A. Sagadevan, “Safeguards Approach for Spent Nuclear Fuel in Dry Cask Storage using Remote Monitoring Systems”, Ph.D. Dissertation, Nuclear Engineering, Texas A&M University, College Station, TX (2020).
With spent fuel pools at nuclear power reactors reaching their design capacity and the lack of a long-term storage solution for the spent nuclear fuel (SNF), interim storage of SNF in dry casks is currently the practiced method. SNF can contain up to 20 significant quantities of special nuclear material (in this case, plutonium) in a single dry cask, which contains 32 pressurized water reactor SNF assemblies. However, once the cask is sealed, there is no way of verifying its contents. This poses a nuclear safeguards concern from the potential misuse of the SNM inside the dry cask. In this work, two new remote monitoring systems (RMSs) for SNF stored in dry casks are proposed. A RMS can perform continuous monitoring so that the International Atomic Energy Agency (IAEA) can fulfil its requirement of maintaining continuity of knowledge, CoK, and thus verify the contents of the dry casks without opening them. Simulations of the RMS response to assembly diversions are characterized for various SNF loading patterns with regards to fuel burnup and cooling time. Multiple assembly diversion scenarios are studied. Every diversion scenario simulated includes the removal and substitution of SNF assemblies with dummy assemblies. The Monte Carlo N-Particle (MCNP) transport code was used to simulate the RMS design and the dry cask containing SNF. The main objective of this work is to design and analyze the RMS neutron signal output so that CoK of the SNF content in dry casks can be maintained. The RMS response is calculated for each assembly diversion scenario by setting a false alarm probability, α, and calculating the corresponding non-detection probabilities, β. Two RMS designs are studied and, for both RMS designs, the β probabilities proved to be under 20% for all SNF diversion cases. A set of proof-of-concept experiments were conducted using 252Cf sources, and the same methodology was applied to calculate β probabilities. The analysis of the results of these experiments concluded that neutron source diversion mimicking the diversion of SNF was detectable. Hence, this technology is shown to be accurate, cost effective and a viable alternative to in-person inspections. rn