Japan Atomic Energy Agency's studies on high burnup LWR fuel behaviour under reactivity-initiated accident conditions

反応度事故時の高燃焼度軽水炉燃料のふるまいに関するJAEAの研究

谷口 良徳 ; 宇田川 豊  

Taniguchi, Yoshinori; Udagawa, Yutaka

The Japan Atomic Energy Agency (JAEA) has performed extensive research programs to better understand the transient behavior of LWR fuels under reactivity-initiated accident (RIA) conditions. RIA-simulated pulse irradiation tests on high burnup LWR fuels, irradiated in commercial reactors, were conducted at the Nuclear Safety Research Reactor (NSRR) primarily in the framework of the Advanced LWR Fuel Performance and Safety (ALPS) research program and in the subsequent ALPS-II program launched in 2010. These experimental programs have thus far added more than 20 data points to the RIA-test database and extended its burnup range to 84 GWd/t. Main conclusions derived through associated post-test examinations and analyses include the primary importance of hydrogen embrittlement and clad temperature on the failure limit irrespective of fuel types and burnup, significant increase in transient fission gas release with burnup, significant enhancement of clad surface heat transfer attributed to surface condition change by irradiation, and so on. The document is to summarize the test results and discuss the influence of the updated knowledge on the current acceptance criteria as well as knowledge gap to be addressed in the future R&D activities.