GB2318902A - Neutron absorbing coating for a fuel element - Google Patents
Neutron absorbing coating for a fuel element Download PDFInfo
- Publication number
- GB2318902A GB2318902A GB9722926A GB9722926A GB2318902A GB 2318902 A GB2318902 A GB 2318902A GB 9722926 A GB9722926 A GB 9722926A GB 9722926 A GB9722926 A GB 9722926A GB 2318902 A GB2318902 A GB 2318902A
- Authority
- GB
- United Kingdom
- Prior art keywords
- enclosure
- fuel element
- coating
- gadolinium
- 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.)
- Granted
Links
- 239000000446 fuel Substances 0.000 title claims abstract description 48
- 238000000576 coating method Methods 0.000 title claims abstract description 31
- 239000011248 coating agent Substances 0.000 title claims abstract description 29
- CMIHHWBVHJVIGI-UHFFFAOYSA-N gadolinium(iii) oxide Chemical compound [O-2].[O-2].[O-2].[Gd+3].[Gd+3] CMIHHWBVHJVIGI-UHFFFAOYSA-N 0.000 claims abstract description 38
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 16
- 239000010439 graphite Substances 0.000 claims abstract description 16
- 239000011358 absorbing material Substances 0.000 claims abstract description 14
- UIWYJDYFSGRHKR-UHFFFAOYSA-N gadolinium atom Chemical compound [Gd] UIWYJDYFSGRHKR-UHFFFAOYSA-N 0.000 claims description 25
- 229910052688 Gadolinium Inorganic materials 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 21
- 239000000463 material Substances 0.000 claims description 17
- 239000003085 diluting agent Substances 0.000 claims description 4
- 239000003758 nuclear fuel Substances 0.000 claims description 4
- 238000005240 physical vapour deposition Methods 0.000 claims description 3
- 238000007750 plasma spraying Methods 0.000 claims description 3
- 239000000843 powder Substances 0.000 claims description 3
- 239000012876 carrier material Substances 0.000 claims description 2
- 239000003795 chemical substances by application Substances 0.000 claims description 2
- 150000001875 compounds Chemical class 0.000 claims description 2
- -1 gadolinia Chemical compound 0.000 claims description 2
- 230000001737 promoting effect Effects 0.000 claims description 2
- 229910052770 Uranium Inorganic materials 0.000 description 9
- 239000002574 poison Substances 0.000 description 9
- 231100000614 poison Toxicity 0.000 description 9
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 description 9
- 230000000694 effects Effects 0.000 description 7
- 230000000994 depressogenic effect Effects 0.000 description 4
- 238000011109 contamination Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000006096 absorbing agent Substances 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 238000005253 cladding Methods 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000012864 cross contamination Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 239000002925 low-level radioactive waste Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000002915 spent fuel radioactive waste Substances 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C7/00—Control of nuclear reaction
- G21C7/02—Control of nuclear reaction by using self-regulating properties of reactor materials, e.g. Doppler effect
- G21C7/04—Control of nuclear reaction by using self-regulating properties of reactor materials, e.g. Doppler effect of burnable poisons
-
- 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
- G21C3/02—Fuel elements
- G21C3/04—Constructional details
- G21C3/16—Details of the construction within the casing
- G21C3/20—Details of the construction within the casing with coating on fuel or on inside of casing; with non-active interlayer between casing and active material with multiple casings or multiple active layers
-
- 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)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Monitoring And Testing Of Nuclear Reactors (AREA)
Abstract
A fuel element for a nuclear reactor core has an enclosure which has a coating of a neutron absorbing material on an outer surface thereof. The enclosure may be a graphite sleeve 12 of a fuel cage 10 and the coating may comprise gadolinia.
Description
NEUTRON ABSORBING CQATING The present invention relates to the coating of enclosures for fuel cages for nuclear reactors with a neutron absorbing material.
A nuclear reactor fuel core comprises a plurality of fuel "stringers" loaded in parallel alignment; each stringer comprises two or more fuel elements joined in an axial end-to-end relationship; and, each fuel element comprises a plurality of uranium material fuel pins in a parallel, spaced-apart array. In an advanced gas cooled reactor (AGR) for example, there are approximately three hundred stringers comprising the reactor core. From time to time it is necessary to replace individual stringers as the fuel becomes depleted and the stringer is no longer delivering the required power output. Stringer replacement is generally carried out with the reactor "on-load", i.e. still delivering power.
