CA2099324A1 - Fuel bundle for a heavy-water moderated thermal breeder - Google Patents
Fuel bundle for a heavy-water moderated thermal breederInfo
- Publication number
- CA2099324A1 CA2099324A1 CA002099324A CA2099324A CA2099324A1 CA 2099324 A1 CA2099324 A1 CA 2099324A1 CA 002099324 A CA002099324 A CA 002099324A CA 2099324 A CA2099324 A CA 2099324A CA 2099324 A1 CA2099324 A1 CA 2099324A1
- Authority
- CA
- Canada
- Prior art keywords
- fuel
- region
- bundle
- fissile material
- fissile
- 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.)
- Abandoned
Links
- 239000000446 fuel Substances 0.000 title claims abstract description 118
- XLYOFNOQVPJJNP-ZSJDYOACSA-N Heavy water Chemical compound [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 title claims abstract description 28
- 239000000463 material Substances 0.000 claims abstract description 65
- 238000000034 method Methods 0.000 claims abstract description 21
- 238000001228 spectrum Methods 0.000 claims abstract description 13
- 238000009395 breeding Methods 0.000 claims abstract description 3
- 230000001488 breeding effect Effects 0.000 claims abstract description 3
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 claims description 18
- OYEHPCDNVJXUIW-FTXFMUIASA-N 239Pu Chemical compound [239Pu] OYEHPCDNVJXUIW-FTXFMUIASA-N 0.000 claims description 3
- ZSLUVFAKFWKJRC-UHFFFAOYSA-N thorium Chemical compound [Th] ZSLUVFAKFWKJRC-UHFFFAOYSA-N 0.000 claims 2
- JFALSRSLKYAFGM-OIOBTWANSA-N uranium-235 Chemical compound [235U] JFALSRSLKYAFGM-OIOBTWANSA-N 0.000 claims 2
- 229910052778 Plutonium Inorganic materials 0.000 description 15
- OYEHPCDNVJXUIW-UHFFFAOYSA-N plutonium atom Chemical compound [Pu] OYEHPCDNVJXUIW-UHFFFAOYSA-N 0.000 description 15
- 229910052770 Uranium Inorganic materials 0.000 description 13
- 230000008569 process Effects 0.000 description 10
- 230000004992 fission Effects 0.000 description 9
- 238000004519 manufacturing process Methods 0.000 description 9
- 239000002826 coolant Substances 0.000 description 8
- 239000000126 substance Substances 0.000 description 6
- 238000012958 reprocessing Methods 0.000 description 4
- 239000002915 spent fuel radioactive waste Substances 0.000 description 4
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- OOAWCECZEHPMBX-UHFFFAOYSA-N oxygen(2-);uranium(4+) Chemical compound [O-2].[O-2].[U+4] OOAWCECZEHPMBX-UHFFFAOYSA-N 0.000 description 3
- FCTBKIHDJGHPPO-UHFFFAOYSA-N uranium dioxide Inorganic materials O=[U]=O FCTBKIHDJGHPPO-UHFFFAOYSA-N 0.000 description 3
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 230000014509 gene expression Effects 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000003758 nuclear fuel Substances 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 230000009257 reactivity Effects 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910001093 Zr alloy Inorganic materials 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000012993 chemical processing Methods 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 231100001261 hazardous Toxicity 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C7/00—Control of nuclear reaction
- G21C7/26—Control of nuclear reaction by displacement of the moderator or parts thereof by changing the moderator concentration
- G21C7/27—Spectral shift control
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
- G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
- G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
- G21C3/326—Bundles of parallel pin-, rod-, or tube-shaped fuel elements comprising fuel elements of different composition; comprising, in addition to the fuel elements, other pin-, rod-, or tube-shaped elements, e.g. control rods, grid support rods, fertile rods, poison rods or dummy rods
- G21C3/328—Relative disposition of the elements in the bundle lattice
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C1/00—Reactor types
- G21C1/04—Thermal reactors ; Epithermal reactors
- G21C1/06—Heterogeneous reactors, i.e. in which fuel and moderator are separated
- G21C1/08—Heterogeneous reactors, i.e. in which fuel and moderator are separated moderator being highly pressurised, e.g. boiling water reactor, integral super-heat reactor, pressurised water reactor
- G21C1/10—Heterogeneous reactors, i.e. in which fuel and moderator are separated moderator being highly pressurised, e.g. boiling water reactor, integral super-heat reactor, pressurised water reactor moderator and coolant being different or separated
-
- 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
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Monitoring And Testing Of Nuclear Reactors (AREA)
Abstract
ABSTRACT
A method and apparatus is described for breeding fissile material in a pressure tube heavy water moderated reactor containing a plurality of fuel bundles, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein. A first group of fuel rods containing fertile material is arranged in a first region of the fuel bundle. A second group of fuel rods containing fissile material is arranged in a second region of the fuel bundle such that it surrounds the first region of fertile material. This arrangement results in that the second region of fissile material being relatively impenetrable to thermal neutrons generated in the moderator while exposing the fissile material, initially during an early part of its life in the reactor, to an epithermally rich neutron spectrum to breed fissile material in the second region, while the fissile material is depleted in the first region. The bred fissile material in the second region, is placed in a thermally rich neutron spectrum, to convert the bred fissile material to energy, thereby increasing the amount of energy produced from a fuel bundle over the fuel life.
