We are physicists from the University of Bristol, ask us anything about our 'Diamond Battery' made from nuclear waste & can last for 5k years

Could more radioactive isotopes of different elements be used to produce a greater energy yield? As far as I can remember C14 isn't one of the problematic constituents of nuclear waste.

I would imagine though that if more radioactive materials were used in these devices it would limit their possible applications due to the public safety risk.

P.S You lectured me at bristol, weird to stumble upon this AMA :)

Thanks for your question - for waste graphite from our UK reactors the single biggest problem radionuclide is C-14. Most other radioisotopes have, in the majority, decayed away within 20 years of the reactors being turned off but the C-14 (with a half life of 5730 years) represents a more persistent problem.

You are indeed correct that we could use other radioisotopes that decay by beta emission e.g. Ni-63 or tritium. The emitted beta particle energies are different between these isotopes and hence this would make the device more or less effective. However, by sticking to C-14 we can grow a single diamond device which is isotopically layered between C-14, C-13 and C-12 in one single crystal structure. By doing this we avoid energy losses for electrical current generation which would otherwise occur by having a physical interface between the beta-emitting material and the diamond generator.

How much does it cost?

The exact costs for waste processing to retrieve C14 are not known, but are likely to dominate the cost of the device. The actual cost of manufacture of the devices once a suitable feedstock gas is available is relatively small and so should be economically viable. In addition, by harvesting the C-14 from waste irradiated reactor graphite we reduce the residual radioactivity level of the graphite and thereby significantly reduce the onward cost requirement for its disposal.

What are the everyday life implications of this discovery?

The technology is still in development, but we have received a number of ideas from the public as to how this could be used in everyday life. Take a look at our recent blog which shares some of the ideas so far: http://cabot-institute.blogspot.co.uk/2016/12/the-diamond-battery-your-ideas-for.html. Let us know if you have any to add!

Maybe a stupid question, but how would it work with background radiation? Would it just be a lower yield?

It wouldn't generate much power on the ground, but potentially if it was used in space (where the background radiation is more intense) it could find some use.

I'd also add that we have a different type of diamond device which works on harvesting energy from x-ray and gamma-ray photons. This is less efficient than the C-14 device but presents the possibility of a self powered monitoring device for use in highly radioactive environments. It also presents the possibility of creating a gamma-voltaic 'shroud' which could be lowered around a canister of high level nuclear waste to hook it up as a power unit. This is another potential benefit for the technology.

Do you think this innovation will help change public perception of 'nuclear' in the long term?

A great question! We sincerely hope that we can change public perception for the better. A common bugbear for the public around nuclear is that when you have nuclear power reactors you generate waste which is dangerous for a very long time. Our work shows that there is potential economic value to be extracted from a proportion of this waste. If we're successful, one day I hope we might refer to the irradiated graphite as 'battery feedstock' rather than waste.

I recently experienced a great example of changing perception when shortly after launching our technology at the @CabotInstitute annual lecture, an elderly lady approached me. She volunteered that she had been a campaigner against nuclear energy for 20 years and that our battery device and the associated concept of extracting value from the waste (whilst also making it safer) had changed her perception such that she now supported nuclear power as a preferred low-carbon alternative to fossil fuel burning!

We certainly hope it will improve the public perception of nuclear; this is one way of making nuclear waste into really useful technology!

Though you have to admit that radioactive diamond battery perhaps isn't the best marketing name.

We would be keen to canvas ideas from the public about names for the technology. We thought about calling it a TCD (Trickle charging diamond).

Big fan of the idea. But I am wondering what discharge currents were you able to achieve and what voltage does it produce?

What voltage does the diamond produce? The Ni63 version has produced close to 1.9V. The C14 version would be expected to achieve at least 2V.

What is the capability of the Diamond Battery versus a normal battery?

Standard alkaline AA batteries are designed for short timeframe discharge: one battery weighing about 20g has an energy storage rating of 700J/g. If operated continuously, this would run out in 24 hours.

In comparison, a diamond beta-battery would be designed to last longer. The actual amount of C14 in each battery has yet to be decided but as a rough guide, one battery, containing 1g of C14 will deliver 15J per day (based on calculations extrapolated from Ni63 prototype). On the face of it, this is less than an AA battery.

However, it will continue to produce this level of output for 5,730 years, so its total energy storage rating is very high (2.7TeraJ aka million million Joules).

What are your thoughts on oatmeal cookies?

Delicious - though we are equally fond of other cookies!