GB2249658A - A sintered nuclear body and the production thereof - Google Patents

A sintered nuclear body and the production thereof Download PDF

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Publication number
GB2249658A
GB2249658A GB9120403A GB9120403A GB2249658A GB 2249658 A GB2249658 A GB 2249658A GB 9120403 A GB9120403 A GB 9120403A GB 9120403 A GB9120403 A GB 9120403A GB 2249658 A GB2249658 A GB 2249658A
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United Kingdom
Prior art keywords
gadolinia
nuclear
oxide
sintering
mixture
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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.)
Withdrawn
Application number
GB9120403A
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GB9120403D0 (en
Inventor
Geoffrey Alan Wood
Paul Arthur Jackson
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Sellafield Ltd
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British Nuclear Fuels PLC
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Publication date
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Publication of GB9120403D0 publication Critical patent/GB9120403D0/en
Publication of GB2249658A publication Critical patent/GB2249658A/en
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    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21CNUCLEAR REACTORS
    • G21C3/00Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/42Selection of substances for use as reactor fuel
    • G21C3/58Solid reactor fuel Pellets made of fissile material
    • G21C3/62Ceramic fuel
    • G21C3/623Oxide fuels
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/50Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on rare-earth compounds
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00Energy generation of nuclear origin
    • Y02E30/30Nuclear fission reactors

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

Gadolinia-doped nuclear oxide material pellets have the gadolinia free and undissolved in the nuclear oxide material to improve the thermal conductivity of the body. The pellets may be made by mixing together gadolinia and nuclear oxide material, shaping the mixture, and subsequently heating the shaped mixture to a sintering temperature. The heating and duration at the sintering temperature and the environment in which the sintering is performed are selected to inhibit the dissolution of the gadolinia in the nuclear oxide material. Aluminium oxide may also be present in the pellets. <IMAGE>