A method and apparatus is described for breeding fissile material in a pressure tube heavy water moderated reactor containing a plurality of fuel bundles, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein. A first group of fuel rods containing fertile material is arranged in a first region of the fuel bundle. A second group of fuel rods containing fissile material is arranged in a second region of the fuel bundle such that it surrounds the first region of fertile material. This arrangement results in that the second region of fissile material being relatively impenetrable to thermal neutrons generated in the moderator while exposing the fissile material, initially during an early part of its life in the reactor, to an epithermally rich neutron spectrum to breed fissile material in the second region, while the fissile material is depleted in the first region. The bred fissile material in the second region, is placed in a thermally rich neutron spectrum, to convert the bred fissile material to energy, thereby increasing the amount of energy produced from a fuel bundle over the fuel life.
Description
20~932~
FUEL BUNDLE FOR A HEAVY-WATER MODERATED
THERM~L BREEDER
FIELD OF THE INVENTION
The present invention relates to a fuel bundle for a pressure tube type heavy water moderated reactor, that provides an increased production in energy from a given mass of natural uranium than heretofore achieved.
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BACKGROUND OF THE INVENTION
In a world of dwindling energy resources there are several incentives at the present time to maximize energy produced from uranium which is used in nuclear reactors. As is well known that natural uranium which is used as nuclear fuel contains only about 0.7% of the fissionable isotope U235. The more abundant U238, (99.3%) in natural uranium, will undergo fission by fase neutrons that have energy greater than 1 MeV. However, it is not possible to sustain a critica1 chain reaction in a heavy water reactor by using fast neutron fission of U238 and the U238 must be first converted into a fissionable species such as plutonium. Known methods to date for maximising energy produced from uranium by producing plutonium involve generally two capital intensive and hazardous technologies with wide economic and political ` . consequences.
First is the extraction of fissile material extracted from the spent fuel of nuclear reactors. This involves transportation of the spent fuel to a chemical reprocessing plant wherein the separation of fissile material and nuclear waste from spent fuel elements is accomplished. The nuclear waste is dumped while the recovered fissile material, generally plutonium, is transported to a fuel fabrication or enrichment plant wherein new fuel is :~ ~ made for use in the reactor. The hazards involved with the various steps in the above process needs no further discussion.
- Second, is the implementation of fast breeder reactors which facilitate the efflcient conversion of U238 to plutonium. Existing breeder reactors use a mixture of uranium and plutonium as fuel. Liquid sodium is used as a ~ .
:`:
FUEL BUNDLE FOR A HEAVY-WATER MODERATED
THERM~L BREEDER
FIELD OF THE INVENTION
The present invention relates to a fuel bundle for a pressure tube type heavy water moderated reactor, that provides an increased production in energy from a given mass of natural uranium than heretofore achieved.
' .
BACKGROUND OF THE INVENTION
In a world of dwindling energy resources there are several incentives at the present time to maximize energy produced from uranium which is used in nuclear reactors. As is well known that natural uranium which is used as nuclear fuel contains only about 0.7% of the fissionable isotope U235. The more abundant U238, (99.3%) in natural uranium, will undergo fission by fase neutrons that have energy greater than 1 MeV. However, it is not possible to sustain a critica1 chain reaction in a heavy water reactor by using fast neutron fission of U238 and the U238 must be first converted into a fissionable species such as plutonium. Known methods to date for maximising energy produced from uranium by producing plutonium involve generally two capital intensive and hazardous technologies with wide economic and political ` . consequences.
