In order to assess effects of additives for fuel pelleton the fuel behavior during a reactivity-initiatedaccident (RIA), fuels with additives irradiated incommercial light water reactors (LWRs) in Europe up tohigh burnup were subjected to pulse-irradiationexperiments in Nuclear Safety Research Reactor (NSRR)of Japan Atomic Energy Agency (JAEA). Two tests wereperformed: test LS-4 with chromia-doped UO_2 and Zry-2cladding with liner and test OS-1 with ADOPT™(chromia-and-alumina-doped UO_2) pellet and Zry-2cladding with liner. The test fuel rod of LS-4 did not fail.The test fuel rod of OS-1 was considered to be failed byhydride-assisted pellet-cladding mechanical interaction(PCMI). The fuel failure limit in OS-1 was the lowestamong the test results ever obtained at the NSRR insimilar burnup range. The morphology of the hydridesprecipitated in the fuel cladding of OS-1 was investigatedby metallography and compared with previous resultsobtained in JAEA in connection focusing fuel failure limit.It was suggested that the observed lower limit of fuelfailure was related to the amount and length of thehydride precipitated along the radial direction ofcladding.
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