Development and validation of analysis code for spallation products behavior in LBE coolant system of ADS comparing with the distribution data in MEGAPIE spallation target

Abstract

It is important to evaluate the inventories and the release and transport behavior of the spallation products (SPs) including polonium-210 in the Lead-Bismuth Eutectic (LBE) coolant system of Accelerator Driven System (ADS) for the safety studies of the radiological hazard both in the cases of normal operation and accident. Especially, the transport and deposition inside the coolant circulation system and the evaporation from the coolant to the cover gas are dominant mechanisms to evaluate the release and transport behavior of SPs. University of Fukui and Japan Atomic Energy Agency (JAEA) have been developing the computer analysis code TRAIL (Transport of RAdionuclides In Liquid metal systems) which predicts the time dependent behavior of SPs within the LBE coolant system of ADS for the wide range of operational events. The TRAIL code is intended to deal with the SPs transport, deposition and evaporation behavior mechanistically in consideration of a variety of the physicochemical configuration of SPs in LBE. The physicochemical configuration of the SPs is essential to evaluate the release and transport behavior because the physical and chemical properties such as the molecular weight, the density, the solubility in LBE and the vapor pressure depend on the configuration. The SPs behavior modelled in the code are based on the generalized flow network model including pipe and tank components. The flow network model is constituted from mass and energy conservation equations in consideration of the mass and energy transfer due to coolant flow effect, deposition or adsorption of SPs onto the structure surfaces, transport into the cover gas due to evaporation and radioactive decay of the radioactive SPs. The source term of both radioactive and stable SPs in the LBE coolant is given as input and the radioactive decay chain model for the radioactive SPs is implemented in the code to evaluate the effect of precursors on the SPs mobility. This paper presents the recent advancement status of the code development and the validation results comparing with the distribution data of volatile SPs in MEGAPIE spallation target.