Beryllium in nuclear fuel
A new use for Beryllium to improve the thermal conductivity of nuclear fuel pellets is being investigated by IBC Advanced Alloys in Vancouver, Canada. Michael Forrest reports.
Beryllium and base metals form alloys that are light and strong, and have high melting points and heat conductivity, making them ideal for use in harsh environments faced by military hardware and space applications. Beryllium oxide (beryllia) can also be formed into a lightweight and rigid ceramic that is able to dissipate heat faster than most other materials. Its thermal conductivity is ten times that of alumina, and it is a valuable substrate for electrical circuits that generate a lot of heat. The low dielectric constant of the material also enables improved electrical performance, especially at high frequencies.
A new use is being developed by IBC Advanced Alloys Inc (IBC), Vancouver, Canada, which specialises in beryllium-based products, including copper alloys and its newly introduced Beralcast alloy – the only castable beryllium aluminium alloy on the market.
‘This research is focused on the nuclear industry,’ states CEO Anthony Dutton, ‘and its objective is to produce a new type of nuclear fuel to solve the inherent problem of low thermal conductivity of existing uranium oxide fuel. Low thermal conductivity leads to a large temperature gradient across the fuel pellet, which limits the operational performance of nuclear reactors due to thermal stresses that cause pellet cladding interaction and the release of fission product gases.
‘We have been reviewing the addition of beryllium Spor mountain, Utah oxide to uranium fuel pellets since 2008. Earlier this year we received the results of the research and initial testing, which concluded that uranium oxideberyllium oxide fuel is longer lasting, more efficient and provides a larger safety margin than current nuclear fuels,’ continues Dutton.
‘These tests include nuclear engineering simulations and thermal modelling, which successfully demonstrate the potential benefits of this fuel in light water reactor systems. The experimental and computational work carried out provides a solid understanding of unirradiated uranium oxide-beryllium oxide behaviour and a clear path for additional work.’
In hot water
The beryllium oxide added to the uranium oxide needs to be disseminated, as separate clumps would not be able to channel heat away from the centre of the fuel pellets. Uranium oxide pellets are made of small granules sintered together. The firm says it is simple to introduce beryllium oxide powder in concentrations of five to eight per cent prior to sintering, thereby surrounding the uranium granules with high thermal conductivity beryllium oxide and channeling heat away from the centre towards the surface. Minimal capital investment is claimed to be necessary to modify existing fuel pellet manufacturing facilities.
The modelled results indicate that temperatures in the centre of the fuel pellet will drop from 800°C to 600°C, while keeping the surface temperature constant, which, in turn, determines the power output. It is predicted that the decrease in the pellet’s centre temperature will lead to a longer life span. Furthermore, beryllium oxide has a positive effect on the neutronics, meaning that up to four per cent less U-235 (uranium isotope) would be consumed for the same power output.
This research, carried out at Purdue University, Lafayette, Indiana, and Texas A&M University, both in the USA, forms part of the company’s collaborative research agreements. Early work indicates that less thermal stress allows higher fuel burn-up and reactor safety with the reduction of fission product gases. Uranium oxide-beryllium oxide fuel functions in existing unmodified nuclear reactors.
The next stage of the programme is to move towards the production of beryllium-enhanced fuel pellets for boiling water reactors (BWR). To that end IBC has signed a memorandum of understanding (MOU) with Global Nuclear Fuel America (GNFA), which has a fabricator plant in Wilmington, North Carolina, USA. The MOU will combine IBC’s patent-pending technology and GNFA’s manufacturing capabilities.
Commenting on the collaboration, Nicole Holmes, President and CEO of GNFA, says, ‘the potential benefits of the improved thermal conductivity fuel include lower operating temperatures, while delivering the same energy to the reactor system will enhance products that are sold worldwide.’
The basis for this technology is a supply of beryllium, a hard, silvery-white, light metal with a high melting point. At present, IBC has a binding three-year supply agreement with the Ulba Metallurgical Plant in Kazakhstan. Beryllium occurs in the earth’s crust in economic forms as beryl, a semi-precious stone found in pegmatites, and in bertrandite, a hydrous beryllium silicate. Global production is around 160t with the USA being the largest producer, based on bertrandite ores in Utah.
‘IBC’s 371 mineral claims cover 3,102ha in Juab County, Utah, and include part of the Spor Mountain deposit that was discovered in 1959 and has been the major source of metal in the western world for over 40 years. They are adjacent to Materion Corp’s (formerly Brush Wellman) mine that has been responsible for the majority of USA production, although reserves and output have been falling in recent years,’ notes Dutton.
Spor Mountain is within the Basin and Range Province that dominates the geology of the western states. The host rock is a sequence of dolomites of early Ordovician to late Devonian age, with a total thickness of 1,465m. Some 300m years later they were intruded by a volcano, forming a caldera and associated ejected tuff and silica-rich lavas. These rocks are the hosts to fluorite, uranium and beryllium mineralisation that occurs in tabular deposits situated along major faults and fractures in an altered water-laid rhyolitic tuff within a valley that once was part of paleo-Lake Bonneville. Mineralisation is confined to the member that lies on top of a mostly unmineralised porphyritic rhyolite with associated faults and vents.
The horizon is porous to both hydrothermal mineralising fluids and groundwater, and contains carbonate clasts, which reacted with fluorine-rich fluids to precipitate fluorite and beryllium. The volcanic complex is part of an east-west trending belt of igneous activity that developed late in the evolution of the Cordilleran orogen and extends from the Sierra Nevada to the Wasatch Range in Utah.
IBC has embarked on a comprehensive exploration programme at Spor Mountain. Dutton says, ‘Our claims are located on extensions of these geologic structures initially described by United States Geological Survey geologists, and are being mined by a supplier of engineered enabling materials, Materion. Our analysis of topographic data and high-resolution aerial photography of the area has revealed the presence of an unmapped extinct volcanic caldera that may prove to be the source of structural control, hydrothermal fluids, and beryllium mineralisation in this area.
‘The presence of this caldera poses the possibility of more extensive beryllium mineralisation on the company’s claims than has been encountered at the Materion mine site.’
He adds, ‘In September 2010 an airborne magnetic and radiometric geophysical survey was commissioned that revealed several extensive northeast-trending fracture zones that had not been identified or mapped because of the volcanic tuffs that blanket the prospect area. These fracture zones extend up to 6.4km within IBC claims and will be the subject of a drilling programme this year.’
The use of beryllium oxide in uranium fuel pellets represents a major development in nuclear reactor technology. IBC’s research has indicated a four per cent improvement in reactor output and at the same time is reducing the fuel pellet temperature. Furthermore, the established beryllium resources in Utah will go a long way to reassure supply security to many governments.