Behavior of LWR fuels with additives under reactivity-initiated accident conditions

反応度事故条件下における添加物入り軽水炉燃料の挙動

三原 武  ; 宇田川 豊  ; 天谷 政樹  ; 谷口 良徳 ; 垣内 一雄 

Mihara, Takeshi; Udagawa, Yutaka; Amaya, Masaki; Taniguchi, Yoshinori; Kakiuchi, Kazuo

In order to assess effects of additives for fuel pellet on the fuel behavior during a reactivity-initiated accident (RIA), fuels with additives irradiated in commercial light water reactors (LWRs) in Europe up to high burnup were subjected to pulse-irradiation experiments in Nuclear Safety Research Reactor (NSRR) of Japan Atomic Energy Agency (JAEA). Two tests were performed: test LS-4 with chromia-doped UO and Zry-2 cladding with liner and test OS-1 with ADOPT (chromia-and-alumina-doped UO) pellet and Zry-2 cladding with liner. The test fuel rod of LS-4 did not fail. The test fuel rod of OS-1 was considered to be failed by hydride-assisted pellet-cladding mechanical interaction (PCMI). The fuel failure limit in OS-1 was the lowest among the test results ever obtained at the NSRR in similar burnup range. The morphology of the hydrides precipitated in the fuel cladding of OS-1 was investigated by metallography and compared with previous results obtained in JAEA in connection focusing fuel failure limit. It was suggested that the observed lower limit of fuel failure was related to the amount and length of the hydride precipitated along the radial direction of cladding.