First is the extraction of fissile material extracted from the spent fuel of nuclear reactors. This involves transportation of the spent fuel to a chemical reprocessing plant wherein the separation of fissile material and nuclear waste from spent fuel elements is accomplished. The nuclear waste is dumped while the recovered fissile material, generally plutonium, is transported to a fuel fabrication or enrichment plant wherein new fuel is :~ ~ made for use in the reactor. The hazards involved with the various steps in the above process needs no further discussion.
- Second, is the implementation of fast breeder reactors which facilitate the efflcient conversion of U238 to plutonium. Existing breeder reactors use a mixture of uranium and plutonium as fuel. Liquid sodium is used as a ~ .
:`:
2~9932~
, .
coolant in some instances. The chemical reactivity and radioactivity induced in liquid sodium by neutron irradiation pose serious problems, thus to date these reactors have not proven to be economically or technologically viable - or feasible.
S The prior art has attempted a solution to some of these problems but still requires at least chemical reprocessing. United States Patents 4,678,619;
4,716,006, 4,710,340 and 4,693,862 utilize uranium enriched with fissile material, i.e. they presuppose some form of chemical separation. Emphasis is placed on the use of moderator displacement for reactor control by suppression of excess reactivity at the beginning of the fuel cycle.
There is therefore a need for a method or process that eliminates or minimises the processing and transportation steps outlined above as well as being able to use existing reactor technology and fuel cycle. The process must also not require the modification of the reactor lattice and consequently does not involve long term and expensive programs to develop and manufacture new types of fuel channels. Another important requirement is that the process is to achieve increased fuel utilization without having to make use of the chemical reprocessing of spent reactor fuel, as these processes involving large injections of capital into the nuclear industry and leading to severe economic and political repercussions.
SUMMARY OF THE INVENTION
` ~; The invention seeks to pronde a fuel bundle which achieves a considerable increase in energy production from a given amount of a natural : ~ uranium and consequently achieves a re1ative conservation of natural resources.
The theory behind the present fuel bundle design is based on the application of neutron spectral shift, i.e. changing the neutron energy - spectrum during the life of the fuel to simultaneously increase the production ~ ~ and destruction of fissile plutonium.
`' ~ , -` 2~99~2~
, .
coolant in some instances. The chemical reactivity and radioactivity induced in liquid sodium by neutron irradiation pose serious problems, thus to date these reactors have not proven to be economically or technologically viable - or feasible.
S The prior art has attempted a solution to some of these problems but still requires at least chemical reprocessing. United States Patents 4,678,619;
4,716,006, 4,710,340 and 4,693,862 utilize uranium enriched with fissile material, i.e. they presuppose some form of chemical separation. Emphasis is placed on the use of moderator displacement for reactor control by suppression of excess reactivity at the beginning of the fuel cycle.
There is therefore a need for a method or process that eliminates or minimises the processing and transportation steps outlined above as well as being able to use existing reactor technology and fuel cycle. The process must also not require the modification of the reactor lattice and consequently does not involve long term and expensive programs to develop and manufacture new types of fuel channels. Another important requirement is that the process is to achieve increased fuel utilization without having to make use of the chemical reprocessing of spent reactor fuel, as these processes involving large injections of capital into the nuclear industry and leading to severe economic and political repercussions.
SUMMARY OF THE INVENTION
` ~; The invention seeks to pronde a fuel bundle which achieves a considerable increase in energy production from a given amount of a natural : ~ uranium and consequently achieves a re1ative conservation of natural resources.
The theory behind the present fuel bundle design is based on the application of neutron spectral shift, i.e. changing the neutron energy - spectrum during the life of the fuel to simultaneously increase the production ~ ~ and destruction of fissile plutonium.
`' ~ , -` 2~99~2~
It has been established that plutonium is produced more efficiently in a neutron spectrum that is rich in epithermal neutrons. On the other hand plutonium is destroyed more efficiently in a spectrum that is rich in thermal neutrons.
