DIRECT MEASUREMENT OF INITIAL ENRICHMENT AND BURN-UP OF SPENT FUEL ASSEMBLY WITH A DIFFERENTIAL DIE-AWAY TECHNIQUE BASED INSTRUMENT

A key objective of the Next Generation Safeguards Initiative (NGSI) is to utilize non-destructive assay (NDA) techniques to determine the elemental plutonium (Pu) content in a commercialgrade nuclear spent fuel assembly (SFA). In the third year of the NGSI Spent Fuel NDA project [1], the research focus is on the integration of several sets of NDA techniques. One of the reoccurring challenges to the accurate determination of Pu content has been the explicit dependence of the measured signal on the presence of neutron absorbers which build up in the assembly in accordance with its operating and irradiation history. The history of any SFA is often summarized by the parameters of burn-up (BU), initial enrichment (IE) and cooling time (CT). While such parameters can typically be provided by the operator, the ability to directly measure and verify them would significantly enhance the autonomy of the IAEA inspectorate. Within this paper, we demonstrate that an instrument based on a Differential Die-Away technique is in principle capable of direct measurement of IE and, should the CT be known, also the BU.