Diamond battery is the name of a prototype battery proposed by the University of Bristol Cabot Institute during their annual lecture held on 25 November 2016 at the Wills Memorial Building. This battery is proposed to run on the radioactivity of waste graphite blocks (previously used as neutron moderator material in nuclear reactors) and would last for thousands of years.
The battery, developed by the University of Bristol, is a betavoltaic cell using carbon-14 (C-14) in the form of diamond-like carbon (DLC) as the beta radiation source, and additional normal-carbon DLC to make the necessary semiconductor junction and encapsulate the carbon-14.
Potential prototype characteristics
- Voltage – 2 V estimated (Ni-63 1.9 V measured).
- Energy – 15.8 MJ over first 5,000 years, or total of 4.4 kWh.
- Prototype size – 10 mm × 10 mm × 0.5 mm (plus electrodes).
- Temperature – physically stable at 750 °C.
The source of these values is unclear.
These beta particles, having an average energy of 50 keV, undergo inelastic collisions with other carbon atoms, thus creating electron-hole pairs which then contribute to an electric current. This can be restated in terms of band theory by saying that due to the high energy of the beta particles, electrons in the carbon valence band jump to its conduction band, leaving behind holes in the valence band where electrons were earlier present.
C-14 has been chosen as the source of radioactivity mainly because its beta particle radiation is easily absorbed by any solid. The use of diamond, one of the hardest solids on earth, will not only increase the quantity of current generated but will also prevent radiation from leaking out of the battery.
Extracting C-14 from nuclear waste
In graphite-moderated reactors, fissile uranium rods are placed inside graphite blocks. These blocks act as neutron moderators whose purpose is to slow down fast-moving neutrons so that nuclear chain reactions can occur with thermal neutrons. During their use, some of the non-radioactive Carbon-12 and Carbon-13 isotopes in graphite get converted into radioactive C-14 by capturing neutrons. Once the graphite blocks are removed during station decommissioning their induced radioactivity qualifies them as low-level waste, and disposal is a tough job.
Researchers at the University of Bristol earlier showed that radioactive C-14 developed in waste blocks is mainly concentrated on the outer parts of the block. Due to this, much of it can be effectively removed from the blocks. This can be done by heating them to the sublimation point of 3915 K (3642 °C, 6588 °F) which will release the carbon in gaseous form. After removal, blocks will be less radioactive and easier to dispose of.
Researchers propose that C-14 gas obtained by heating the radioactive graphite waste will be collected and subjected to low pressure and elevated temperature, to produce a man-made diamond by a process known as chemical vapor deposition. A diamond made of radioactive C-14 will also be radioactive, and its radioactivity may allow it to act as a betavoltaic device, generating small electrical currents. For practical and safe use it would be enclosed inside a non-radioactive man-made diamond (made from C-12). More diamond will make more current, even with the same radioactivity, and the outer diamond will shield the user from the radiation emitted by the inner diamond.
Its long life, similar to other Betavoltaic devices suits it to applications similar to those of RTGs, supplying very little power for thousands of years without charging or replacing conventional batteries. Its power density will be far lower than that of conventional chemical batteries, restricting its use to extremely low-power electrical devices.
- It will possess long life because it will run on radioactivity which takes an enormous amount of time to decay. The half life of C-14 is 5,730 years, so it will take that long to lose 50% of its power.
- It will ease the disposal of waste graphite blocks (a small part of the world's radioactive waste) by extracting much of the block's radiocarbon and putting it in various electronic devices.
- Betavoltaic batteries wouldn't require any coils, moving parts, etc., hence will be more durable than conventional batteries.
- Being made of diamond (one of the hardest materials on earth) it will be more rugged than conventional batteries.
- Coupled with modern rechargeable battery technology, betavoltaic batteries would enable the product of self regenerative packs, allowing for the conventional use of higher output batteries, with the long lived potential of the betavoltaic cells.
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