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NetworkLlama t1_iyvd13n wrote

Reply to comment by DataHead127 in Why not use hydrogen and deuterium in fusion reaction rather than tritium and deuterium? by Curious_user4445

Deuterium is easy, tritium is not. The entire world's supply is about 20 kg and it's only produced in a few reactors around the world. It decays rapidly with a half-life of only 12 years, making holding on to what you have a temporary prospect at best. Much of what is produced goes into keeping nuclear weapons active, and when ITER comes online, it will get much of the rest unless its lithium blanket for breeding tritium works spectacularly well.

The lack of easy tritium production is a major reason various projects around the world are looking at alternate means.

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the_geth t1_iyvg3in wrote

Really? I read about everywhere that it’s easy to produce with the lithium blanket (including in a classical fission reactor if needed). The reason we don’t have much production is simply… that we don’t need it (or rather, that the amount we have is enough for our CURRENT use)

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NetworkLlama t1_iyvlbjf wrote

Lithium blankets are still very much in the research stage. The US gets its tritium for it's nuclear arsenal by irradiating special rods called tritium producing burnable absorber rods (TPBARs) containing lithium-6 in a nuclear reactor, specifically Watts Bar Reactors 1 and 2 at the TVA. Each TPBAR is about ten feet long and less than half an inch in diameter. Over about 500 days of burning, each produces about 1.2 grams of tritium.

Civilian sources are primarily from CANDU reactors, but building more of these can be problematic as they're heavy-water reactors (they produce tritium by deuterium neutron capture) and are considered to be proliferation risks, raising both political and legal problems. They also don't produce that much. According tothis paper on sourcing tritium for fusion use, the CANDU 6 reactor, a 700 MW design, can generate only 130 grams of tritium per year, though not all of this can be captured.

According to ITER's own numbers, 800 MW of fusion-generated electricity will require 300 grams of tritium per day. Lithium blankets are the most promising way to get this done, but they present their own technical challenges. This is why research is happening on other approaches like laser confinement and Z-pinch to find ways of using just deuterium.

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the_geth t1_iyw8h5l wrote

Super interesting, thank you for the thoughtful answer!

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beaded_lion59 t1_iywmi7r wrote

Who’s working on Z-pinch fusion now? I did D-D fusion in the 80’s in a Z-pinch, but the process would require a lot of pulse-power advances to make it practical for energy production.

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beaded_lion59 t1_iyxuv6e wrote

I did this at a 7 TW pulsed power system at a company in the Bay Area using deuterium gas. The system could do 3 shots/day. Sandia’s shot rate is probably less. They’re more like NIF at Livermore.

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Relevant_Monstrosity t1_iyviaco wrote

There's probably both a lack of demand, and necessary capitalization to meet potential demand. So you can look for projects to increase the supply to kick off as new users come online.

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ukezi t1_iyvjnee wrote

It's more of a in theory it should be "easy". There are still a lot of details to figure out.

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the_geth t1_iyw8nz0 wrote

I see. It’s interesting this was not (until I hear it here) mentioned as a potential problem.

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MortalPhantom t1_iyvhxac wrote

I know it's rare but then why was it used on watches? Even current watches some of them use tritium and you can find them prelaatively cheap 500-1000 usd, and I doubt tritium is a considerable part of that price.

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karlnite t1_iyvm70b wrote

Canadian nuclear plants pay millions a year to remove tritium from our cooling and moderator water. It’s a pesky problem and we are always looking for ways to get rid of tritium. We currently keep barrels upon barrels of our most tritiated water sitting around to decay off so we can use the deuterium content again safely one day. We would pay fusion companies to take our tritium away. They could set up a device to harvest it from our reactors or waste just like we do for the global supply of medical isotopes currently. We have determined a myriad of medical isotopes that could be harvested, we just need investors willing to set up the systems to harvest them who have connections to medical companies that can utilize the isotopes (our industry doesn’t have the experience to do this all ourselves as we make power and that is hard enough). I don’t see why we couldn’t do that for tritium too.

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NetworkLlama t1_iywq9xk wrote

There's probably not as much tritium in that water as you think. According to this paper on sourcing tritium, a 700 MW CANDU-6 reactor can make only about 130 grams of tritium per year. There probably aren't dozens of kilograms of tritium sitting in those barrels.

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karlnite t1_iywuaul wrote

That’s very likely, I have not done the math to calculate to mass of tritium in the systems.

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chemhobby t1_iyvlxfh wrote

the amount used in gaseous tritium light sources is absolutely miniscule

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NetworkLlama t1_iyvmmco wrote

A tiny fraction of a gram is used, with a maximum of 25 millicuries allowed per timepiece. A little bit goes a long way for that purpose.

Edit: I looked up some numbers, and the amount of tritium in any given timepiece is apparently measured in micrograms, not even milligrams. I'm having trouble finding exact amounts, but a very rough calculation based on a specific activity of 9650 Cu/g and 25 millicuries results in .025 mCu-g/9650 Cu = 2.6 micrograms per watch. That's a very, very tiny amount.

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vokzhen t1_iyx4njh wrote

For those who don't grasp what this means very well, those numbers mean a gram of tritium is enough for about 400,000 watches.

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ukezi t1_iyvjtw7 wrote

Before tritium paint they used radium to get the phosphor to glow. The problem is that radium is highly toxic and carcinogenic.

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boycey10802002 t1_iyvl6qk wrote

That I had heard the horror stories of. It just didnt seem to make sense to me to use a super-limited resource like tritium for watches and thought titanium would be a more likely candidate for a mid-level, rugged watch.

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Lazzer555 t1_iywefn7 wrote

Tritium is only used for making the hands and face of the watch glow in the dark, titanium would be used for something like the body of the watch.

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[deleted] t1_iyvjddl wrote

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zutnoq t1_iyvlecc wrote

20 kg is probably not as small an amount as you might think. The energy equivalent of that mass is around 500 TWh of which something on the order of half a percent is released in the reaction IIRC, so say something on the order of 2 TWh worth of energy of which you could extract say 1 TWh worth of electricity (if we assume 50% efficiency which might be optimistic but probably not orders of magnitude off). Global yearly electricity production/usage is currently around 22 TWh so scaling up the production of tritium to meet this demand seems more than feasible to me.

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NetworkLlama t1_iyvn7k3 wrote

I explained in another comment the details and challenges of production. In short, scaling up is difficult and requires either special rods that produce 1.2 grams per 10-foot rod per 500 days of irradiation in a light-water reactor or else heavy water reactors that can create up to 130 grams per 700 MW reactor per year. It's extremely inefficient either way.

Lithium blankets are being researched, but they're not yet proven.

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Real-Patriotism t1_izffbc6 wrote

I have Tritium in my watch that makes it glow in the dark. While probably a minuscule amount, why would this be done if there is such a low supply of Tritium?

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NetworkLlama t1_izfjlpq wrote

Because it's micrograms and because the current supply somewhat outweighs the demand. Most fusion concepts now under investigation rely on tritium but it's still years away from needing significant amounts. Once fusion power is a reality, tritium is going to be in enormous demand (ITER is expected to use most of the world's supply just in experiments) unless we have a way to generate it more freely, such as with lithium-6 blankets.

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