Scope of STACY experiments for criticality benchmark data on low enriched uranium and plutonium solution system

The Static Experiment Critical Facility, STACY was constructed in the Nuclear Fuel Cycle Safety Engineering Research Facility, NUCEF of the Japan Atomic Energy Research Institute in order to produce the fundamental critical data of uranyl nitrate solution, plutonium nitrate solution and their mixture. A series of experiments using single core tank have been performed using 10% enriched uranyl nitrate solution since the first criticality in 1995. Benchmark data of STACY are now used for verification of Japanese criticality safety code system and nuclear data libraries. Kinetic parameters, temperature coefficients and reflector effects of structural material are also measured using single homogeneous core. It is on schedule to make experiments for neutron interaction effect and for simulating the dissolving process with a heterogeneous core using low enriched uranyl nitrate solution. After these experiments, systematic critical and subcritical experiments on plutonium nitrate solution will start in five years. This paper reviews the main results of STACY since the initial criticality and describes the criticality properties of the experimental cores in the future program. (author)