Roles for Process Monitoring in Support of Nuclear Materials Accounting

摘要

The Next Generation Safeguards Initiative includes a process monitoring (PM) project with near-term and long-term objectives. One role for PM is to support nuclear materials accounting (NMA), particularly in cases where NMA cannot meet loss detection goals, such as at large throughput facilities. At large facilities, interim inventory verifications are frequent, perhaps every 10 days, and there is limited ability to reduce in-process inventory, which is often measured with relatively high uncertainty. Therefore, in-process inventory can have a relatively large impact on NMA performance as measured by the standard error of the material balance. In the context of safeguarding a large aqueous reprocessing facility to recover plutonium from spent nuclear fuel, this paper describes four roles for solution monitoring (SM) as a type of PM in support of NMA. First, SM helps understand facility status at the time of interim inventory. Second, SM can provide a "by-difference" estimate and associated uncertainty of material holdup in process equipment that is not directly measureable but is bracketed by measurement points. Third, SM can assess the adequacy of measurement error models such as those used to quantify the uncertainty in solution volume measurements. Fourth, SM together with models of unit operations can provide an inferred or estimated "book value" for waste or other low-Pu-mass streams that allows tighter control limits than are possible with NMA alone.