CA1191626A - Mechanical spectral shift reactor - Google Patents
Mechanical spectral shift reactorInfo
- Publication number
- CA1191626A CA1191626A CA000413521A CA413521A CA1191626A CA 1191626 A CA1191626 A CA 1191626A CA 000413521 A CA000413521 A CA 000413521A CA 413521 A CA413521 A CA 413521A CA 1191626 A CA1191626 A CA 1191626A
- Authority
- CA
- Canada
- Prior art keywords
- core
- rods
- displacer
- reactor
- fuel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- 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
Landscapes
- Monitoring And Testing Of Nuclear Reactors (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The mechanical spectral shift reactor provides a method and apparatus for controlling a nuclear reactor comprising inserting a plurality of reactor coolant dis-placer members into the reactor at the beginning of the core life. The displacer members reduce the volume of reactor coolant moderator in the core at the start-up. As the reactivity of the core declines with fuel depletion, a selected number of displacer members are withdrawn from the core at selected time intervals. The withdrawal of the displacer member allows reactor coolant water to enter the core which increases core moderation at a time when fuel reactivity is declining. Thus for a given amount of nuclear fuel the life of the core can be extended or for a given life of a core the uranium fuel requirements can be reduced.
The mechanical spectral shift reactor provides a method and apparatus for controlling a nuclear reactor comprising inserting a plurality of reactor coolant dis-placer members into the reactor at the beginning of the core life. The displacer members reduce the volume of reactor coolant moderator in the core at the start-up. As the reactivity of the core declines with fuel depletion, a selected number of displacer members are withdrawn from the core at selected time intervals. The withdrawal of the displacer member allows reactor coolant water to enter the core which increases core moderation at a time when fuel reactivity is declining. Thus for a given amount of nuclear fuel the life of the core can be extended or for a given life of a core the uranium fuel requirements can be reduced.
Description
47, 948I
MECHANICAL SPECTRAL SHIFT REACTOR
B~CKGROUND OF THE INVENT;ION
The invention relates to spectral shift reactor control and more particularly to mechanical means for spectral shift reactor control.
In typical nuclear reactors, reactivity control is accomplished by varying the amount of neutron absorbing material (poisons) in the reactor core. Generally, neutron absorbing control rods are utilized to perform this func-; tion by varying the number and location of the control rods with respect to the reactor core. In addition to con~rol rods, burnable poisons and poisons dissol.ved in the reactor coolant can be used to control reactivity.
In the conventional designs of pressurized water reactors, an excessive amount of reactivity is designed into the reactor core at start-up so that as the reactivity is depleted over the life of ~he core the excess reactivity may be employed to lengthen the core life. Since an excessive amount of reactivity is designed into the reactor core at the beginning of core life, neutron absorbing material such as soluble boron must be placed in the core at that time in order to properly control the excess reactivity. Over the core life, as reactivity is consumed, the neutron absorbing material is gradually removed from ~3~
MECHANICAL SPECTRAL SHIFT REACTOR
B~CKGROUND OF THE INVENT;ION
The invention relates to spectral shift reactor control and more particularly to mechanical means for spectral shift reactor control.
In typical nuclear reactors, reactivity control is accomplished by varying the amount of neutron absorbing material (poisons) in the reactor core. Generally, neutron absorbing control rods are utilized to perform this func-; tion by varying the number and location of the control rods with respect to the reactor core. In addition to con~rol rods, burnable poisons and poisons dissol.ved in the reactor coolant can be used to control reactivity.
In the conventional designs of pressurized water reactors, an excessive amount of reactivity is designed into the reactor core at start-up so that as the reactivity is depleted over the life of ~he core the excess reactivity may be employed to lengthen the core life. Since an excessive amount of reactivity is designed into the reactor core at the beginning of core life, neutron absorbing material such as soluble boron must be placed in the core at that time in order to properly control the excess reactivity. Over the core life, as reactivity is consumed, the neutron absorbing material is gradually removed from ~3~
2 47,9~8I
the reactor core so that the original excess reactivity may be used. While this arrangement provides one means of controlling a nuclear reactor over an extended core life, the neutron absorbing material used during core life absorbs neutrons and removes reactivity from the reactor core that could otherwise be used in a more productive manner such as in plutonium fuel production. The consump-tion of reactivity in this manner without producing a useful product results in a less efficient depletion of uranium and greater fuel costs than could otherwise be achieved. Therefore, it would be advantageous to be able to extend the life of the reactor core without suppressing excess reactivity with neutron absorbing mate~ial thereby providing an extended core life with a significantly lower fuel cost.
One such method of producing an extended core life while reducing the amount of neutron absorbing mater-ial in the reactor core is by the use of "Spectral Shift Control". As is well understood in the art, in one such method the reduction of excess reactivity (and thus neutron absorbing material) is achieved by replacing a large portion of the ordinary reactor coolant water with heavy watec. This retards the chain reaction by shifting the neutron spectrum to higher energies and permits the reactor to operate at full power with reduced neu~ron absorbing material. This shift in the neutron spectrum to a "hard-ened" spectrum also causes rnore of the U238 to be converted to plutonium that is eventually used to produce heat.
Thus, the shift from a "soft" to a "hard" spectrum resul-ts in more neutrons being consumed by U238 in a useful manner rather than by poisons. As reactivity is consumed, the heavy water is gradually replaced with ordinary water so that the reactor core activity is maintained at a proper level. By the end of core life, essentially all the heavy water has been replaced by ordinary water while the core reactivity has been maintainecl. Thus, the reactor can be controlled without the use of neutron absorbing material 6;~6
the reactor core so that the original excess reactivity may be used. While this arrangement provides one means of controlling a nuclear reactor over an extended core life, the neutron absorbing material used during core life absorbs neutrons and removes reactivity from the reactor core that could otherwise be used in a more productive manner such as in plutonium fuel production. The consump-tion of reactivity in this manner without producing a useful product results in a less efficient depletion of uranium and greater fuel costs than could otherwise be achieved. Therefore, it would be advantageous to be able to extend the life of the reactor core without suppressing excess reactivity with neutron absorbing mate~ial thereby providing an extended core life with a significantly lower fuel cost.
One such method of producing an extended core life while reducing the amount of neutron absorbing mater-ial in the reactor core is by the use of "Spectral Shift Control". As is well understood in the art, in one such method the reduction of excess reactivity (and thus neutron absorbing material) is achieved by replacing a large portion of the ordinary reactor coolant water with heavy watec. This retards the chain reaction by shifting the neutron spectrum to higher energies and permits the reactor to operate at full power with reduced neu~ron absorbing material. This shift in the neutron spectrum to a "hard-ened" spectrum also causes rnore of the U238 to be converted to plutonium that is eventually used to produce heat.
