PURPOSE: To prevent the critical state by emitting an alarm by measuring, calculating and evaluating the number of neutrons from plutonium (Pu) to compare the same with a preset Pu concn. upper limit control value to detect the abnormality of concn.
CONSTITUTION: The neutron generated from a small amount of Pu contained in the waste extract (aqueous nitric acid solution or org. solvent solution) supplied to a mixer settler is measured by the neutron detection part 1 constituted of the counter surrounded by a neutron decelerating material. The signal from the detection part 1 is inputted to a Pu concn. calculator 3 as a count rate through a counter circuit 2. Pu isotope composition ratio analytical data also becomes the input data of the calculator 3. Further, a neutron effective multiplication constant memory apparatus 4 stores the data showing the relation between a neutron effective multiplication constant and Pu concn. on the basis of theoretical calculation and the calculator 3 refers to said data to correct neutron multiplication effect to calculate the concn. of Pu. The Pu concn. calculation value outputted from the calculator is sent to an alarm generator 5 to be compared with a Pu concn. upper limit value and, when the Pu concn. calculation value becomes said limit value or more, an alarm is emitted.
KIKUCHI SHIGETO
KIYONO TAKESHI
