the conventional pressure tube type nuclear reactor in which the pressure tubes are arranged so as to form a square lattice configuration, the pressure tubes and the calandria tubes are inserted into the calandria tank. Therefore, if the interval between the formed CA 0202~713 1998-02-11 lattices of the pressure tubes is narrowed, the pitch of through holes formed in the surface of the calandria tank is also narrowed, causing the strength of the calandria tank to be deteriorated. Therefore, it has been difficult for the interval between the disposed lattices of the pressure tubes to be narrowed. If the interval between the disposed lattices of the pressure tubes is widened, the ratio of heavy water to nuclear fuel is raised. The pressure tube type nuclear reactor of the type described above tends to show a large positive void reactivity, causing the self-control performance of the nuclear reactor to become unsatisfactory.
In order to overcome the above-described problem, the above-described structures (1) to (5) have been disclosed. However, according to the structure (1), the pitch of the positions of the pressure tubes become non-uniform and complicated. Therefore, the evaluation of the performance of the core and operational control become unsatisfactory. ~urthermore, since the pitch of the positions of the pressure tubes is partially narrowed, the strength of the calandria tank at the position at which the pressure tube passes through may be partially deteriorated. In order to overcome the above-described problem, the size of the calandria tank must be enlarged. According to the structure (2), heavy water is replaced by carbon rods, in part. However, since the carbon rod is a relatively large neutron-absorber, the neutron economy becomes deteriorated. In addition, since CA 0202~713 1998-02-11 the carbon rods are disposed simply in parallel and among the pressure tubes, spaces in which the carbon rods are provided and spaces around the carbon rods must be provided, causing the overall size of the calandria tank to be enlarged. According to the structure (3), since the heavy water tubes are disposed simply in parallel to the pressure tubes, similar to the structure (2), the size of the calandria tank becomes too large. According to the structure (4), the fuel pins in the pressure tubes are in part replaced by the water sealing rods in the pressure tubes. Therefore, the quantity of the fuel is reduced. In order to compensate for the reduced space for the fuel, the size of the pressure tube for accommodating the fuel and the calandria tank for accommodating the pressure tubes are enlarged excessively. According to the structure (5), the diameter of the calandria tube at its intermediate portion is arranged to be larger than that at other portions. Therefore, the diameter of the hole formed in the calandria tank for the purpose of inserting the calandria tube is necessarily enlarged. As a result, the interval of the holes must be enlarged for the purpose of securing the strength of the calandria tank. Therefore, the size of the calandria tank becomes too large.
When the size of the calandria tank becomes too large, the quantity of heavy water to be contained therein becomes too large or a satisfactory effect of reducing the quantity of heavy water cannot be obtained.
CA 0202~713 1998-02-11 .
Therefore, the improvement in the self-control performance of the nuclear reactor by reducing the volume ratio of heavy water to fuel cannot be achieved, and what is even worse, the size of the calandria tank becomes too large.
An object of the present invention is to improve the self-control performance of a pressure-tube type nuclear reactor without enlarging the size of the calandria tank.
In order to achieve the above-described object, a first aspect of the present invention lies in a pressure-tube type heavy-water moderated nuclear reactor arranged in such a manner that pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes disposed in a calandria tank which contains heavy water, the pressure-tube type nuclear reactor comprising:
a structure arranged in such a manner that the pressure tu~es are arranged so as to form an equilateral triangular lattice configuration. As a result, the volume ratio of heavy water to fuel can be reduced without shortening the distance between pressure tubes.
A second aspect of the present invention lies in a pressure-tube type heavy-water moderated nuclear reactor arranged in such a manner that pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes disposed in a calandria tank CA 0202~713 1998-02-11 '_ which contains heavy water, the pressure-tube type - nuclear reactor comprising: a structure arranged in such a manner that a member which replaces the heavy water positioned near the outer surface of the calandria tube is positioned near the outer surface of the same. Since the member is disposed around the calandria tube so as to replace heavy water, the quantity of heavy water around - the calandria tube can be reduced. Therefore, the volume ratio of heavy water to fuel can be reduced. Since the member to replace heavy water is disposed around the pressure tube, the size of the calandria tank can be reduced in comparison to a structure arranged in such a manner that the member is disposed between the calandria tubes after it has been separated from the pressure tube.
A third aspect of the present invention lies in a method of assembling a pressure-tube type nuclear reactor in which spaces for containing heavy water are formed by hermetically fastening calandria tubes which are inserted into a calandria tank to the component part of the calandria tank, the method of assembling a pressure-tube type nuclear reactor comprising the steps of: securing the calandria tubes to the component part of the calandria tank; introducing cylinders each of which is made of a material which does not excessively absorb neutrons and which is sectioned into a plurality of sections into portions around the calandria tubes; and assembling the cylinders sectioned into the plurality of sections so as to cover the outer surfaces of the calandria tubes. Since a member to replace a portion of - heavy water is divided into sections so as to be introduced into a portion around the calandria tube before it is fastened to the portion around the calandria tube, the working space for fitting the member to replace heavy water and the interval between the pressure tubes can be reduced. As a result, the volume ratio of heavy - water to fuel can be improved without enlarging the calandria tank.
A fourth aspect of the present invention lies in a method of assembling a pressure-tube type nuclear reactor in which spaces for containing heavy water are formed by hermetically fastening calandria tubes which are inserted into a calandria tank to the component part of the calandria tank, the method of assembling a pressure-tube type nuclear reactor comprising the steps of: introducing cylinder members each of which is made of a material which does not excessively absorb neutrons into the spaces for containing heavy water; inserting the calandria tubes into the cylindrical members thus introduced when the calandria tubes are inserted into the component part of the calandria tank; and fastening the calandria tubes to the component part of the calandria tank. When the calandria tube is inserted into the calandria tank, the cylinder member is previously introduced into the calandria tank. Then, the calandria tube is inserted into the cylinder member simultaneously with the insertion of the calandria tube into the ",~
CA 0202~713 1998-02-11 calandria tank. Therefore, the cylinder member serving -- as the member to replace heavy water can be disposed around the calandria tube without the necessity of preparing a wide working space in the calandria tank.
A fifth aspect of the present invention lies in a member to replace a heavy water moderator of a pressure-tube type nuclear reactor to be disposed around - a calandria tube, the member to replace a heavy water moderator comprising: an assembled structure in the form of a cylinder into which the calandria tube can be introduced. Since a cylindrical member to replace heavy water for surrounding the calandria tube can be obtained, it can be used so as to surround the calandria tube. As a result, heavy water around the calandria tube can be replaced by the member so that the volume ratio of heavy water to fuel can be improved.
A sixth aspect of the present invention lies in a pressure-tube type nuclear reactor according to first aspect, wherein the volume ratio of heavy water to fuel is arranged to be 9.0 or less. In addition to the effect obtainable from the first aspect, the void reactivity coefficient of the coolant in the pressure tube can be assuredly made closer to zero or negative values since the pressure tubes are disposed in the equilateral lattice configuration in such a manner that the density of the configuration is determined so as to make the volume ratio of heavy water to fuel 9.0 or less.
, . .
CA 0202~713 1998-02-11 Therefore, the self-control performance of the core of the nuclear reactor can be further improved.
A seventh aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the volume ratio of heavy water to fuel is arranged to be 9.0 or less. In addition to the effect obtainable from the second aspect, the void reactivity coefficient of the coolant in the pressure tube can be assuredly made closer to zero or negative values since the members to replace heavy water are disposed around the pressure tubes in such a manner that the density of the configuration is determined so as to make the volume ratio of heavy water to fuel 9.0 or less.
Therefore, the self-control performance of the core of the nuclear reactor can be further improved.
An eighth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein some of the pressure tubes are replaced by control rod guide tubes, neutron instrumentation guide tubes or poison tubes for the pressure-tube type nuclear reactor at the position at which the pressure tubes are posltioned and the volume ratio of heavy water to fuel is arranged to be 9.0 or less. In addition to the effect obtainable from the first aspect, all of the tubes such as the pressure tubes, control rod guide tubes, neutron instrumentation guide tubes or poison tubes for the nuclear reactor can be arranged in the triangular lattice configuration with , ~ , .
CA 0202~713 1998-02-11 which the quantity of heavy water can be reduced.
Therefore, the quantity of heavy water can be easily reduced.
A ninth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein a control rod with a fuel follower is positioned in a coolant in some of the pressure tubes.
In addition to the effect obtainable from the first aspect, an effect can be obtained in that the control rods with a fuel follower inserted into the coolant in some of the pressure tubes can be cooled by the coolant which passes through the pressure tube.
A tenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein a cylinder surrounding the outer surface of the calandria tube is disposed so as to replace heavy water. In addition to the effect obtainable from the first aspect, the neutron economy can be maintained at a satisfactory level since the member to replace heavy water surrounding the calandria tube does not excessively absorb neutrons. In addition, since the calandria tube is surrounded by a cylinder, heavy water can be equally replaced by the cylinder from the outer surface of the calandria tube. Therefore, the intensity of the neutrons effecting the fuel can be distributed equally around the calandria tubes.
An eleventh aspect of the present invention lies in a pressure-tube type nuclear reactor according to CA 0202~713 1998-02-11 the second aspect, wherein the member for replacing heavy water is disposed in such a manner that the member forms a cylinder which surrounds the calandria tube after assembled. In addition to the effect obtainable from the second aspect, heavy water can be equally replaced by the cylinder from the outer surface of the calandria tube since the calandria tube is surrounded by the cylinder.
Therefore, the intensity of the neutrons effecting the fuel can be distributed equally around the calandria tubes.
A twelfth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein a cylinder surrounding the outer surface of the calandria tube is disposed so as to replace heavy water and the cylinder has its wall arranged to be a hollow shape. In addition to the effect obtainable from the first aspect, the neutron economy can be further improved since the cylinder has a hollow wall.
In addition, since heavy water for the volume for the hollow portion can be replaced, a large quantity of heavy water can be replaced by a light weight structure.
A thirteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the member for replacing heavy water is a cylinder which surrounds the calandria tube and the cylinder has its wall arranged to be a hollow shape. In addition to the effect obtainable from the second aspect, the neutron economy can be further CA 0202~713 1998-02-11 ~~ improved since the wall of the cylinder is in the hollow shape. Furthermore, since heavy water can be replaced by the volume for the hollow portion, a large quantity of heavy water can be replaced by a light weight structure.
A fourteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the member which replaces heavy water is made of a zirconium alloy, aluminum or an aluminum alloy. In addition to the effect obtainable from the second aspect, an improved neutron economy can be obtained since the member to replace heavy water is made of a material such as a zirconium alloy, aluminum or aluminum alloy which do not easily absorb neutrons.
A fifteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the calandria tubes are arranged to be in an equilateral triangular lattice configuration. In addition to the effect obtainable from the second aspect, the volume ratio of heavy water to fuel can be improved by the arrangement of the equilateral triangular lattice configuration of the calandria tubes and the substitution of heavy water by the member. Therefore, if the volume ratio of heavy water to fuel cannot be easily adjusted by either of the above-described means, both of the above-described means are employed so that it can be easily adjusted.
A sixteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to CA 0202~713 1998-02-11 the second aspect, wherein the member which replaces - heavy water is disposed in a region which shows a relatively high output density in the calandria tank. In addition to the effect obtainable from the second aspect, the distribution of the outputs can be uniformed by arranging the balance of the outputs from a region in which the output density is high and that from a region in which the output density is low since the above-described cylinder is positioned in the region in which the output denslty is relatively high.
A seventeenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the member which replaces heavy water is arranged in such a manner that its thickness is enlarged in proportion to the output density. In addition to the effect obtainable from the second aspect, the quantity of heavy water to be replaced can be enlarged in proportion to the output density in the region in which the output density is high since the above-described cylinder is arranged to have an increased thickness in proportion to the output density.
Therefore, the volume ratio of heavy water to fuel can be, in proportion to the output density, adjusted in the region in which the output density is high.
Other and further objects, features and advantages of the invention will appear more fully from the following description provided in conjunction with the accompanying drawings, in which:
CA 0202~713 1998-02-11 -Fig. 1 illustrates a first embodiment of the present invention and is a plan view which illustrates the plan configuration of calandria tubes of a pressure-tube type nuclear reactor;
Fig. 2 illustrates the first embodiment of the present invention and is a vertical cross sectional view which illustrates the core of the pressure-tube type nuclear reactor;
Fig. 3 illustrates the first embodiment of the present invention and is an enlarged view which illustrates the configuration of pressure tubes each of which serves as a unit of a portion including control rod guide tubes or neutron instrumentation tubes shown in Fig. 1;
Fig. 4 is a graph which illustrates the relationship between void reactivity coefficient and volume ratio of heavy water to fuel of the pressure-tube type nuclear reactor;
Fig. 5 illustrates a second embodiment of the present invention and is a plan cross sectional view which illustrates the relationship among the calandria tubes, cylinder disposed outside the calandria tubes and control rod guide tubes or neutron instrumentation tubes disposed in the calandria tank of the pressure-tube type nuclear reactor;
Fig. 6 illustrates a second embodiment of the present invention and is a vertical cross sectional view which illustrates the calandria tubes and cylindrical CA 0202~713 1998-02-11 portions disposed outside the calandria tubes according to the embodiment shown in Fig. 5;
Fig. 7 illustrates the second embodiment of the present invention and is a plan view which illustrates the configuration of the tubes and the cylinders when viewed from a portion above an upper tube sheet according to the embodiment shown in Fig. 6;
Fig. 8 illustrates the second embodiment of the present invention and is a plan view which illustrates the overall configuration of the tubes in the calandria tank of the pressure-tube type nuclear reactor;
Fig. 9 illustrates the second embodiment of the present invention and is a perspective view which illustrates the cylinder;
Fig. 10 illustrates the second embodiment of the present invention and is a plan cross sectional view which illustrates a fastener portion for the cylinder;
Fig. 11 illustrates the first embodiment of the present invention and is a plan view which schematically illustrates the equilateral triangular lattice configuration of the tubes;
Fig. 12 illustrates a conventional structure and is a plan configuration view which schematically illustrates square lattice configuration of the tubes;
Fig. 13 illustrates a third embodiment of the present invention and is a plan configuration view which partially illustrates a hollow cylinder;
. . .
CA 0202~713 1998-02-11 -~- Fig. 14 illustrates a conventional structure and is a plan configuration view which illustrates the overall plan configuration of the calandria tubes of the pressure-tube type nuclear reactor;
Fig. 15 illustrates a conventional structure and is a plan configuration view which illustrates a portion of the configuration of the pressure tubes shown in Fig. 14 in an enlarged manner;
Fig. 16 is a graph which illustrates the relationship between the neutron multiplication factor and the volume ratio of heavy water to fuel of the pressure-tube type nuclear reactor;
Fig. 17 illustrates a fourth embodiment of the present invention and is a plan configuration view which illustrates the plan configuration of the tubes in a quarter portion of the core of the pressure-tube type nuclear reactor;
Fig. 18 illustrates the fourth embodiment of the present invention and is a vertical cross sectional view which illustrates a half portion of the core of the pressure-tube type nuclear reactor;
Fig. 19 illustrates the fourth embodiment of the present invention and is a plan cross sectional view which illustrates a quarter portion of the calandria tube; and Fig. 20 is a graph which illustrates the output peaking coefficient in the axial direction of the core according to the present invention.
CA 0202~713 1998-02-11 The quantity of heavy water for one pressure tube can be expressed by hatched area Slin the cross sectional view of Fig. 11, the area S1 being obtained from the following equation:
S1 = 2~ Q12 ~ ~R12 ~-- (1) where ~1: interval between lattices R1: outer radius of calandria tube On the other hand, the quantity of heavy water for one pressure tube arranged in a square lattice configuration can be expressed by hatched area S2 in the cross sectional view of Fig. 12, the area S2 being obtained from the following equation:
S = (e)2 _ ~(R)2 ...................... (2) where ~2: interval between lattices R2: outer radius of calandria tube Assuming that the triangular lattice and the square lattice have the same interval between lattices and the diameter of the calandria tube and therefore el = ~2 = ~ and Rl= R2= R, heavy water volume reduction ratio ~M for one pressure tube, obtained from a comparison made between the equilateral triangular lattice configuration and the square lattice configuration, can be expressed by the following equation:
~M = (S2 - Sl)/S2 = (1 - ~3/2) x {1 - ~(R/Q)2}-l (3) Specifically, it is assumed that ~ = 24 cm and R = 8 cm so as to be substituted into Equation (3), a reduction ~0 ratio ~M of about 0.21 is obtained.
CA 0202~713 1998-02-11 Reduction ratio ~L of the diameter of the core portion which is a critical factor to determine the size of the calandria tank can be obtained from the following equation:
~L = {ez ~ (2~3 )oSel}/e2 = 1 - (~3)os . 0.07 (4) That is, assuming that the lattice intervals are the same, the quantity of heavy water can be significantly reduced (about 21~ according to the above-described example) and the diameter of the core can be reduced by 7~.
Therefore, according to the equilateral triangular lattice configuration, the volume of heavy water can be reduced without shortening the interval between the pressure tubes and the volume ratio of heavy water to fuel can be reduced. Therefore, the size of the calandria tank can be reduced, causing a satisfactory operational performance and an economical advantage to be obtained.
With respect to the second aspect of the present invention, the volume ratio of heavy water to fuel (D/F) can be obtained from the following equation in the case where the member having a thickness t is successively placed around the pressure tube (the member having a cylindrical shape):
D/F = {e - ~(R + t)2}/n~r2 CA 0202~713 1998-02-11 - where ~ = interval between lattices R = outer radius of calandria tube t = thickness of cylinder n = number of fuel pins per fuel assembly r = radius of fuel pellet The improved degree QD/F of the volume ratio D/F of heavy water to fuel can be obtained from Equation (5) as follows:
~D/F = -{7r(R + t) 2 _ 7rR2}/n~r2 ... (6) A first embodiment of the present invention will now be described.
A plurality of calandria tubes 1, control rod guide tubes 4 and neutron instrumentation tubes 5 are inserted into a calandria tank 2 in which heavy water 10 serving as a neutron moderator is enclosed.
A pressure tube 3 is inserted into the calandria tube 1, the lower end of the pressure tube 3 being connected to a pipe 31 through which light water passes through. The other end of the pressure tube 3 is connected to another pipe 32.
The pressure tube 3 accommodates a fuel assembly constituted by binding a plurality of fuel pins each of which contains nuclear fuel.
Light water is introduced into the pressure tube 3 through the pipe 31 by a pump (not shown). As a result, light water in the pressure tube 3 is heated by the fuel assembly so that it boils. As a result, light water becomes a two phase ~low consisting o~ steam and CA 0202~713 1998-02-11 ' _ - liquid at high temperature and high pressure so that the two phase flow passes through the pipe 32. It is then taken outside the core so as to act as energy to rotate the turbine of a generator.
As shown in Fig. 1, according to this embodiment, the calandria tubes 1 are arranged to be in the form of equilateral triangular lattices each of which includes a control rod guide tube 4 or a neutron instrumentation tube 5.
The above-described calandria tubes 1, the control rod guide tubes 4 and the neutron instrumentation tubes 5 are hermetically connected to an upper tube sheet 6 and a lower tube sheet 7, as shown in Fig. 2, in order to enable the calandria tank 2 to contain heavy water.
According to the above-described equilateral triangular lattice arrangement of the calandria tubes 1, an effect can be obtained in that the necessary volume of heavy water can be reduced in comparison to a conventional square lattice arrangement shown in Figs. 14 and 15.
The manner in which to dispose the control rod guide tube 4 will be described.
As shown in Fig. 3, when the control and instrumentation pipes such as the control rod guide tube 4, the neutron instrumentation tube 5, a poison tube and the like are disposed in the central portion of the triangular lattice, predetermined mechanical strength must be secured in a joint (usually a rolled joint) CA 0202~713 1998-02-11 '~_ ~ between the above-described pipes and the calandria pipe 1 and the upper tube sheet 6. Therefore, a minimum gap 8 must be secured between the pipe having the largest outer diameter (usually, the control rod guide pipe 4) and the calandria tube 1. As a result, the maximum diameter of the above-described pipes are determined.
