Alternatives to the burnup strategy and fuel material of the EM2 modular reactor

Abstract

The Energy Multiplier Module (EM2) is a modular high-temperature helium-cooled fast reactor developed by General Atomics (GA). It contemplates a convert-and-burn core, in which fertile fuel is converted to fissile fuel for on-site burning. These features allow the reactor to achieve a core lifetime of 32 years without refueling with different types of fuel materials, like thorium, natural uranium, depleted uranium (DU), and spent fuel. The objective of this study is to evaluate the neutronic performance of the EM2 reactor under four types of fuel material combinations (Low enriched uranium [LEU]/DU, LEU/Th, U-Pu/DU and U/Th) with two burnup strategies. The first strategy was taken from the GA model (configuration 1) and the second was proposed in this paper (configuration 2). The Serpent Monte Carlo code with ENDF/B-VII cross section library was used to perform the calculations. The following parameters were analyzed for each scenario: the effective neutron multiplication factor (keff), the conversion ratio, reactivity coefficients, and the effective delayed neutron fraction (βeff). The fissile inventory and fission rate contribution of the main isotopes were also discussed. The results obtained show that the scenarios with configuration 2 had a higher peak excess reactivity than those with configuration 1. For the scenarios with DU as a fertile fuel, 238U produced ∼20 % of the fission throughout the fuel cycle. In contrast, in the scenarios with thorium as fertile fuel, the 232Th fission rate was negligible. As for the reactivity coefficients, all scenarios presented negative Doppler coefficient and positive void reactivity; both values increased along burnup. On the other hand, the βeff decreased with burnup on and did not vary significantly between both configurations.