Use of Fast Calorimetry to Perform Mass Attribute Measurements

The attribute measurement technique provides a means to determine whether or not an item containing special nuclear material possesses attributes that fall within an agreed-upon range. One potential attribute measurement would nondestructively determine whether the mass of a given item is larger than some negotiated threshold value. While the historical focus on measuring mass attributes has been on using neutron measurements, fast calorimetry measurements may be a viable alternative for measuring mass attributes for plutonium-bearing items. Traditionally, calorimetry measurements have provided a highly precise and accurate determination of the thermal power that is being generated by an item. In order to achieve this high level of precision and accuracy, the item must reach thermal equilibrium inside the calorimeter prior to determining the thermal power of the item. Because the approach to thermal equilibrium is exponential in nature, a large portion of the approach to equilibrium is spent with the item being within ~10% of its final equilibrium value inside the calorimeter. Thus, in the case of mass attribute measurements that need only to ascertain that an item has a mass higher than a threshold value, measurement times using calorimetry may become comparable in speed to radiation-based nondestructive assay techniques. To determine the feasibility of using heat-flow calorimeters to perform mass attribute measurements, a series of twodimensional heat-flow calculations have been performed in a variety of verification scenarios to estimate the limitations on the accuracy, precision, and measurement times for this technique. Results from this study will be presented along with a discussion of the applicability of using heatflow calorimeters to perform mass attribute measurements on plutonium-bearing items.