Neutronics Code Benchmark for Fluoride-Salt-Cooled Reactors

Abstract

The fluoride-salt-cooled high-temperature reactor (FHR) is an advanced reactor design that aims to improve on the efficiency, cost, safety and non-proliferation security of nuclear energy, while exploiting existing technologies to minimize the design and licensing burden. FHRs share many design features with the high-temperature gas-cooled reactor (HTGR), namely using the same fuel form: a bed of graphite spheres, each with thousands of small coated fuel particles (TRISO) dispersed throughout it. However, rather than using a gas as a coolant, the FHR uses a molten salt which changes the behavior of the system; in particular, from a neutronics perspective, the coolant is no longer effectively transparent to neutrons, but rather contributes both to neutron moderation and absorption. It is difficult to perform exploratory reactor physics experiments for new reactor concepts, as the regulation and cost surrounding a fuel experiment is often highly restrictive and prohibitive. As such, researchers and design engineers must rely heavily on simulation capability to develop a working knowledge for how the reactor physics of a pre-prototypical reactor might behave. It is then essential to have confidence that simulation codes provide credible results. As there are no instances of FHRs deployed to date, nor are there any experimental data available on neutron behavior of pebble fuel immersed in salt, the first step is to perform a code-to-code verification of idealized scenarios that capture the physics involved with an FHR system. This summary describes the development of a code-to-code benchmark for FHR with the purpose of code verification and presents preliminary results. (authors)