S In accordance with this invention there is provided a method for breeding fissile material while producing energy in a fuel bundle, for use in a pressure tube heavy water moderated reactor, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein, comprising the steps of; arranging a first group of fuel rods containing fertile material in a first region of saidfuel bundle; arranging a second group of fuel rods containing fissile material in a second region of said fuel bundle to surround said first region of fertile ~ material, so that second region of fissile material is relatively impenetrable - to thermal neutrons generated in the moderator; exposing said fissile lS material, initially during an early part of its life in said reactor, to an epithermally rich neutron spectrum to breed fissile material in said second region, while said fissile material is depleted in said first region; placing said bred fissile material in said second region in a thermally richneutron spectrum, to convert said bred fissile material to energy, thereby increasing the amount of energy produced from a fuel bundle over the fuel life.
In accordance with a further aspect of the invention there is provided a fuel bundle, for use in a pressure tube heavy water moderated reactor, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein? said bundle comprising: a first group of fuel rods each containing fertile material and being disposed in a predetermined first region of said fuel bundle; and ` a second group of fuel rods each containing fissile material and being disposed in a second region of said fuel bundle, said fissile material being arranged in said bundle to surround said first region of fertile material, so 3U that second refion of fissile material is relatively impenetrable to thermal ' ~
.
.
-`" 209~321 neutrons generated in the moderator that surround the pressure tube in said reactor.
BRIEF DESCRIP~ION OF THE DRAWINGS
These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:
Figure l(a) shows a perspective view of a typical nuclear reactor core;
. Figure l(b) is a schematic cross-section of a fuel bundle;
Figure 2 is a schematic cross-sectional view of a fuel bundle according to an embodiment of the present invention;
Figures 3(a)-3(b) are a cross-sectional view of a fuel bundle according ` to an embodiment of the present invention;
Figure 4 is a cross-sectional view of further embodiment of a fuel bundle according to the present invention; and Figure S is a plot of the energy extracted from natural uranium as a function of the fissile content of the fuel in the reactor.
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- ~ DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to Figure l(a), the cross-section of a heavy water reactor core such as the Candu~ reactor is shown generally by numeral 1. The reactor contains a plurality of fuel charmels 4 each of which contains a plurality of fuel bundles 6, generally arranged end to end. Each fuel bundle C in turn contains a set of fuel rods, elements or pencils 8 which are mechanically assembled together, as shown in FIGI~RE l(b). The fuel bundles are placed inside the fuel charmel and coolant flows over the fuel bundles to cool the fuel and remove the heat from the fission process. This heat is transferred by the coolant to steam generators (not shown) which in turn produce steam which run the steam turbines and generators (not shov,m) to produce electrical energy. Heavy water coolant 10 flows through water gaps 15 in each fuel bundle 6 and, in particular through the gaps between the . . ~ .
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- 2~99324 :- 5 fuel rods 8. The coolant water 10 is continuously heated as it flows through the fuel bundles 6.
The fuel bundle 6 shown in Figure 1(b) consists of a set of thirty seven pins 8 which have been assembled together and spaced apart by spacers 18 such that they are mechanica11y stable both when they are outside the reactor ' and especially during the* operation inside the reactor. The group of th*ty ,, seven fuel pins 8 are encased by a pressure tube 24. A calandria tube 26 is spaced from and encases the pressure tube 24. A moderator, in this case heavy water flows around the calandria tube 26, Each of the fuel pins 8 consist of a cylindrical sheath 18 of zirconium alloy which surrounds uranium dioxide ceramic pellets. The fuel pins 8 are held together by end plates (not shown). The fuel pins 8 are divided into two regions, as shown in Figure 2, the pins 8 that constitute a first region 20 of fertile material and a second region 22 of fissile material. The fissile region ~ 15 22 of fuel pins contain pellets of enriched uranium dioxide (U238 and U235).
- The fertile region 20 of fuel bundle consists of pins containing uranium dioxide that is depleted in U235.
The fissile region 22 fuel pins form the outer boundary of the fuel bundle. As mentioned earlier, the coolant 10 which is heavy water flows through the spaces between the fuel pins 8.
The neutronics of a reactor core utilizing fuel bundles 6 according to an embodiment of the present invention may be explained as follows.
As a result of the fission process, neutrons are born in the uranium ; dioxide contained in the fuel pins. These neutrons have various energies and migrate across the material of the lattice. When the U23s concentration in the outer fissile region 22 of the fuel bundle is high, the rate of neutron production in this region 22 is relatively high compared with the fertile region20. It must be remembered that u235 is fissionable by neutrons of all energies whereas U238 undergoes fission by fast neutrons.
