Numerical thermal-hydraulic simulations of LBE target mock-up loop "IMMORTAL" by using RELAP5-3D

Watanabe, Nao  ; Obayashi, Hironari  ; Nishihara, Kenji  

JAEA investigates lead-bismuth eutectic alloy (LBE) as a candidate of coolant and spallation target of Accelerator Driven System (ADS). Construction of an experimental facility for LBE spallation target is planned within the J-PARC project for feasibility study of ADS's beam window, which is exposed to high temperature LBE flow and strong proton and neutron irradiation environment. As a demonstration, an LBE target mock-up loop "IMMORTAL" was constructed to confirm the operation of a primary cooling system and to implement integration tests of developing components of LBE technologies. One of important subjects is the thermal-hydraulic characteristic of LBE, however, studies about it are still limited compared with that of light water. In this study, numerical thermal-hydraulic simulation of IMMORTAL was implemented by using RELAP5-3D code, and the calculation results were evaluated. A calculation model of the primary LBE loop of IMMORTAL was configurated. In terms of heat balance, except for a module heater (MH) and two heat exchangers (HXs), the adiabatic assumption is considered. The MH have 18 heater rods, but in this model the heat source was simulated as if a rod having the same heat transfer area as the actual. In addition, since RELAP5-3D code is unable to describe directly a configuration of the HXs, positive and negative virtual power source terms were installed to the model. Comparing to the measured values, it overestimated the temperatures in the primary loop by around 20 K. It seems to be caused by the uncertainties in the LBE-side Nusselt correlation and by a possible underestimation of the fin efficiency.