Since the equilateral angular lattice enables the above-described maximum diameter to be reduced in comparison to the square lattice, the control rod guide pipe 4 must be disposed to the same position at which the pressure tube 1 is disposed in the case where a large-diameter control rod guide tube 4 must be employed. In this case, since the necessity of a space in which the control rod guide tube 4 is disposed in the equilateral triangular lattice can be eliminated, the gap between the pressure tubes 1 can be narrowed. Therefore, a preferable volume ratio of heavy water to fuel can be realized even if the pressure tube 1 is replaced by the control rod guide tube 4.
Furthermore, in some instances, fuel control rods are inserted into some pressure tubes 1 in the equilateral triangular lattices so as to replace the control rod guide tubes 4. In order to prevent a deterioration in the volume ratio of heavy water to fuel due to the above-described provision of the control rods, the gap between the pressure tubes 1 must be reduced by the degree which corresponds to the eliminated space in which the control rod guide tube 4 is disposed in the equilateral triangular lattice area. In this case, since light water is, as the coolant, passed through the pressure tubes 1, the control rod in the pressure tube 1 can be satisfactorily cooled. Therefore, a control rod with a fuel follower can be employed as the control rod.
In a structure in which the control rod with a fuel follower is employed, the fuel can be introduced by the degree of the gradual removal of the control rod from the core at the end stage of the combustion. Therefore, the deterioration in the output at the final stage of the combustion in the core can be prevented.
A specific example of the equilateral triangular lattice will be described. When the control rod guide tube 4 is positioned at the position at which the pressure tube 1 has been disposed, essential dimensions of a large-size reactor arranged for the purpose of realizing a desired volume ratio of 8.0 between heavy water and fuel are as follows, where the size of the lattice is 25 cm and the number of the fuel pins in the fuel assembly is 54:
Distance between lattices ~ : 25.0 cm Inner diameter of pressure tube: 12 cm Configuration: Equilateral triangular lattice configuration Number of fuel pins in fuel assembly: 54 Diameter of fuel pellet: 1.0 cm Outer diameter of calandria tube: 16 cm , CA 0202~713 1998-02-11 As a result, the above-described volume ratio - of 8.0 between heavy water and fuel can be achieved.
A second embodiment of the present invention will be described.
Referring to Figs. 5 and 6, a second embodiment of the present invention, structured in such a manner that a cylinder is disposed around each of the pressure tubes arranged to be in a square lattice configuration, will be described. Fig. 5 illustrates a unit of the lattices in the calandria tank 2 according to the present invention, the unit being composed of four calandria tubes 1 arranged to be square lattice configuration. A
pad 30 is held between the calandria tube 1 and a cylinder 9 in order to form a proper gap around the calandria tube 1. The cylinder 9 is then placed on a lower tube sheet. The cylinder 9 is made of a material such as metal of a type which does not excessively absorb neutrons and which has satisfactory strength, the metal being exemplified by Zircalloy-2, zirconium-niobium alloy and aluminum alloy. The cylinder 9 can be sectioned into two or three sections in its circumferential direction so as to be fastened easily as described above. A fastener 11 is slid in a direction designated by an arrow 12 as shown in Fig. 9, so as to realize the state of the fastening as shown in Fig. 10. If necessary, the cylinder 9 may be shortened in its axial direction (by 50 cm to 200 cm), so that it can be introduced into the calandria tank 2 and easily fastened there as shown in CA 0202~713 1998-02-11 Fig. 6 after the calandria tube 1 has been connected to the upper tube sheet 6 and the lower tube sheet 7 of the calandria tank 2. After all of the cylinders 9 have been fastened as described above, heavy water serving as the moderator is introduced into the calandria tank 2.
As shown in Fig. 7, the portion at which the control rod guide tube 4 passes through the upper tube sheet 6 of the calandria tank 2 must secure predetermined mechanical strength at the joint between the calandria tube 1 and the control rod guide tube 4 and the upper tube sheet 6. Therefore, the minimum gap 8 between the calandria tube 1 and the control rod guide tube 4 must have the necessary size.
Usually, it is difficult to enlarge the diameter of the calandria tube 1 at the upper tube sheet 6. Therefore, the diameter of the calandria tube 1 in the core in the calandria tank 2 is made larger than that in its upper portion.
However, the enlargement of the diameter of the calandria tube or the arrangement of the drawing of the shape of it encounters a certain limit in terms of the manufacturing difficulty and the mechanical structure.
Therefore, it is difficult to considerably enlarge the diameter of the calandria tube in the calandria tank.
Therefore, according to the present invention, the cylinder 9 is disposed around the calandria tube 1 so as to overcome the above-described difficulty.
CA 0202~713 1998-02-11 The control rod guide tubes 4 and the neutron instrumentation tubes 5 of a number necessary to control and to measure the output from a nuclear reactor are, as shown in Fig. 7, disposed properly in the gaps between the calandria tubes 1.
A specific example which is able to quantitatively realize the effect of the cylinders 9 will be described.
In this case, the configuration is arranged to be the square lattice configuration as shown in Fig. 8.
Lattice interval ~: 24.5 cm Calandria tube outer radius R: 8 cm Number n of fuel pins of fuel assembly: 54 Fuel pellet radius r: 0.5 cm Cylinder thickness: 1.0 cm - As a result of the effect of the cylinder provided, the volume ratio of heavy water to fuel can be improved from 9.4 to 8.1.
A third embodiment of the present invention, provided with a cylinder having a different structure from that of the cylinder 9 according to the second embodiment, will be described. According to the third embodiment, an economical effect can be obtained. The difference in the structure of the cylinder 9 will be described.
As shown in Fig. 13, the wall portion of the cylinder 9 is arranged to be a hollow structure. An outer plate 13 and an inner plate 14 of the hollow CA 0202~713 1998-02-11 cylinder is made of Zircalloy-2 or an aluminum alloy - (1100). If necessary, a spacer 16 may be disposed so as to maintain the gap in the hollow portion and separated portions 15 are joined by the fastener 11 or by welding.
The above-described separated portions 15 are connected to each other by the fastener 11, the portions 15 in which the circumferential end portions of the outer plate 13 and those of the inner plate 14 are hermetically welded by a welded portion 18. Furthermore, the axial end portions of the hollow cylinder are hermetically closed so that a hollow portion 17 is formed. The effective thickness of the hollow cylinder is defined from the outer surface of the outer plate 13 to the inner surface of the inner plate 14.
The volume ratio of heavy water to fuel can be improved from 10 to 8.2 when a hollow cylinder having the effective thickness t = 1.2 cm is used in a square lattice core arranged as follows:
Lattice interval e 24 cm Calandria tube outer radius R: 8 cm Number n of fuel pins of fuel assembly: 48 Fuel pellet radius r: 0.5 cm An example of a structure arranged in such a manner that the control rod guide tube 4 is disposed at the central portion of the triangular lattice and the cylinder is disposed around the calandria tube for the purpose of sufficiently improving the volume ratio of CA 0202~713 1998-02-11 heavy water to fuel will be described. In this case, the - arrangements and the effect are as follows:
Inner diameter of pressure tube: 12 cm Configuration: Equilateral triangular lattice configuration Lattice pitch: 25.5 cm Number n of fuel pins of fuel assembly: 54 - Fuel pellet diameter: 1.0 cm Outer diameter of calandria tube in the core portion: 16 cm Outer diameter of calandria tube at the upper tube sheet: 15 cm Outer diameter of control rod guide tube: 5 cm Minimum gap at the upper tube sheet: 4.7 cm lS Effective thickness of the cylindrical wall:
0.5 cm Volume ratio of heavy water to fuel: 7.9 According to the above-described examples, the volume ratio of heavy water to fuel can be properly designed.
The void coefficient changes depending upon the type of fuel (oxide fuel containing plutonium or uranium dioxide fuel), the composition, the enrichment and the like. However, since the volume ratio of heavy water to fuel can be arranged to be 7.9 to 8.2, according to the present invention, the void coefficient can be made a value in the vicinity of zero, in the order of 10-5 ~k/k/~
CA 0202~713 1998-02-11 void. Therefore, an excellent operating efficiency can - be obtained.
Furthermore, since the diameter of the core and the quantity of heavy water can be reduced, an economical S effect can be obtained.
An example of a method of fastening the cylinder 9 to the portion around the calandria tube 1 will be described.
The manufactured cylinder 9 is placed on the lower tube sheet 7 prior to the fastening of the calandria tube 1 to the calandria tank 2. The calandria tube 1 is then inserted into the lower tube sheet 7. At this time, the calandria tube 1 is also inserted into the cylinder 9. Thus, the structure in which the cylinder 9 as an alternative to heavy water is disposed around the calandria tube 1 can be manufactured.
According to the above-described manufacturing method, the necessity of the work for assembling the cylinder 9 around the calandria tube 1 performed in a narrow space can be eliminated. Furthermore, the necessity of providing a wide working space around the calandria tube 1 can be eliminated. It is preferable that the cylinder 9 be disposed in such a manner that it is held between the upper and the lower tube sheets 7 and 8 via a spacer.
Accordingly, the structure is arranged in such a manner that the calandria tubes 1 are disposed in the core in the form of a triangular lattice, the volume CA 0202~713 1998-02-11 ratio of heavy water to fuel can be properly determined - and the coolant void reactivity coefficient can be made closer to negative values as much as possible.
Therefore, the self-control performance peculiar to a nuclear reactor can be improved. For example, since the quantity of heavy water can be reduced by about 20~ and the diameter of the core can be reduced by about 7~ in the same lattice interval as that of the conventional structure, an economical effect can be obtained.
Furthermore, when a cylinder is, as an alternative to heavy water, fastened around the calandria tube 1, the coolant void reactivity coefficient can be made a value further closer to a negative value.
Therefore, the self-control performance can be improved.
In addition, when both the above-described triangular lattice configuration and the cylinder are simultaneously employed, the design can be significantly freely made for the purpose of improving the operation efficiency and the economical effect.
A fourth embodiment of the present invention further established for the purpose of making the distribution of outputs from the pressure type nuclear reactor uniform will be described.