It has been found that, of the neutrons born in the fissile region 22, approximately half rnigrate to the heavy water moderator surrounding the fuel 209~2~1 , ~
channel and approximately the other half migrate to the fertile region 20. In the moderator the neutrons are slowed down from the high speeds at which they are born to speeds corresponding to thermal energies by collision with the moderator nuclei.
,,i .
S More than 95~o of thermal neutrons that exist in the fuel were born- in adjacent or other fuel channels. These are the neutrons that are most efficient in burning plutonium. The principle of operation is to shield the fertile region 20 to prevent thermal neutrons entering the fertile region 20 during the early part of the fuel life, and allowing them to enter at a predetermined time later in the fuel life, to burn accumulated plutonium. It is to be noted that the lack of thermal neutrons would obviously increase the relative population of epithermal neutrons which are derived from the fission process taking place in the fue1 channel being considered.
Thus the fissile region 22 is located around the outer region of the fuel bundle in order to prevent the thermal neutrons from reaching the fissile region 20 which is located in the central region of the bundle. This is achieved by the use of enriched uranium fuel in fissile region 22, since enriched fuel absorbs thermal neutrons with high efficiency. The probability that a thermal neutron will penetrate the fissile region 22 and reach the fertile region 20 is quite low.
The neutrons that migrate to the fertile region 20 therefore consist of high speed (unmoderated) neutrons that were born in the fissile region 22.
The purpose of bombarding the fertile region 20 with relatively high speed (epithermal) neutrons is to take advantage of the relatively high efflciency with which high speed neutrons can produce plutonium (Pu239 or fissionable isotope) by absorption in U238 which is the main component of the fertile region. Fertile material (depleted uranium) is placed in the region of high epithermal neutron flux. The presence of fertile materiæl in a region of high epithermal flux increases the plutonium production rate. Following the accumulation of sufficient quantities of plutonium the spectrum in the fertile region is shifted toward the thermal range.
~, - 2Q9~32~
As the process of fission in the fissile region progresses, n~igration of high speed neutrons and subsequent moderation to thermal energies in the ,,j moderator continues, the fissile region becomes depleted of fissile material.
At the same time the fertile region becomes concentrated with fissionable material, mainly plutonium 239, to the preferential absorption of high speed neutrons by U238.
The loss of fissile material from the fissile region facilitates the transmission of thermal neutrons from the moderator to the fertile region.
Thermal neutrons are relatively more efficient at burning Pu239. As a result the Pu239 that is accumulated in the fertile region is now made use of for the production of energy. The total energy produced per unit mass of natural uranium resource that is used to provide the materials for the fertile and - fissile regions is more than doubled by the subject invention compared with the present state of the art. This is illustrated in Figure S wherein, the plot lS 50 shows energy produced by current fuel bundles for a given amount of fuelenrichment. Whereas plot 52 shows the energy output for a fuel bundle according to the present invention. It may therefore be seen that the chemical processing steps referred to in the background of the invention are obviated and in fact that present invention eliminates the chemical reprocessing, and transportation steps that were heretofore necessary.
In order to control the neutron spectrum in the fertile region highly enriched uranium is placed in a predetermined configuration around the fertile region. In the embodiment shown in Figures 2 and 3 this fissile region is at the periphery of the fuel bundle. The spectrum of neutrons in the fertile region is a result of fission neutrons being scattered by the coolant of the fuel channel. Since ~he volume of coolant is relatiYely small in this region of the fuel channel the neutron spectrum is richer in epithermal neutrons which results in an increase in plutonium production rate. As the fuel travels -; through the fuel channel during its lifetime in the reactor the fissile region is depleted of fissile material and its impenetrability to thermal neutrons -`` 2~9932~
decreases which in turn increases the relative population of thermal neutrons in the fertile region.
The fission rate in the accumulated plutonium therefore increases, with a result that these processes lead to almost complete depletion of fissile S material in the fissile and fertile regions with a result that the spent fuel fissile content is relatively low.
Various configurations for the fuel pins in the fissile and fertile regions may be implemented, as shown in figures 3(a)-3(b).
Typically, the diameter of the pressure tube 24 is 10.16 cm, while the radius on the fuel pins 8 may range from 0.48 cm to 1.06 cm, with the radii of the circumference on which the fuels pins are placed, range from 4.5 cm to O cm.
While the invention has been described in connection with a specific embodiment thereof and in a specific use, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.
The terms and expressions which have been employed in the specification are used as terms of description and not of limitations, and thereis no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claims to the in~ention.
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~, ' .
