PURPOSE:To enable prevention from getting a criticality by providing an alarming device that generates an alarm by comparison of an effective multiplication factor fed from a calculating device of an effective multiplication factor, with a predetermined upper limiting value of the effective multiplication factor. CONSTITUTION:A concentration distribution of nuclear fuel materials in a mixer-settler and a pulse-column, is calculated by a calculating device 2 of the concentration distribution of nuclear fuel materials, based on an acidity of a supplied nitric acid solution, concentrations of nuclear fuel materials such as a uranium, a plutonium and so on, in the solution, and concentration of each element in the nitric acid solution and in an organic solvent, all of which are measured by a measurement device 1 for process controlling. At a calculating device 3 of an effective multiplication factor, a relationship between the effective multiplication factor, and the nuclear fuel material concentrations corresponding to the nitric acid solution and to the organic solvent at each their own concentration, is stored. With using effective multiplication factor data supplied from a storage device 4 of the effective multiplication factor, the effective multiplication factor at each position in the mixer-settler and the pulse- column, and of whole the device, are calculated. Then, the effective multiplication factor and a predetermined upper limiting value of the effective multiplication factor is compared and when the former exceeds the latter, an alarm is generated from an alarming device 5.
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