Characterization of neutron fields in the experimental fast reactor Joyo MK-III core

Maeda, Shigetaka   ; Ito, Chikara   ; Okawachi, Yasushi ; Sekine, Takashi ; Aoyama, Takafumi 

In 2003 the Joyo reactor upgrade to the MK-III core was completed to increase the irradiation testing capability. This study describes the detail distributions of neutron flux and reaction rate in the MK-III core were experimentally obtained by characterization test during the first two operating cycles. Accuracy of the calculated methods in fast reactor was evaluated by comparing results of DORT, TORT and MCNP. The all calculated reaction rates of U(n,f) agreed well with the measured values about 5% in the fuel region and less than 10% in the reflector region and BC shielding subassembly. However, a large discrepancy more than 10% was observed in the central non-fuel irradiation test subassembly and radial reflector region by DORT and TORT. The MCNP can reduce this discrepancy to 6%. Specific areas of difference, such as uranium fission reaction in non-fuel subassemblies, are understood and correction methods were identified.