Modeling Non-Destructive Assay Based Signatures for Application to Safeguarding Pyroprocessing

摘要

Development of safeguards for pyroprocessing technologies faces several challenges. Traditional nuclear material accountancy (NMA) has limitations in its current format to reach the stated detection limits by the International Atomic Energy Agency (IAEA). Thus, other methods for detection measures must be utilized in conjunction with NMA to reach the necessary detection uncertainty limits. One of these proposed complimentary methods is Signature Based Safeguard (SBS). SBS is defined as the identification and monitoring of measurable indicators of the diversion of special nuclear material. To determine these said signatures, a proper understanding of the unit operations and changes within them and their effect on observables such as voltage reading or radiation dose must be understood. To accomplish the goal of determining these special signatures, models are being developed for each unit operation and measurement. Our research focuses in particular on the electrorefiner and the measurement of its products. For the purpose of investigating these processes, two separate models have been developed and are working iteratively with one another to determine these signatures. One model is responsible for modeling the electrorefiner while the other is used to model the Non Destructive Assay (NDA) measurement of the electrorefiner product. The model of the electrorefiner is called Enhanced REFIN with Anodic Dissolution (ERAD), which was jointly developed by the Seoul National University and Korea Advanced Institute for Science and Technology. It solves for both mass transport and current density within the electrorefiner. The NDA measurement model is based on the Canberra High Level Neutron Coincidence Counter (HLNCC) in MCNPX. Work is currently being performed on an iterative method by which both these different models are coupled together. To do this, the cathode deposit in the electrorefiner is first calculated to determine uranium, plutonium, and zirconium masses based on a set of system conditions. Changes in the cathode deposit were predicted based on changes in the current density at the cathode. Each cathode deposit case was inputted into the MCNP model with isotopic composition calculated based on 25 years of cooldown. The MCNP model utilizes ft8 coincidence counting tallies which take into account both gross counts as well as double and triple counts. Results of these MCNP runs are then correlated with the changes in conditions from the ERAD model to determine the viability of utilizing NDA determined signatures. Results and analysis of the model runs are presented.