OPERATIONAL EXPERIENCE IN RADIOMETRIC INSTRUMENTATION FOR SPENT FUEL MONITORING

As the global quantity of spent nuclear fuel steadily grows and the regulatory basis for the U.S spent fuel disposal program is developing, radiometric monitoring requirements are becoming increasingly important. Spent fuel measurements can be used for burn-up credit (for storage and transport), safeguards verification and radionuclide inventory quantification to meet disposal criteria. Verification measurements reduce reliance on operator data and ensure that the fuel is fully compliant with the prescribed envelope. Measurement assists in the confirmation of the identity of each assembly by verifying fuel history parameters. BNFL Instruments has developed a series of modular spent fuel monitoring systems. This series is based on systems that have been used to monitor more than one million fuel items at the UK’s Sellafield reprocessing plant. The radiometric measurement techniques employed include high resolution gamma spectrometry, passive neutron measurements and active neutron measurements. This paper presents BNFL Instruments’ global operational experience in spent fuel monitoring under wet and dry conditions. Systems have been deployed to verify the cooling time, burn-up and enrichment of fuel assemblies in dry fuel handling facilities and storage ponds. In the United States, at Arkansas Nuclear One (ANO), in-pool measurements were performed to provide burn-up credit prior to cask loading. Calibration, validation and operational experience with these systems is presented. Recommendations are given on the use of measurement systems to provide an acceptable level of confidence in the measurement result to allow these activities to take place safely and with the support of the regulators and the public.