Description

A Sintered Nuclear Bodv and the Production thereof This invention relates to a sintered nuclear body, and the production thereof, and more particularly to an oxide nuclear body containing gadolinia.
It is known to include gadolinia as a burnable poison dopant in uranium oxide or mixed uranium oxide, plutonium oxide fuel.
It is an object of the present invention to provide such a gadolinia-doped oxide nuclear fuel having an improved thermal conductivity.
According to one aspect, the invention provides a sintered body comprising nuclear oxide material having free gadolinia dispersed therein, thereby to improve the thermal conductivity of the body.
According to another aspect the invention provides a method of producing a sintered body comprising nuclear oxide material having free gadolinia dispersed therein, the method comprising mixing together gadolinia and nuclear oxide material, shaping the mixture, and subsequently heating the shaped mixture to a sintering temperature, the heating and the duration at said sintering temperature and the environment in which said sintering is performed being selected to inhibit the dissolution of the gadolinia in the oxide nuclear material.
The sintering may be performed by heating the shaped mixture to a sintering temperature of about 21000C at a rate of about 2000C/min, holding said mixture at the sintering temperature for about 200 seconds, and cooling said mixture at a rate of about 300'C/min, said sintering being performed in an environment comprising moist hydrogen.
Alternatively, the sintering may be performed by heating the shaped mixture to a sintering temperature of about 1200 C, holding said mixture at the sintering temperature for about two hours, said sintering being performed in an environment comprising carbon dioxide, and subsequently heating said mixture in an environment comprising hydrogen at about 1150 C.
Preferably, between 4% and 12% by weight of gadolinia is included in the shaped mixture, at particle sizes of between 50 and 250 microns, for example between 50 and 100 microns, or between 100 and 150 microns, or between 150 and 250 microns.
The invention also includes a sintered body made by the method of the invention.
The invention further includes a method of testing sintered gadolinia-doped oxide nuclear material articles, the method comprising measuring the electrical resistance of the articles, thereby to determine the extent to which the gadolinia has dissolved in the oxide nuclear material.
The invention will now be further described in the following examples: Example I Gadolinia granules were prepared by adding binder to gadolinia powder together with a conventional binder solvent. The solvent was allowed to evaporate and the resulting paste was broken up into granules by stirring when fully dry the granules were sieved into fractions between 100 and 250 microns. The sieved gadolinia granules were mixed with granules (-1200 vm) of uranium dioxide and pressed into pellets. The binder in the gadolinia granules in the pellets was removed by "debonding" in carbon dioxide at about 800 C.
The pellets were divided into three batches and subsequently sintered by: 1. In hydrogen containing l% carbon dioxide at 1700"C for 5 hours - (a conventional sintering process).
2. Heating to 2100"C at about 200 C/min, holding at this temperature for 200 seconds, followed by cooling at 300 C/min. The same hydrogen environment was used as in batch (1) above.
3. Heating to 1200"C for 2 hours in carbon dioxide, followed by reduction in hydrogen at 1150 C.
The sintered pellets were examined by scanning electron microscopy for the presence of free and dissolved gadolinia. The scanning revealed essentially free gadolinia with little or no dissolved gadolinia in the batches (2) and (3) but batch (1) had dissolved gadolinia.
Example II Gadolinia granules prepared as in Example I were heated to 1500 C to 1800"C in hydrogen or air following binder removal at 800 C in air. The granules were then sieved into size fractions 100-150 ijrn and 150-250 m.
Material from each fraction was mixed with a respective quantity of UO2 powder at approximately 10% by weight, and the mixture pressed into pellets. The pellets were sintered as in batches (1) to (3) of Example 1. The sintered pellets were examined as in Example 1 and similar results were obtained, ie essentially undissolved gadolinia in a matrix of UO2 resulted in the case of pellets sintered as in batches (2) and (3) of Example I with some dissolution of the gadolinia resulting after sintering as in batch (1) of Example I.
Example III Gadolinia granules prepared as in Example I were pressed into pellets. The pellets were crushed through sieves and the fractions 50-100 pm, 100-150 pm, and 150-250 pm obtained. Material from each fraction was mixed with a respective quantity of UO2 powder at approximately 10% by weight, pressed into pellets, and sintered as in Example I. On examination as in Example I, little gadolinia was found to have dissolved in the pellets sintered as in batches (2) and (3) of Example I, but some dissolution of gadolinia occurred from sintering as in batch (1) of Example I.
Example IV Pellets of gadolinia as obtained in Example III, after binder removal, were sintered in hydrogen at 1800"C for 2 hours to a high density. The sintered pellets were crushed and the size fractions 50-100 pm, 100-150 pm and 150-250 pm obtained. Material from each fraction was mixed with a respective UO2 powder at approximately 8% by weight.The mixtures were pressed into pellets, and samples of each pellet were sintered in conditions selected as follows: 1. for 5 hours in hydrogen containing ;% carbon dioxide at 1700"C, 2. at 2100"C for 200 seconds in an atmosphere of moisturised hydrogen after heating to temperature in approximately 10 minutes, and 3. sintered in carbon dioxide at 1300"C for 1 hour prior to reduction in hydrogen at 1150"C for 1 hour.
Electron microscopy revealed that sintering of the pellets in condition (3) above resulted in little or no dissolution of gadolinia in the UO2. This was less than that produced under condition (2) above but this in turn resulted in appreciably less dissolution of the gadolinia than in condition (1) which represents conventional sintering conditions.
The electrical resistance of each of the 9 sample types from Example IV was measured using a digital multimeter and the normalised resistances (per mm of thickness) were as follows: Normalised Resistance (k ohm) size range sintering sintering sintering (microns) condition (1) condition (2) condition (3) 50-100 .35 1.38 6.50 100-150 .57 2.42 10.90 150-250 1.04 5.43 24.91 It can be seen that the electrical resistance increases from condition ( (2) + (3) for all size ranges and that dissolved gadolinia decreases as observed via microscopic examination as the resistance increases.
It is envisaged that other techniques such as plasma melting may be used to produce the gadolinia granules and that furthermore gadolinia may be added in combination with another material such as aluminium oxide. In this case gadolinium aluminate would be the material added to UO2 powder.
Using proprietary data the thermal conductivity of UO2 containing dispersed gadolinia has been calculated using an established formula (Kingery, Bowen and Uhlman, Introduction To Ceramics, 2nd edition, page 636, John Wiley & Sons 1976). Significant improvements in thermal conductivity were obtained for the compositions examined compared to the case where the gadolinia is dissolved in the UO2, as shown below. Furthermore it can be shown that even if the gadolinia makes no contribution to the overall thermal conductivity there is still an improvement over the case of dissolved gadolinia.
Effect of Dispersed Gadolinia On The Thermal Conductivity of UO2 At 1000"C: Weight % Gadolinia Ratio of Thermal Improvement tO Conductivities* 4 1.10 10 8 1.09 9 12 1.15 15 * Thermal conductivity of dispersed gadolinia doped nuclear fuel/thermal conductivity of dissolved gadolinia-doped nuclear fuel.
At temperatures lower than 1000"C it is envisaged that the improvements in thermal conductivity will increase as the temperature decreases.

Claims (23)

