The path for innovative severe accident neutronics studies in ZPRs. part I.2 - Interpretation of SNEAK-12A experiment for core disruption in LMFBRs impact of nuclear data uncertainties on reactivity coefficients

Abstract

The present work details a further investigation of the SNEAK-12A experimental program, which aimed to study material relocation in Sodium Fast Reactors (SFRs) leading to core degradation. The further investigation include sensitivity and uncertainty propagation analysis. In this paper, a comparison is made using two codes, a Monte Carlo based code Serpent 2 and the deterministic system code ERANOS. A sensitivity analysis was made utilizing the two codes, with comparison of two nuclear data libraries (ENDF/B-VII.1 and JEFF-3.1.1). The code-to-code comparison resulted in a very good agreement, while the comparison of libraries showed large discrepancies, manly due to the differences in the sodium cross-section data. The sensitivity analysis, was followed by a complete propagated uncertainty analysis based on the covariance evaluated data available in the COMAC data evaluation. The results of the uncertainties show that there are still large discrepancies linked to the nuclear data. This work is done within the frame work of new core design capacities and new ways of conducting in Zero Power Reactors, such as the ZEPHYR project led independently by CEA.

Modeling representative Gen-IV molten fuel reactivity effects in the ZEPHYR fast/thermal coupled ZPRs. Part I-Assembly level

“…15,16,22,23,31 UCOM-V01AB was created for the sole purpose of this project to studying the sensitivity of the optimization process to the changes in the ND uncertainties. The COMAC-V01 contains rather high uncertainties on several key isotopes, as presented in the paper, while UCOM-V01AB is updated by using older experimental data available from SNEAK-12A/B severe accident studies experimental program.…”

“…15,16 Therefore, the minimal accepted representativity factor for this project is set to r RE = 0.85. In the limit of r RE = 1 and the ratio δE 2 =ϵ 2 E →0, the reduction factor, ϵ * R =ϵ R , can vanish.…”

“…The UCOM-V01AB is an adjusted version of the COMAC-V01 version using an experimental data available from the recently published SNEAK-12A/B benchmark, 15,16,22,23 which focused on severe accident in liquid metal-cooled fast reactors. The results of the benchmark calculation based on the JEFF-3.1.1 library with the Serpent 2 code show excellent agreement.…”

“…Detailed interpretation of similar programs 15,16 showed that in case the change in the material balance between different SCA configurations is not large, the sensitivity vector and the propagated uncertainties remain quite similar. Therefore, to determine the largest contributors to the total propagated uncertainty on the multiplication factor, the examination of the reference configuration should suffice.…”

“…Previous experiment analysis of similar programs such as SNEAK-12A and 12B pointed out the removal of sodium from the core as the largest impact on the reactivity variation (Δρ) sensitivity/uncertainty parameters, 15,16,29 while the geometrical changes have a much lower impact. 16 Furthermore, in the current study, the reactivity variation between the different cases are large (Tables 4 and 5), which in turn substantially reduces both the sensitivity vectors and the propagated uncertainties on Δρ.…”