Effects of sparging gas entrainment on void and temperature coefficients in the Transatomic Power molten salt reactor core

Abstract

A model of the Transatomic Power Molten Salt Reactor core was simulated using the Monte Carlo code Serpent 2 to determine the effects of sparging gas entrainment on the void and temperature coefficients. The reactor core showed a positive void coefficient of around + 170 pcm per 1% increase in void and a shift in transition temperatures from negative to positive temperature coefficient of around –24 K per 1% increase in void. These observations were similar for the homogeneous model chosen in this work and for a heterogeneous (explicit bubble) model. The observed characteristics were caused by decreased fuel mixture self–shielding as gas entrainment levels increase and its synergistic effect with gas thermal expansion. Due to the important safety implications from the observed characteristics, similar reactor designs should be evaluated for their void and temperature coefficients with respect to gas entrainment levels.