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Evaluation of Neutronic and Thermophysical Characteristics of Molten Salts Specialized for Long-Lived Fission Products Transmutation in a Fusion Reactor

Taku KITASAKA, Hiroki SHISHIDO and Hidetoshi HASHIZUME

Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan

(Received 29 November 2019 / Accepted 15 June 2020 / Published 4 November 2020)

Abstract

This study proposes new molten salts, which are specialized for transmuting long-lived fission products (LLFP) using a helical fusion reactor FFHR-d1, as a neutron source. Molten salts are binary systems consisting of BeF₂ and LLFP fluorides, such as BeF₂–ZrF₂, BeF₂–PdF₄, or BeF₂–CsF. This study evaluates the effect of molten salts on the transmutation performance, and the amount of heat generated was evaluated by Monte Carlo-based neutron transport and burnup calculations. Therefore, when the transmutation area was fixed at 4% of the blanket system volume, the higher molar ratio of LLFP fluorides leads to higher transmutation performance. Also, the viscosity, specific heat, and thermal conductivity of BeF₂–CsF were evaluated by molecular dynamics (MD) simulations. The heat transfer characteristics were evaluated by calculating the Prandtl number from MD simulation results. The Prandtl number of 50% CsF, which produced the lowest melting point (475°C), was evaluated to be 29.23, which was 60% larger compared to the Prandtl number of Flibe (LiF–BeF₂) when the BeF₂ molar ratio was 50%. This result suggested that the heat transfer performance was inferior to that of Flibe.

Copyright (c) 2020 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

Monte Carlo method, burnup calculation, molecular dynamics, BeF₂, Prandtl number, LLFP

DOI: 10.1585/pfr.15.2405077

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