As shown in Fig. 4, in a design range of a nuclear reactor which uses heavy water as the moderator, when the volume ratio of heavy water to fuel is reduced, the coolant void reactivity coefficient is usually reduced (the self-control performance is improved). As CA 0202~713 1998-02-11 shown in Fig. 16, the neutron multiplication factor is reduced when the ratio of the volume of a heavy water moderator to the volume of fuel has become reduced.
Usually, the more the neutron multiplication factor is, the more the burn-up of the same fuel can be enlarged (the fuel economy can be improved). Therefore, a proper volume ratio of heavy water to fuel can be selected in such a manner that both the self-control performance and the fuel economy are maintained at a satisfactory degree.
Since a larger quantity of neutrons leak in the peripheral portion in the core in comparison to that in the central portion of the core, the neutron multiplication factor becomes reduced. Therefore, the output density becomes lowered and a uniform output distribution cannot be obtained.
Accordingly, according to the fourth embodiment, an improvement of the self-control performance and a uniform output distribution can be simultaneously achieved.
Fig. 17 illustrates a quarter portion of the arrangement of calandria tubes 1, neutron instrumentation tubes and control rod guide tubes in the calandria tank 2.
As shown in Fig. 19, the calandria tube 1 includes the pressure tube 3 through which a coolant 22 passes. The pressure tube 3 also includes fuel pins 21 which contain pellet nuclear fuel. In the calandria tank CA 0202~713 1998-02-11 2 which contains heavy water 10, the calandria tubes 1 are disposed in a square lattice configuration by the number necessary to obtain the rated output from the pressure tube type nuclear reactor. Furthermore, the control rod guide tubes 4 and the neutron instrumentation tubes 5, which are necessary to control the core or to perform the instrumentation, are properly disposed among the above-described lattices. If necessary, poison tubes for introducing poison for controlling the output of the core are provided. The above-described tubes are inserted into the calandria tank 2 and are hermetically joined to the upper tube sheet 6 and the lower tube sheet 7 of the calandria tank 2 so that the calandria tank 2 contains heavy water.
As shown in Figs. 17, 18 and 19, the cylinder 9 is disposed around the calandria tube 1 disposed at the central portion of the core in the calandria tank 2.
The cylinder 9 may be fastened in such a manner that it is supported by the calandria tube 1 or by the lower tube sheet 7 via a spacer.
The cylinder 9 is made of a material, which does not excessively absorb neutrons, such as a zirconium alloy (Zircalloy-2, Zircalloy-4, zirconium-niobium alloy or the like), aluminum or an aluminum alloy.
In order to enlarge the volume which can be replaced by heavy water, the wall of the cylinder 9 is arranged so as to form the hollow portion 17 which contains a chemically stable gas such as helium or argon.
CA 0202~713 1998-02-11 It is preferable that the hollow portion 17 be filled with a chemically stable gas such as helium or argon in the structure according to the above-described embodiments in the case where the cylinder 9 is arranged to be the hollow portion. In order to seal the thus enclosed gas, the hollow portion 17 is hermetically sealed similar to the above-described embodiments. The cylinder 9 may be sectioned into sections similar to the above-described embodiments. In this case, the end portions thus sectioned are structured so as to be joined to each other by a fastener similar to the above-described embodiments.
Sixty fuel pins are collected so as to form a fuel assembly which is included in the pressure tube. An example, arranged in such a manner that the cylinder 9 having hollow wall portion is disposed around the calandria tube 1 as an alternative to heavy water, will be described in terms of the quantitative effect.
According to this example, the present invention is applied to a 1,000 MW electric output pressure tube type nuclear reactor in which heavy water is used as the moderator and light water is used as the coolant. A specific example of the structure is as follows:
Power output: 1000 MW Number of pressure tubes:
Number n of fuel pins of fuel assembly: 60 Effective height of the core portion: 3.7 m Radius of core portion: 7.8 m ~ Fuel pellet radius r: 0.475 cm Inner diameter of pressure tube: 12.3 cm Pressure tube lattice interval Q: 24.5 cm Outer radius R of calandria tube: 8.25 cm Outer diameter of the control rod guide tube:
9.5 cm Effective thickness of hollow cylinder: 1.8 cm Number of calandria tubes 1 in which hollow cylinders are provided: 344 Axial length in which the hollow cylinder is disposed: 2.22 m Minimum interval in the upper tube sheet (between the calandria tube 1 and the control rod guide tube 4): 4.3 cm According to this example, the volume ratio of heavy water to fuel in the portion to which no cylinder is fastened is 9.1, while that in the portion (the central portion of the core) to which the cylinder is fastened is 6.7. As described above, when the volume ratio of heavy water to fuel in the central portion of the core is lowered with respect to that in the peripheral portion, the neutron multiplication factor in the central portion of the core becomes reduced in comparison to that in the peripheral portion. Therefore, the number of neutrons generated in the central portion is reduced, causing a curve showing the power density distribution to be changed from the dotted line to a CA 0202~713 1998-02-11 solid line as shown in Fig. 20 as well due to the - deterioration in the power distribution in the peripheral portion caused from the neutron leakage in the peripheral portion. As a result, the power distribution in the axial direction (vertical direction) of the core can be made more uniform. Since a similar effect can be obtained in the radial direction of the core, the power distribution in both the axial direction and the radial direction of the core can be made more uniform.
10As a result, the total (effective) volume ratio of heavy water to fuel in the core can be made a value in the vicinity of 8. Therefore, as shown in Fig. 4, the void coefficient can be made a value in the vicinity of zero in an order of 10-5 ~k/k/% void. As a result, a satisfactory operating performance can be obtained and the power distribution can be improved by about 20%
without deterioration in the neutron economy, causing an economical effect to be obtained. As described above, according to the present invention, the volume ratio of heavy water to fuel can be determined to a desired value so that the coolant void coefficient can be made a value further closer to the negative side. As a result, the self-control performance peculiar to the neutron reactor can be improved. Furthermore, since the cylinders 9 can be partially disposed in the portions showing a high power density so as to make the power distribution in the core to be uniform, the number of the control rods necessary to uniform the power distribution can be ''. ,' ' CA 0202~713 1998-02-11 reduced. In addition, the performance of the core can be easily controlled, the operation performance can be improved and an economical effect can be obtained.
A structure arranged in such a manner that the thickness of each of the cylinders 9 is enlarged in inverse proportion to the distance from the radial center of the core will further enable the power distribution in ~ the radial direction to be uniformed. In addition, a structure arranged in such a manner that the thickness of each of the cylinders 9 is enlarged in inverse proportion to the distance from the axial center will enable the power distribution in the axial direction to be uniformed.
Furthermore, if the calandria tubes are disposed in a triangular lattice configuration, the volume ratio of heavy water to fuel can be adjusted without the necessity of enlarging the calandria tank.
Therefore, the adjustment and design can be further freely performed.
In any of the above-described embodiments, it is preferable that a certain gap be provided between the calandria tube and the cylinder for the purpose of passing heavy water.
In the conventional pressure tube type nuclear reactor in which the pressure tubes are arranged so as to form a square lattice configuration, the pressure tubes and the calandria tubes are inserted into the calandria tank. Therefore, if the interval between the formed CA 0202~713 1998-02-11 lattices of the pressure tubes is narrowed, the pitch of through holes formed in the surface of the calandria tank is also narrowed, causing the strength of the calandria tank to be deteriorated. Therefore, it has been difficult for the interval between the disposed lattices of the pressure tubes to be narrowed. If the interval between the disposed lattices of the pressure tubes is widened, the ratio of heavy water to nuclear fuel is raised. The pressure tube type nuclear reactor of the type described above tends to show a large positive void reactivity, causing the self-control performance of the nuclear reactor to become unsatisfactory.
In order to overcome the above-described problem, the above-described structures (1) to (5) have been disclosed. However, according to the structure (1), the pitch of the positions of the pressure tubes become non-uniform and complicated. Therefore, the evaluation of the performance of the core and operational control become unsatisfactory. ~urthermore, since the pitch of the positions of the pressure tubes is partially narrowed, the strength of the calandria tank at the position at which the pressure tube passes through may be partially deteriorated. In order to overcome the above-described problem, the size of the calandria tank must be enlarged. According to the structure (2), heavy water is replaced by carbon rods, in part. However, since the carbon rod is a relatively large neutron-absorber, the neutron economy becomes deteriorated. In addition, since CA 0202~713 1998-02-11 the carbon rods are disposed simply in parallel and among the pressure tubes, spaces in which the carbon rods are provided and spaces around the carbon rods must be provided, causing the overall size of the calandria tank to be enlarged. According to the structure (3), since the heavy water tubes are disposed simply in parallel to the pressure tubes, similar to the structure (2), the size of the calandria tank becomes too large. According to the structure (4), the fuel pins in the pressure tubes are in part replaced by the water sealing rods in the pressure tubes. Therefore, the quantity of the fuel is reduced. In order to compensate for the reduced space for the fuel, the size of the pressure tube for accommodating the fuel and the calandria tank for accommodating the pressure tubes are enlarged excessively. According to the structure (5), the diameter of the calandria tube at its intermediate portion is arranged to be larger than that at other portions. Therefore, the diameter of the hole formed in the calandria tank for the purpose of inserting the calandria tube is necessarily enlarged. As a result, the interval of the holes must be enlarged for the purpose of securing the strength of the calandria tank. Therefore, the size of the calandria tank becomes too large.
When the size of the calandria tank becomes too large, the quantity of heavy water to be contained therein becomes too large or a satisfactory effect of reducing the quantity of heavy water cannot be obtained.
CA 0202~713 1998-02-11 .
Therefore, the improvement in the self-control performance of the nuclear reactor by reducing the volume ratio of heavy water to fuel cannot be achieved, and what is even worse, the size of the calandria tank becomes too large.
An object of the present invention is to improve the self-control performance of a pressure-tube type nuclear reactor without enlarging the size of the calandria tank.
