Bahavior of HTGR particle fuel under reactivity initiated accident condition

反応度事故条件下におけるHTGR粒子燃料挙動

梅田 幹 ; 植田 祥平   ; 杉山 智之 

Umeda, Miki; Ueta, Shohei; Sugiyama, Tomoyuki

Pulse irradiation experiments using the Nuclear Safety Research Reactor (NSRR) were performed in order to clarify the failure mechanism of the HTGR fuel coating and evaluate the failure limit under RIA condition. Unirradiated TRISO-coated particle was used for the experiments. The energy deposition in the experiments ranged from 580 to 1870 J/gUO and the corresponding peak temperatures at the center of fuel particles were estimated from 1240 to 3680 C by the computer analysis. Visual observation, X-ray radiography, ceramography, etc. were carried out after the pulse irradiation. The coated fuel particle started to fail at 1440 J/gUO (at which the corresponding peak fuel temperature was 2970 C) and mostly failed above 1870 J/gUO (3680 C). The ceramograph indicated that the fuel kernel expanded and the PyC buffer layer became dense in case of fuel failure. The columnar grain growth and the void generation were also observed at the center of the fuel kernel above 1640 J/gUO (3210 C) by ceramograph. It was suggested from the results that the thermal expansion due to the melting of fuel kernel might be a key factor in the fuel particle failure within the range of the present experimental conditions.