Multigroup cross-section & precursor data for the CNRS benchmark

The feedback.py script was used to apply salt thermal expansion feedback on the relevant diffusion coefficients and cross-sections (DIFFCOEF, FISS, NSF, REMXS, & SP0) based on the formula provided by Tiberga et al. [1].

benchmark_CHIT.txt is a duplicate of benchmark_CHIP.txt because Moltres requires CHIT input data even if it doesn't use them in any calculations.

References

[1] Tiberga et al., "Results from a multi-physic numerical benchmark for codes dedicated to molten salt fast reactors," Annals of Nuclear Energy, vol. 142, July 2020, 107428.