In order to achieve the above-described object, a first aspect of the present invention lies in a pressure-tube type heavy-water moderated nuclear reactor arranged in such a manner that pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes disposed in a calandria tank which contains heavy water, the pressure-tube type nuclear reactor comprising:
a structure arranged in such a manner that the pressure tu~es are arranged so as to form an equilateral triangular lattice configuration. As a result, the volume ratio of heavy water to fuel can be reduced without shortening the distance between pressure tubes.
A second aspect of the present invention lies in a pressure-tube type heavy-water moderated nuclear reactor arranged in such a manner that pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes disposed in a calandria tank CA 0202~713 1998-02-11 '_ which contains heavy water, the pressure-tube type - nuclear reactor comprising: a structure arranged in such a manner that a member which replaces the heavy water positioned near the outer surface of the calandria tube is positioned near the outer surface of the same. Since the member is disposed around the calandria tube so as to replace heavy water, the quantity of heavy water around - the calandria tube can be reduced. Therefore, the volume ratio of heavy water to fuel can be reduced. Since the member to replace heavy water is disposed around the pressure tube, the size of the calandria tank can be reduced in comparison to a structure arranged in such a manner that the member is disposed between the calandria tubes after it has been separated from the pressure tube.
A third aspect of the present invention lies in a method of assembling a pressure-tube type nuclear reactor in which spaces for containing heavy water are formed by hermetically fastening calandria tubes which are inserted into a calandria tank to the component part of the calandria tank, the method of assembling a pressure-tube type nuclear reactor comprising the steps of: securing the calandria tubes to the component part of the calandria tank; introducing cylinders each of which is made of a material which does not excessively absorb neutrons and which is sectioned into a plurality of sections into portions around the calandria tubes; and assembling the cylinders sectioned into the plurality of sections so as to cover the outer surfaces of the calandria tubes. Since a member to replace a portion of - heavy water is divided into sections so as to be introduced into a portion around the calandria tube before it is fastened to the portion around the calandria tube, the working space for fitting the member to replace heavy water and the interval between the pressure tubes can be reduced. As a result, the volume ratio of heavy - water to fuel can be improved without enlarging the calandria tank.
A fourth aspect of the present invention lies in a method of assembling a pressure-tube type nuclear reactor in which spaces for containing heavy water are formed by hermetically fastening calandria tubes which are inserted into a calandria tank to the component part of the calandria tank, the method of assembling a pressure-tube type nuclear reactor comprising the steps of: introducing cylinder members each of which is made of a material which does not excessively absorb neutrons into the spaces for containing heavy water; inserting the calandria tubes into the cylindrical members thus introduced when the calandria tubes are inserted into the component part of the calandria tank; and fastening the calandria tubes to the component part of the calandria tank. When the calandria tube is inserted into the calandria tank, the cylinder member is previously introduced into the calandria tank. Then, the calandria tube is inserted into the cylinder member simultaneously with the insertion of the calandria tube into the ",~
CA 0202~713 1998-02-11 calandria tank. Therefore, the cylinder member serving -- as the member to replace heavy water can be disposed around the calandria tube without the necessity of preparing a wide working space in the calandria tank.
A fifth aspect of the present invention lies in a member to replace a heavy water moderator of a pressure-tube type nuclear reactor to be disposed around - a calandria tube, the member to replace a heavy water moderator comprising: an assembled structure in the form of a cylinder into which the calandria tube can be introduced. Since a cylindrical member to replace heavy water for surrounding the calandria tube can be obtained, it can be used so as to surround the calandria tube. As a result, heavy water around the calandria tube can be replaced by the member so that the volume ratio of heavy water to fuel can be improved.
A sixth aspect of the present invention lies in a pressure-tube type nuclear reactor according to first aspect, wherein the volume ratio of heavy water to fuel is arranged to be 9.0 or less. In addition to the effect obtainable from the first aspect, the void reactivity coefficient of the coolant in the pressure tube can be assuredly made closer to zero or negative values since the pressure tubes are disposed in the equilateral lattice configuration in such a manner that the density of the configuration is determined so as to make the volume ratio of heavy water to fuel 9.0 or less.
, . .
CA 0202~713 1998-02-11 Therefore, the self-control performance of the core of the nuclear reactor can be further improved.
A seventh aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the volume ratio of heavy water to fuel is arranged to be 9.0 or less. In addition to the effect obtainable from the second aspect, the void reactivity coefficient of the coolant in the pressure tube can be assuredly made closer to zero or negative values since the members to replace heavy water are disposed around the pressure tubes in such a manner that the density of the configuration is determined so as to make the volume ratio of heavy water to fuel 9.0 or less.
Therefore, the self-control performance of the core of the nuclear reactor can be further improved.
An eighth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein some of the pressure tubes are replaced by control rod guide tubes, neutron instrumentation guide tubes or poison tubes for the pressure-tube type nuclear reactor at the position at which the pressure tubes are posltioned and the volume ratio of heavy water to fuel is arranged to be 9.0 or less. In addition to the effect obtainable from the first aspect, all of the tubes such as the pressure tubes, control rod guide tubes, neutron instrumentation guide tubes or poison tubes for the nuclear reactor can be arranged in the triangular lattice configuration with , ~ , .
CA 0202~713 1998-02-11 which the quantity of heavy water can be reduced.
Therefore, the quantity of heavy water can be easily reduced.
A ninth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein a control rod with a fuel follower is positioned in a coolant in some of the pressure tubes.
In addition to the effect obtainable from the first aspect, an effect can be obtained in that the control rods with a fuel follower inserted into the coolant in some of the pressure tubes can be cooled by the coolant which passes through the pressure tube.
A tenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein a cylinder surrounding the outer surface of the calandria tube is disposed so as to replace heavy water. In addition to the effect obtainable from the first aspect, the neutron economy can be maintained at a satisfactory level since the member to replace heavy water surrounding the calandria tube does not excessively absorb neutrons. In addition, since the calandria tube is surrounded by a cylinder, heavy water can be equally replaced by the cylinder from the outer surface of the calandria tube. Therefore, the intensity of the neutrons effecting the fuel can be distributed equally around the calandria tubes.
An eleventh aspect of the present invention lies in a pressure-tube type nuclear reactor according to CA 0202~713 1998-02-11 the second aspect, wherein the member for replacing heavy water is disposed in such a manner that the member forms a cylinder which surrounds the calandria tube after assembled. In addition to the effect obtainable from the second aspect, heavy water can be equally replaced by the cylinder from the outer surface of the calandria tube since the calandria tube is surrounded by the cylinder.
Therefore, the intensity of the neutrons effecting the fuel can be distributed equally around the calandria tubes.
A twelfth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the first aspect, wherein a cylinder surrounding the outer surface of the calandria tube is disposed so as to replace heavy water and the cylinder has its wall arranged to be a hollow shape. In addition to the effect obtainable from the first aspect, the neutron economy can be further improved since the cylinder has a hollow wall.
In addition, since heavy water for the volume for the hollow portion can be replaced, a large quantity of heavy water can be replaced by a light weight structure.
A thirteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the member for replacing heavy water is a cylinder which surrounds the calandria tube and the cylinder has its wall arranged to be a hollow shape. In addition to the effect obtainable from the second aspect, the neutron economy can be further CA 0202~713 1998-02-11 ~~ improved since the wall of the cylinder is in the hollow shape. Furthermore, since heavy water can be replaced by the volume for the hollow portion, a large quantity of heavy water can be replaced by a light weight structure.
A fourteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the member which replaces heavy water is made of a zirconium alloy, aluminum or an aluminum alloy. In addition to the effect obtainable from the second aspect, an improved neutron economy can be obtained since the member to replace heavy water is made of a material such as a zirconium alloy, aluminum or aluminum alloy which do not easily absorb neutrons.
A fifteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the calandria tubes are arranged to be in an equilateral triangular lattice configuration. In addition to the effect obtainable from the second aspect, the volume ratio of heavy water to fuel can be improved by the arrangement of the equilateral triangular lattice configuration of the calandria tubes and the substitution of heavy water by the member. Therefore, if the volume ratio of heavy water to fuel cannot be easily adjusted by either of the above-described means, both of the above-described means are employed so that it can be easily adjusted.
A sixteenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to CA 0202~713 1998-02-11 the second aspect, wherein the member which replaces - heavy water is disposed in a region which shows a relatively high output density in the calandria tank. In addition to the effect obtainable from the second aspect, the distribution of the outputs can be uniformed by arranging the balance of the outputs from a region in which the output density is high and that from a region in which the output density is low since the above-described cylinder is positioned in the region in which the output denslty is relatively high.
A seventeenth aspect of the present invention lies in a pressure-tube type nuclear reactor according to the second aspect, wherein the member which replaces heavy water is arranged in such a manner that its thickness is enlarged in proportion to the output density. In addition to the effect obtainable from the second aspect, the quantity of heavy water to be replaced can be enlarged in proportion to the output density in the region in which the output density is high since the above-described cylinder is arranged to have an increased thickness in proportion to the output density.
Therefore, the volume ratio of heavy water to fuel can be, in proportion to the output density, adjusted in the region in which the output density is high.
Other and further objects, features and advantages of the invention will appear more fully from the following description provided in conjunction with the accompanying drawings, in which:
CA 0202~713 1998-02-11 -Fig. 1 illustrates a first embodiment of the present invention and is a plan view which illustrates the plan configuration of calandria tubes of a pressure-tube type nuclear reactor;
Fig. 2 illustrates the first embodiment of the present invention and is a vertical cross sectional view which illustrates the core of the pressure-tube type nuclear reactor;
Fig. 3 illustrates the first embodiment of the present invention and is an enlarged view which illustrates the configuration of pressure tubes each of which serves as a unit of a portion including control rod guide tubes or neutron instrumentation tubes shown in Fig. 1;
Fig. 4 is a graph which illustrates the relationship between void reactivity coefficient and volume ratio of heavy water to fuel of the pressure-tube type nuclear reactor;
Fig. 5 illustrates a second embodiment of the present invention and is a plan cross sectional view which illustrates the relationship among the calandria tubes, cylinder disposed outside the calandria tubes and control rod guide tubes or neutron instrumentation tubes disposed in the calandria tank of the pressure-tube type nuclear reactor;
Fig. 6 illustrates a second embodiment of the present invention and is a vertical cross sectional view which illustrates the calandria tubes and cylindrical CA 0202~713 1998-02-11 portions disposed outside the calandria tubes according to the embodiment shown in Fig. 5;
Fig. 7 illustrates the second embodiment of the present invention and is a plan view which illustrates the configuration of the tubes and the cylinders when viewed from a portion above an upper tube sheet according to the embodiment shown in Fig. 6;
Fig. 8 illustrates the second embodiment of the present invention and is a plan view which illustrates the overall configuration of the tubes in the calandria tank of the pressure-tube type nuclear reactor;
Fig. 9 illustrates the second embodiment of the present invention and is a perspective view which illustrates the cylinder;
Fig. 10 illustrates the second embodiment of the present invention and is a plan cross sectional view which illustrates a fastener portion for the cylinder;
Fig. 11 illustrates the first embodiment of the present invention and is a plan view which schematically illustrates the equilateral triangular lattice configuration of the tubes;
Fig. 12 illustrates a conventional structure and is a plan configuration view which schematically illustrates square lattice configuration of the tubes;
Fig. 13 illustrates a third embodiment of the present invention and is a plan configuration view which partially illustrates a hollow cylinder;
. . .
