Development and validation of fully open-source R2S shutdown dose rate capabilities in OpenMC ^*

Abstract

We present the first fully open-source capabilities for shutdown dose rate
(SDR) calculations of fusion energy facilities based on the Rigorous 2-Step
(R2S) methodology. These capabilities have been implemented in the OpenMC
Monte Carlo particle transport code, building on its existing capabilities
while also leveraging new features that have been added to the code to support
SDR calculations, such as decay photon source generation. Each of the
individual physics components in the R2S workflow---neutron transport,
activation, decay photon source generation, and photon transport---have been
verified through code-to-code comparisons with MCNP6.2 and FISPACT-II 4.0. These
comparisons generally demonstrate excellent agreement between
codes for each of the physics components. The full cell-based R2S workflow was
validated by performing a simulation of the first experimental campaign from
the Frascati Neutron Generator (FNG) ITER dose rate benchmark problem from
the Shielding INtegral Benchmark Archive and Database (SINBAD). For short cooling
times, the dose calculated by OpenMC agrees with the experimental measurements
within the stated experimental uncertainties. For longer cooling times, an
overprediction of the shutdown dose was observed relative to experiment, which
is consistent with previous studies in the literature. Altogether, these features constitute
a combination of capabilities in a single, open-source codebase to provide the
fusion community with a readily-accessible option for SDR
calculations and a platform for rapidly analyzing the performance of fusion technology.