Thus, the shift from a "soft" to a "hard" spectrum resul-ts in more neutrons being consumed by U238 in a useful manner rather than by poisons. As reactivity is consumed, the heavy water is gradually replaced with ordinary water so that the reactor core activity is maintained at a proper level. By the end of core life, essentially all the heavy water has been replaced by ordinary water while the core reactivity has been maintainecl. Thus, the reactor can be controlled without the use of neutron absorbing material 6;~6
3 47,94~I
and without the use of excess reactivity at start-up which results in a significant uranium fuel cost savings. The additional plutonium production also reduces the U 3 enrichment requirements. While the use of heavy water as a substitute for ordinary water can be used to effect the "spectral shift", the use of heavy water can be an expen-sive and complicated technology.
While there exist in the prior art numerous ways of controlling a nuclear reactor, what is needed is a method and apparatus for controlling neutron moderation in a manner that provides for reduced uranium fuel costs and for an extended reactor core life.
SUMMARY OF THE INVENTION
The mechanical spectral shift reactor provides a method and apparatus for controlling a nuclear reactor comprising inserting a plurality of reactor coolant dis-placer members into the reactor at the beginning of the core life. The displacer members reduce the volume of reactor coolant-moderator in the core at start-up. As the reactivity of the core declines with fuel depletion, a selected number of displacer members are withdrawn from the core at selected time intervals. The withdrawal of the displacer members allows more reactor coolant water to enter the core which increases core moderation at a time when fuel reactivity is declining. Thus for a given amount of nuclear fuel the life of the core can be extended or for a given life of a core the uranium fuel requirements can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
_ _ While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the invention, it is believed the inven-tion will be better understood from the following descrip-tion taken in conjunction with the accompanying drawings, wherein:
Figure 1 is a cross-sectional view in elevation of the reactor vessel;
and without the use of excess reactivity at start-up which results in a significant uranium fuel cost savings. The additional plutonium production also reduces the U 3 enrichment requirements. While the use of heavy water as a substitute for ordinary water can be used to effect the "spectral shift", the use of heavy water can be an expen-sive and complicated technology.
While there exist in the prior art numerous ways of controlling a nuclear reactor, what is needed is a method and apparatus for controlling neutron moderation in a manner that provides for reduced uranium fuel costs and for an extended reactor core life.
SUMMARY OF THE INVENTION
The mechanical spectral shift reactor provides a method and apparatus for controlling a nuclear reactor comprising inserting a plurality of reactor coolant dis-placer members into the reactor at the beginning of the core life. The displacer members reduce the volume of reactor coolant-moderator in the core at start-up. As the reactivity of the core declines with fuel depletion, a selected number of displacer members are withdrawn from the core at selected time intervals. The withdrawal of the displacer members allows more reactor coolant water to enter the core which increases core moderation at a time when fuel reactivity is declining. Thus for a given amount of nuclear fuel the life of the core can be extended or for a given life of a core the uranium fuel requirements can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
_ _ While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the invention, it is believed the inven-tion will be better understood from the following descrip-tion taken in conjunction with the accompanying drawings, wherein:
Figure 1 is a cross-sectional view in elevation of the reactor vessel;
4 47J948I
Figure 2 is a cross-sectional view in elevation of the top portion of the fuel assembly;
Figure 3 is a cross-sectional view in elevation ; of the botto~ portion of the fuel assembly;
Figure 4 is a view in perspective of displacer rods and their respective fuel assembly;
Figure 5 is a cross-sectional view in elevation of a displacer rod guide structure;
Figure 6 is a view along line VI-VI of Figure 5;
Figure 7 is a diagram of a quarter core of the reactor;
Figure 8 is an enlarged view of a portion of the quarter core;
Figure 9 is an enlarged view of a portion of the ~uarter core;
Figure lO is cross-sectional diagram of a typical fuel assembly; and Figure ll is a diagram of a section of the core.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the operation o a commercial pressurized water reactor it is desirable to be able to prolong the life of the reactor core to better utilize the uranium fuel thereby reducing the fuel costs. The invention described herein provides a means to extend reactor core life by controlling reactor core moderation.
Referring to Figure 1, the nuclear reactor is referred to generally as 20 and comprises a reactor vessel 22 with a removable closure head 24 attached to the top end thereof. An inlet nozzle 26 and an outlet nozzle 28 are connected to reactor vessel 22 to allow a coolant such as water to circulate through reactor vessel 22. A core plate 30 is disposed in the lower portion of reactor vessel 22 and serves to support fuel assemblies 32. Fuel assemblies 32 are arranged in reactor vessel 22 and com-prise reactor core 34. As is well understood in the art, - fuel assemblies 32 generate heat by nuclear fissioning of the uraniu~ therein. The reactor coolant flowing through 47,948I
reactor vessel 22 in heat transfer relationship with fuel assemblies 32 transfers the heat from fuel assemblies 32 to electrical generating equipment located remote from nuclear reactor 20. A plurality of control rod drive mechanisms 36 which may be chosen from those well known in the art such as the one described in U.S. Patent No.
3,882,353 issued May 6, 1975 in the name of J. L. DeWeese are disposed on closure head 24 for inserting or withdraw-ing control rods {not shown) from fuel assemblies 32. In addition, a plurality of displacer rod drive mechanisms 38 are also disposed on closure head 24 for inserting or withdrawing displacer rods 40 from fuel assemblies 32.
Displacer rod drive mechanisms 38 may be similar to the one described in Canadian Patent Application Serial No. 389,969, filed November 12, 1981 in the name of L. Veronesi et al.
entitled "Hydraulic Drive Mechanism" and assigned to the Westinghouse Electric Corporation. For purposes of clarity, only a selected number of displacer rods 40 are shown in Figure 1. However, it should be understood, that the number of displacer rods 40 are chosen to correspond to the number of displacer rod guide tubes in fuel assemblies 32.
A plurality of displacer rod guide structures 42 are located in the upper section of reactor vessel 22 with each bei.ng in alignment with a displacer rod drive mechanism 38 for guiding the movement of displacer rods 4Q through the upper section of reactor vessel 22. A calandria 44 may be arranged between fuel assernblies 32 and displacer rod guide structures 42 and comprises a multiplicity of hollow stainless steel tubes arranged in colinear alignment with each displacer rod and control rod for providing guidance of the displacer rods and control rods through the calandria area and for minimizing flow induced vibrations in the displacer rods and control rods.
Referring now to Figures 2-4, fuel assemblies 32 comprise fuel elements 487 grids 50, bottom nozzle 52, top nozzle 54, and guide tubes 56. Fuel elements 48 may be 62~
6 47,948I
elongated cylindrical metallic tubes containing nuclear fuel pellets and having both ends sealed by end plugs.
Fuel elements 48 may be arranged in a substantially 20 x 20 rectangular array and are held in place by grids 50.