CA 0202~713 1998-02-11 -~- Fig. 14 illustrates a conventional structure and is a plan configuration view which illustrates the overall plan configuration of the calandria tubes of the pressure-tube type nuclear reactor;
Fig. 15 illustrates a conventional structure and is a plan configuration view which illustrates a portion of the configuration of the pressure tubes shown in Fig. 14 in an enlarged manner;
Fig. 16 is a graph which illustrates the relationship between the neutron multiplication factor and the volume ratio of heavy water to fuel of the pressure-tube type nuclear reactor;
Fig. 17 illustrates a fourth embodiment of the present invention and is a plan configuration view which illustrates the plan configuration of the tubes in a quarter portion of the core of the pressure-tube type nuclear reactor;
Fig. 18 illustrates the fourth embodiment of the present invention and is a vertical cross sectional view which illustrates a half portion of the core of the pressure-tube type nuclear reactor;
Fig. 19 illustrates the fourth embodiment of the present invention and is a plan cross sectional view which illustrates a quarter portion of the calandria tube; and Fig. 20 is a graph which illustrates the output peaking coefficient in the axial direction of the core according to the present invention.
CA 0202~713 1998-02-11 The quantity of heavy water for one pressure tube can be expressed by hatched area Slin the cross sectional view of Fig. 11, the area S1 being obtained from the following equation:
S1 = 2~ Q12 ~ ~R12 ~-- (1) where ~1: interval between lattices R1: outer radius of calandria tube On the other hand, the quantity of heavy water for one pressure tube arranged in a square lattice configuration can be expressed by hatched area S2 in the cross sectional view of Fig. 12, the area S2 being obtained from the following equation:
S = (e)2 _ ~(R)2 ...................... (2) where ~2: interval between lattices R2: outer radius of calandria tube Assuming that the triangular lattice and the square lattice have the same interval between lattices and the diameter of the calandria tube and therefore el = ~2 = ~ and Rl= R2= R, heavy water volume reduction ratio ~M for one pressure tube, obtained from a comparison made between the equilateral triangular lattice configuration and the square lattice configuration, can be expressed by the following equation:
~M = (S2 - Sl)/S2 = (1 - ~3/2) x {1 - ~(R/Q)2}-l (3) Specifically, it is assumed that ~ = 24 cm and R = 8 cm so as to be substituted into Equation (3), a reduction ~0 ratio ~M of about 0.21 is obtained.
CA 0202~713 1998-02-11 Reduction ratio ~L of the diameter of the core portion which is a critical factor to determine the size of the calandria tank can be obtained from the following equation:
~L = {ez ~ (2~3 )oSel}/e2 = 1 - (~3)os . 0.07 (4) That is, assuming that the lattice intervals are the same, the quantity of heavy water can be significantly reduced (about 21~ according to the above-described example) and the diameter of the core can be reduced by 7~.
Therefore, according to the equilateral triangular lattice configuration, the volume of heavy water can be reduced without shortening the interval between the pressure tubes and the volume ratio of heavy water to fuel can be reduced. Therefore, the size of the calandria tank can be reduced, causing a satisfactory operational performance and an economical advantage to be obtained.
With respect to the second aspect of the present invention, the volume ratio of heavy water to fuel (D/F) can be obtained from the following equation in the case where the member having a thickness t is successively placed around the pressure tube (the member having a cylindrical shape):
D/F = {e - ~(R + t)2}/n~r2 CA 0202~713 1998-02-11 - where ~ = interval between lattices R = outer radius of calandria tube t = thickness of cylinder n = number of fuel pins per fuel assembly r = radius of fuel pellet The improved degree QD/F of the volume ratio D/F of heavy water to fuel can be obtained from Equation (5) as follows:
~D/F = -{7r(R + t) 2 _ 7rR2}/n~r2 ... (6) A first embodiment of the present invention will now be described.
A plurality of calandria tubes 1, control rod guide tubes 4 and neutron instrumentation tubes 5 are inserted into a calandria tank 2 in which heavy water 10 serving as a neutron moderator is enclosed.
A pressure tube 3 is inserted into the calandria tube 1, the lower end of the pressure tube 3 being connected to a pipe 31 through which light water passes through. The other end of the pressure tube 3 is connected to another pipe 32.
The pressure tube 3 accommodates a fuel assembly constituted by binding a plurality of fuel pins each of which contains nuclear fuel.
Light water is introduced into the pressure tube 3 through the pipe 31 by a pump (not shown). As a result, light water in the pressure tube 3 is heated by the fuel assembly so that it boils. As a result, light water becomes a two phase ~low consisting o~ steam and CA 0202~713 1998-02-11 ' _ - liquid at high temperature and high pressure so that the two phase flow passes through the pipe 32. It is then taken outside the core so as to act as energy to rotate the turbine of a generator.
As shown in Fig. 1, according to this embodiment, the calandria tubes 1 are arranged to be in the form of equilateral triangular lattices each of which includes a control rod guide tube 4 or a neutron instrumentation tube 5.
The above-described calandria tubes 1, the control rod guide tubes 4 and the neutron instrumentation tubes 5 are hermetically connected to an upper tube sheet 6 and a lower tube sheet 7, as shown in Fig. 2, in order to enable the calandria tank 2 to contain heavy water.
According to the above-described equilateral triangular lattice arrangement of the calandria tubes 1, an effect can be obtained in that the necessary volume of heavy water can be reduced in comparison to a conventional square lattice arrangement shown in Figs. 14 and 15.
The manner in which to dispose the control rod guide tube 4 will be described.
As shown in Fig. 3, when the control and instrumentation pipes such as the control rod guide tube 4, the neutron instrumentation tube 5, a poison tube and the like are disposed in the central portion of the triangular lattice, predetermined mechanical strength must be secured in a joint (usually a rolled joint) CA 0202~713 1998-02-11 '~_ ~ between the above-described pipes and the calandria pipe 1 and the upper tube sheet 6. Therefore, a minimum gap 8 must be secured between the pipe having the largest outer diameter (usually, the control rod guide pipe 4) and the calandria tube 1. As a result, the maximum diameter of the above-described pipes are determined.
Since the equilateral angular lattice enables the above-described maximum diameter to be reduced in comparison to the square lattice, the control rod guide pipe 4 must be disposed to the same position at which the pressure tube 1 is disposed in the case where a large-diameter control rod guide tube 4 must be employed. In this case, since the necessity of a space in which the control rod guide tube 4 is disposed in the equilateral triangular lattice can be eliminated, the gap between the pressure tubes 1 can be narrowed. Therefore, a preferable volume ratio of heavy water to fuel can be realized even if the pressure tube 1 is replaced by the control rod guide tube 4.
Furthermore, in some instances, fuel control rods are inserted into some pressure tubes 1 in the equilateral triangular lattices so as to replace the control rod guide tubes 4. In order to prevent a deterioration in the volume ratio of heavy water to fuel due to the above-described provision of the control rods, the gap between the pressure tubes 1 must be reduced by the degree which corresponds to the eliminated space in which the control rod guide tube 4 is disposed in the equilateral triangular lattice area. In this case, since light water is, as the coolant, passed through the pressure tubes 1, the control rod in the pressure tube 1 can be satisfactorily cooled. Therefore, a control rod with a fuel follower can be employed as the control rod.
In a structure in which the control rod with a fuel follower is employed, the fuel can be introduced by the degree of the gradual removal of the control rod from the core at the end stage of the combustion. Therefore, the deterioration in the output at the final stage of the combustion in the core can be prevented.
A specific example of the equilateral triangular lattice will be described. When the control rod guide tube 4 is positioned at the position at which the pressure tube 1 has been disposed, essential dimensions of a large-size reactor arranged for the purpose of realizing a desired volume ratio of 8.0 between heavy water and fuel are as follows, where the size of the lattice is 25 cm and the number of the fuel pins in the fuel assembly is 54:
Distance between lattices ~ : 25.0 cm Inner diameter of pressure tube: 12 cm Configuration: Equilateral triangular lattice configuration Number of fuel pins in fuel assembly: 54 Diameter of fuel pellet: 1.0 cm Outer diameter of calandria tube: 16 cm , CA 0202~713 1998-02-11 As a result, the above-described volume ratio - of 8.0 between heavy water and fuel can be achieved.
A second embodiment of the present invention will be described.
Referring to Figs. 5 and 6, a second embodiment of the present invention, structured in such a manner that a cylinder is disposed around each of the pressure tubes arranged to be in a square lattice configuration, will be described. Fig. 5 illustrates a unit of the lattices in the calandria tank 2 according to the present invention, the unit being composed of four calandria tubes 1 arranged to be square lattice configuration. A
pad 30 is held between the calandria tube 1 and a cylinder 9 in order to form a proper gap around the calandria tube 1. The cylinder 9 is then placed on a lower tube sheet. The cylinder 9 is made of a material such as metal of a type which does not excessively absorb neutrons and which has satisfactory strength, the metal being exemplified by Zircalloy-2, zirconium-niobium alloy and aluminum alloy. The cylinder 9 can be sectioned into two or three sections in its circumferential direction so as to be fastened easily as described above. A fastener 11 is slid in a direction designated by an arrow 12 as shown in Fig. 9, so as to realize the state of the fastening as shown in Fig. 10. If necessary, the cylinder 9 may be shortened in its axial direction (by 50 cm to 200 cm), so that it can be introduced into the calandria tank 2 and easily fastened there as shown in CA 0202~713 1998-02-11 Fig. 6 after the calandria tube 1 has been connected to the upper tube sheet 6 and the lower tube sheet 7 of the calandria tank 2. After all of the cylinders 9 have been fastened as described above, heavy water serving as the moderator is introduced into the calandria tank 2.
