State of development of burnup measuring method

Recently in the facilities of transporting and storing spent fuel, the criticality safety design considering the effect of the lowering of neutron multiplication rate of fuel (the application of burnup credit) has been investigated. Also in Japan, this design concept is adopted. When the criticality safety design based on this concept is carried out, it is necessary to grasp and confirm the burnup of fuel. There are three methods as this means of confirmation: the method of measuring the burnup of spent fuel, the method of measuring the reactivity of spent fuel (neutron multiplication rate) and the method based on the analysis of burnup using core control data (calculation). As the nondestructive method of measuring burnup for spent fuel assemblies, gamma-ray spectrum measuring method and gross gamma-ray measuring method, emitted neutron measuring method, multiplied neutron measuring method and passive neutron multiplication measuring method are explained. The state of development of the method of measuring burnup in various countries is reported. As the example of burnup measuring devices, the combination of three kinds of measurement and Fork Detector device are shown. (K.I.)