The ATHLET-MF code and its application to heavy liquid metal cooled systems

Abstract

This report presents a system thermal-hydraulic analysis code ATHLET-MF --- a new version of ATHLET. This code has been developed on the basis of ATHLET for the thermal-hydraulic analysis of multi-fluid systems, includingthe liquid LBE-cooled systems. A fluid index was introduced in ATHLET-MF so that the user can easily adapt the code for various fluids. The current version of ATHLET-MF has the fluid options of water, liquid LBE and Diphyl THT. Empirical equations of physical properties of liquid LBE and of Diphyl THT, and the heat transfer correlation of liquid LBE were implemented in ATHLET-MF for its application to the LBE-cooled ADS systems. The physical properties and heat transfer correlation of liquid LBE were used based on the comprehensive review and assessment of the thermophysical properties of liquid LBE and of the heat transfer correlations for heat transfer in heavy liquid metals in the open literature. The ATHLET-MF code was applied to the analyses of the target cooling systems of XADS, MEGAPIE and MITS under various transient conditions. The code was assessed against two home-made system analysis codes HERETA and HETRAF by performing the simulation of the dynamic behavior of the target cooling system of XADS under beam power switch-on conditions. Results from the three different codes show a good agreement, indicating the applicability of the ATHLET-MF code to LBE cooled systems. Simulation of the beam power interruption of XADS shows that transient with longer beam interrupt time undergoes a deeper drop of the fluid temperature and of the mass flow rate. However, the drop of fluid temperature is limited by the heat transferred from the reactor pool and the reactor core after the switch-off of the beam power. It is shown that the beam interrupts with duration shorter than 0.1 s are less critical than those with duration longer than 0.1 s. In the case of loss of heat sink, the proton beam should be switched off in 200 s after the occurrence of the transient in order to avoid the failure of the window. For the beam trips of MEGAPIE and MITS, a proper regulation of the 3-way valve in the intermediate cooling loop can effectively limit the LBE temperature fluctuation at the exit of the target heat exchanger. The peaks of LBE temperatures at the inlet and exit of the target heat exchanger after the beam power recovery can be reduced or even eliminated by opening the 3-way valve in the intermediate cooling loop at an early time. Comparison shows that the drop of fluid temperature under the transient of beam trip of MITS is much smaller than that of the MEGAPIE. The steady state natural circulation of LBE is established after the loss of pump power supply for both MEGAPIE and MITS. The natural circulation flow rate is about 46% of its initial value for MEGAPIE and about 37% of its initial value for MITS, which is about 24% less than that calculated based on the proposed scaling principles of a scaled experiment.