A New Approach to Holdup Measurement in Uranium Enrichment Facilities

The Distributed source-term analysis (DSTA) technique represents a new approach to measuring in-process material holdup that is a significant departure from traditional hold-up measurement methodology. The DSTA method is a means of determining the mass of uranium within a large diffuse volume. The total neutron count rate from spontaneous fission and UF6 (~,n) reactions are measured to determine the total uranium holdup in the enrichment hall. This approach is a much more efficient than traditional methods of holdup measurement in cascade halls. An enrichment cascade hall survey can be completed in a few hours as compared to the many weeks required to arrive at a result using traditional methods. The error ascribed to a DSTA survey result would generally be less than that from traditional methods. Also, the negative bias ascribed to gamma-ray methods does not exist because the DSTA method uses neutrons which are more penetrating than gamma rays. The DSTA method can be broken down into three basic components: Monte Carlo modeling of the transport properties of the enrichment cascade hall to derive a calibration curve that relates the average count rate to the mass of uranium holdup, a survey of the cascade hall to measure the average neutron count rate, and determination of the total uranium holdup mass from the survey data using the calibration curve.