RECENT ADVANCES IN HARDWARE AND SOFTWARE TO IMPROVE SPENT FUEL MEASUREMENTS

Vast quantities of spent fuel are available for safeguard measurements, primarily in Commonwealth of Independent States (CIS) of the former Soviet Union. This spent fuel, much of which consists of long-cooling-time material, is going to become less unique in the world safeguards arena as reprocessing projects or permanent repositories continue to be delayed or postponed. The long cooling time of many of the spent fuel assemblies being prepared for intermediate term storage in the CIS countries promotes the possibility of increased accuracy in spent fuel assays. This improvement is made possible through the process of decay of the Curium isotopes and of fission products. An important point to consider for the future that could advance safeguards measurements for reverification and inspection would be to determine what safeguards requirements should be imposed upon this “new” class of spent fuel. Improvements in measurement capability will obviously affect the safeguards requirements. What most significantly enables this progress in spent fuel measurements is the improvement in computer processing power and software enhancements leading to user-friendly Graphical User Interfaces (GUI’s). The software used for these projects significantly reduces the IAEA inspector’s time expenditure for both learning and operating computer and data acquisition systems. At the same time, by standardizing the spent fuel measurements, it is possible to increase reproducibility and reliability of the measurement data. Hardware systems will be described which take advantage of the increased computer control available to enable more complex measurement scenarios. A specific example of this is the active regulation of a spent fuel neutron coincident counter’s 3He tubes’ high voltage, and subsequent scaling of measurement results to maintain a calibration for direct assay of the plutonium content of Fast Breeder Reactor spent fuel. The plutonium content has been successfully determined for the fast breeder reactor assemblies with contact radiation levels as high as 105 Rads/hr. Using limited facility information and multiple measurements along the length of the assembly, the combined measurement and facility declaration error is ~8%. A simplified one-point measurement procedure and generalized analysis leads to a combined measurement and facility declaration error of ~13%.