NDA neutron method for UO2 powder humidity

In technology of low enriched uranium (up to 5%) dioxide powder production there is a need to restrict the hydrogen content and to measure the moisture content. The considered nondestructive method of the measurement is based on continuous irradiating of powder by fast neutrons from an external Pu-Be source with yield 106 n/sec and registration moderated neutrons with 3He detector. In spite of the fact that the neutron moderation in hydrogen is overwhelming, elastic scattering on oxygen nuclei and inelastic scattering on uranium nuclei is essential. Therefore generated spectrum on neutrons is less rigid in comparison with a initial spectrum of a source. This effect can be considerably strengthened if a volume under measurement has metal reflector. Due to high albedo such reflector decrease of neutron leakage. Mock-up calculations executed by Monte Carlo method and real experiments have confirmed validity of the choice of such reflector. As a result of investigation, geometry of the device have to be as following ∼ (100/250) mm cylinder with reflector. The external fast neutrons source was placed outside of the reflector, the detector 3He with was placed in reflector at the opposite side. The general accuracy of measurement does not exceed 0.15 wt%. Duration of analysis ∼10 minutes. In the reality absolute error of measurement go up by factor 2.5 at attainment of threshold moisture 2 wt%, at the expense of a systematic error due to the value of bulk density of powder. (author)