# Rococo – a system of providing nuclear data for Monte Carlo reactor calculations

3/23/2018 2018 - #01 Physics and technology of nuclear reactors

Zherdev G.M. Kislitsyna T.S. Nikolaev M.N.

https://doi.org/10.26583/npe.2018.1.05

### UDC: 621.039.31.17

The ROCOCO [1] system is designed to provide Monte Carlo calculations of neutron fields and gamma fields generated by them. The initial database of nuclear data used in the system is the Russian national library of evaluated neutron data (ROSFOND) [2 – 4]. The specific feature of the system is that the estimator is provided with the opportunity to optimize the levels of descriptions of neutron cross-section energy dependences. The cross-sections of the main fuel and structural materials as well as those of the coolant can be described in such detail as provided for by the evaluated data; the cross-sections of the secondary nuclides (minor actinides, fission products, etc.) can be described in the 299-group ABBB approximation [5] with allowance for resonance self-shielding by the subgroup method or without regard for self-shielding at all. The energy dependence of gamma rays is described in the 127-group P-5 approximation [6]. Optimizing the level of detail makes it possible to significantly reduce the counting time without any significant impact on the result and its error. If desired, when 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 elastic scattering anisotropy is detalized in the case of a group or subgroup description of the cross-sections by specifying 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 the ideal gas approximation or with the help of 72-group thermalization matrices built on the basis of thermalization files included in the ROSFOND library (in cases where such files are contained therein).

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 established with the help of an energy-dependent effective atomic weight.

The programs of the system are written in FORTRAN. The system is easilyintegrated into the calculation programs implementing the Monte Carlo method.

### References

- Kislitsyna T.S., Nikolaev M.N. ROCOCO. Certificate of state registration of the computer program No. 2016612400 of February 26, 2016 (in Russian).
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nuclear data radiation field calculation using the Monte Carlo method combination of detailed and group descriptions of cross-section energy dependences