A multiphysics model for analysis of inert gas bubbles in Molten Salt Fast Reactor
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A multiphysics model for analysis of inert gas bubbles in Molten Salt Fast Reactor Parikshit Bajpai , Stefano Lorenzi, Antonio Cammia Department of Energy, Nuclear Engineering Division, Politecnico di Milano, Via La Masa 34, 20156 Milan, Italy Received: 29 May 2019 / Accepted: 29 April 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Molten salt reactors (MSRs) have gained worldwide interest in recent years due to their appealing safety and resource utilisation characteristics. These reactors have a unique feature, i.e. the presence of nuclear fuel in the form of a molten fluoride or chloride salt containing the fissile and fertile materials. The fuel salt also acts as the coolant, and this dual role results in a complex, highly coupled multiphysics system which poses a challenge in modelling and simulation of MSRs. This paper presents the development of a simulation model for the Molten Salt Fast Reactor (MSFR) to predict the behaviour of inert gas bubbles in the core and to quantify their impact on the reactivity. Inert gas bubbles in MSFR have been modelled using a multiphysics approach coupling computational fluid dynamics for fluid flow and heat transfer with neutron diffusion equation for neutronics and a balance equation with diffusion and advection terms for taking into account the drift of the delayed neutron precursors. The two-phase flow has been modelled using a simplified Euler–Euler model for small volume fraction of the dispersed phase, i.e. for small bubble fraction, which combines the momentum and continuity equation of the liquid and gas phases and adds a gas-phase transport equation to track the void fraction. Simulations reveal that the bubble distribution in the core has a significant impact on reactivity resulting in a difference in the bubbling feedback coefficient compared to studies using a homogeneous distribution.
1 Introduction The Molten Salt Fast Reactor (MSFR) is the reference circulating-fuel reactor selected under the framework of Generation-IV International Forum. This reactor concept was initially studied under the Euratom Evol project and was subsequently developed under the Horizon-2020 Samofar project [1,2]. In MSRs, a molten fluoride salt acts as both the fuel and coolant. While this peculiar feature offers several advantages over solid-fuelled reactors, it also poses a challenge in terms of reactor design and modelling. In MSFR, the velocity field has a significant impact on the distribution of the delayed neutron precursors (DNPs), thus affecting the reactor kinetics and resulting in a tightly coupled multiphysics problem [3].
Focus Point on Advances in the physics and thermohydraulics of nuclear reactors edited by J. Ongena, P. Ravetto, M. Ripani, P. Saracco. a e-mail: [email protected] (corresponding author)
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Moreover, a bubbling system has been proposed in the MSFR design for online removal of fission products. In addition t
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