(514f) Safeguarding the Next Generation Reprocessing Plant-Solution Monitoring

Allen J. Bakel, John F. Krebs and Candido Periera

Argonne National Laboratory

It has been shown that, in large throughput plants such as the Rokkasho Reprocessing Plant (RRP) there is a low detection probability for losses of interest to the IAEA (8 kg of Pu) using even the most optimistic near-real-time accounting methods.  The goal of this study is to develop an approach to improve that probability.  A particularly low detection probability is seen in the dissolver where shipper declarations (reactor burnup calculations) have relatively large uncertainties (5-10%).  Currently, a product monitoring system is applied by the IAEA to the continuous dissolver at RPP that utilizes semi-quantitative neutron assay of hull batches to detect changes in the neutron count rate.  To provide a framework, a scenario was developed and evaluated where fuel and its contained Pu is purposely left undissolved.  The magnitude of the scenario was calculated based on the loss of 8 kg of Pu over the course of 90 working days.  Based on the chemical models and materials calculations presented here, relatively large changes in temperature, acid concentration or reaction time are needed for the stated material loss.  Further, these process changes would be easily observable using current process monitoring technologies, but further work is needed to evaluate authentication strategies and performance under plant and long term conditions.  Total uncertainties will depend upon the errors associated with model calculations and measurement errors.  Estimation of these uncertainties is the next logical step for understanding the value of process monitoring in this scenario.