Fuels, Reactors and Reprocessing

The fuel post irradiation evaluation team has been involved in a vast range of activities from working on Windscale’s Advanced Gas-cooled Reactor (WAGR) to receiving both Magnox and AGR fuel from power stations. Much of the development work for the UK fuel requirements was carried out by the team in the UK’s only high active PIE laboratory, which NNL operates. Since 2006, 435 AGR fuel elements have entered the facility with the team examining over 3000 fuel pins.

Focusing on fuel, the team uses a variety of techniques to assess fuel behaviour, which includes monitoring surface conditions, identifying surface defects of fuel pins and examination of other nuclear items. The team also has the capability to process spent and failed fuel. Post irradiation examination techniques lead to a better understanding of material behaviour helping to support the lifespan of commercial reactor fleets, enhancing nuclear safety cases whilst making the case for reactor life extension.

Within the team are PIE Technicians, Deputy Delivery Managers, Technical Leads and Team Managers, meaning the team has considerable experience in developing new techniques to meet customer requirements. One of our main strengths is flexibility, with the ability to handle a full range of fuel and irradiated materials.

Capabilities: To assess ex-service materials to; determine behaviour in nuclear reactors during normal operating conditions and determine behaviour during nuclear incidents, the fuel PIE team uses the following techniques to provide customers with detailed analysis:

• Air abrasion – air abrasion is a non-destructive technique for giving point measurements of the thickness of carbonaceous deposit which forms on the outer surface of the fuel pin within a civil Advanced Gas-cooled Reactor (CAGR). These measurements are required to understand the formation and thickness of pin deposit. The data is used in conjunction with on station measurements made by the endoscope inspection team. Both measurements are used for validation of the reactor safety case.
• Gamma spectroscopy – gamma spectroscopy provides non-destructive analysis of nuclear materials, detailing isotopic distribution, qualitative and quantitative analysis, fission gas predictions and burnup analysis of nuclear materials such as irradiated fuel pins. Gamma spectroscopy can be used to identify physical characteristics and features of nuclear items such as anti-stacking grooves and pellet interfaces.
• Nitrous oxide leak testing (NOLT) – NOLT is a non-destructive technique which ‘soaks’ the fuel pin in nitrous oxide, feeds the pin through the sniffer head and any escaping nitrous oxide is detected by the gas analyser. The technique enables the team to identify whether the primary containment cladding has failed as well as indicating the location of such failure(s). NOLT aids other techniques such as visual inspection by identifying the region of failure(s) sites.
• Pin puncture/ fission gas release – pin puncturing is a destructive technique which measures fission gas release from irradiated fuel pins, detailing the composition and quantity of gasses released. Measurements taken helps to determine the void volume and the internal pressure of the irradiated fuel pin.
• Visual inspection – visual inspection takes place on nuclear items such as graphite sleeves and nuclear fuel pins. Inspection involves monitoring surface conditions and identifying surface defects of the materials that have occurred during its lifetime in the reactor. Visual inspection also identifies deposit type and can indicate deposit thickness, acting as a validation technique for the results obtained by other rigs such as air abrasion.

Customers: EDF Energy Sellafield Ltd, NDA, RWM Rolls Royce

Skills: Laboratory fellows, chartered through professional institutes.

Facilities: Active Handling Facility (AHF) Hot Cells are the core specialist equipment including the large variety of PIE techniques.

Collaborations: Links with some universities and this has included doctoral candidates working with members of the capability. We also have members of NEA and IAEA expert panels and have collaborated with/partnered with Studsvik, ORNL, INL and ITU at various times.