Current RIA-related regulatory criteria in Japan and their technical basis

反応度事故時燃料挙動に関する日本の現行安全基準とその技術的根拠

更田 豊志; 杉山 智之 

Fuketa, Toyoshi; Sugiyama, Tomoyuki

This paper will describe current Japanese regulatory criteria concerning fuel behavior during postulated reactivity-initiated accident (RIA) and experimental data providing technical basis with those criteria. The current safety evaluation guideline for the reactivity-initiated events in light water reactors was established by the Nuclear Safety Commission (NSC) of Japan in 1984 based mainly on the results of the NSRR experiments. In the guideline, an absolute limit of fuel enthalpy during an RIA is defined to avoid mechanical forces generation. The guideline also defines an allowable limit of fuel enthalpy for fuel design as a function of difference between rod internal pressure and system pressure. Because only limited number of data had been available, a series of experiments with pre-irradiated fuel rods were initiated in 1989 in the NSRR. After a series of experiments, the NSC issued a regulatory report regarding behavior of burnup fuels during a postulated RIA in 1998.