Measuring method and measuring device for fissile material

The present invention directly measures fissile materials of nuclear fuel rods without undergoing influence of γ-rays. Neutron moderation member contains neutron moderators. At least one material to be measured such as a nuclear fuel rod is removably inserted into the neutron moderation member. If thermal neutrons are irradiated to the material to be measured by way of the moderators, the material to be measured causes nuclear fission to generate fast neutrons. The fast neutrons are monitored to measure the amount of fissile materials in the material to be measured. With such procedures, fast prompt neutrons generated by nuclear fission can be selectively measured. The amount of the fissile materials contained in the material to be measured such as a nuclear fuel rod can be measured easily and accurately based on the result of the measurement without undergoing any influence of γ-ray fields. As a result, enrichment degree of pellets can be evaluated directly. (I.S.)