Passive and Active Field Assay Methods for Spent Fuel in Transportation and Storage Containers – consideration of some potentially cost effective portable solutions

Basic gamma dose rate provides estimates of total irradiation of fuel while neutron dose rate is proportional to combined plutonium content with alpha-neutron production rates. Gamma spectrometry can provide relative abundance of 137Cs, 154Eu, 134Cs, 106Ru and 144Ce which when evaluated as ratios can provide estimates of burn-up, initial enrichment and cool down from external measurements of spent fuel in a transportation and storage cask where a potentially improved approach to cool down estimation is suggested here with the only specific case considered being a Westinghouse 15x15 system. Neutron spectrometry using Bonner spheres can provide estimates of fast, thermal and epithermal neutron flux which can be used to verify poison content and total neutron production rates. Modeling a fuel storage container in detail can also provide thermal transport models which can be compared to external thermography images where total heat production rate is proportional to total activity. Finally, gross active interrogation can be approximated by using an external neuron source coupled with the same measurement done for the passive case. If the neutron source is not a DT or DD design then a shuffler source could provide useful information from dwell measurements with the source present compared to when it is absent. This paper reviews these concepts with attention to small portable options.