As shown in Fig. 7, the portion at which the control rod guide tube 4 passes through the upper tube sheet 6 of the calandria tank 2 must secure predetermined mechanical strength at the joint between the calandria tube 1 and the control rod guide tube 4 and the upper tube sheet 6. Therefore, the minimum gap 8 between the calandria tube 1 and the control rod guide tube 4 must have the necessary size.
Usually, it is difficult to enlarge the diameter of the calandria tube 1 at the upper tube sheet 6. Therefore, the diameter of the calandria tube 1 in the core in the calandria tank 2 is made larger than that in its upper portion.
However, the enlargement of the diameter of the calandria tube or the arrangement of the drawing of the shape of it encounters a certain limit in terms of the manufacturing difficulty and the mechanical structure.
Therefore, it is difficult to considerably enlarge the diameter of the calandria tube in the calandria tank.
Therefore, according to the present invention, the cylinder 9 is disposed around the calandria tube 1 so as to overcome the above-described difficulty.
CA 0202~713 1998-02-11 The control rod guide tubes 4 and the neutron instrumentation tubes 5 of a number necessary to control and to measure the output from a nuclear reactor are, as shown in Fig. 7, disposed properly in the gaps between the calandria tubes 1.
A specific example which is able to quantitatively realize the effect of the cylinders 9 will be described.
In this case, the configuration is arranged to be the square lattice configuration as shown in Fig. 8.
Lattice interval ~: 24.5 cm Calandria tube outer radius R: 8 cm Number n of fuel pins of fuel assembly: 54 Fuel pellet radius r: 0.5 cm Cylinder thickness: 1.0 cm - As a result of the effect of the cylinder provided, the volume ratio of heavy water to fuel can be improved from 9.4 to 8.1.
A third embodiment of the present invention, provided with a cylinder having a different structure from that of the cylinder 9 according to the second embodiment, will be described. According to the third embodiment, an economical effect can be obtained. The difference in the structure of the cylinder 9 will be described.
As shown in Fig. 13, the wall portion of the cylinder 9 is arranged to be a hollow structure. An outer plate 13 and an inner plate 14 of the hollow CA 0202~713 1998-02-11 cylinder is made of Zircalloy-2 or an aluminum alloy - (1100). If necessary, a spacer 16 may be disposed so as to maintain the gap in the hollow portion and separated portions 15 are joined by the fastener 11 or by welding.
The above-described separated portions 15 are connected to each other by the fastener 11, the portions 15 in which the circumferential end portions of the outer plate 13 and those of the inner plate 14 are hermetically welded by a welded portion 18. Furthermore, the axial end portions of the hollow cylinder are hermetically closed so that a hollow portion 17 is formed. The effective thickness of the hollow cylinder is defined from the outer surface of the outer plate 13 to the inner surface of the inner plate 14.
The volume ratio of heavy water to fuel can be improved from 10 to 8.2 when a hollow cylinder having the effective thickness t = 1.2 cm is used in a square lattice core arranged as follows:
Lattice interval e 24 cm Calandria tube outer radius R: 8 cm Number n of fuel pins of fuel assembly: 48 Fuel pellet radius r: 0.5 cm An example of a structure arranged in such a manner that the control rod guide tube 4 is disposed at the central portion of the triangular lattice and the cylinder is disposed around the calandria tube for the purpose of sufficiently improving the volume ratio of CA 0202~713 1998-02-11 heavy water to fuel will be described. In this case, the - arrangements and the effect are as follows:
Inner diameter of pressure tube: 12 cm Configuration: Equilateral triangular lattice configuration Lattice pitch: 25.5 cm Number n of fuel pins of fuel assembly: 54 - Fuel pellet diameter: 1.0 cm Outer diameter of calandria tube in the core portion: 16 cm Outer diameter of calandria tube at the upper tube sheet: 15 cm Outer diameter of control rod guide tube: 5 cm Minimum gap at the upper tube sheet: 4.7 cm lS Effective thickness of the cylindrical wall:
0.5 cm Volume ratio of heavy water to fuel: 7.9 According to the above-described examples, the volume ratio of heavy water to fuel can be properly designed.
The void coefficient changes depending upon the type of fuel (oxide fuel containing plutonium or uranium dioxide fuel), the composition, the enrichment and the like. However, since the volume ratio of heavy water to fuel can be arranged to be 7.9 to 8.2, according to the present invention, the void coefficient can be made a value in the vicinity of zero, in the order of 10-5 ~k/k/~
CA 0202~713 1998-02-11 void. Therefore, an excellent operating efficiency can - be obtained.
Furthermore, since the diameter of the core and the quantity of heavy water can be reduced, an economical S effect can be obtained.
An example of a method of fastening the cylinder 9 to the portion around the calandria tube 1 will be described.
The manufactured cylinder 9 is placed on the lower tube sheet 7 prior to the fastening of the calandria tube 1 to the calandria tank 2. The calandria tube 1 is then inserted into the lower tube sheet 7. At this time, the calandria tube 1 is also inserted into the cylinder 9. Thus, the structure in which the cylinder 9 as an alternative to heavy water is disposed around the calandria tube 1 can be manufactured.
According to the above-described manufacturing method, the necessity of the work for assembling the cylinder 9 around the calandria tube 1 performed in a narrow space can be eliminated. Furthermore, the necessity of providing a wide working space around the calandria tube 1 can be eliminated. It is preferable that the cylinder 9 be disposed in such a manner that it is held between the upper and the lower tube sheets 7 and 8 via a spacer.
Accordingly, the structure is arranged in such a manner that the calandria tubes 1 are disposed in the core in the form of a triangular lattice, the volume CA 0202~713 1998-02-11 ratio of heavy water to fuel can be properly determined - and the coolant void reactivity coefficient can be made closer to negative values as much as possible.
Therefore, the self-control performance peculiar to a nuclear reactor can be improved. For example, since the quantity of heavy water can be reduced by about 20~ and the diameter of the core can be reduced by about 7~ in the same lattice interval as that of the conventional structure, an economical effect can be obtained.
Furthermore, when a cylinder is, as an alternative to heavy water, fastened around the calandria tube 1, the coolant void reactivity coefficient can be made a value further closer to a negative value.
Therefore, the self-control performance can be improved.
In addition, when both the above-described triangular lattice configuration and the cylinder are simultaneously employed, the design can be significantly freely made for the purpose of improving the operation efficiency and the economical effect.
A fourth embodiment of the present invention further established for the purpose of making the distribution of outputs from the pressure type nuclear reactor uniform will be described.
As shown in Fig. 4, in a design range of a nuclear reactor which uses heavy water as the moderator, when the volume ratio of heavy water to fuel is reduced, the coolant void reactivity coefficient is usually reduced (the self-control performance is improved). As CA 0202~713 1998-02-11 shown in Fig. 16, the neutron multiplication factor is reduced when the ratio of the volume of a heavy water moderator to the volume of fuel has become reduced.
Usually, the more the neutron multiplication factor is, the more the burn-up of the same fuel can be enlarged (the fuel economy can be improved). Therefore, a proper volume ratio of heavy water to fuel can be selected in such a manner that both the self-control performance and the fuel economy are maintained at a satisfactory degree.
Since a larger quantity of neutrons leak in the peripheral portion in the core in comparison to that in the central portion of the core, the neutron multiplication factor becomes reduced. Therefore, the output density becomes lowered and a uniform output distribution cannot be obtained.
Accordingly, according to the fourth embodiment, an improvement of the self-control performance and a uniform output distribution can be simultaneously achieved.
Fig. 17 illustrates a quarter portion of the arrangement of calandria tubes 1, neutron instrumentation tubes and control rod guide tubes in the calandria tank 2.
As shown in Fig. 19, the calandria tube 1 includes the pressure tube 3 through which a coolant 22 passes. The pressure tube 3 also includes fuel pins 21 which contain pellet nuclear fuel. In the calandria tank CA 0202~713 1998-02-11 2 which contains heavy water 10, the calandria tubes 1 are disposed in a square lattice configuration by the number necessary to obtain the rated output from the pressure tube type nuclear reactor. Furthermore, the control rod guide tubes 4 and the neutron instrumentation tubes 5, which are necessary to control the core or to perform the instrumentation, are properly disposed among the above-described lattices. If necessary, poison tubes for introducing poison for controlling the output of the core are provided. The above-described tubes are inserted into the calandria tank 2 and are hermetically joined to the upper tube sheet 6 and the lower tube sheet 7 of the calandria tank 2 so that the calandria tank 2 contains heavy water.
As shown in Figs. 17, 18 and 19, the cylinder 9 is disposed around the calandria tube 1 disposed at the central portion of the core in the calandria tank 2.
The cylinder 9 may be fastened in such a manner that it is supported by the calandria tube 1 or by the lower tube sheet 7 via a spacer.
The cylinder 9 is made of a material, which does not excessively absorb neutrons, such as a zirconium alloy (Zircalloy-2, Zircalloy-4, zirconium-niobium alloy or the like), aluminum or an aluminum alloy.
In order to enlarge the volume which can be replaced by heavy water, the wall of the cylinder 9 is arranged so as to form the hollow portion 17 which contains a chemically stable gas such as helium or argon.
CA 0202~713 1998-02-11 It is preferable that the hollow portion 17 be filled with a chemically stable gas such as helium or argon in the structure according to the above-described embodiments in the case where the cylinder 9 is arranged to be the hollow portion. In order to seal the thus enclosed gas, the hollow portion 17 is hermetically sealed similar to the above-described embodiments. The cylinder 9 may be sectioned into sections similar to the above-described embodiments. In this case, the end portions thus sectioned are structured so as to be joined to each other by a fastener similar to the above-described embodiments.
