PSI Methodologies for Nuclear Data Uncertainty Propagation with CASMO-5M and MCNPX: Results for OECD/NEA UAM Benchmark Phase I

TLDR

The study aims to implement nonintrusive black‑box uncertainty‑quantification techniques in production‑quality codes routinely used for nuclear‑data analyses. The authors developed two complementary methods—direct perturbation, which computes sensitivity coefficients and folds them with variance/covariance matrices for local first‑order uncertainty propagation, and stochastic sampling, which draws inputs from joint probability distributions to provide a global all‑order uncertainty analysis—implemented in the lattice physics code CASMO‑5MX and a preliminary version in MCNPX. The methods were applied to the UAM benchmark exercises I‑1 (cell) and I‑2 (assembly), yielding uncertainty‑quantified results for these cases.

Abstract

Capabilities for uncertainty quantification (UQ) with respect to nuclear data have been developed at PSI in the recent years and applied to the UAM benchmark. The guiding principle for the PSI UQ development has been to implement nonintrusive “black box” UQ techniques in state-of-the-art, production-quality codes used already for routine analyses. Two complimentary UQ techniques have been developed thus far: (i) direct perturbation (DP) and (ii) stochastic sampling (SS). The DP technique is, first and foremost, a robust and versatile sensitivity coefficient calculation, applicable to all types of input and output. Using standard uncertainty propagation, the sensitivity coefficients are folded with variance/covariance matrices (VCMs) leading to a local first-order UQ method. The complementary SS technique samples uncertain inputs according to their joint probability distributions and provides a global, all-order UQ method. This paper describes both DP and SS implemented in the lattice physics code CASMO-5MX (a special PSI-modified version of CASMO-5M) and a preliminary SS technique implemented in MCNPX, routinely used in criticality safety and fluence analyses. Results are presented for the UAM benchmark exercises I-1 (cell) and I-2 (assembly).