Measurement of loss-of-coolant reactivity of two-region core using 36-rod plutonium fuel clusters

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

Loss-of-coolant reactivity of all channels and that of central channel have been measured in two-region core partially loaded with nine 36-rod PuO-UO clusters. Lattice pitch is 25.0-cm throughout the core, and poison content in DO moderator is O or 3.2 ppm with B concentration. These 36-rod PuO-UO clusters were placed in a central 33 channels of the core and the surrounding region was occupied with eighty-eight 28-rod 1.2 wt% enriched UO clusters. Enrichment of plutonium in the 36-rod PuO-UO fuel is 0.54 wt% or 0.87 wt%, and the fissile content in total plutonium of both PuO-UO fuels is about 91 wt% (standard grade type Plutonium). Neutron flux distributions were also measured by -counting of irradiated copper wire, in order to evaluate the change of neutron flux in the core before and after loss-of-coolant. Reactivities due to loss-of-coolant were obtained by integrating the level reactivity coefficient of moderator (p/H) of the perturbed core between the critical levels at the non-voided core and at the perturbed core. Values of (p/H) were obtained by converting doubling time of neutron flux due to small rise of moderator level (H) to small reactivity(p). Experimental result of loss-of-coolant reactivities (v) is tabled as below together with the ones of the core loaded with nine 28-rod PuO-UO clusters and calculated values by WIMS-CITATION code. The measured v were determined within 50 ￠ of uncertainty. If PuO-UO clusters were placed in the central 3 3 channels of the core, 36-rod PuO-UO clusters is more effective in shifting the v to the negative side in comparison with 28-rod PuO-UO clusters ; the nine 36-rod PuO-UO clusters makes the v ...