Measurements of intra-cell thermal neutron flux distributions in plutonium fuel lattices; Experiments of multi-rod fuel clusters

not registered; Fukumura, Nobuo*; not registered; Takemura, Morio*; not registered; not registered

Intra-cell thermal neutron flux distributions have been measured in 36-rod and 54-rod plutonium fuel clusters by mean of dysprosium foil activation method. Enrichments of PuO in PuO-UO fuels used are 0.54 wt% for 36-rod cluster and 0.79 wt% for 54-rod cluster. In the central region of the Deuterium Critical Assembly, nine 36-rod or 54-rod fuel clusters were loaded and the surrounding region was occupied with 1.2 wt% UO fuel clusters arranged in square lattice arrays of 25.0 cm pitch. The measurements were made using air or light water as coolant in the pressure tube. The measurement uncertainty in the present experiment was 2 % which was almost the same as that in the previous experiments on plutonium lattices. The dependence of thermal neutron distributions on the number of plutonium fuel rods in the cluster were made clear by the results of present experiments. The present experimental resolts were compared with three calculation code ; the METHUSELAH-II code, the WIMS-D code and the LAMP-DCA code system. The results relevant to averaged thermal neutron flux in the fuel cluster of the METHUSELAH-II code agreed with the experimental results to within 7 %. The results calculated by the WIMS-D agreed with the experimental results within 6 %. On the other hand, the calculated values by the LAMP-DCA were in good agreement with the experimental results within 5 %.