Covariance matrices of the hydrogen neutron cross sections bound in light water for the JEFF-3.1.1 neutron library

Abstract

In the international neutron libraries, the behavior with the energy of the neutron cross sections of hydrogen in light water depends on the Thermal Scattering Laws tabulated in terms of S(α,β). For the Joint Evaluated Fission and Fusion library (JEFF), Mattes and Keinert have established Thermal Scattering Laws by using the LEAPR module of the NJOY code. However, uncertainties on the corresponding S(α,β) were never reported. Such missing information was recently calculated with the nuclear data code CONRAD by determining the covariances between the model parameters involved in LEAPR. The obtained uncertainties were propagated to reactivity coefficients calculated for critical assemblies operating in “cold” conditions (temperature below 80°C) and for PWR in “hot” operating conditions (300°C). For the integral benchmarks investigated in this work, we found that the uncertainty on the calculated keff, due to the S(α,β) uncertainties, is close to ±130pcm at room temperature and ±50pcm at 300°C.