Advanced Gas-cooled reactors technology for enabling molten-salt reactors design - Estimation of coolant impact on neutronic performance

Abstract

It has been shown that the Fluoride Salt-Cooled High-Temperature Reactors (FHR) can benefit from adopting some features of well-established Advanced Gas-cooled Reactors (AGR) technology pioneered in the United Kingdom. AGRs offer a number of technological advantages that can potentially speed up the development of FHRs, such as experience with operation at high temperatures, graphite moderated core, fuel design, on-line refuelling, and experience in manufacturing and construction of large concrete pressure vessels with steel liners. This paper summarises relevant information available in the open literature on AGR core operation and design, focusing on neutronic characteristics. The obtained information was used to test the capabilities of Monte Carlo code Serpent to reproduce fuel temperature coefficient of a typical AGR. Then, the paper presents a neutronic analysis of the impact of CO2 coolant substitution with molten salt (FLiBe). The results obtained from the analysis showed that Serpent accurately reproduces the value and behaviour of fuel temperature coefficient both for fresh and depleted fuel conditions. However, subsequent sensitivity and uncertainty analysis showed high uncertainties in the calculated fuel temperature coefficients. The change of the coolant results in significant variation of an AGR neutronic characteristics. The analysis suggests that the use of FLiBe salt as a coolant in AGR-type reactors introduces additional design challenges related to the uncertainties in nuclear data. This work summarises an initial stage of AGRESR project, which was aiming to review the AGR technology relevant to FHR development.