Year
2008
Abstract
There are a variety of reasons for quantifying plutonium (Pu) in spent fuel such as (a) recovering continuity of knowledge, (b) determining the shipper/receiver difference, and (c) quantifying the input at a reprocessing facility. Behind each of these reasons is a regulatory structure with MC&A requirements. In the cases of the IAEA, the accountable quantity is elemental plutonium. The material in spent fuel (fissile isotopes, fission products, etc.) emits signatures that provide information about the content and history of the fuel. A variety of nondestructive assay (NDA) techniques are available to quantify these signatures. Given that (a) the majority of NDA techniques do not directly measure elemental Pu and (b) the few that do (X-ray fluorescence and nuclear resonance fluorescence) would likely provide better results if combined with another NDA technique, it is recommended that integration among techniques is needed. Given, (a) the high cost of working experimentally with spent fuel, and (b) decades worth of investment in quantifying the underlying physics that the various NDA techniques depend upon, a code that pulls the relevant physics together provides an ideal platform for integrating the various NDA techniques; MCNPX is such a tool. An MCNPX based research effort to quantify the expected performance of ~11 NDA techniques is underway. The capability of each technique will be quantified on a “library of PWR assemblies.” All the pins in this assembly are modeled with high spatial resolution (~10 im radial length on the edge). Furthermore, the assemblies will span a wide range of burnup, cooling time and initial enrichment so as to exemplify the wide range of measurement situation expected. Finally, integration is needed between experiment and modeling. Although measurements are expensive, they are necessary to provide realism. It is easy to make simplifying assumption in modeling that can not be realistically fulfilled in the field.