Guide tubes 56 which may number 25 are arranged in a generally 5 x 5 array within each fuel assembly 32. Each guide tube 56 occupies the space of about four fuel ele-ments 48 and extend from bottom nozzle 52 to top nozzle 54 and provide a means to support grids 50 ! top nozzle 54 and bottom nozzle 52. Guide tubes 56 may be hollow cylindrical metallic tubes manufactured ~rom Zircaloy ~ and capable of accommodating rods such as displacer rods 40 or control rods. Displacer rods 40 and control rods are manufactured to be approximately the same size so that each guide tube 56 can equally accommodate either a displacer rod or a control rod. When not occupied by a rod, guide tubes 56 are filled with reactor coolant; however~ when displacer rods 40 are inserted in guide tubes 56 displacer rods 40 displace the coolant therein.
: ?0 Grids 50 are positioned at various locations along the length of fuel assembly 32 and serve to space fuel elements 48 and guide tubes 56 at appropriate dis-tances from each other and to allow the reactor coolant to circulate in heat transfer relationship with fuel elements 48. A more detailed description of a similar grid may be found in United States Patent Nos. 3,379,617 and 3,379,619, both issued in the name of H. N. Andrews et al. As can be seen in Figure 4, displacer rods 40 are elongated cylin-drical substantially hollow rods which can be manufactured out of Zircaloy ~ and may be of the type described in Canadian Patent Application Serial No. 391,903 entitled "Displacer Rod For Use In A Mechanical Spectral Shift Reactor" filed December 9, 19~1 in the name of R. K.
Gjertsen et al. and assigned to the Westinghouse Elec-tric Corporation. Displacer rods 40 may also contain ZrO2or A1203 pellets for weighting the rod and enhancing its lowerability. Displacer rods 40 are arranged so as to be 7 47,948I
in colinear alignment with guide tube 56 so that displacer rods 40 ~ay be inserted in guide tubes 56 when it is desired. Displacer rods 40 are supported from a common attachment known as a spider 58. Spider 58 comprises a body 60 with struts 62 radially extending from body 60.
Displacer rods 40 are individually attached to each strut 62 to form an array corresponding to the array of guide tubes 56 into which displacer rods may be inserted.
Spider 58 is attached to drive shaft 64 which is connected to displacer rod drive mechanism 38. Activation of dis-placer rod drive mechanism 38 causes drive shaft 64 to be ! either lowered or raised thereby inserting or withdrawing displacer rods 40 from fuel assemblies 32 of core 34.
It is important to note that each spider 58 is arranged to be able to insert displacer rods 40 into more than one fuel assembly 32. For example, as shown in Figure 4, spider 58 is capable of inserting 25 displacer rods in center fuel assembly 32 and 4 displacer rods in each of the adjacent 4 fuel assemblies. In this manner displacer rods 40 can be moved in and out of fuel assem-blies 32 wihout increasing the number of spiders and drive mechanisms.
Referring now to Figures 5 and 6, displacer rod guide structures 42 comprise a plurality of split tube guides 70 which are designed to allow rods such as dis-placer rods or control rods to pass therethrough. Dis-placer rod guide structures 42 are located between calan-dria 44 and closure head 24 as shown in Figure 1 and are arranged to correspond to each displacer rod drive mechan-ism 38. A number of spacers 72 are located at variouslocations along split tube guides 70 and together wlth split tube guides 70 serve to guide displacer rods 40 through the upper section of reactor vessel 22. As can be seen in Figure 6, 8 split tube guides 70 may be provided for guiding displacer rods 40. The "split" in split tube guides 70 along with slots 74 in spacers 7~ a~low spider 58 to pass therethrough while maintaining alignment of the 8 47,948I
rods with guide tubes 55 in fuel assemblies 32. A center slot 76 is also provided for accommodating drive shaft 64 so that spider 58 may be moved therethrough.
Referring again to Figure l, calandria 44 which comprises a multiplicity of tubes provides guidance for the rods such as displacer rods 40 through the calandria area. In general, the tubes in calandria 44 are not split tubes, as are split tube guides 70, so that spider 58 stops its descent when spider 58 nears the top of the tubes in calandria 44. When stopped at the top of caland-ria 44 all rods extend through the calandria tubes and are fully inserted in fuel assembly 32. While inserted in the calandria tubes, the rods are protected from the flow of reactor coolant thereby minimizing vibrations that would otherwise be induced by the velocity of the reactor coolant in that area.
In the invention as described herein, at least three different types of rods are capable of being inserted into quide tubes 56. For example, ~isplacer rods, control rods, and gray rods may be arranged to be inserted in guide tubes 56. All of the rods are approximately the same size and configuration, but because of the materials with which they are made serve different purposes. Dis-placer rods 40 which may be either a hollow thick walled tube or may contain a low neutron absorbing-material such as ZrO2 or Al203 pellets are used to displace reactor coolant and thereby control reactor moderation. Control rods contain neutron absorbing material as is well under-stood in the art and serve to control core reactivity in a commonly understood fashion. Gray rods are similar to displacer rods 40 but are made of an intermediate neutron absorbing material such as stainless steel so that their reactivity worth per rod is greater than that of displacer rods 40.
Referring now to Fiqures 7-11, the ~uarter core arrangement of fuel elements 48, displacer rods 40, control rods 80, gray rods 82, and unrodded locations 84 are .
9 47,948I
shown. It is to be understood that the full reactor core configuration can be established by extrapolating the quarter core sho~-?n in Figure 7. Actually, the quarter core sho~?n in Figure 7 is a mirror image of the eighth core taken a]ong line A-A of Figure 7. However~ the quarter core of Figure 7 is being shown for clarity.
As can be seen in Figure 10, each fuel assembly 32 comprises an array of fuel elements 4~ and an array of guide tubes 56. Generally, control rods 38 and gray rods 82 are used only in the diagonally arranged guide tu~es 56 while displacer rods 40 are generally used in all guide tubes 56 of a given fuel assembly. In addition, an in-strument tube 88 is provided near the center of each fuel assembly 32 for accommodating data instrumentacion such as movable fission chambers. While each fuel assembly 32 is essentially identical to the one shown in Figure 10, each fuel assembly 32 can produce a different function depending on whether guide tubes 56 are occupied by reactor coolant, displacer rods 40, control rods 80, or gray rods 82. Dis-placer rods 40 and gray rods 82 are generally chosen to beapproximately the same size so as to displace approximate-ly the same volume of water. ~However, gray rods 82 can be thick walled stainless steel cylindrical rods which can have higher reactivity worths than do displacer rods 40 so that they may be used to offset the effects of xenon transients during load follow operations in addition to moderator displacement as described in Canadian Patent Application Serial No. 391>869 filed December 9, 1981 in the name of W. R. Carlson et al. enti~led "Spectral Shift Reactor" and assigned to the Westinghouse Electric Corporation.
