A Self-Occluding He-3 Neutron Detector For Reliable Surveillance Of Spent Fuel Cask Movement

The International Atomic Energy Agency (IAEA) uses Unattended Monitoring Systems (UMS) to support safeguarding nuclear material in facilities around the world. These UMS are required to operate continuously without the intervention of inspectors or technicians. Some UMS are used for monitoring the movements of dry casks containing spent fuel. This can be done by placing multiple neutron detectors throughout a facility and observing the relative change in neutron count rates as the cask is moved. However, options for the positioning of these detectors are often limited and emplacing multiple detectors can be costly. Being able to reliably track the movement of a spent fuel cask using fewer detector locations is therefore desirable. This work presents the development of a self-occluding neutron detector system that can reliably monitor the direction of movement of a spent fuel cask from few locations. The IAEA continuously aims to improve efficiency and effectiveness when implementing Safeguards under its mandate. Therefore, UMS design considerations include cost, reliability, and the ease of interpretation of measurement results for efficiently supporting the drawing of safeguards conclusions.