Experiments and Analyses on Sodium Void Reactivity Worth in Mock-up Cores of Metallic Fueled and MOX Fueled Fast Reactors at FCA

摘要

Sodium void reactivity worth in two metallic fueled fast reactors and a MOX fueled one was measured at the Fast Critical Assembly (FCA). Using the measured reactivity worth, bias factors to be applied to the calculation were determined for the non-leakage term and the leakage term separately by a least squares method. Based on these bias factors, the calculation accuracy for each term was assessed.For the non-leakage term, JENDL-3.2 showed good agreement with the experiments. No difference in the calculation accuracy was observed between the metallic fuel and the MOX fuel, though their neutron spectra were largely different. When the enriched uranium was contained in the void region together with plutonium, however, JENDL-3.2 overestimated the non-leakage term by about 6%. The effect of the plutonium isotope composition was also examined.For the leakage term, it was found that the accuracy of the current calculation depended upon the void fraction in the cell. The directional diffusion coefficient based on the Benoist's theory was validated by transposing the plate direction. Moreover, the design concept of LMFBR with the sodium plenum, which aims at the reduction of the sodium void reactivity, was also examined.