Measurement of relative power distribution in axially heterogeneous core by gamma-counting of each fuel plate.

Abstract

In order to understand physics properties of axially heterogeneous LMFBR cores, relative power distribution was measured using a γ-counting method in zone-type partial mockup cores. By introducing an inner blanket at the core midplane, flat power distribution is achieved compared with that of conventional homogeneous cores. Axial power peaking factor is obtained from the measured power distribution in the cores having the inner blanket of different geometries. Investigation is also made on distortion of the power distribution caused by simulated B4C control rods having different 10B enrichments (20 and 55%), which are partially inserted into an upper half of the core. Discussions are made on degree of power distortion and its propagation distance. It is observed that the inner blanket mitigates this disturbance caused in the upper half of the core to a lower half of the core. The calculated distribution agrees quite well with the measured power distribution within experimental errors both in the inner blanket and core regions, while significant discrepancy is observed in an outer blanket region. The calculation predicts well the degree of the distortion of the power distribution caused by the simulated B4C control rods.