ML20210V090
| ML20210V090 | |
| Person / Time | |
|---|---|
| Issue date: | 09/26/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20210V076 | List: |
| References | |
| NUDOCS 8610100497 | |
| Download: ML20210V090 (5) | |
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6 Topical Report Evaluation Report Number: XN-NF-85-92(P)
Report
Title:
Exxon Nuclear Uranium Dioxide /Gadolinia Irradiation Examination and Thermal Conductivity Results Report Date: August 1985 Originating Organization:
Exxon Nuclear Company 1.
Introduction We previously approved ENC's gadolinia fuel properties in a report entitled, "Gadolinia Fuel properties for LWR Fuel Safety Evaluation" (XN-NF-79-56, Revision 1) up to 5 w/o concentration. Recently ENC submitted an update of gadolinia fuel properties in another topical report " Exxon Nuclear Uranium Dioxide /Gadolinia Irradiation Examination and Thermal Conductivity Results" (XN-NF-85-92). ENC has performed irradiation programs and conducted post-irradiation examinations on gadolinia fuel of higher concentration to support the update on material properties.
Although the ENC topical report only addresses thermal conductivity and fission gas release properties, ENC justifies the use of old approved models of thermal expansion, melting temperature, specific heat, and fuel densification for higher gadolinia concentrations in a response to NRC questions. Because of different data acquired at different gadolinia concentrations, e.g., thermal conductivity acquired at 12 w/o, fissions gas release at 8 w/o, we limit the approval of XN-NF-85-92 to the lower concentration of 8 w/o gadolinia concentration. The conclusions of our review are provided in the following.
2.
Thermal Conductivity Thennal conductivity measurements for U02-Gd203 compositions up to 12 w/o were collected from public reports and testing sponsored by ENC. Three sets of data including ENC's own test results have been used to develop a best-estimate equation to predict the thermal conductivity of gadolinia fuel with GD203 concentrations up to 12 w/o. The best-estimate equation shows that the maximum deviation from the fitted data is about 7% at low gadolinia concentrations and temperatures, and 10% at low gadolinia concentrations and high temperatures.
In general, the equation fits most of the data from 0-8 w/o gadolinia (which is the limit of this review) and temperatures between 400*C and 2000 C.
Based on the minimal deviations and the good fit, we conclude that the thermal conduc-tivity equation is acceptable for use at gadolinia concentration up to 8 w/o.
8610100497 860926 PDR TOPRP EMVEXXN C
3.
Fission Gas Release ENC stated that the gadolinia fuel rods examined have consistently shown little fission gas release even for high gadolinia concentrations. This is primarily attributed to the low power of the rods during irradiation because of the ENC design requirement that gadolinia rods are never the limiting rods in the core.
We agree with the ENC observation that little fission gas will be released for high gadolinia concentration provided that these gadolinia fuel rods reside at low power regions.
If, for any reason, ENC changes the requirement by moving burnable poison rods to high power regions, ENC will be reouired to verify that the fission gas release for gadolinia fuel is consistent with the UO2 fission gas release model or ENC should propose a new model for gadolinia fuel. Therefore, we approve the fission gas release up to 8 w/o gadolinia concentration.
4.
Thermal Expansion The ENC model for thermal expansion of gadolinia fuel is the same as the thermal expansion model for U02. The use of the U02 model for gadolinia fuel thermal expansion is based on Wada, et. al. data for gadolinia concentration up to 10 w/o (Ref. 1) and the DOE sponsored program up to 8.5 w/o 7
gadolinia concentration (Ref. 2). None of these programs detect any measurable thermal expansion. Therefore, we conclude that the use of the U02 thermal expansion model is acceptable for gadolinia fuel up to 8 w/o (which is the limit of this review).
5.
Melting Temperature ENC extended the applicability of an approved fuel melting temperature correlation for gadolinia fuel from 5 w/o to 8 w/o based on experimental results (Ref. 3). The results showed good agreement for high gadolinia concentrations, We thus conclude that the approved fuel melting temperature correlation in XN-NF-79-56, Revision 1 can be used up to 8 w/o gadolinia concentration (which is the limit of this review).
6.
Specific Heat There were no measurable differences in specific heat between gadolinia fuel and pure U02 fuel. ENC used a U02 specific heat model for gadolinia fuel based on a DOE gadolinia program up to 8.5 w/o (Ref. 2). We thus conclude that there is reasonable assurance that the U02 specific heat model can be applied to gadolinia fuel up to 8 w/o Gd203.
7.
Densification According to ENC experience, the gadolinia bearing pellets are manufactured with the identical resinter requirements as the pure UO2 pellets.
In a letter l
dated August 15, 1986 from G. N. Ward (ENC) to C. H. Berlinger (NRC), ENC i
shows that the resinter behavior of both pellets is similar for gadolinia fuel up to 8 w/o concentrations according to post-irradiation measurements. Thus i
i i
ENC continues to use the U02 densification model for both pure U02 fuel and gadolinia fuel from 5 to 8 w/o concentration. We conclude that the use of UO2 densification model is acceptable for gadolinia fuel up to 8 w/o concentration.
8.
Conclusion We have reviewed the ENC gadolinia fuel properties described in the topical report XN-NF-85-92 entitled " Exxon Nuclear Uranium Dioxide /Gadolinia Irradiation Examination and Thermal Conductivity Results." Based on ENC test results and the commitment to an in-reactor irradiation program to confirm that U02 fission gas release model is adequate for gadolinia/UO2 fuel, we conclude that the gadolinia fuel properties are acceptable for licensing applications up to 8 w/o gadolinia concentration.
References 1.
Wada, T., Noro, K., and Tsukui, K., " Behavior of UO2-GD203 Fuel", BNES Conference (London) 1973.
2.
Newman, C. W., Thorton, T.
A., and Wrona, B.
tl., " Thermal and Physical Properties for Urania-Gado11nia Fuel", May 1984, DOE /ET/34212-43 BAW-1759.
3.
Busch, R. A., " Properties of the Urania-Gadolinia System (Part 1),
RPX101-3, Semiannual Report", Nuclear Fuel Industry Research Group, October 1985, NFIR-RP-03-04.
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