Postirradiation Examination of the ATF-1 Experiments - 2018 Status
The Advanced Fuels Campaign in collaboration with industry are working to develop enhanced accident tolerant fuels for light water reactors. The initial irradiations of these concepts were performed in the Idaho National Laboratory Advanced Test Reactor using simple drop-in style irradiations. These irradiations are collectively referred to as ATF 1. The postirradiation examination of ATF 1 has begun and some concepts have now completed initial examination. This report describes the results of examinations on ATF 1 irradiations designed to test the feasibility of enhancing UO2 thermal conductivity with additives, ATF 1 irradiations of uranium silicide, and the current status of ATF 1 irradiations that are in process at the hot cell. Enhanced thermal conductivity uranium dioxide composites containing silicon carbide (UO2 SiC) and diamond (UO2 diamond) have been irradiated to low burnup. The conditions of this irradiation test and subsequent postirradiation examinations are discussed. These irradiations evaluate fuel microstructure and potential fuel cladding interaction under representative light water reactor power conditions. Both non destructive and destructive techniques have been used to evaluate fuel integrity, fission gas release, fission product distribution, burnup, fuel swelling and cladding strain. Examination of the UO2 SiC pellets revealed enhanced cracking when compared to a UO2 rodlet also irradiated under similar conditions. Additionally, instability of the SiC whiskers in the uranium dioxide matrix was observed in the pellet central region, where the local temperatures exceeded 1300 °C. The microstructure of the diamond added UO2 was severely disrupted during irradiation, resulting in local migration of cesium along the fuel stack and increased fission gas release when compared with the expected release from the Vitanza curve at corresponding values of burnup and irradiation temperature. The postirradiation examination results cast doubt on the suitability of these additives to improve UO2 fuel performance in a way that would lead to enhanced accident tolerance. Additionally, postirradiation examination data of U3Si2 fuels at low burnup (i.e., < 20 GWd/tHM) for application in advanced Light Water Reactor (LWR) is presented. The U3Si2 pellets show limited cracking in comparison to the expected behavior of UO2 at same power level. In addition, gamma scanning data did not reveal migration of fission products. Minor homogeneous hardening along the pellet radius due to accumulation of fission products and radiation damage was measured by microindentation. The fission gas release and swelling remains very low. Formation of fission gas bubbles resolvable with optical microscopy occurs from the pellets center outward to approximately 60% of the fuel pellet radius. The overall data suggest a good performance of this accident tolerant fuel candidate at low burnup. Finally, the current status of postirradiation examination on other ATF 1 irradiations will be discussed. These irradiations include UO2 clad in an FeCrAl alloy, an alternative uranium silicide compound U3Si5 also clad in a FeCrAl alloy, and an interaction test between UO2 and different FeCrAl alloys.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE Office of Nuclear Energy (NE), Fuel Cycle Technologies (NE-5)
- DOE Contract Number:
- AC07-05ID14517
- OSTI ID:
- 1484529
- Report Number(s):
- INL/EXT-18-51497-Rev000
- Country of Publication:
- United States
- Language:
- English
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