For design add operation of reprocessing plant, the criticality safety control is one of the important requirements. JAERI has two solution fuel critical facilities, the STAGY and the TRACY, in NUCEF. The STAGY aims to provide benchmark data on critical mass of solution fuel such as low enriched uranium nitrate solution, plutonium nitrate solution and mixture of both. The purpose of the TRACY is to obtain the data on a postulated critical accident phenomena with low enriched uranium nitrate solution. Prior to experiments with the STAGY and the TRACY, concentration and nitric acid molarity of solution fuel are analyzed for their safety operation. In this paper, the outline of both facilities, management of solution fuel, results obtained in reactor operations and future program are shown.