Evaluating the Uncertainty in the Temperature Reactivity Coefficient of Terrestrial Energy's Integral Molten Salt Reactor Design

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Terrestrial Energy of Oakville, Ontario has recently received a major award from Sustainable DevelopmentTechnology Canada, allowing it to proceed with the development of its promising novel nuclear reactor design,the Integral Molten Salt Reactor (IMSR). This reactor has a number of features which places it well in thecurrent global electricity market, from the perspectives of cost, size, maintainability and safety.One of the outstanding features of this reactor design is its inherent safety. As the nuclear fuel is dissolved inmolten salts, there is no possibility for a core meltdown. Also, by design, the reactor has a negative reactivitycoefficient of temperature. This means that an inherent feedback mechanism will shut down the chain reactionin the core when the temperature of the core rises, as may happen under hypothetical accident conditions.The reactivity coefficient of temperature is a consequence of the nuclear-physics processes that take place inthe core and govern the creation and absorption of neutrons in the chain reaction. It is a relatively small effectarising from the difference of competing effects, which for the IMSR was determined to be negative over thelifetime of the reactor.The study proposed here will determine the uncertainty in the value of the reactivity coefficient of temperaturefor the IMSR, which is essential to establish the margin of safety for reactor operation over its lifetime. Thestudy will use state-of-the-art modelling tools developed internationally for nuclear safety analysis. In additionto calculations for the proposed fuel composition, the study will also be applied to a number of alternate fuelcompositions.The study proposed here is an essential contribution to demonstrating the inherent safety features of the design.