Cause analysis of the fire and explosion of asphalt-salt mixture in a nuclear wastes processing plant

In order to explain the detailed cause of the fire and explosion of asphalt-salt mixture (ASM) that happened at a nuclear wastes processing plant in Japan on March 11, 1997, a special experiment device was designed to prepare the ASM samples under different feeding rate of the waste and in different concentration of phosphate in the waste. The structure and diameter distribution of salt particles in the ASMs were examined by using a scanning electron microscope, the specific surface area of the salt particles was measured by the BET method, and the reactivity of ASMs was measured by using a heat flux calorimeter (C80). It was found that both the concentration of phosphate in the waste and the feeding rate of the waste have great influences on the structure of salt particles and the reactivity of the ASM. Most of the salt particles in the ASM are porous and have larger specific surface area when prepared at low feeding rate of the waste containing phosphate, which causes the ASM has lower onset temperature and self-accelerating decomposition temperature (SADT).