MEASUREMENTS AND ANALYSES OF REACTIVITY EFFECT OF FISSION-PRODUCT NUCLIDES IN EPITHERMAL ENERGY-RANGE

Experimental data usable for evaluating cross sections of main fission product elements (Rh, Cs, Nd, Sm, Eu and Gd) in the epithermal energy range were measured. A cadmium-covered vessel containing a pure water or an aqueous solution of a fission product element was inserted at t he center of TCA (Tank-type Critical Assembly) core. Reactivity effect s were obtained bg the difference in the critical water levels between a pure water and an aqueous solution in the vessel. The measured reac tivity was more than Ic and it was greater than the experimental uncer tainties. Since the adjoint thermal flux below the cadmium-cutoff ener gy are largely depressed in the vessel, the reactivity effects in epit hermal energy range could be measured. The analyses for the experiment s were performed using the SRAC code system and neutron transport calc ulation code TWOTRAN. The exact perturbation theory Nas applied to cal culate the reactivity effects of fission product elements. The calcula ted reactivity effects using JENDL-3.2 and ENDF/B-IV cross-section lib raries were compared against the measured values. The analyses using J ENDL-3.2 gave reasonable results for these measurements.