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Fig. 4-7 Bird's-eye view of STACY and TRACY

When spent fuels from a nuclear power plant are reprocessed for recycling, uranium and plutonium are dissolved in nitric acid and treated chemically. This nitric acid must be treated with much care because a fission reaction can occur under certain conditions. STACY (Static Experiment Critical Facility) is an experimental reactor in NUCEF. It is the only facility in Japan that uses liquid nuclear fuel. STACY will be used to study conditions that cause a fission reaction in nitric acid containing uranium or plutonium. Studies on STACY will unquestionably increase the safety and reduce the cost of reprocessing facilities. STACY achieved the first self-sustained nuclear chain reaction (criticality) on February 23, 1995, when about 113 liters of uranyl nitrate solution that contained about 35 kg of 10wt% enriched uranium was transferred to the stainless steel cylindrical tank in the water pool. STACY exhibited good experimental accuracy and proper functioning of machinery.

Reference T. Tsujino, et al., Back End of Fuel Cycle and NUCEF Project : Fuel Cycle Safety Engineering Research Facililty That Begins to Move, Nucl. Eng. 40 (5), p.9-12, 26 (1994).

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