Red oil hazards in nuclear fuel reprocessing

The risk of thermal runaway in a nuclear fuel reprocessing plant due to red-oil reactions is discussed using the uranyl nitrate evaporator in the THORP plant as an illustrative example. The paper sets down the lessons learned from previous incidents and discusses the research and development work undertaken to enhance understanding of the nature and kinetics of these reactions. This work is used to analyse evaporator behaviour and to identify scenarios which result in thermal runaway. The probabilistic risk assessment (PRA) approach to define the frequency of red-oil hazards is then outlined.