Reevaluation of Experimental Data and Analysis with the Latest Reactor Physics Calculation Method on Fast Experimental Reactor JOYO MK-I Perfomance Tests

Yokoyama, Kenji   ; Numata, Kazuyuki*; Shono, Akira; Ishikawa, Makoto

"JOYO" MK-I has a typical fast breeder reactor core which was fuelled by plutonium-uranium mixed oxide (MOX) and the fuel region was surrounded by blanket consisting of depleted uranium oxide. Since it has a simple core geometry without any other special irradiation subassembly, it is suitable for the reactor physics analysis. The experimental data acquired in the "JOYO" MK-I performance tests are analyzed with the latest analysis methods in order to resister the data in the IRPhE (International Reactor Physics Benchmark Experiments) project. For this analysis, nominal values and uncertainties of the experimental data were reevaluated by using knowledge obtained after the MK-I performance test and calculation results based on the latest analysis methods. As the nuclear characteristics for the analysis, we selected the criticality, the control rod worth, the isothermal temperature coefficient, the fuel replacement reactivity worth and the sodium void reactivity worth, which were measured in unburnt cores prior to the first power ascension to 50MWth. In this evaluation, not only the measurement uncertainty but also geometry uncertainty and composition uncertainty are considered. All the uncertainties are evaluated with a classification into the random and the systematic components, according as the guideline of IRPhE. The analysis of "JOYO" MK-I was previously carried out in the fiscal year of 1999. In this report, the analysis is totally carried out again with the revised group constants and the latest analysis codes such as the ultra-fine group lattice calculation code. In order for use in the benchmark problem preparation, the analytical results are shown with various correction factors that are estimated from the difference between analytical models. The uncertainties of analysis results are also evaluated by considering the correction factors. Furthermore, a consistency evaluation with the other existing critical experiment data is carried out by performing ...