One way of classifying the power output of a nuclear reactor is by the so-called "mean stringer irradiation" method which is the amount of power delivered by a stringer during its life prior to removal. Until relatively recently a figure of 18GW was the accepted power output per tonne of Uranium. However, this figure has been increasing due to the desire for greater power output from existing plant; the increased power being derived from the use of uranium fuel having higher levels of enrichment. More recently, the burn-up cycle per tonne of Uranium has been raised to about 24 GW.
For practical reasons and as is known in the art it is desirable to operate a nuclear reactor at a mean or relatively constant power level. Therefore, a frequently repeated problem is encountered when a new stringer is loaded into a reactor core amongst partially expended stringers since the mean power output of the new stringer may be considerably more than that of the surrounding stringers and "hot spots" arise in the reactor core. In order to temporarily reduce the power output of new stringers, so-called poison cables are used to absorb some of the "excess" neutrons and so reduce effective power output. Known poison cables comprise stainless steel tubes which are packed with a mixture of gadolinia as the neutron absorber and alumina as a diluent.
Gadolinium is a very powerful neutron absorber and, in order to put this into context; boron which is used as the moderator to control the nuclear reaction per se in the core has a neutron capture cross section of 700 Barns whilst the figure for gadolinium is 49000 Barns. However, generally the higher the neutron capture cross section, the shorter is the half-life of the material and that for gadolinium is 4 hrs. The poison cables are designed to provide a flux depressant effect of a certain magnitude which will decay slowly over a certain period of time.
The start magnitude of the depressant effect is controlled by the size and number of the poison cables whereas the time period is achieved by the density and geometry (diameter) of the gadolinium contents. The higher the density and greater the diameter increases the self shielding effect on the inner layers of atoms and prolongs the life of the cable as a significant neutron depressant. The cable is designed such that it is burntup in a "linear" manner; the outer material initially absorbing neutrons until burnt-up and then the underlying material being burnt-up until all the "layers" of gadolinium have been burnt-up and no further significant neutron absorbing capability exists. Poison cables such as those described above have been used for many years to moderate the initially high power output of new stringers and once the power output of the stringer has naturally declined to that of the required mean power output, all of the gadolinia in the cables has been depleted and therefore has no further effect. The amount of burnable poison required depends on the fuel management arrangements but as a general rule for stringers having an 18 GW/teZ output no poison cables are required. For 21 GW/tez the amount of gadolinia in the mixture in the cables is about 2%; and, for 24 GW/tep the amount is about 50%.
However, due to the desire for ever increasing power outputs it has become necessary to find a means of further reducing initial high power output of new stringers during high power on-load installation by about 20 to 40 % for a very short period of time to enable installation and start-up without producing an unwanted initial hot-spot in the reactor core. Such a power reduction is desirable without substantially changing the existing poison cables and thus necessitating a substantial redesign of the fuel cages.
It has been suggested to put gadolinia into the uranium fuel per se. An addition of about 100ppm would produce an initial reduction of power output of about 20%. However, this is a very undesirable step as not all reactors are
AGRs and do not have the same problem to solve and the gadolinium level in fuel is generally specified as lppm max. Only a relatively small proportion of all uranium fuel produced is used for AGRs and the problem of cross contamination would be difficult and very costly to solve; the only sure route being to build a dedicated uranium fuel production line for AGRs which would be prohibitively expensive. Furthermore, there is no current method of recovering waste material which is contaminated with significant amounts of gadolinium. Thus, it would be necessary to store such waste material at significant cost until a recovery route could be developed.
W095/26426A describes a process and apparatus for sputter coating the inside of nuclear fuel rod cladding tubes with neutron absorbing material. However, this is undesirable for the reasons given above of possible contamination of the fuel with gadolinium which must be maintained below lppm.
US-A-5272735 also describes the coating of the inside of fuel rod cladding tubes and mentions the use of gadolinia. However, the same disadvantages exist as with
W095/26426A.
An object of the present invention is to provide a method of initially reducing power output of a stringer for a relatively very short time without the problem of contaminating uranium fuel with gadolinium.
According to a first aspect of the present invention, there is provided an enclosure for a cage of a nuclear fuel element, the enclosure having an outer surface having a coating of a neutron absorbing material.
The neutron absorbing material may be gadolinium and may be in the form of a compound of gadolinium such as gadolinia, Gd203, for example.
The fuel cage is the structure which supports the fuel rods in the fuel element.
