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Nuclear Safeguards Education Portal

Overview of Safeguards Systems for SNF

Now that we have reviewed all of the systems and techniques used to safeguard spent nuclear fuel, let's take a look at how these systems can be implemented at a facility.

Below you will see a diagram of a CANDU-6 reactor taken from an IAEA document that gives recommendations for safeguards system implementation for future water-cooled nuclear power plants (Ref. 28). This is an interactive diagram with overlays showing the various systems that could be used in implementing safeguards at this hypothetical facility. 

The implementation of safeguards at a facility is a matter of coordination between the facility management and the IAEA, so each facility will have its own unique system of safeguards that is facility-specific.  As such, the systems shown below are just suggestions of safeguards systems that could be employed for a CANDU reactor scenario.

Item accountancy and maintaining continuity of knowledge using C/S measures form the basis of the CANDU safeguards approach. Direct verification of the operator's declared nuclear material inventory is implemented for fresh and spent fuel. Although fuel bundles in the core remain inaccessible for verification, continuity of knowledge is maintained by a monitoring system when they are discharged. C/S covers the discharge of spent fuel from the reactor and storage in the spent fuel bays to provide continuity of knowledge

The following activity is best viewed on a computer monitor or large tablet using one of the following broswers: Google Chrome 17 or later; Safari 5.1 or later; or Internet Explorer 9 or later.  Clicking the link under the diagram will open it in its own window.

The buttons on the right side of the diagram can be used to toggle on and off the various systems used in implementing safeguards at this hypothetical facility.

If you have difficulty viewing this activity embedded into the website, you can open it in its own window here

NMA System

The first system that can be toggled on and off is the Nucelar Material Accountancy (NMA) system. Here we see the entire facility is included in the MBA. We have inventory KMPs over the fresh fuel storage/loading area and the spent fuel storage bay, with flow KMPs as fresh fuel is delivered and as spent fuel is transferred to the spent fuel storage bay. For a CANDU reactor, fuel bundles in the reactor core are inaccessible for verification, so no inventory KMP is possible.  In the recommendation for this facility given by the IAEA, a physical inventory is done for the fresh fuel area, with accoutancy in the spent fuel area being accomplished by spent fuel bundle counters, since direct verification of the spent fuel is difficult.

Sealing System

The Sealing System toggle shows suggestions of areas that could possibly be monitored with IAEA seals.  Seals are placed at the facility access points, on segments of the fresh fuel storage, and on the crane that moves spent fuel in and out of the spent fuel storage bay.   

C/S Systems

The diagram has the option to show two alternative C/S systems to verify and provide continuity of knowledge, each using a combination of different equipment. These systems illustrate how nondestructive assay elements, like the specialized unattended monitoring systems for CANDU fuel shown here, can be combined with surveillance elements to provide a complete safeguards system for the facility.

In C/S System-1,  spent fuel bundle counters monitor the movement of fuel into and out of the reactor containment area. Surveillance cameras are used to survey the areas where fresh fuel and spent fuel are stored.  The reactor containment area is equipped with multiple surveillance cameras to record activity within the whole reactor containment area, including the reactor faces and fuelling machine transfer routes. Surveillance cameras are also used to monitor the reception and shipping bay. Four thermoluminescent dosimeters (yes/no monitors), or PIN detectors, are placed at the new fuel and auxiliary ports to monitor a possible diversion pathway of reverse flow through the new fuel ports. 

For C/S System-2, the system uses core discharge monitors to record the spent fuel item count and monitor the reactor face for a pulse of radiation when fuel is discharged.  Spent fuel bundle counters are used to confirm the item count into the spent fuel storage area.  Optical surveillance is used to monitor the ara for unusual activity and undeclared shipments.  This system also relies on sealing containers for long-term storage.

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