Multiphysics Analysis Of An In-Core Fission Product Removal System For The Molten Salt Fast Reactor

This work deals with the in-core helium injection system proposed for the Molten Salt Fast Reactor (MSFR), whose stated purpose is the online removal of both gaseous and metallic fission products. In order to properly analyse this system, we add the capability to simulate production, transport, and mass transfer of an arbitrary number of gaseous fission products (GFPs) to a pre-existing multiphysics solver, built with the OpenFOAM suite. We aim at starting a comprehensive analysis of the bubbling system, focusing on GFPs, focussing on some operational and safety-related features. Investigations of the first kind include quantifying the efficiency of GFP removal through a characteristic removal time, estimating the poisoning effect of GFPs, and evaluating the activity and decay heat of the removed gas, an aspect which crucially enters the design of the off-gas unit. Among the safety-related studies, the developed multiphysics tool allows evaluating the void coefficient, determining upper bounds on the He flow-rate in order to avoid prompt supercriticality in case of loss of He injection. In addition, two different possible accidents are evaluated involving complete loss of He injection, and complete loss of He removal. Results show the relevance of the thermal-hydraulic behaviour in preventing prompt supercriticality in case of loss of He injection.