Referring now to Figure 11, a fuel assembly 32 in which no control rods 80 or gray rods 82 are used and in which only displacer rods 40 are used in guide tubes 56 is referred to generally as displacer assembly 90. A fuel assembly 32 in which both displacer rods 40 and control rods 80 are employed (but no gray rods) is referred to as `.?. i . ` !i".
L62~
47,948I
control assembly 92. Similarly, a fuel assembly 32 in which both displacer rods 40 and gray rods 82 are used is called a gray assembly 94. It should be noted that in Figure 11 fuel elements 48 have been omitted for clarity and that those fuel assemblies are similar ~o those shown in Figure 10.
Still referring to Figure 11, each of the control rods 80 and gray rods 82 are attached to a spider (not shown) similar to spider 58 except that the spider for control rods 80 or gray rods 82 generally only affects one fuel assembly. In this manner, all control rods 80 or gray rods 82 in a given uel assembly can be raised or lowered by a single drive mechanism. Furthermore, since each dis-placer rod spider 58 can extend into the adjacent fuel assemblies (as illustrated in the center portion of Figure 11 and in Figure 4), the displacer rod spider's 58 move-ment affects the control on five fuel assemblies and re~
duces the number of displacer rod drive mechanisms needed.
0 course, on the periphery of the ~uarter core (as shown in Figure 7) the particular spiders may move less than the usual number of rods because there are no adjacent fuel assemblies or there are unrodded locations 84.
! Referring again to Figures 8 and ~ which com~
prise Fi~ure 7, a ~uarter core arrangement, each row or partial row is numbered 100-114 and each column or partial column is numbered 116-130 and comprises:
Fuel Assemb~y (100,116) quarter displacer assembly (100,118) half control assembly 30 (100,120) half displacer assembly : (100,122) half control assembly (100,124) half displacer assembly (100,126) half control assembly (100,128) half displacer assembly 35 (100,130) half gray assembly 6~
11 47,948I
~102,116) half control assemb_y (102,118) ull displacer assembly (102,120) full gray assernbly (102,122) full displacer assembly (102,124) full gray assembly (102,126) full displacer assembly (102,128) full control assembly (102,130) full displacer assembly (104,116) half displacer assembly (104,118) full gray assembly ( (104,120) full displacer assembly (104,122) full control assembly (104,124) full displacer assembly (104,126) full cont.rol assembly ~104,128) full displacer assembly (104,130) parti.al control-unrodded assembly (106,116) half control assembly (106,118) full displacer assembly (106,120) full control assembly (106,122) full displacer assembly (106,124) full control assembly (106,126) full displacer assembly (106,128) full control assembly (106,130) full displacer assembly 2~ (108,116) half displacer assembly (108,118) full gray assembly (108,120) full displacer assernbly (108,122) full control assembly (108,124) full displacer assembly (108,126) full control assembly (108,128) full displacer assembly 6~i 12 47,948I
(110,116) half control assembly (110,118) full displacer assembly ~110,120~ full control assembly (110,122) full displacer assembly (110,124) ~ull control assembly (110,126) full displacer assembly (110,~128) partial displacer unrodded assembly (112,116) half displacer assembly (112,118) full control assembly (112,120) full displacer assembly ( (112,122) full control assembly (112,124) full displacer assembly (112,126) partial displacer unrodded assembly (114,116) half gray assembly (114,118) full displacer assembly (114,120) partial control unrodded assembly (114,122) full displacer assembly As can be seen from the above description of the quarter core, the core configuration based on this concept can be illustrated generally as shown in Figure 11.
`- Basically, the fuel assembly in the center of the full core as represented by fuel assembly (100,11.6) in Figure 7 can be chosen to be either a control assembly 92 or pre-ferably a displacer assembly 90. Once this is chosen, the Z5 four fuel assemblies immediately adjacent to the flat sides of the center fuel assembly are chosen to be the other type and the fuel assemblies on the diagonal are chosen to be the same type as the center assembly. This pattern is then continued in an alternating fashion. For example, the center fuel assembly (100,116) in Figure 7 was chosen to be a displacer assembly 90 so that the fuel assemblies on its adjacent flat sides are chosen to be either control assemblies ~2 or gray assemblies 94 while those on the diagonal are chosen to be displacer assemblies 13 47,948I
90. This pattern is repeated in alternating fashion until the periphery of the core is reached where the end fuel assemblies may be chosen to be hybrid assemblies based on the nuclear physics of the particular core. Whether a particular assembly is chosen to be a control assembly 92 or a gray assembly 94 is determined by first selecting the number and location of control assemblies needed based on conventional core design. The remainder of the assemblies not chosen to be control assemblies 92 are then used as gray assemblies 94 Thus, substantially the entire core can be arranged on an alternating pattern of displacer ! assemblies and control or gray assemblies with practically all the fuel assemblies being served by at least one displacer rod spider 58 and with each displacer rod spider 58 serving generally 5 fuel assemblies. Moreover, each fuel assembly is served by at least one drive mechanism for either displacer rods, control rods or gray rods.
The illustrated core arrangement provides a means by which the neutron spectrum can be controlled in a "spectral shift" fashion by controlling the moderator volume in the core. This can be accomplished by displacing and replacing the water coolant in the core at appropriate times thereby changing the moderation of the core. In the present invention, displacer rods 40 and gray rods 82 can be used to affect this moderation change.
In operation, all displacer rods 40 and gray rods 82 are inserted in core 34 at the beginning of the core life. However, none of the control rods 80 need be inserted at that time. The insertion of displacer rods 40 and gray rod 82 is done by activating the appropriate drive mechanism such as displacer rod drive mechanism 38.
When the drive mechanism is activated, displacer rods 40 and gray rods 82 fall into the appropriate guiAe tubes 56 in fuel assemblies 32. The displacer rods and gray rods will displace their volume of coolant (water) thus reducing the volume of moderator in core 34. The reduction of moderator hardens the neutron spectrum of the core and 2~
14 47,9~i8I
increases plu~onium production. This hardening of the neutron spectrum is generally referred to as "spectral shift". The harder neutron spectrum reduces boron chemical shim re~uirements, results in a more negative moderator temperature coefficient, and reduces or eliminates burnable poison requirements. As the uranium fuel in the core is depleted over the life of the core, a certain number of displacer rods 40 and/or gray rods 82 may be withdrawn from the core by activa~ing their respective drive mechan-isms. The withdrawal of the rods allows more water-moderator into the core region and increases moderation of the core. This, in effect, introduces reactivity worth at a time when fuel depletion is causing a reactivlty worth depletion. Thus, the reactivity of the core can be main-tained at appropriate levels for a longer time. Thewithdrawal of the rods can continue at a selective rate (depending on core conditions) until, near the end of core life, all displacer rods 40 and all gray rods 82 have been withdrawn from the core. The selection and manipulation of the displacer rods can be chosen in the manner disclosed in Canadian Patent Application Serial No. 390l698 filed November 23, 1981 in the name of A. J. Impink entitled "Spectral Shift Reactor Control Method" and assigned to the Westinghouse Electric Corporation.
