CORE PERFORMANCE TESTS AT LOW POWER FOR THE JOYO UPGRADE TO MK-III

Aoyama, Takafumi ; Robert, W. S.; Maeda, Shigetaka   ; Sekine, Takashi 

Many changes were made in the recent upgrade of the JOYO experimental fast reactor to the MK-III design. Among the core changes made to achieve a four fold increase in irradiation capacity are the introduction of a second enrichment zone, an increase in core radius and a smaller decrease in core height. Performance tests done at low power, which focus on the neutronics characteristics, are presented. These tests include nuclear instrumentation system response, the approach to critical and excess reactivity, control rod calibrations performed several ways, and isothermal temperature coefficient evaluation. The measurements are emphasized but comparisons with calculated predictions are included. The design predictions are consistent with the performance test results, and all technical safety specifications are satisfied. The JOYO MK-III core will provide enhanced irradiation testing capability, as well as serving as a test bed for improving fast reactor operations, performance and