JOYO MK-III core performance tests and results

Sekine, Takashi ; Maeda, Shigetaka   ; Yokoyama, Kenji   ; Chiba, Go; Aoyama, Takafumi ; Maeda, Yukimoto

The fast neutron fluence is 1.3 times larger in the JOYO MK-III core than in the MK-II core. To achieve this, the fuel region was expanded and subdivided into two enrichment zones, two of six control rods were shifted from 3rd row to 5th row, and reflector subassemblies were replaced by shielding subassemblies in the outer two rows. To accommodate the resulting 40 % power increase, the sodium coolant flow rate in the primary system was increased from 1100 t/h to 1350 t/h, and the two intermediate heat exchangers and four dump heat exchangers were replaced.MK-III performance tests began in July 2003 to characterize the upgraded core and heat transfer system.As a result of the reactor physics tests at low power, which were completed by early September, it was confirmed that calculation results agreed with the measurements within uncertainties. Thus, the validity of the nuclear design calculation was confirmed.