The displacer rods can be used at start-up to displace approximately 20% of the core water volume and can remain inserted until the boron shim concentration nears zero ppm which is approximately 60% into the fuel cycle. The use of displacer rods in this manner can result in approximately 10% reduction in uranium fuel requirements for a given core life which results in an 10%
fuel cost savings. In addition, the use of burnable poison rods can be effectively eliminated, a further cost reduction.
In controlling the operation of a nuclear reac-tor, it is well known in the art tha~ banks of control rods 80 are sequentially inserted or withdrawn in accor-47,948I
dance with the desired energy output of the nuclear reac-tor. The output of the reactor is increased if control rods 80 are positionally withdrawn ~rom the reactor and decreased if control rods 80 are positionally inserted into the reactor.
Typically, control rods 80 are arranged in a plurality of banks comprising a plurality of control rod clusters. When it is desired to increase the output of the reactor, one bank of rods will be sequenced, that is, a first bank of rods will be incrementally withdrawn from the reactor, others will be withdrawn if more power is ( required. It is generally desirable to begin to withdraw other banks before the first bank has been withdrawn its maximum distance.
Since each bank is composed of one or more clusters of rods, when a bank is inserted or withdrawn, each of these clusters are incrementally moved in the desired direction. If the direction of the rods is changed, usually the last cluster of rods which have been moved prior to the change in direction, is the first to be moved in the opposite direction when the change of direc-tion is called for. This is so in order to maintain proper alignment of the rods within the reactor and the desired control over the operation of the reactor.
Since this movement of control rods 80 will result in a change in core reactivity (either increased or decreased) and since movement of displacer rods 40 and gray rods 82 will also either increase or decrease core reactivity, it is desirable to coordinate the movement of displacer rods 40, control rods 80 and gray rods 82 to achieve the desired level and distribution of reactivity and power throughout the core. The appropriate power level and power distribution can be attained by monitoring the reactivity condition of the core together with the reactivity requirements and then selecting the proper type and location of either displacer rod 40, control rod 80, or gray rod 82 to be moved. ~ecause displacer rods 40, 16 47,948I
control rods 80, and gray rods 82 have different reactivity worths and because each type rod is dispersed in various locations throughout the core, the proper selection and manipulation of the rods results in greater flexibility in attaining the desired core power l~vel and power distribu-tion than was achievable with control rods alone. Thus, the use of displacer rods 40, control rods 80, and gray rods 82, in various combinations, provides great advantages in the control of a nuclear reactor.
10~herefore, it can be seen that the invention provides a means to effectively control the reactivity of ( a nuclear reactor through moderator control by the use of displacer rods.
Figure 2 is a cross-sectional view in elevation of the top portion of the fuel assembly;
Figure 3 is a cross-sectional view in elevation ; of the botto~ portion of the fuel assembly;
Figure 4 is a view in perspective of displacer rods and their respective fuel assembly;
Figure 5 is a cross-sectional view in elevation of a displacer rod guide structure;
Figure 6 is a view along line VI-VI of Figure 5;
Figure 7 is a diagram of a quarter core of the reactor;
Figure 8 is an enlarged view of a portion of the quarter core;
Figure 9 is an enlarged view of a portion of the ~uarter core;
Figure lO is cross-sectional diagram of a typical fuel assembly; and Figure ll is a diagram of a section of the core.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the operation o a commercial pressurized water reactor it is desirable to be able to prolong the life of the reactor core to better utilize the uranium fuel thereby reducing the fuel costs. The invention described herein provides a means to extend reactor core life by controlling reactor core moderation.
Referring to Figure 1, the nuclear reactor is referred to generally as 20 and comprises a reactor vessel 22 with a removable closure head 24 attached to the top end thereof. An inlet nozzle 26 and an outlet nozzle 28 are connected to reactor vessel 22 to allow a coolant such as water to circulate through reactor vessel 22. A core plate 30 is disposed in the lower portion of reactor vessel 22 and serves to support fuel assemblies 32. Fuel assemblies 32 are arranged in reactor vessel 22 and com-prise reactor core 34. As is well understood in the art, - fuel assemblies 32 generate heat by nuclear fissioning of the uraniu~ therein. The reactor coolant flowing through 47,948I
reactor vessel 22 in heat transfer relationship with fuel assemblies 32 transfers the heat from fuel assemblies 32 to electrical generating equipment located remote from nuclear reactor 20. A plurality of control rod drive mechanisms 36 which may be chosen from those well known in the art such as the one described in U.S. Patent No.
3,882,353 issued May 6, 1975 in the name of J. L. DeWeese are disposed on closure head 24 for inserting or withdraw-ing control rods {not shown) from fuel assemblies 32. In addition, a plurality of displacer rod drive mechanisms 38 are also disposed on closure head 24 for inserting or withdrawing displacer rods 40 from fuel assemblies 32.
Displacer rod drive mechanisms 38 may be similar to the one described in Canadian Patent Application Serial No. 389,969, filed November 12, 1981 in the name of L. Veronesi et al.
entitled "Hydraulic Drive Mechanism" and assigned to the Westinghouse Electric Corporation. For purposes of clarity, only a selected number of displacer rods 40 are shown in Figure 1. However, it should be understood, that the number of displacer rods 40 are chosen to correspond to the number of displacer rod guide tubes in fuel assemblies 32.
A plurality of displacer rod guide structures 42 are located in the upper section of reactor vessel 22 with each bei.ng in alignment with a displacer rod drive mechanism 38 for guiding the movement of displacer rods 4Q through the upper section of reactor vessel 22. A calandria 44 may be arranged between fuel assernblies 32 and displacer rod guide structures 42 and comprises a multiplicity of hollow stainless steel tubes arranged in colinear alignment with each displacer rod and control rod for providing guidance of the displacer rods and control rods through the calandria area and for minimizing flow induced vibrations in the displacer rods and control rods.
Referring now to Figures 2-4, fuel assemblies 32 comprise fuel elements 487 grids 50, bottom nozzle 52, top nozzle 54, and guide tubes 56. Fuel elements 48 may be 62~
6 47,948I
elongated cylindrical metallic tubes containing nuclear fuel pellets and having both ends sealed by end plugs.
Fuel elements 48 may be arranged in a substantially 20 x 20 rectangular array and are held in place by grids 50.
