Abstract
One of the parameters affecting the neutron multiplication factor keff of a system containing fissile material is the system temperature. Therefore, the effect of temperature on criticality safety analyses is an area of international interest. In this context, the Working Party on Nuclear Criticality Safety (WPNCS) of the OECD Nuclear Energy Agency (NEA) formed a subgroup to define and execute a code-to-code comparison benchmark to investigate the effect of temperature on keff for PWR fuel assemblies. Two configurations of a generic water-moderated PWR fuel assembly were analysed at different temperatures between 233 K and 588 K, and with different assembly burnups. Based on this benchmark, GRS performed an additional study to investigate the impact of the moderator densities, the neutron reaction cross sections and the thermal scattering data on keff separately. The benchmark results show the expected decrease of keff with temperature and a considerable jump in keff at the phase transition of the moderator. The additional investigation demonstrates that the jump in keff is mainly caused by the change of the moderator density due to the phase transition. The change of the thermal scattering data due to the phase transitions leads to a similar but smaller jump in keff. Furthermore, the actual impact of the different parameters on keff depend strongly on the considered fuel assembly configuration.
Highlights
In criticality safety analyses of fissile material, the most unfavourable configurations need to be analysed considering normal and credible abnormal conditions
Thermal scattering data of hydrogen bound in ice was recently included in the newest releases of nuclear data libraries, e.g. ENDF/B-VIII.0 [3] or JEFF-3.3 [4]
The nuclear data were taken from the latest ENDF/B-VIII.0 library [3, 11], which contains scattering data of hydrogen and oxygen bound in ice
Summary
In criticality safety analyses of fissile material, the most unfavourable configurations need to be analysed considering normal and credible abnormal conditions. Thermal scattering data of hydrogen bound in ice was recently included in the newest releases of nuclear data libraries, e.g. ENDF/B-VIII.0 [3] or JEFF-3.3 [4] In this context, the Working Party on Nuclear Criticality Safety (WPNCS) of the OECD Nuclear Energy Agency (NEA) formed a Sub Group to define and execute an code-to-code code comparison benchmark to investigate the effect of temperature on keff for PWR fuel assemblies [5, 6]. The keff of two configurations of a generic water-moderated PWR fuel assembly were analysed at temperatures between 233 K and 588 K Based on this benchmark, GRS performed an additional study on the effect of the temperature on keff to investigate the temperature-dependent impact of the reaction cross sections, the thermal scattering data and the moderator density on the neutron multiplication factor separately, while the OECD/NEA benchmark analysed only the combined effect. The GRS contribution to this benchmark and the additional investigations are described in this paper
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