ROCOCO: A constants supply system for Monte-Carlo reactor calculation

Abstract

The ROCOCO system (Kislitsyna and Nikolayev 2016) is designed to supply constants for Monte-Carlo calculations of both neutron fields and the gamma fields they generate. The initial database of nuclear data used in the system is the Russian national library of evaluated neutron data (ROSFOND) (Nikolayev 2006, Zabrodskaya et al. 2007, RUSFOND 2017). ROCOCO is specific in that it enables the estimator to optimize the level of detail when describing neutron cross-section energy dependences. Cross-sections of key fuel, structural and coolant materials can be described in such detail as the evaluated data permits; cross-sections of secondary nuclides (minor actinides, fission products, etc.) can be described in a 299-group BNAB approximation (Manturov et al. 1996) with regard for the resonance self-shielding by subgroup method or without regard for self-shielding altogether. The energy dependence of gamma rays is described in a 127-group P5 approximation (Koshcheyev et al. 2014). Optimizing the level of detail makes it possible to reduce to a great extent the counting time with no major effect on the result and its error. Where desired, in the process of calculating the energy release in neutron reactions or in gamma-quanta formation matrices, contributions from the decay of radionuclides formed in these reactions (with a half-life of less than three years) can be taken into account. The energy dependence of the elastic scattering anisotropy is described in detail, or in the event of a group or subgroup description of cross-sections, by defining 33 boundaries of 32 equiprobable cosine intervals of the scattering angle. The thermalization effects in calculations of neutron fields are taken into account either in an ideal gas approximation or using 72-group thermalization matrices built based on thermalization files contained (if any) in the ROSFOND library.It should be noted that the system contains descriptions of detailed dependences of elastic scattering cross-sections and angular distributions on all multi-isotope elements; the relationship between the scattering angle and the energy loss in this case is determined with the use of the energy-dependent effective atomic weight.The system’s programs are written in the FORTRAN language. The system is easily integrated in Monte-Carlo codes.