Guide tubes 56 which may number 25 are arranged in a generally 5 x 5 array within each fuel assembly 32. Each guide tube 56 occupies the space of about four fuel ele-ments 48 and extend from bottom nozzle 52 to top nozzle 54 and provide a means to support grids 50 ! top nozzle 54 and bottom nozzle 52. Guide tubes 56 may be hollow cylindrical metallic tubes manufactured ~rom Zircaloy ~ and capable of accommodating rods such as displacer rods 40 or control rods. Displacer rods 40 and control rods are manufactured to be approximately the same size so that each guide tube 56 can equally accommodate either a displacer rod or a control rod. When not occupied by a rod, guide tubes 56 are filled with reactor coolant; however~ when displacer rods 40 are inserted in guide tubes 56 displacer rods 40 displace the coolant therein.
: ?0 Grids 50 are positioned at various locations along the length of fuel assembly 32 and serve to space fuel elements 48 and guide tubes 56 at appropriate dis-tances from each other and to allow the reactor coolant to circulate in heat transfer relationship with fuel elements 48. A more detailed description of a similar grid may be found in United States Patent Nos. 3,379,617 and 3,379,619, both issued in the name of H. N. Andrews et al. As can be seen in Figure 4, displacer rods 40 are elongated cylin-drical substantially hollow rods which can be manufactured out of Zircaloy ~ and may be of the type described in Canadian Patent Application Serial No. 391,903 entitled "Displacer Rod For Use In A Mechanical Spectral Shift Reactor" filed December 9, 19~1 in the name of R. K.
Gjertsen et al. and assigned to the Westinghouse Elec-tric Corporation. Displacer rods 40 may also contain ZrO2or A1203 pellets for weighting the rod and enhancing its lowerability. Displacer rods 40 are arranged so as to be 7 47,948I
in colinear alignment with guide tube 56 so that displacer rods 40 ~ay be inserted in guide tubes 56 when it is desired. Displacer rods 40 are supported from a common attachment known as a spider 58. Spider 58 comprises a body 60 with struts 62 radially extending from body 60.
Displacer rods 40 are individually attached to each strut 62 to form an array corresponding to the array of guide tubes 56 into which displacer rods may be inserted.
Spider 58 is attached to drive shaft 64 which is connected to displacer rod drive mechanism 38. Activation of dis-placer rod drive mechanism 38 causes drive shaft 64 to be ! either lowered or raised thereby inserting or withdrawing displacer rods 40 from fuel assemblies 32 of core 34.
It is important to note that each spider 58 is arranged to be able to insert displacer rods 40 into more than one fuel assembly 32. For example, as shown in Figure 4, spider 58 is capable of inserting 25 displacer rods in center fuel assembly 32 and 4 displacer rods in each of the adjacent 4 fuel assemblies. In this manner displacer rods 40 can be moved in and out of fuel assem-blies 32 wihout increasing the number of spiders and drive mechanisms.
Referring now to Figures 5 and 6, displacer rod guide structures 42 comprise a plurality of split tube guides 70 which are designed to allow rods such as dis-placer rods or control rods to pass therethrough. Dis-placer rod guide structures 42 are located between calan-dria 44 and closure head 24 as shown in Figure 1 and are arranged to correspond to each displacer rod drive mechan-ism 38. A number of spacers 72 are located at variouslocations along split tube guides 70 and together wlth split tube guides 70 serve to guide displacer rods 40 through the upper section of reactor vessel 22. As can be seen in Figure 6, 8 split tube guides 70 may be provided for guiding displacer rods 40. The "split" in split tube guides 70 along with slots 74 in spacers 7~ a~low spider 58 to pass therethrough while maintaining alignment of the 8 47,948I
rods with guide tubes 55 in fuel assemblies 32. A center slot 76 is also provided for accommodating drive shaft 64 so that spider 58 may be moved therethrough.
Referring again to Figure l, calandria 44 which comprises a multiplicity of tubes provides guidance for the rods such as displacer rods 40 through the calandria area. In general, the tubes in calandria 44 are not split tubes, as are split tube guides 70, so that spider 58 stops its descent when spider 58 nears the top of the tubes in calandria 44. When stopped at the top of caland-ria 44 all rods extend through the calandria tubes and are fully inserted in fuel assembly 32. While inserted in the calandria tubes, the rods are protected from the flow of reactor coolant thereby minimizing vibrations that would otherwise be induced by the velocity of the reactor coolant in that area.
In the invention as described herein, at least three different types of rods are capable of being inserted into quide tubes 56. For example, ~isplacer rods, control rods, and gray rods may be arranged to be inserted in guide tubes 56. All of the rods are approximately the same size and configuration, but because of the materials with which they are made serve different purposes. Dis-placer rods 40 which may be either a hollow thick walled tube or may contain a low neutron absorbing-material such as ZrO2 or Al203 pellets are used to displace reactor coolant and thereby control reactor moderation. Control rods contain neutron absorbing material as is well under-stood in the art and serve to control core reactivity in a commonly understood fashion. Gray rods are similar to displacer rods 40 but are made of an intermediate neutron absorbing material such as stainless steel so that their reactivity worth per rod is greater than that of displacer rods 40.
Referring now to Fiqures 7-11, the ~uarter core arrangement of fuel elements 48, displacer rods 40, control rods 80, gray rods 82, and unrodded locations 84 are .
9 47,948I
shown. It is to be understood that the full reactor core configuration can be established by extrapolating the quarter core sho~-?n in Figure 7. Actually, the quarter core sho~?n in Figure 7 is a mirror image of the eighth core taken a]ong line A-A of Figure 7. However~ the quarter core of Figure 7 is being shown for clarity.
As can be seen in Figure 10, each fuel assembly 32 comprises an array of fuel elements 4~ and an array of guide tubes 56. Generally, control rods 38 and gray rods 82 are used only in the diagonally arranged guide tu~es 56 while displacer rods 40 are generally used in all guide tubes 56 of a given fuel assembly. In addition, an in-strument tube 88 is provided near the center of each fuel assembly 32 for accommodating data instrumentacion such as movable fission chambers. While each fuel assembly 32 is essentially identical to the one shown in Figure 10, each fuel assembly 32 can produce a different function depending on whether guide tubes 56 are occupied by reactor coolant, displacer rods 40, control rods 80, or gray rods 82. Dis-placer rods 40 and gray rods 82 are generally chosen to beapproximately the same size so as to displace approximate-ly the same volume of water. ~However, gray rods 82 can be thick walled stainless steel cylindrical rods which can have higher reactivity worths than do displacer rods 40 so that they may be used to offset the effects of xenon transients during load follow operations in addition to moderator displacement as described in Canadian Patent Application Serial No. 391>869 filed December 9, 1981 in the name of W. R. Carlson et al. enti~led "Spectral Shift Reactor" and assigned to the Westinghouse Electric Corporation.
Referring now to Figure 11, a fuel assembly 32 in which no control rods 80 or gray rods 82 are used and in which only displacer rods 40 are used in guide tubes 56 is referred to generally as displacer assembly 90. A fuel assembly 32 in which both displacer rods 40 and control rods 80 are employed (but no gray rods) is referred to as `.?. i . ` !i".
