Developing a neutronic model of the MHTGR-350 SMR for regulatory research

Abstract

The Modular High-Temperature Gas-Cooled Reactor (MHTGR-350) is a Generation-IV small modular reactor that incorporates advanced safety features, high efficiency with high temperatures, and scalability compared to older nuclear reactors. These types of Generation-IV reactors were implemented to avoid repetitions of nuclear disasters like the Chernobyl disaster. Numerous research studies have been conducted on these types of reactors to increase their reliability and to adhere to the safety requirements established by the IAEA. This study aligns with the enhancement of safety in nuclear reactors by performing a neutronic analysis for the MHTGR-350 prismatic design for regulatory research. The use of theoretical and computational calculations was used to analyse the effect of temperature modifications on safety parameters such as the temperature coefficients of the fuel and moderator. These are the two parameters that were used in this study to analyse the behaviour of the reactor when temperatures of the materials in the model that directly affect the behaviour of the reactor are changed. Before the calculations were performed, verification of the Serpent and KENO-VI model was carried out and the results showed that the KENO-VI model could not be run to completion, resulting in the use of the Serpent model to carry out the aim of this study. The fuel reactivity coefficient was negative and the moderator reactivity coefficient was slightly positive and showed that using a difference of 5 to calculate the value was adequate. A literature source shows that a slightly positive value for the moderator reactivity coefficient can be expected for graphite reactors. The effect of the problem for radius and height for neutronic calculations was also shown to be important.

The study has tested the hexagonal structure modelling in version 3 of North-West University Reactor Code Suite (NWURCS) which was not carried out thus far in other studies of the research group. It has shown that while Serpent calculations produced consistent results, the KENO-VI model still needs to be developed, so that the "neutron leakage" of the geometry is fixed.

This work is not intended to be used directly in a safety analysis report; rather, it serves as a starting point in neutronic regulatory research for this type of reactor for the research group. To expand the study, more safety parameters should be included together with thermal fluid coupling. Transient studies should also be considered.