Method of measuring multiplication factors of subcritical assemblies

Purpose: To simplify the operation of preparing a calibration curve in a method of measuring multiplication factors in the subcritical system of fuel assemblies. Method: For the measurement of effective neutron multiplication factors in a subcritical system such as fuel assemblies, subcritical systems having two known values greatly different from each other is required. However, such conditions are not easily realized in a facility, for example, a spent fuel receiving pool. In view of the above, a neutron source is disposed on one side and a neutron detector is disposed on the other side of a subcritical system placed in water. A measuring system in which the compensating factor takes a value of about 1.0 independent of the effective neutron multiplication factor is previously determined by simulated experiment or analysis. Then, the effective neutron multiplication factor is determined based on the neutron fluxes in the subcritical system measured under the same conditions as those in the thus obtained measuring system. While two standard subcritical systems with the effective neutron multiplication factors being greatly different from each other have been required, a calibration curve can be prepared using only one known standard system and the value can be determined with ease. (Kamimura, M.)