Passive Neutron Assay of Irradiated Nuclear Fuels

Passive neutron assay of irradiated nuclear fuel has been investigated by calculations and experiments as a simple, complementary technique to the gamma assay. From the calculations we have found that the neutron emission arises mainly from the curium isotopes, the neutrons exhibit very good penetrability of the assemblies, and the neutron multiplication is not affected by the burnup. From the experiments on BWRand PWR assemblies, we have found that the neutron emission rate is proportional to burnup raised to 3.4 power. Our investigations indicate that the passive neutron assay is a simple and useful technique to determine the consistency of burnups between assemblies.