Nuclear kinetic characteristics for 54(60)-Rod plutonium fuel lattice; Pulsed-neutron-source experiment in a 25-cm pitch lattice

not registered; not registered; not registered; not registered; not registered

Parameters of nuclear kinetic characteristics (/) and loss-of-coolant reactivities have been measured in a 25-cm pitch DO lattice loaded with 28-rod(1.2wt% enriched) UO clusters and/or 54(or60)-rod PuO-UO clusters. The fissile content of the 54(or60)-rod PuO-UO fuel is 0.79wt%. The measurement was done by use of pulsed-neutron-source method. Experimental data are corrected to the values at 22C of the core temperature. Prompt decay constants measured in pulsed-neutron experiment are given as a function of axial buckling which is decided from the -scanning of irradiated copper wire. The parameters (/) are obtained from the value of prompt decay constants at critical. Loss-of-coolant reactivities are converted from the prompt decay constants at the axial bucklings of the core with or without coolant using Simmons & King's formula. The following results are clarified from this measurement. Dependence of the parameters (/) on the fuel composition and coolant void fraction is very small and they are in the range of 19 to 21 sec. On the other hand, the loss-of-coolant reactivities () are strongly depend on the fuel composition. The 54(60)-rod PuO-UO fuel is more effective in shifting the loss-of-coolant reactivity to the negative side than the 60-rod PuO-UO fuel. The 54(60)-rod PuO-UO cluster makes the loss-of-coolant reactivity to the larger negative side in comparison with the 28-rod UO cluster. Measured in the core loaded with 54-rod clusters is more negative than calculated one (Aihara et al, PNC SN941 79-77) by WIMS-CITATION code. The discrepancy between calculation and experiment is about 0.6$ (10%).