L62~
47,948I
control assembly 92. Similarly, a fuel assembly 32 in which both displacer rods 40 and gray rods 82 are used is called a gray assembly 94. It should be noted that in Figure 11 fuel elements 48 have been omitted for clarity and that those fuel assemblies are similar ~o those shown in Figure 10.
Still referring to Figure 11, each of the control rods 80 and gray rods 82 are attached to a spider (not shown) similar to spider 58 except that the spider for control rods 80 or gray rods 82 generally only affects one fuel assembly. In this manner, all control rods 80 or gray rods 82 in a given uel assembly can be raised or lowered by a single drive mechanism. Furthermore, since each dis-placer rod spider 58 can extend into the adjacent fuel assemblies (as illustrated in the center portion of Figure 11 and in Figure 4), the displacer rod spider's 58 move-ment affects the control on five fuel assemblies and re~
duces the number of displacer rod drive mechanisms needed.
0 course, on the periphery of the ~uarter core (as shown in Figure 7) the particular spiders may move less than the usual number of rods because there are no adjacent fuel assemblies or there are unrodded locations 84.
! Referring again to Figures 8 and ~ which com~
prise Fi~ure 7, a ~uarter core arrangement, each row or partial row is numbered 100-114 and each column or partial column is numbered 116-130 and comprises:
Fuel Assemb~y (100,116) quarter displacer assembly (100,118) half control assembly 30 (100,120) half displacer assembly : (100,122) half control assembly (100,124) half displacer assembly (100,126) half control assembly (100,128) half displacer assembly 35 (100,130) half gray assembly 6~
11 47,948I
~102,116) half control assemb_y (102,118) ull displacer assembly (102,120) full gray assernbly (102,122) full displacer assembly (102,124) full gray assembly (102,126) full displacer assembly (102,128) full control assembly (102,130) full displacer assembly (104,116) half displacer assembly (104,118) full gray assembly ( (104,120) full displacer assembly (104,122) full control assembly (104,124) full displacer assembly (104,126) full cont.rol assembly ~104,128) full displacer assembly (104,130) parti.al control-unrodded assembly (106,116) half control assembly (106,118) full displacer assembly (106,120) full control assembly (106,122) full displacer assembly (106,124) full control assembly (106,126) full displacer assembly (106,128) full control assembly (106,130) full displacer assembly 2~ (108,116) half displacer assembly (108,118) full gray assembly (108,120) full displacer assernbly (108,122) full control assembly (108,124) full displacer assembly (108,126) full control assembly (108,128) full displacer assembly 6~i 12 47,948I
(110,116) half control assembly (110,118) full displacer assembly ~110,120~ full control assembly (110,122) full displacer assembly (110,124) ~ull control assembly (110,126) full displacer assembly (110,~128) partial displacer unrodded assembly (112,116) half displacer assembly (112,118) full control assembly (112,120) full displacer assembly ( (112,122) full control assembly (112,124) full displacer assembly (112,126) partial displacer unrodded assembly (114,116) half gray assembly (114,118) full displacer assembly (114,120) partial control unrodded assembly (114,122) full displacer assembly As can be seen from the above description of the quarter core, the core configuration based on this concept can be illustrated generally as shown in Figure 11.
`- Basically, the fuel assembly in the center of the full core as represented by fuel assembly (100,11.6) in Figure 7 can be chosen to be either a control assembly 92 or pre-ferably a displacer assembly 90. Once this is chosen, the Z5 four fuel assemblies immediately adjacent to the flat sides of the center fuel assembly are chosen to be the other type and the fuel assemblies on the diagonal are chosen to be the same type as the center assembly. This pattern is then continued in an alternating fashion. For example, the center fuel assembly (100,116) in Figure 7 was chosen to be a displacer assembly 90 so that the fuel assemblies on its adjacent flat sides are chosen to be either control assemblies ~2 or gray assemblies 94 while those on the diagonal are chosen to be displacer assemblies 13 47,948I
90. This pattern is repeated in alternating fashion until the periphery of the core is reached where the end fuel assemblies may be chosen to be hybrid assemblies based on the nuclear physics of the particular core. Whether a particular assembly is chosen to be a control assembly 92 or a gray assembly 94 is determined by first selecting the number and location of control assemblies needed based on conventional core design. The remainder of the assemblies not chosen to be control assemblies 92 are then used as gray assemblies 94 Thus, substantially the entire core can be arranged on an alternating pattern of displacer ! assemblies and control or gray assemblies with practically all the fuel assemblies being served by at least one displacer rod spider 58 and with each displacer rod spider 58 serving generally 5 fuel assemblies. Moreover, each fuel assembly is served by at least one drive mechanism for either displacer rods, control rods or gray rods.
The illustrated core arrangement provides a means by which the neutron spectrum can be controlled in a "spectral shift" fashion by controlling the moderator volume in the core. This can be accomplished by displacing and replacing the water coolant in the core at appropriate times thereby changing the moderation of the core. In the present invention, displacer rods 40 and gray rods 82 can be used to affect this moderation change.
In operation, all displacer rods 40 and gray rods 82 are inserted in core 34 at the beginning of the core life. However, none of the control rods 80 need be inserted at that time. The insertion of displacer rods 40 and gray rod 82 is done by activating the appropriate drive mechanism such as displacer rod drive mechanism 38.
When the drive mechanism is activated, displacer rods 40 and gray rods 82 fall into the appropriate guiAe tubes 56 in fuel assemblies 32. The displacer rods and gray rods will displace their volume of coolant (water) thus reducing the volume of moderator in core 34. The reduction of moderator hardens the neutron spectrum of the core and 2~
14 47,9~i8I
increases plu~onium production. This hardening of the neutron spectrum is generally referred to as "spectral shift". The harder neutron spectrum reduces boron chemical shim re~uirements, results in a more negative moderator temperature coefficient, and reduces or eliminates burnable poison requirements. As the uranium fuel in the core is depleted over the life of the core, a certain number of displacer rods 40 and/or gray rods 82 may be withdrawn from the core by activa~ing their respective drive mechan-isms. The withdrawal of the rods allows more water-moderator into the core region and increases moderation of the core. This, in effect, introduces reactivity worth at a time when fuel depletion is causing a reactivlty worth depletion. Thus, the reactivity of the core can be main-tained at appropriate levels for a longer time. Thewithdrawal of the rods can continue at a selective rate (depending on core conditions) until, near the end of core life, all displacer rods 40 and all gray rods 82 have been withdrawn from the core. The selection and manipulation of the displacer rods can be chosen in the manner disclosed in Canadian Patent Application Serial No. 390l698 filed November 23, 1981 in the name of A. J. Impink entitled "Spectral Shift Reactor Control Method" and assigned to the Westinghouse Electric Corporation.
