Features

• Fully integrated system for unattended monitoring of PuO₂ canisters.
• Combines passive neutron measurement with gamma ray measurement for increased accuracy.
• Utilizes intelligent front end acquisition devices for maximum data compression and redundancy.
• Sophisticated analysis of gamma spectra using MGA⁷.
• Central CPU system connected remotely, and used for data analysis, storage and review.
• Secure architecture protects system from unauthorized access.

Description

The concept of unattended plutonium safeguards using NonDestructive Assay (NDA) systems has been developed previously^1,2,3 and is implemented at several nuclear facilities. Normally installed at large automated facilities, these unattended systems are designed to reduce the amount of time that an inspector spends on-site, thus reducing potential dose, impact on the plant operator and the manpower costs associated with more conventional attended systems. Typically these facilities have many different acquisition stations, with the following potential data sources at each one:

• Neutron data collected using passive neutron measurement systems.
• Gamma-ray data collected using high-purity germanium detectors.
• Sensor information which might indicate item identity, position, direction of motion, etc.

These acquisition stations might be located at the entrance to a processing plant so that incoming fuel can be assayed, near a common fuel storage area, at a location which corresponds to the end product of the plant, etc. Since the physical dimensions of the facility are in general quite large, one approach to unattended safeguards is to place one or two computer(s) at each acquisition station; two computers would be installed if redundancy was needed. Each computer would be responsible for acquisition control, data storage, data analysis and report generation at a particular acquisition station.

The drawback to this type of system is that the most convenient location for the computer might be in a potentially hostile and highly controlled area. In addition, integration of the results from all facility acquisition stations would be difficult given the large number of independent stations.

An alternate approach is possible within a facility that has a Local Area Network (LAN, e.g. a coaxial or fiber optic cable) that connects each of the acquisition stations. Consider for example the system shown in Figure 1, which has four different acquisition stations. A LAN cable connects each of the individual acquisition stations. At a different, and possibly remote, location we have a host computer. With this type of system, each acquisition station will contain a computer which is responsible only for data acquisition. Each computer (one at each station) would send the raw data to a common host computer, which implies that a user logged on to the host will have access to all of the facility's safeguards data. This type of system also lends itself well to real-time analysis of raw data and real-time generation of system alarms. It allows the inspector to quickly assess the state of all of the facility's safeguards components during the inspector's infrequent visits.

Just such a system has been designed for the Euratom Safeguards Directorate. The system consists of major subcomponents for:

• Passive neutron/gamma measurement devices.
• Data Acquisition Subsystem (DAS) for combining and buffering neutron, gamma and sensor data.
• A host computer for analysis, record keeping and reporting.

The operation of each subsystem is discussed in the application note.