Facility for nondestructive monitoring of 235U content in VVER-440 fuel assembly

A study was made of the spatial distribution of the rate of fission in the volume of the fuel assembly, the spatial distribution of the probability of detection of the delayed neutrons emitted from different sections of the fuel assembly, and the distribution of the response proportional to the probability for detecting a unit mass of 235U at different points of the fuel assembly. A model was constructed of the systematic errors of the method and to characterize the error in determining the fuel content when the enrichment and its spatial distribution over the volume in the real object does not agree with that of the standard object. The source of delayed neutrons was a 235U3O8 powder sample. The absolute value of the delayed-neutron detection efficiency was calculated from the delayed-neutron yield known for 235U after the number of fission events in the samples was assessed by the radiochemical method of separating and measuring the β activity of 140Ba preparations. The facility for nondestructive monitoring of the fuel assembly and the shaper of the neutron distribution in the working chamber are shown