Measurement and analysis of gamma-ray distributions in Kyoto University Critical Assembly, KUCA

Gamma-ray distributions in an undermoderated core of the Kyoto University Critical Assembly, KUCA-B, were measured with four thermoluminescence dosimeters (TLDs), magnesium, strontium and barium orthosilicate (Mg2SiO4 (Tb), Sr2SiO4(Tb) and Ba2SiO4(Tb)); and calcium sulfate (CaSO4(Tm)). In advance of the measurements, the response of these TLDs to gamma-rays was calibrated with a 60Co source and that of Mg2SiO4(Tb) to neutrons was tested. The neutron and gamma-ray flux distributions in the core of KUCA were simultaneously calculated by a transport code ANISN-JR, using a combined cross section set generated by RADHEAT-V3. The distribution of the gamma-rays from fission products was independently calculated. In order to obtain the absorbed dose of each TLD, the following three components were summed up: (1) prompt gamma-rays, (2) fission product gamma-rays and (3) neutrons. All data were normalized by the reaction rate of 58Ni(n,p) 58Co at the core center. In general, the absolute values and the shape of the absorbed dose distribution measured with the four TLDs agree with the calculated ones very well. However, the measured values in the reflector region with Sr2SiO4(Tb), Ba2SiO4(Tb) and CaSO4(Tm) are considerably larger than the calculated results