Boiling and Drying Accident of High-Level Liquid Waste in a Reprocessing Plant: Examination of the Time-Dependent Temperature Increase of the Waste and of the Generation Rates of the Individual Components Released into the Gas Phase

Using the amount, composition, and decay power density of high-level liquid waste in a storage tank, the temperature change of the waste up to 600°C and the corresponding vapor and gas release rates of H₂O, HNO₃, NO₂, NO, and O₂ as a function of time after the loss of cooling function were obtained by the following method. The heat balance equations in and around the tank were derived, and the solution of the waste temperature change was numerically obtained using the vaporization rates of H₂O and HNO₃ and the generation rate of NOx, which were both obtained from the experiments using the simulated liquid waste. Utilizing the temperature versus time curve obtained from the equation, the release rates of the components described above were obtained as a function of time. This information on the progress of the accident can be used to study the Leak Path Factor of radioactive materials, especially of volatilized Ru, and further, it becomes basic information when considering accident management and suppressing the impact of a disaster.