Measurements of Reaction Rate Ratios as Indexes of Breeding Performance in Mock-up Cores of FCA Simulating Metallic-fueled LMFBR and MOX-fueled LMFBR

Measurements and analysis for reaction rate ratio of 238U capture to 239Pu fission (C8/F9) and that of 238U capture to 235U fission (C8/F5), which are important as indexes of breeding behavior of a fast breeder reactor, were made at Fast Critical Assembly (FCA) of Japan Atomic Energy Research Institute. The measurements were made by a foil activation technique at two assemblies simulating metallic-fueled liquid metal fast breeder reactor and an assembly simulating a MOX-fueled one. The analysis was made based on JENDL3.2 nuclear data file. Calculation to experiment ratios of C8/F9 and C8/F5 were 0.99–1.02 and 1.0–1.03 respectively. Furthermore, the 238U capture rate and the 235U fission rate were measured in a thermal neutron standard field in Heavy Water Facility of Kyoto University Research Reactor to verify accuracy of the present foil activation technique itself and to confirm these C/E values.