The enclosure may be generally cylindrical in form.
The enclosure may be formed of graphite.
According to a second aspect of the present invention, there is provided a method for initially reducing the power output of a fuel element for a nuclear reactor core; the fuel element including an outer enclosure of a moderator material wherein the method includes the step of providing a coating of a neutron absorbing material on an outer surface of said enclosure.
The neutron absorbing material may be gadolinium or a gadolinium containing material such as gadolinia, Gd203, for example.
The coating material may be mixed with a carrier material and/or a diluent material. A suitable carrier/diluent material may be based on silica and/or alumina for example. Gadolinia powder does not flow easily and a flow promoting agent may also be mixed with the gadolinia powder.
The coating may be applied by a physical vapour deposition process such as plasma spraying for example, however, any other suitable coating process may be employed.
The moderator material of which the enclosure material is made may preferably be graphite. The shape of the enclosure may be of a generally cylindrical form.
The coating is applied to the outer surface of the enclosure so that no contamination of the fuel rods can occur.
The thickness of the coating may be any that contains sufficient neutron absorbing material to absorb excess neutrons until the power output from the fuel element has reduced to a desired level. In practice, the coatings used in experiments have been very thin, substantially amounting to a layer of gadolinium containing molecules embedded in the surface of the graphite enclosure to a depth of about 2Zm. Cun . Coating rates of about 12g/m2 are presently envisaged as producing the desired effect of reducing initial power output by about 20 to 4096 for a relatively very short time, the effect reducing to less than 1% within about 10 days.
The coating may be deposited onto the generally cylindrical enclosure by rotating the enclosure about its axis and causing a plasma spray gun, for example, to be traversed relative to the enclosure; the rate of rotation and the speed of traverse controlling the rate, and hence the thickness, of deposition.
Various pre-treatment steps of the enclosure may be carried out prior to deposition of the coating. Such steps may include in the case of a graphite enclosure, preheating of the surface to burn off any pitch which may be present, for example, so as to produce a consistent surface on which to deposit the coating.
Unlike poison cables, the deposited coating is required to exhibit a maximum depressant effect (20-40%) for a minimum period of time (4-48 hrs). In order to do this, without adversely affecting the economics of the reactor operation, it is desirable to ensure that the minimum number of gadolinium atoms are employed. This is achieved by having a large surface area of coverage and a thin film so that no significant self shielding is achieved. In this geometry the gadolinium is burnt out quickly following closely its half life characteristic curve of 4 hours.
An advantage of the method of the present invention is that the gadolinium only contacts the fuel element enclosure and never comes into contact with uranium fuel per se and thus there is never any danger of fuel contamination. When the fuel stringer is finally spent and removed from the core, the graphite enclosure may be removed and treated as so-called low level waste (LLW) and treated accordingly. The spent fuel may be reprocessed according to known procedures and subsequently recycled.
In order that the present invention may be more fully understood, an example will now be described by way of illustration only with reference to the accompanying drawing which shows a schematic cross section of an enclosure for a fuel element.
The drawing shows an part of a fuel cage 10 of a fuel element for an AGR core. The cage comprises a generally cylindrical shaped sleeve 12 made of graphite (merely for the purpose of lending scale to the drawing, the sleeve is about lm in length). The cage has a lower load bearing grid 14 to which are fixed a plurality of fuel pins or rods (not shown) and two braces 16, 18 which provide radial support for the fuel pins and maintain them in alignment with the sleeve axis 20 and mutually parallel in a spaced-apart array. A central tube 22 provides protection for a tie bar (not shown) which joins a number of the fuel elements together to form a stringer. At least two elements are joined together in an axial endto-end relationship to constitute a fuel stringer for insertion into the reactor core.
The outer surface 24 of the enclosure sleeve 12 has a coating 26 of gadolinia.
In order to deposit the coating 26 the graphite sleeve 12 is rotated about its longitudinal axis whilst it is plasma sprayed with a mixture of gadolinia and a flow promoter (3-4% by weight) using a nozzle which is traversed axially at about 2 to 4 inches from the graphite surface. The graphite surface is simultaneously cooled by a carbon dioxide gas spray. The surface coating of gadolinium is achieved by one or more passes axially of the nozzle.
Prior to plasma spraying of the coating it is desirable, in the case of a graphite enclosure, to prime the surface 24 to receive the deposited coating 26. This may be achieved by first removing all graphite dust which may be present from an earlier machining operation by use of a high pressure air jet followed by a pass of the plasma generation head at the preset speeds and feeds to heat the graphite surface to burn off any residual pitch which may be present on the surface and to assist subsequent adhesion of the gadolinia coating 26.
