JOYO MK-III Performance Test; Criticality Test, Excess Reactivity Measurement and Burn-up Coefficient Measurement

Maeda, Shigetaka   ; Sekine, Takashi ; Kitano, Akihiro ; Nagasaki, Hideaki*

The MK-III performance test began in June 2003 to fully characterize the upgraded core and heat transfer system. This paper describes the results of the approach to criticality, excess reactivity evaluation and burn-up coefficient measurement. In the approach to criticality test, the MK-III core achieved the initial criticality at control rod bank position of 412.8 mm on 14:03 July 2nd, 2003. Because the replacement of the outer two rows of reflector subassemblies with shielding subassemblies reduced source range monitor signals by a factor of 3 at the same reactor power, we measured the change of detector response and decide the count rate to define zero power criticality as 2 10 cps. In the excess reactivity evaluation, Based on the measured critical rod bank position and the measured control rod worths, the zero power excess reactivity at 250C was 2.990.10%k/kk'. The prediction by JOYO core management code system HESTIA, which is 3.130.16% k/kk', agree with the measured value well. On the other hand, the measured excess reactivity was within a safety requirement limit. In the burn-up coefficient measurement, the reactivity change against the reactor burn-up. The measurement method was adopted to measure control rod position at rated power operation. Finally, -2.1210 k/kk'/Mwd was obtained as a measured of burn-up coefficient. The calculated value by HESTIA became -2.1210 k/kk'/Mwd and it agree with the measured value well. 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.