Determination of the ~(235)U Mass and Enrichment within Small UF_6 Cylinders via a Neutron Coincidence Well Counting System

摘要

The construction of three new uranium enrichment facilities in the United States has sparked renewed interest in the development and enhancement of methods to determine the enrichment and fissile mass content of UF_6 cylinders. We describe the design and examine the expected performance of a UF_6 bottle counter developed for the assay of Type 5A cylinders. The counter, as designed and subsequently constructed, is a tall passive neutron well counter with a clam-shell configuration and graphite end plugs operated in fast neutron mode. Factory performance against expectation is described. The relatively high detection efficiency and effectively 4π detection geometry provide a near-ideal measurement configuration, making the UF_6 bottle counter a valuable tool for the evaluation of the neutron coincidence approach to UF_6 cylinder assay. The impacts of non-uniform filling, voids, enrichment, and mixed enrichments are examined.