Claims (20)
1. An enclosure for a cage of a nuclear fuel element, the enclosure having an outer surface having a coating of a neutron absorbing material.
2. An enclosure according to claim 1 wherein the neutron absorbing material contains gadolinium.
3. An enclosure according to either claim 1 or claim 2 wherein the gadolinium is in the form of a compound of gadolinium such as gadolinia, Gd203
4. An enclosure according to any one preceding claim wherein the coating rate is about 12g/m2.
5. An enclosure according to any one preceding claim wherein the enclosure comprises graphite.
6. A method for initially reducing the power output of a fuel assembly for a nuclear reactor core; the fuel assembly including an outer enclosure of a moderator material wherein the method includes the step of providing a coating of a neutron absorbing material on an outer surface of said enclosure.
7. A method according to claim 6 wherein the neutron absorbing material is gadolinium or a gadolinium containing material such as gadolinia, Gd203.
8. A method according to either claim 6 or claim 7 wherein the coating material is mixed with a carrier material and/or a diluent material.
9. A method according to any one preceding claim from 6 to 8 wherein a flow promoting agent is mixed with gadolinia powder.
10. A method according to any one preceding claim from 6 to 9 wherein the coating is applied by a physical vapour deposition process.
11. A method according to claim 10 wherein the physical vapour deposition process is plasma spraying.
12. A method according to any one preceding claim from 6 to 11 wherein the enclosure material is graphite.
13. A method according to any one preceding claim from 6 to 12 wherein the coating is applied to the outer surface of the enclosure at a rate of about 12g/m2.
14. A fuel element for a nuclear reactor core, the fuel element having an enclosure which has a coating of a neutron absorbing material on an outer surface thereof.
15. A fuel element according to claim 14 wherein the enclosure comprises graphite.
16. A fuel element according to either claim 14 or claim 15 wherein the neutron absorbing material comprises gadolinium.
17. A fuel element according to claim 16 wherein the gadolinium is in the form of gadolinia.
18. An enclosure for a cage of a fuel element for the core of a nuclear reactor substantially as hereinbefore described with reference to the accompanying description and drawing.
19. A method for initially reducing the power output of a fuel element for a nuclear reactor core; the fuel element including an outer enclosure of a moderator material substantially as hereinbefore described with reference to the accompanying description and drawing.
20. A fuel element for a nuclear reactor core substantially as hereinbefore described with reference to the accompanying description and drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9722926A GB2318902B (en) | 1996-11-02 | 1997-10-31 | Neutron absorbing coating |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB9622897.8A GB9622897D0 (en) | 1996-11-02 | 1996-11-02 | Coating of graphite |
| GB9722926A GB2318902B (en) | 1996-11-02 | 1997-10-31 | Neutron absorbing coating |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9722926D0 GB9722926D0 (en) | 1998-01-07 |
| GB2318902A true GB2318902A (en) | 1998-05-06 |
| GB2318902B GB2318902B (en) | 1998-09-23 |
Family
ID=26310332
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9722926A Expired - Fee Related GB2318902B (en) | 1996-11-02 | 1997-10-31 | Neutron absorbing coating |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2318902B (en) |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB931286A (en) * | 1958-03-14 | 1963-07-17 | Babcock & Wilcox Co | Improvements in or relating to nuclear reactors |
| GB2151068A (en) * | 1983-12-09 | 1985-07-10 | Kernforschungsanlage Juelich | Process for storing fuel elements |
| US5280504A (en) * | 1992-06-30 | 1994-01-18 | Combustion Engineering, Inc. | Zirconium alloy tube with a boron-containing layer |
-
1997
- 1997-10-31 GB GB9722926A patent/GB2318902B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB931286A (en) * | 1958-03-14 | 1963-07-17 | Babcock & Wilcox Co | Improvements in or relating to nuclear reactors |
| GB2151068A (en) * | 1983-12-09 | 1985-07-10 | Kernforschungsanlage Juelich | Process for storing fuel elements |
| US5280504A (en) * | 1992-06-30 | 1994-01-18 | Combustion Engineering, Inc. | Zirconium alloy tube with a boron-containing layer |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2318902B (en) | 1998-09-23 |
| GB9722926D0 (en) | 1998-01-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20071031 |