What to expect from microscopic nuclear modelling for k$_{\rm eff}$ calculations ?

TL;DR

This paper quantifies how microscopic nuclear inputs generated by TALYS affect fast neutron criticality predictions, using ACE files to drive MCNP calculations of $k_{\rm eff}$ for ICSBEP benchmarks and comparing against the JEFF-3.3 library. It shows that, even without adjustments, microscopic models yield integral results close to JEFF-3.3, with larger biases and dispersion than the evaluated library but generally better than other non-adjusted model sets. After targeted parameter adjustment for $^{239}$Pu, the microscopic model performance approaches JEFF-3.3 in both bias and spread, illustrating the strong potential of microscopic ingredients for integral observables. The results underscore substantial progress in microscopic nuclear reaction inputs and suggest pathways to improve differential data while maintaining or enhancing integral accuracy for fast systems.

Abstract

Comparisons between predicted and benchmark k$_{\rm eff}$ values from criticality-safety systems are often used as metrics to estimate the quality of evaluated nuclear data libraries. Relevant nuclear data for these critical systems generally come from a mixture of expert knowledge and phenomenological predictions. In the present work, we use solely microscopic nuclear modelling from TALYS to estimate actinides cross sections and angular distributions, and we compare the calculated MCNP k$_{\rm eff}$ values for fast systems between the JEFF-3.3 evaluated library, phenomenological and microscopic modelling. The conclusion is that even if the evaluated library leads to the most adequate results, the microscopic nuclear modelling can reach very similar results for these integral quantities. It demonstrates the remarkable advances in the recent decades of microscopic nuclear reaction ingredients for applied integral observables.

Figures (6)

• Figure 1: Fission cross sections for $^{239}$Pu from the JEFF-3.3 library (adjusted to experimental data), the two different models, and the EXFOR (measured) values.
• Figure 2: Distribution of C/E for the 195 k$_{\rm eff}$ criticality benchmarks for the libraries and considered models.
• Figure 3: Distributions of the average C/E values (left) and standard deviations (right) for the 960 model combinations, with 195 k$_{\rm eff}$ criticality benchmarks for each combination.
• Figure 4: Distribution of C/E for the 90 $^{239}$Pu k$_{\rm eff}$ criticality benchmarks for the libraries and considered models. Top: non adjusted calculations; bottom: with adjusted parameters for the microscopic and phenomenological models.
• Figure 5: Fission cross sections for $^{239}$Pu from the JEFF-3.3 library, EXFOR and the two different models adjusted on criticality benchmarks.