Post-irradiation examinations and high-temperature tests on undoped large-grain UO2 discs

作者：Noirot J^*; Pontillon Y; Yagnik S; Turnbull J A

来源：Journal of Nuclear Materials, 2015, 462: 77-84.

DOI：10.1016/j.jnucmat.2015.03.008

Within the Nuclear Fuel Industry Research (NFIR) programme, several fuel variants -in the form of thin circular discs - were irradiated in the Halden Boiling Water Reactor (HBWR) at burn-ups up to similar to 100 GWd/t(HM). The design of the fuel assembly was similar to that used in other HBWR programmes: the assembly contained several rods with fuel discs sandwiched between Mo discs, which limited temperature differences within each fuel disc. One such variant was made of large-grain UO2 discs (3D grain size = similar to 45 mu m) which were subjected to three burn-ups: 42, 72 and 96 GWd/t(HM).
Detailed characterizations of some of these irradiated large-grain UO2 discs were performed in the CEA Cadarache LECA-STAR hot laboratory. The techniques used included electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). Comparisons were then carried out with more standard grain size UO2 discs irradiated under the same conditions. Examination of the high burn-up large-grain UO2 discs revealed the limited formation of a high burn-up structure (HBS) when compared with the standard-grain UO2 discs at similar burn-up. High burn-up discs were submitted to temperature transients up to 1200 degrees C in the heating test device called Merarg at a relatively low temperature ramp rate (0.2 degrees C/s). In addition to the total gas release during these tests, the release peaks throughout the temperature ramp were monitored. Tests at 1600 degrees C were also conducted on the 42 GWd/t(HM) discs. The fuels were then characterized with the same microanalysis techniques as those used before the tests, to investigate the effects of these tests on the fuel's microstructure and on the fission gas behaviour.
This paper outlines the high resistance of this fuel to gas precipitation at high temperature and to HBS formation at high burn-up. It also shows the similarity of the positions, within the grains, where HBS forms at high burn-up and where bubbles appear during the low burn-up high temperature tests.

• 出版日期2015-7
• 单位中国地震局