Experimental data acquired during experimental fast reactor JOYO MK-I performance tests in the late 1970s have been reevaluated and analyzed with a nuclear analysis system for fast reactors employed by the Japan Atomic Energy Agency. For the purpose of improving the prediction accuracy of nuclear characteristics, nominal values and uncertainties of the experimental data were reevaluated in light of knowledge obtained after the MK-I performance test and calculation results based on the latest reactor physics analysis methods. All nominal values were corrected by a formulation of control rod interaction effects proposed in the present paper, and all possible uncertainty factors were evaluated and quantified.

The analysis results agreed well with measured values within the experimental and nuclear-induced uncertainties for all the nuclear characteristics of criticality, control rod worth, sodium void reactivity, fuel replacement reactivity, and isothermal temperature coefficient.

Meanwhile, the present reevaluated data have been registered with the International Reactor Physics Benchmark Experiments Project with the expectation that these data will be widely used.