Miriam Kreher, Massachusetts Institute of Technology

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In order to achieve high-fidelity multiphysics simulations of full nuclear reactors, we couple Monte Carlo neutronics with temperature/fluid calculations. Running full Monte Carlo simulations between temperature updates is not only extremely expensive, it is also plagued by instabilities due to temperature feedback effects in nuclear cross sections. These instabilities have been reproduced in steady-state and shown to subside by physically under-relaxing the system. This consists in running fewer particles between temperature updates, exchanging unconverged Monte Carlo results as a way of contaminating the solution with previous updates. We have run single-batch Monte Carlo coupling and shown that it is more stable while also accelerating the calculation significantly.

Abstract Author(s): Miriam A. Kreher, Benoit Forget, Kord Smith