Process Attribute Monitoring Approach to Gaseous Centrifuge Enrichment Plant Safeguards

Unattended and remote monitoring systems for the early detection of gas centrifuge enrichment plant (GCEP) misuse have long been sought by the International Atomic Energy Agency (IAEA) safeguards inspectorate, but have yet to be realized for most GCEPs. The primary misuse of concern is high enriched uranium (HEU) production but additionally include excess low enriched uranium (LEU) production and material diversion.

The current research is a feasibility study that investigates a process monitoring approach combined with passive gamma spectroscopy techniques to monitor GCEPs. In the current research, a simulated reference cascade and monitoring system is used to demonstrate several techniques to monitor ²³⁵U [uranium-235] enrichment, monitor cascade ideality, detect changes in facility operations, and attribute those changes to specific normal, abnormal, or misuse scenarios. In other words, the monitoring system detects misuse and indicates to inspectors where to look for supporting physical evidence.

The techniques for the detection of GCEP misuse introduced in the current research are different from all previous efforts in six fundamental ways. First, previous efforts used custom and complex equipment which could not be sustained by the IAEA safeguards inspectorate; the current research only employs existing IAEA equipment and techniques in routine use. Second, previous efforts used radioactive sources and other invasive equipment and techniques; the current research only utilizes passive and non-invasive gamma spectroscopy. Third, previous efforts relied on measurements at a single point that could be bypassed; the current research includes techniques to additionally monitor entire cascades and production units. Fourth, previous efforts used measurements of the 186 keV [kiloelectron volt] gamma line and the UF₆ [uranium hexafluoride] gas pressure; the current study utilizes measurements of the ²³¹Th [thorium-231], ²³⁴Th [thorium-234], ²³⁴U [uranium-234], and ²³⁵U [uranium-235] gamma lines. Fifth, no techniques currently exist for the detection of excess LEU production and gas flow stoppage; the current research presents techniques for the detection and attribution of these scenarios. Sixth, no previous techniques utilize the minor isotope safeguards techniques (MIST); the current research utilizes the ²³⁴U [uranium-234] gamma lines and the ratio of ²³⁵U [uranium-235] to ²³⁴U [uranium-234] to detect and attribute GCEP misuse.