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S In accordance with this invention there is provided a method for breeding fissile material while producing energy in a fuel bundle, for use in a pressure tube heavy water moderated reactor, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein, comprising the steps of; arranging a first group of fuel rods containing fertile material in a first region of saidfuel bundle; arranging a second group of fuel rods containing fissile material in a second region of said fuel bundle to surround said first region of fertile ~ material, so that second region of fissile material is relatively impenetrable - to thermal neutrons generated in the moderator; exposing said fissile lS material, initially during an early part of its life in said reactor, to an epithermally rich neutron spectrum to breed fissile material in said second region, while said fissile material is depleted in said first region; placing said bred fissile material in said second region in a thermally richneutron spectrum, to convert said bred fissile material to energy, thereby increasing the amount of energy produced from a fuel bundle over the fuel life.
In accordance with a further aspect of the invention there is provided a fuel bundle, for use in a pressure tube heavy water moderated reactor, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein? said bundle comprising: a first group of fuel rods each containing fertile material and being disposed in a predetermined first region of said fuel bundle; and ` a second group of fuel rods each containing fissile material and being disposed in a second region of said fuel bundle, said fissile material being arranged in said bundle to surround said first region of fertile material, so 3U that second refion of fissile material is relatively impenetrable to thermal ' ~
.
.
-`" 209~321 neutrons generated in the moderator that surround the pressure tube in said reactor.
BRIEF DESCRIP~ION OF THE DRAWINGS
These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:
Figure l(a) shows a perspective view of a typical nuclear reactor core;
. Figure l(b) is a schematic cross-section of a fuel bundle;
Figure 2 is a schematic cross-sectional view of a fuel bundle according to an embodiment of the present invention;
Figures 3(a)-3(b) are a cross-sectional view of a fuel bundle according ` to an embodiment of the present invention;
Figure 4 is a cross-sectional view of further embodiment of a fuel bundle according to the present invention; and Figure S is a plot of the energy extracted from natural uranium as a function of the fissile content of the fuel in the reactor.
;.:
- ~ DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to Figure l(a), the cross-section of a heavy water reactor core such as the Candu~ reactor is shown generally by numeral 1. The reactor contains a plurality of fuel charmels 4 each of which contains a plurality of fuel bundles 6, generally arranged end to end. Each fuel bundle C in turn contains a set of fuel rods, elements or pencils 8 which are mechanically assembled together, as shown in FIGI~RE l(b). The fuel bundles are placed inside the fuel charmel and coolant flows over the fuel bundles to cool the fuel and remove the heat from the fission process. This heat is transferred by the coolant to steam generators (not shown) which in turn produce steam which run the steam turbines and generators (not shov,m) to produce electrical energy. Heavy water coolant 10 flows through water gaps 15 in each fuel bundle 6 and, in particular through the gaps between the . . ~ .
' .
- 2~99324 :- 5 fuel rods 8. The coolant water 10 is continuously heated as it flows through the fuel bundles 6.
The fuel bundle 6 shown in Figure 1(b) consists of a set of thirty seven pins 8 which have been assembled together and spaced apart by spacers 18 such that they are mechanica11y stable both when they are outside the reactor ' and especially during the* operation inside the reactor. The group of th*ty ,, seven fuel pins 8 are encased by a pressure tube 24. A calandria tube 26 is spaced from and encases the pressure tube 24. A moderator, in this case heavy water flows around the calandria tube 26, Each of the fuel pins 8 consist of a cylindrical sheath 18 of zirconium alloy which surrounds uranium dioxide ceramic pellets. The fuel pins 8 are held together by end plates (not shown). The fuel pins 8 are divided into two regions, as shown in Figure 2, the pins 8 that constitute a first region 20 of fertile material and a second region 22 of fissile material. The fissile region ~ 15 22 of fuel pins contain pellets of enriched uranium dioxide (U238 and U235).
- The fertile region 20 of fuel bundle consists of pins containing uranium dioxide that is depleted in U235.
The fissile region 22 fuel pins form the outer boundary of the fuel bundle. As mentioned earlier, the coolant 10 which is heavy water flows through the spaces between the fuel pins 8.
The neutronics of a reactor core utilizing fuel bundles 6 according to an embodiment of the present invention may be explained as follows.
