Abstract
Risk information obtained from probabilistic risk assessment (PRA) can be used to evaluate the effectiveness of measures against severe accidents in nuclear facilities. The PRA methods used for reprocessing facilities are considered immature compared with those for nuclear power plants, and to make the methods mature, reducing the uncertainty of accident scenarios is crucial. In this review, we summarized the results of a literature survey on the event progression of evaporation to dryness caused by boiling of high-level liquid waste (HLLW), which is a severe accident in reprocessing facilities. In addition, migration behavior of associated radioactive materials was also summarized. Since one of the important characteristics of ruthenium is its tendency to form volatile compounds over the course of the event progression, the migration behavior of ruthenium is categorized into four stages (early boiling stage, late boiling stage, drying stage and after drying stage) on the basis of temperature. Although no ruthenium is released from the waste in the after drying stage, other volatile elements such as cesium can be released. Sufficient experimental data, however, have not yet been obtained. Thus, it is, necessary to further clarify the migration behavior of radioactive materials, which predominantly depends on temperature in this region.
