Evaluation of the neutron-induced cross sections of actinides using the CONRAD code

Abstract

The CONRAD computer code is being developed by the nuclear data group of CEA Cadarache since mid-2000. It was originally designed to analyse neutron-induced reactions in the resonance energy range and then, was extended to higher energies (several MeV) treatment with inclusion of charged-particles penetration factor. In the thermal energy range, a procedure was implemented to manage the so-called Thermal Neutron Constants, especially devoted to the 239Pu, 241Pu, 233U and 235U nuclei. In the resonance range, nuclear models implemented in the CONRAD program rely on R-matrix model fits with in particular, improved treatment of the fission penetration factor and fluctuations of the prompt neutron multiplicity via a two-step (n,γf) process. Above the resonance range, the neutron continuum energy region of the observed cross sections can be analysed either with the TALYS code or with an in-house optical model code named CCCP that is followed by Hauser-Feshbach calculations according to the compound nucleus deexcitation channels. Non-model least squares fitting procedures have been also tested for neutron cross sections adjustment in the continuum energy range, and such, applied in the framework of the standard cross section group at the IAEA (Vienna). This paper will only focus on the evaluation works performed in the resonance range of minor and major actinides with special emphasis on the experimental corrections suitable to reproduce time-of-flight experiments.