As a result of the fission process, neutrons are born in the uranium ; dioxide contained in the fuel pins. These neutrons have various energies and migrate across the material of the lattice. When the U23s concentration in the outer fissile region 22 of the fuel bundle is high, the rate of neutron production in this region 22 is relatively high compared with the fertile region20. It must be remembered that u235 is fissionable by neutrons of all energies whereas U238 undergoes fission by fast neutrons.
It has been found that, of the neutrons born in the fissile region 22, approximately half rnigrate to the heavy water moderator surrounding the fuel 209~2~1 , ~
channel and approximately the other half migrate to the fertile region 20. In the moderator the neutrons are slowed down from the high speeds at which they are born to speeds corresponding to thermal energies by collision with the moderator nuclei.
,,i .
S More than 95~o of thermal neutrons that exist in the fuel were born- in adjacent or other fuel channels. These are the neutrons that are most efficient in burning plutonium. The principle of operation is to shield the fertile region 20 to prevent thermal neutrons entering the fertile region 20 during the early part of the fuel life, and allowing them to enter at a predetermined time later in the fuel life, to burn accumulated plutonium. It is to be noted that the lack of thermal neutrons would obviously increase the relative population of epithermal neutrons which are derived from the fission process taking place in the fue1 channel being considered.
Thus the fissile region 22 is located around the outer region of the fuel bundle in order to prevent the thermal neutrons from reaching the fissile region 20 which is located in the central region of the bundle. This is achieved by the use of enriched uranium fuel in fissile region 22, since enriched fuel absorbs thermal neutrons with high efficiency. The probability that a thermal neutron will penetrate the fissile region 22 and reach the fertile region 20 is quite low.
The neutrons that migrate to the fertile region 20 therefore consist of high speed (unmoderated) neutrons that were born in the fissile region 22.
The purpose of bombarding the fertile region 20 with relatively high speed (epithermal) neutrons is to take advantage of the relatively high efflciency with which high speed neutrons can produce plutonium (Pu239 or fissionable isotope) by absorption in U238 which is the main component of the fertile region. Fertile material (depleted uranium) is placed in the region of high epithermal neutron flux. The presence of fertile materiæl in a region of high epithermal flux increases the plutonium production rate. Following the accumulation of sufficient quantities of plutonium the spectrum in the fertile region is shifted toward the thermal range.
~, - 2Q9~32~
As the process of fission in the fissile region progresses, n~igration of high speed neutrons and subsequent moderation to thermal energies in the ,,j moderator continues, the fissile region becomes depleted of fissile material.
At the same time the fertile region becomes concentrated with fissionable material, mainly plutonium 239, to the preferential absorption of high speed neutrons by U238.
The loss of fissile material from the fissile region facilitates the transmission of thermal neutrons from the moderator to the fertile region.
Thermal neutrons are relatively more efficient at burning Pu239. As a result the Pu239 that is accumulated in the fertile region is now made use of for the production of energy. The total energy produced per unit mass of natural uranium resource that is used to provide the materials for the fertile and - fissile regions is more than doubled by the subject invention compared with the present state of the art. This is illustrated in Figure S wherein, the plot lS 50 shows energy produced by current fuel bundles for a given amount of fuelenrichment. Whereas plot 52 shows the energy output for a fuel bundle according to the present invention. It may therefore be seen that the chemical processing steps referred to in the background of the invention are obviated and in fact that present invention eliminates the chemical reprocessing, and transportation steps that were heretofore necessary.
In order to control the neutron spectrum in the fertile region highly enriched uranium is placed in a predetermined configuration around the fertile region. In the embodiment shown in Figures 2 and 3 this fissile region is at the periphery of the fuel bundle. The spectrum of neutrons in the fertile region is a result of fission neutrons being scattered by the coolant of the fuel channel. Since ~he volume of coolant is relatiYely small in this region of the fuel channel the neutron spectrum is richer in epithermal neutrons which results in an increase in plutonium production rate. As the fuel travels -; through the fuel channel during its lifetime in the reactor the fissile region is depleted of fissile material and its impenetrability to thermal neutrons -`` 2~9932~
decreases which in turn increases the relative population of thermal neutrons in the fertile region.
The fission rate in the accumulated plutonium therefore increases, with a result that these processes lead to almost complete depletion of fissile S material in the fissile and fertile regions with a result that the spent fuel fissile content is relatively low.
Various configurations for the fuel pins in the fissile and fertile regions may be implemented, as shown in figures 3(a)-3(b).
