Development of simulation program. SHAWED for analysis of accident of evaporation to dryness by boiling of reprocessed high level liquid waste in tank

An accident of evaporation to dryness by boiling of high level liquid waste (HLLW) is postulated as one of the severe accidents at a fuel reprocessing plant. Two major mechanisms are expected for fission products (FPs) transfer from liquid to vapor phase. One is non-volatiles FPs transfer in the form of mists to the vapor phase in the tank, the other is volatilization of such as Ruthenium. These FPs transferred to the vapor phase in the tank could be released with water and nitric-acid mixed steam and NO₂ gas flow to the environment. NO₂ is generated from denitration of nitrate fission products during dry out phase. These phenomena occurred in this accident originate from the liquid waste boiling in the tank. It is essential for the risk assessment of this accident to simulate thermo-hydraulic and chemical behaviors in the waste tank quantitatively with a versatile computer program. The SHAWED (Simulation of High-level radioActive Waste Evaporation and Dryness) has been developed to realize these requirements. In this report, detailed description of major analytical models is explained based on the features of this accident, and some simulation examples are also described for the use in an actual risk assessment. (author)