The displacer rods can be used at start-up to displace approximately 20% of the core water volume and can remain inserted until the boron shim concentration nears zero ppm which is approximately 60% into the fuel cycle. The use of displacer rods in this manner can result in approximately 10% reduction in uranium fuel requirements for a given core life which results in an 10%
fuel cost savings. In addition, the use of burnable poison rods can be effectively eliminated, a further cost reduction.
In controlling the operation of a nuclear reac-tor, it is well known in the art tha~ banks of control rods 80 are sequentially inserted or withdrawn in accor-47,948I
dance with the desired energy output of the nuclear reac-tor. The output of the reactor is increased if control rods 80 are positionally withdrawn ~rom the reactor and decreased if control rods 80 are positionally inserted into the reactor.
Typically, control rods 80 are arranged in a plurality of banks comprising a plurality of control rod clusters. When it is desired to increase the output of the reactor, one bank of rods will be sequenced, that is, a first bank of rods will be incrementally withdrawn from the reactor, others will be withdrawn if more power is ( required. It is generally desirable to begin to withdraw other banks before the first bank has been withdrawn its maximum distance.
Since each bank is composed of one or more clusters of rods, when a bank is inserted or withdrawn, each of these clusters are incrementally moved in the desired direction. If the direction of the rods is changed, usually the last cluster of rods which have been moved prior to the change in direction, is the first to be moved in the opposite direction when the change of direc-tion is called for. This is so in order to maintain proper alignment of the rods within the reactor and the desired control over the operation of the reactor.
Since this movement of control rods 80 will result in a change in core reactivity (either increased or decreased) and since movement of displacer rods 40 and gray rods 82 will also either increase or decrease core reactivity, it is desirable to coordinate the movement of displacer rods 40, control rods 80 and gray rods 82 to achieve the desired level and distribution of reactivity and power throughout the core. The appropriate power level and power distribution can be attained by monitoring the reactivity condition of the core together with the reactivity requirements and then selecting the proper type and location of either displacer rod 40, control rod 80, or gray rod 82 to be moved. ~ecause displacer rods 40, 16 47,948I
control rods 80, and gray rods 82 have different reactivity worths and because each type rod is dispersed in various locations throughout the core, the proper selection and manipulation of the rods results in greater flexibility in attaining the desired core power l~vel and power distribu-tion than was achievable with control rods alone. Thus, the use of displacer rods 40, control rods 80, and gray rods 82, in various combinations, provides great advantages in the control of a nuclear reactor.
10~herefore, it can be seen that the invention provides a means to effectively control the reactivity of ( a nuclear reactor through moderator control by the use of displacer rods.
Claims
1. A special shift pressurized water nuclear reactor including a reactor vessel having an inlet and an outlet for circulating a water coolant in heat transfer relationship with a core disposed therein comprising:
a plurality of fuel assemblies disposed in said core for generating heat by nuclear fission;
a plurality of incrementally movable control rods disposed in said reactor for controlling the power level and power distribution of said reactor;
a plurality of water displacer elements having a neutron absorbing capability substantially lower than said control rods and arranged to be completely inserted or completely withdrawn from said fuel assemblies for dis-placing water from said core when said displacer elements are inserted in said fuel assemblies thereby reducing the volume of water in said core and thereby reducing core moderation;
an electromechanical control rod drive mechanism mounted on said reactor vessel and connected to said control rods for incrementally moving said control rods relative to said core;
a spider having said displacer elements attached thereto, a drive shaft disposed in said reactor vessel and attached to said spider; and a hydraulic drive mechanism mounted on the closure head of said reactor vessel and attached to said drive shaft for selectively vertically moving said drive shaft and said spider with respect to said fuel assemblies thereby completely inserting or completely withdrawing said displacer elements from said core.
a plurality of fuel assemblies disposed in said core for generating heat by nuclear fission;
a plurality of incrementally movable control rods disposed in said reactor for controlling the power level and power distribution of said reactor;
a plurality of water displacer elements having a neutron absorbing capability substantially lower than said control rods and arranged to be completely inserted or completely withdrawn from said fuel assemblies for dis-placing water from said core when said displacer elements are inserted in said fuel assemblies thereby reducing the volume of water in said core and thereby reducing core moderation;
an electromechanical control rod drive mechanism mounted on said reactor vessel and connected to said control rods for incrementally moving said control rods relative to said core;
a spider having said displacer elements attached thereto, a drive shaft disposed in said reactor vessel and attached to said spider; and a hydraulic drive mechanism mounted on the closure head of said reactor vessel and attached to said drive shaft for selectively vertically moving said drive shaft and said spider with respect to said fuel assemblies thereby completely inserting or completely withdrawing said displacer elements from said core.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31876181A | 1981-11-09 | 1981-11-09 | |
| US318,761 | 1981-11-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191626A true CA1191626A (en) | 1985-08-06 |
Family
ID=23239485
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000413521A Expired CA1191626A (en) | 1981-11-09 | 1982-10-15 | Mechanical spectral shift reactor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1191626A (en) |
-
1982
- 1982-10-15 CA CA000413521A patent/CA1191626A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4432934A (en) | Displacer rod for use in a mechanical spectral shift reactor | |
| US4285769A (en) | Control cell nuclear reactor core | |
| CA1175166A (en) | Fuel assembly for a nuclear reactor | |
| US5124113A (en) | Nuclear reactor with improved efficiency | |
| EP0054790B1 (en) | Spectral shift reactor control method | |
| EP0054789B1 (en) | Spectral shift controlled nuclear reactor | |
| EP0054238B1 (en) | Spectral shift reactor | |
| EP0054787B1 (en) | Spectral shift controlled nuclear reactor | |
| US5386439A (en) | Spectral shift nuclear reactor with improved efficiency | |
| US4716006A (en) | Spectral shift reactor control method | |
| CA1191626A (en) | Mechanical spectral shift reactor | |
| EP0054234B1 (en) | Spectral shift reactor | |
| US4832899A (en) | Mechanical spectral shift reactor | |
| US4716007A (en) | Spectral shift reactor | |
| US4710340A (en) | Mechanical spectral shift reactor | |
| US4692296A (en) | Mechanical spectral shift reactor | |
| US4687620A (en) | Spectral shift reactor control method | |
| Doshi et al. | Mechanical spectral shift reactor | |
| US4826647A (en) | Spectral shift reactor | |
| EP0369305A1 (en) | Fuel assembly containing fuel rods having standardized-length burnable absorber integral with fuel pellets and method of customizing fuel assembly | |
| JPH0244039B2 (en) | ||
| Sherwood et al. | Mechanical spectral shift reactor | |
| Wilson et al. | Mechanical spectral shift reactor | |
| EP1168370B1 (en) | Core configuration for a nuclear reactor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |