Takehiko Yasuno

Effective Cadmium Cutoff Energies for Non-1/V Detectors

Effective cadmium cutoff energies were calculated for 239Pu, 235U, 115In, Au, 119Ir and 176Lu as a function of the cadmium filter thickness, the mast probable energy of the Maxwellian flux and the epi-thermal index. An infinite slab geometry and isotropic flux were assumed in the calculations. The calculated values of the cutoff energies are compared with those for 1/V detector, and are related to the resonance energies near the cutoff energy. If the resonance energy is lower than that of the 1/V detector, and the neutron spectrum and filter are same, the cutoff energy is lower than that of the 1/V detector. Such cases include 235U and 176Lu with thin filter, 191Ir with thick filter, and 239Pu with either thin or thick filter. If the resonance energy is higher than the E c of the 1/V detector, the cutoff energy is higher, such cases being 191Ir with thin filter, 176Lu with thick filter and 115In with either thin or thick filter. And if the resonance energy is very much higher than the E c of the 1/V detec...

EXPERIMENTAL AND THEORETICAL STUDIES OF HEAVY-WATER HOMOGENEOUS TWO-REGION SYSTEM

A series of critical experiments and theoretical analyses has been made on two-region systems in which a heavy water solution of uranyl sulfate with 235U enrichment of about 20% is surrounded by heavy water, poisoned with B or mixed with ThO2. D-to-235U atomic ratios in the core solutions ranged 4,500–1,000, depending on the core diameter and the blanket concentration. The theoretical effective multiplication factor is decreased by treating the leakage of fast neutrons from the core rigorously, and is increased by using spatial-dependent effective cross sections. These treatments are justified by the agreement found between the calculated and measured values for the Cd ratio and the thermal flux distribution. The disagreement seen in the effective multiplication factor between the theoretical and experimental values may be attributed to uncertainty in the resonance integral of 235U. The discrepancy in the effective multiplication factors does not exceed 1%, when the accepted value of νI f -I a is reduced ...