Claims
1. A sintered body comprising nuclear oxide material having free gadolinia dispersed therein, thereby to improve the thermal conductivity of the body.
2. A body as claimed in Claim 1, wherein the gadolinia comprises between 4% and 12% by weight of said body.
3. A body as claimed in Claim 2, wherein the gadolinia comprises up to about 10% by weight.
4. A body as claimed in Claim 2 or Claim 3, wherein the gadolinia comprises up to about 8% by weight.
5. A body as claimed in any one of the preceding Claims, wherein the nuclear oxide material comprises a uranium oxide.
6. A body as claimed in any one of the preceding Claims, wherein the body includes a material comprising aluminium.
7. A method of producing a sintered body comprising nuclear oxide material having free gadolinia dispersed therein, the method comprising, mixing together gadolinia and nuclear oxide material, shaping the mixture, and subsequently heating the shaped mixture to a sintering temperature, the heating and the duration of said sintering temperature and the environment in which said sintering is performed being selected to inhibit the dissolution of the gadolinia in the oxide nuclear material.
8. A method as claimed in Claim 7, wherein the sintering is performed by heating the shaped mixture to a sintering temperature of about 21000C at a rate of about 200C/min, holding said mixture at the sintering temperature for about 200 seconds, and cooling said mixture at a rate of about 300oC/min, said sintering being performed in an environment comprising moist hydrogen.
9. A method as claimed in Claim 7, wherein the sintering is performed by heating the shaped mixture to a sintering temperature of about 12000C, holding said mixture at the sintering temperature for about two hours, said sintering being performed in an environment comprising carbon dioxide, and subsequently heating said mixture in an environment comprising hydrogen at about 1150 C.
10. A method as claimed in any one of Claims 7 to 9 wherein the gadolinia comprises between 4% and 12% by weight in the shaped mixture.
11. A method as claimed in Claim 10, wherein gadolinia comprises up to about 10% by weight.
12. A method as claimed in Claims 10, or Claim 11, wherein the gadolinia comprises up to about 8% by weight.
13. A method as claimed in any one of Claims 7 to 12, wherein the gadolinia comprises particles having particle sizes between 50 and 250 microns.
14. A method as claimed in Claims 13, wherein the gadolinia has particle sizes between 50 and 100 microns.
15. A method as claimed in Claim 13, wherein the gadolinia has particle sizes between 100 and 150 microns.
16. A method as claimed in Claim 13, wherein the gadolinia has particle sizes between 150 and 250 microns.
17. A method as claimed in any one of Claims 7 to 16, wherein a material comprising aluminium is mixed with the gadolinia and the nuclear oxide material.
18. A method as claimed in any one of Claims 7 to 17, wherein the nuclear oxide material comprises a uranium oxide.
19. A method as claimed in Claims 18, wherein the uranium oxide comprises granules of about 1200 microns.
20. A method of producing a sintered body substantially as hereinbefore described with reference to: Example I batch II or III, or, Example II batch II or III, or, Example III batch II or III, or, Example IV batch II or III,
21. A sintered body made by the method as claimed in any one of Claims 7 to 20.
22. A method of testing sintered gadolinia-doped oxide nuclear material articles, the method comprising measuring the electrical resistance of the articles, thereby to determine the extent to which the gadolinia has dissolved in the oxide nuclear material.
23. A method of testing the sintered body as claimed in any one of Claims 1 to 6 or Claim 21, the method comprising measuring the electrical resistance of the body, thereby to determine the extent to which the gadolinia has dissolved in the oxide nuclear material.
GB9120403A 1990-11-09 1991-09-25 A sintered nuclear body and the production thereof Withdrawn GB2249658A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB909024404A GB9024404D0 (en) 1990-11-09 1990-11-09 A nuclear fuel body and the production thereof

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GB2249658A true GB2249658A (en) 1992-05-13

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2330685A (en) * 1997-10-25 1999-04-28 British Nuclear Fuels Plc Production of plutonium containing products

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3872022A (en) * 1970-08-10 1975-03-18 Gen Electric Sintering uranium oxide in the reaction products of hydrogen-carbon dioxide mixtures
EP0026389A1 (en) * 1979-09-28 1981-04-08 Kraftwerk Union Aktiengesellschaft Process for preparing high-density oxidic nuclear-fuel bodies
EP0218924A2 (en) * 1985-09-18 1987-04-22 Ab Asea-Atom A method of manufacturing sintered nuclear fuel bodies
US4671904A (en) * 1984-02-20 1987-06-09 Kraftwerk Union Aktiengesellschaft Method for producing oxidic sintered nuclear fuel bodies
EP0249549A1 (en) * 1986-06-10 1987-12-16 SOCIETE URANIUM PECHINEY, FRAMATOME &amp; COGEMA, &amp; Cie Method of manufacturing uranium oxide-based nuclear-fuel pellets

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3872022A (en) * 1970-08-10 1975-03-18 Gen Electric Sintering uranium oxide in the reaction products of hydrogen-carbon dioxide mixtures
EP0026389A1 (en) * 1979-09-28 1981-04-08 Kraftwerk Union Aktiengesellschaft Process for preparing high-density oxidic nuclear-fuel bodies
US4671904A (en) * 1984-02-20 1987-06-09 Kraftwerk Union Aktiengesellschaft Method for producing oxidic sintered nuclear fuel bodies
EP0218924A2 (en) * 1985-09-18 1987-04-22 Ab Asea-Atom A method of manufacturing sintered nuclear fuel bodies
EP0249549A1 (en) * 1986-06-10 1987-12-16 SOCIETE URANIUM PECHINEY, FRAMATOME &amp; COGEMA, &amp; Cie Method of manufacturing uranium oxide-based nuclear-fuel pellets

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2330685A (en) * 1997-10-25 1999-04-28 British Nuclear Fuels Plc Production of plutonium containing products

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GB9120403D0 (en) 1991-11-06

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