Typically, the diameter of the pressure tube 24 is 10.16 cm, while the radius on the fuel pins 8 may range from 0.48 cm to 1.06 cm, with the radii of the circumference on which the fuels pins are placed, range from 4.5 cm to O cm.
While the invention has been described in connection with a specific embodiment thereof and in a specific use, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.
The terms and expressions which have been employed in the specification are used as terms of description and not of limitations, and thereis no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claims to the in~ention.
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.
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Claims (14)
1. A method for breeding fissile material while producing energy in a fuel bundle, for use in a pressure tube heavy water moderated reactor, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein, comprising the steps of:
arranging a first group of fuel rods containing fertile material in a first region of said fuel bundle;
arranging a second group of fuel rods containing fissile material in a second region of said fuel bundle to surround said first region of fertile material, so that second region of fissile material is relatively impenetrable to thermal neutrons generated in the moderator;
exposing said fissile material, initially during an early part of its life in said reactor, to an epithermally rich neutron spectrum to breed fissile material in said second region, while said fissile material is depleted in said first region;
placing said bred fissile material in said second region in a thermally rich neutron spectrum, to convert said bred fissile material to energy.
arranging a first group of fuel rods containing fertile material in a first region of said fuel bundle;
arranging a second group of fuel rods containing fissile material in a second region of said fuel bundle to surround said first region of fertile material, so that second region of fissile material is relatively impenetrable to thermal neutrons generated in the moderator;
exposing said fissile material, initially during an early part of its life in said reactor, to an epithermally rich neutron spectrum to breed fissile material in said second region, while said fissile material is depleted in said first region;
placing said bred fissile material in said second region in a thermally rich neutron spectrum, to convert said bred fissile material to energy.
2. A method as defined in claim 1, fertile material being depleted uranium.
3. A method as defined in claim 1, said first region being a central region of said fuel bundle.
4. A method as defined in claim 3, said first group of fuel rods having a diameter greater than the diameter of said second group of fuel rods.
5. A method as defined in claim 1, said second region being an outer region of said fuel bundle.
6. A method as defined in claim 1, said fissile material being selected from enriched uranium 235 and plutonium 239.
7. A method as defined in claim 1, said fertile material being selected from a group consisting of uranium 238 and thorium 232.
8. A fuel bundle, for use in a pressure tube heavy water moderated reactor, wherein the bundle has a plurality of elongated fuel rods or fuel elements containing fuel material which are mechanically supported therein, said bundle comprising:
a first group of fuel rods each containing fertile material and being disposed in a predetermined first region of said fuel bundle; and a second group of fuel rods each containing fissile material and being disposed in a second region of said fuel bundle, said fissile material being arranged in said bundle to surround said first region of fertile material, so that second region of fissile material is relatively impenetrable to thermal neutrons generated during the initial stages of fuel life in said reactor.
a first group of fuel rods each containing fertile material and being disposed in a predetermined first region of said fuel bundle; and a second group of fuel rods each containing fissile material and being disposed in a second region of said fuel bundle, said fissile material being arranged in said bundle to surround said first region of fertile material, so that second region of fissile material is relatively impenetrable to thermal neutrons generated during the initial stages of fuel life in said reactor.
9. A fuel bundle as defined in claim 8, fertile material being depleted uranium.
10. A fuel bundle as defined in claim 8, said first region being a central region of said fuel bundle.
11. A fuel bundle as defined in claim 10, said first group of fuel rods having a diameter greater than the diameter of said second group of fuel rods.
12. A fuel bundle as defined in claim 8, said second region being an outer region of said fuel bundle.
13. A fuel bundle as defined in claim 8, said fissile material being selected from enriched uranium 235 and plutonium 239.
14. A fuel bundle as defined in claim 8, said fertile material being selected from a group consisting of uranium 238 and thorium 232.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002099324A CA2099324A1 (en) | 1993-06-28 | 1993-06-28 | Fuel bundle for a heavy-water moderated thermal breeder |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002099324A CA2099324A1 (en) | 1993-06-28 | 1993-06-28 | Fuel bundle for a heavy-water moderated thermal breeder |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2099324A1 true CA2099324A1 (en) | 1994-02-19 |
Family
ID=4151849
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002099324A Abandoned CA2099324A1 (en) | 1993-06-28 | 1993-06-28 | Fuel bundle for a heavy-water moderated thermal breeder |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2099324A1 (en) |
-
1993
- 1993-06-28 CA CA002099324A patent/CA2099324A1/en not_active Abandoned
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