Sixty fuel pins are collected so as to form a fuel assembly which is included in the pressure tube. An example, arranged in such a manner that the cylinder 9 having hollow wall portion is disposed around the calandria tube 1 as an alternative to heavy water, will be described in terms of the quantitative effect.
According to this example, the present invention is applied to a 1,000 MW electric output pressure tube type nuclear reactor in which heavy water is used as the moderator and light water is used as the coolant. A specific example of the structure is as follows:
Power output: 1000 MW Number of pressure tubes:
Number n of fuel pins of fuel assembly: 60 Effective height of the core portion: 3.7 m Radius of core portion: 7.8 m ~ Fuel pellet radius r: 0.475 cm Inner diameter of pressure tube: 12.3 cm Pressure tube lattice interval Q: 24.5 cm Outer radius R of calandria tube: 8.25 cm Outer diameter of the control rod guide tube:
9.5 cm Effective thickness of hollow cylinder: 1.8 cm Number of calandria tubes 1 in which hollow cylinders are provided: 344 Axial length in which the hollow cylinder is disposed: 2.22 m Minimum interval in the upper tube sheet (between the calandria tube 1 and the control rod guide tube 4): 4.3 cm According to this example, the volume ratio of heavy water to fuel in the portion to which no cylinder is fastened is 9.1, while that in the portion (the central portion of the core) to which the cylinder is fastened is 6.7. As described above, when the volume ratio of heavy water to fuel in the central portion of the core is lowered with respect to that in the peripheral portion, the neutron multiplication factor in the central portion of the core becomes reduced in comparison to that in the peripheral portion. Therefore, the number of neutrons generated in the central portion is reduced, causing a curve showing the power density distribution to be changed from the dotted line to a CA 0202~713 1998-02-11 solid line as shown in Fig. 20 as well due to the - deterioration in the power distribution in the peripheral portion caused from the neutron leakage in the peripheral portion. As a result, the power distribution in the axial direction (vertical direction) of the core can be made more uniform. Since a similar effect can be obtained in the radial direction of the core, the power distribution in both the axial direction and the radial direction of the core can be made more uniform.
10As a result, the total (effective) volume ratio of heavy water to fuel in the core can be made a value in the vicinity of 8. Therefore, as shown in Fig. 4, the void coefficient can be made a value in the vicinity of zero in an order of 10-5 ~k/k/% void. As a result, a satisfactory operating performance can be obtained and the power distribution can be improved by about 20%
without deterioration in the neutron economy, causing an economical effect to be obtained. As described above, according to the present invention, the volume ratio of heavy water to fuel can be determined to a desired value so that the coolant void coefficient can be made a value further closer to the negative side. As a result, the self-control performance peculiar to the neutron reactor can be improved. Furthermore, since the cylinders 9 can be partially disposed in the portions showing a high power density so as to make the power distribution in the core to be uniform, the number of the control rods necessary to uniform the power distribution can be ''. ,' ' CA 0202~713 1998-02-11 reduced. In addition, the performance of the core can be easily controlled, the operation performance can be improved and an economical effect can be obtained.
A structure arranged in such a manner that the thickness of each of the cylinders 9 is enlarged in inverse proportion to the distance from the radial center of the core will further enable the power distribution in ~ the radial direction to be uniformed. In addition, a structure arranged in such a manner that the thickness of each of the cylinders 9 is enlarged in inverse proportion to the distance from the axial center will enable the power distribution in the axial direction to be uniformed.
Furthermore, if the calandria tubes are disposed in a triangular lattice configuration, the volume ratio of heavy water to fuel can be adjusted without the necessity of enlarging the calandria tank.
Therefore, the adjustment and design can be further freely performed.
In any of the above-described embodiments, it is preferable that a certain gap be provided between the calandria tube and the cylinder for the purpose of passing heavy water.
Claims (17)
1. A pressure-tube type heavy-water moderated nuclear reactor wherein pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes positioned in a calandria tank which contains heavy water, said pressure-tube type nuclear reactor comprising:
a structure wherein said pressure tubes are arranged so as to form an equilateral triangular lattice configuration.
a structure wherein said pressure tubes are arranged so as to form an equilateral triangular lattice configuration.
2. A pressure-tube type heavy-water moderated nuclear reactor wherein pressure tubes each of which accommodates nuclear fuel and through each of which a coolant passes are accommodated in respective calandria tubes positioned in a calandria tank which contains heavy water, said pressure-tube type nuclear reactor comprising:
a structure wherein a member which replaces said heavy water is positioned near said calandria tube.
a structure wherein a member which replaces said heavy water is positioned near said calandria tube.
3. A method of assembling a pressure-tube type nuclear reactor in which spaces for containing heavy water are formed by hermetically fastening calandria tubes which are inserted into a calandria tank to a component part of said calandria tank, said method of assembling a pressure-tube type nuclear reactor comprising the steps of:
securing said calandria tubes to said component part of said calandria tank;
introducing cylinders each of which is made of a material which does not excessively absorb neutrons and which is sectioned into a plurality of sections into portions around said calandria tubes; and assembling said cylinders sectioned into the plurality of sections so as to cover said calandria tubes.
securing said calandria tubes to said component part of said calandria tank;
introducing cylinders each of which is made of a material which does not excessively absorb neutrons and which is sectioned into a plurality of sections into portions around said calandria tubes; and assembling said cylinders sectioned into the plurality of sections so as to cover said calandria tubes.
4. A method of assembling a pressure-tube type nuclear reactor in which spaces for containing heavy water are formed by hermetically fastening calandria tubes which are inserted into a calandria tank to a component part of said calandria tank, said method of assembling a pressure-tube type nuclear reactor comprising the steps of:
introducing cylinder members each of which is made of a material which does not excessively absorb neutrons into said spaces for containing heavy water;
said calandria tubes also being inserted into said cylindrical members thus introduced when said calandria tubes are inserted into the component part of said calandria tank; and said calandria tubes being fastened to said component part of said calandria tank.
introducing cylinder members each of which is made of a material which does not excessively absorb neutrons into said spaces for containing heavy water;
said calandria tubes also being inserted into said cylindrical members thus introduced when said calandria tubes are inserted into the component part of said calandria tank; and said calandria tubes being fastened to said component part of said calandria tank.
5. A member to replace a heavy water moderator of a pressure-tube type nuclear reactor to be disposed around a calandria tube, said member to replace a heavy water moderator comprising:
an assembled structure in the form of a cylinder into which said calandria tube can be introduced.
an assembled structure in the form of a cylinder into which said calandria tube can be introduced.
6. A pressure-tube type nuclear reactor according to Claim 1, wherein the volume ratio of heavy water to fuel is arranged to be 9.0 or less.
7. A pressure-tube type nuclear reactor according to Claim 2, wherein the volume ratio of heavy water to fuel is arranged to be 9.0 or less.
8. A pressure-tube type nuclear reactor according to Claim 1, wherein some of said pressure tubes are replaced by control rod guide tubes, neutron instrumentation guide tubes or poison tubes for said pressure-tube type nuclear reactor at the position at which said pressure tubes are positioned and the volume ratio of heavy water to fuel is arranged to be 9.0 or less.
9. A pressure-tube type nuclear reactor according to Claim 1, wherein a control rod with a fuel follower is positioned in a coolant in some of said pressure tubes.
10. A pressure-tube type nuclear reactor according to Claim 1, wherein a cylinder surrounding said calandria tube is positioned so as to replace heavy water.
11. A pressure-tube type nuclear reactor according to Claim 2, wherein said member for replacing heavy water is positioned so as to form a cylinder which surrounds said calandria tube after assembled.
12. A pressure-tube type nuclear reactor according to Claim 1, wherein a cylinder having an inner wall surrounds said calandria tube having an outer wall and is positioned so as to replace heavy water and wherein a hollow area is formed between the inner wall of said cylinder and the outer wall of said calandria tube.
13. A pressure-tube type nuclear reactor according to Claim 2, wherein said member for replacing heavy water is a cylinder having an inner wall which surrounds said calandria tube having an outer wall, and wherein a hollow area is formed between the inner wall of the cylinder and the outer wall of said calandria tube.
14. A pressure-tube type nuclear reactor according to Claim 2, wherein said member which replaces heavy water is made of a zirconium alloy, aluminum or of an aluminum alloy.
15. A pressure-tube type nuclear reactor according to Claim 2, wherein said calandria tubes are arranged to be in an equilateral triangular lattice configuration.
16. A pressure-tube type nuclear reactor according to Claim 2, wherein said member which replaces heavy water is disposed in a region which shows a relatively high output density in said calandria tank.
17. A pressure-tube type nuclear reactor according to Claim 2, wherein said member which replaces heavy water is arranged so that its thickness is enlarged in proportion to output density.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP01-242050 | 1989-09-20 | ||
| JP1242050A JPH087270B2 (en) | 1989-09-20 | 1989-09-20 | Pressure tube reactor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2025713A1 CA2025713A1 (en) | 1991-03-21 |
| CA2025713C true CA2025713C (en) | 1998-11-03 |
Family
ID=17083527
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002025713A Expired - Fee Related CA2025713C (en) | 1989-09-20 | 1990-09-19 | Pressure-tube type heavy-water moderated nuclear reactor |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH087270B2 (en) |
| CA (1) | CA2025713C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA3066042A1 (en) * | 2017-06-23 | 2018-12-27 | Candu Energy Inc. | System and method for aligning nuclear reactor tubes and end fittings using tube geometry |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0721546B2 (en) * | 1989-03-16 | 1995-03-08 | 動力炉・核燃料開発事業団 | Reactor with integrated pressure vessel structure |
-
1989
- 1989-09-20 JP JP1242050A patent/JPH087270B2/en not_active Expired - Lifetime
-
1990
- 1990-09-19 CA CA002025713A patent/CA2025713C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH03105285A (en) | 1991-05-02 |
| CA2025713A1 (en) | 1991-03-21 |
| JPH087270B2 (en) | 1996-01-29 |
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| EEER | Examination request | ||
| MKLA | Lapsed |