Conceptual Core Design of a Small Modular Fast Reactor Cooled by Lead-Bismuth Eutectic

Abstract

A preliminary design of a Small Modular Fast Reactor (SMFR) cooled by Lead-Bismuth Eutectic (LBE) and based on the ALFRED core (Advanced Lead-cooled Fast Reactor European Demonstrator) was achieved through three-dimensional simulation core analysis with MC2-3/TWODANT/REBUS-3 - the deterministic code system from Argonne National Laboratory (ANL) for fast reactor analysis. The reactor was designed to achieve a thermal power of 37.5 MW with 40% thermal efficiency assumption. The two major design goals consisted in a cycle length of 30 Effective Full Power Years (EFPYs) and a small-size active core which can be transported in a spent nuclear fuel (SNF) cask (1 m in height and less than 1.2 m in diameter). Several sensitivity tests on fuel material and geometry parameters were conducted to meet these two requirements. The selection of Uranium Nitride (UN) fuel allowed to improve significantly the fuel efficiency while the choice of a fuel pin radius of 0.52 cm, resulting in a fuel-to-coolant volume fraction of 1.413, enabled to increase the core lifetime over 30 years without refueling. The reactivity control system was also evaluated by calculating the shutdown margin and it is checked that the control rods system can provide enough shutdown margins to cover the excess reactivity and the temperature defect. Further study is required to analyze the core safety (void coefficient, fuel Doppler coefficients, expansion coefficients and radiation creep) and reduce the initial excess reactivity (by adding burnable poison, introducing enrichment zoning or increasing the number of control rods). Overall, it is confirmed that the conceptual core satisfies the target design ideas and this preliminary design work constitutes the very first step in a long core design process.