Diamond battery can process nuclear waste and generate electricity

Researchers in the UK outline decommissioning benefits plus potential for reactor core shrouds.

The ASPIRE Project, a collaboration between the University of Bristol and University of Oxford in the UK, has developed a diamond battery that can process nuclear waste and reduce disposal costs.

The project began in early-2017 with the aim of developing remotely located, extreme environment sensors to enable monitoring of nuclear waste packages in their interim and final storage locations.

The proposed solution was to use diamond batteries: advanced radio-voltaic diamond devices to harvest energy from radioactive decay to power small, portable units containing multiple sensors that pass data over wireless networks.

“By removing the Carbon-14 from irradiated graphite directly from the reactor, this would make the remaining waste products less radioactive and therefore easier to manage and dispose of,” Professor Tom Scott, lead researcher, told Nuclear Energy Insider. “Cost estimates for disposing of the graphite waste are 46,000 pounds ($60,000) per cubic meter for Intermediate Level Waste [ILW] and 3,000 pounds ($4,000) per cubic meter for Low-Level Waste [LLW].

“Therefore, if the waste processing to remove the C14 reclassifies the waste as LLW, then any cost under 43,000 pounds ($56,000) per cubic meter will represent a saving to the UK taxpayer. Equally, if we can process the graphite so that it doesn’t require geological disposal then we can save substantially by building a smaller Geological Disposal Facility.”

These diamond batteries are made using a process called chemical vapour deposition (CVD) which is widely used for diamond manufacture and uses a mixed hydrogen and methane plasma to grow diamond films at very high temperatures.

Scientists at ASPIRE have modified the CVD process to enable growth of radioactive diamond, using a radioactive methane containing the radioactive isotope Carbon-14, found enriched on irradiated reactor graphite blocks.

Lab-grown diamond

The diamond is grown in a laboratory inside a sealed CVD system and the radioactive diamond is grown with non-radioactive diamond either side of it, either as a single crystal wafer or polycrystal wafer.

“The diamond battery is technically a beta-voltaic which is a cousin of the photovoltaic (or solar-cell) but converts beta-radiation instead of light to create electricity,” explains Professor Scott.

“We also have a gamma-voltaic device which can directly convert gamma and x-ray radiation into electricity. This presents the possibility of turning some of our very highly active radwaste into power sources without having to modify those packages. All you’d need to do is place gamma-voltaic arrays around or near to the packages to soak up as much of the emitted radiation as possible; converting it to electricity.

“For the gamma-voltaic technology we may be able to achieve more significant power outputs, depending on the radiation levels we can expose them to. It would certainly be possible to add gamma-voltaic shrouds to a reactor core for direct nuclear electric conversion that could be in addition to the electricity derived from steam generation.”

The batteries are expected to produce at least 2V of energy. Based on the use of 1g of Carbon-14, it can deliver around 15J a day of energy for 5,730 years. A standard alkaline AA battery weighing about 20g has an energy storage rating of 700J/g. If operated continuously, this would run out in 24 hours.

Professor Scott says the technology is scalable to a point, but one major limitation is the amount of C14 diamond that can be manufactured, but that gamma-voltaic and one specific version of the beta-voltaic could commence commercial production within just three months.

“The actual cost of manufacture of the devices once a suitable feedstock gas is available is relatively small and so should be economically viable,” says Professor Scott.

“We’ve spent the last nine months doing detailed financial modelling and business case development and project that commercially available devices could be sold for between 2 and 20 pounds ($2.6 to $26) within a few years. If it proves possible on a commercial scale, a site like Berkeley would be ideal – we could harvest C-14 direct from the dormant reactor core and process it in a facility that is literally next door.”

Scott Birch