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Welcome to "Big Bang, outer space and life."

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We continue the comment check

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with Professor Dr. Hartmut Zohm of the Max Planck Institute for Plasma Physics

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here in Garching.

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He published a few nice videos on this channel about nuclear fusion.

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We already discussed a few questions

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and now continue with the topics "Environment characteristics"

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"Sustainability" and "Dangers" of nuclear fusion.

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We start with the first user question (Joba1?)

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"Interesting presentation. I'd like to know how much Lithium and Deuterium

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we'd have to "burn" to Helium each year

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to cover the current global energy consumption.

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Is there enough available and is it regenerative?"

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So... It's not regenerative,

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Lithium indeed is consumed.

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We're talking about a nuclear reaction, not a chemical reaction.

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The energy that is converted with each reaction

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is higher by the factor of 1 million to 10 million.

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Accordingly the consumption rate is 10 million times lower

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compared to chemical reactions.

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The number is huge and I trip over that every time I try to work it out in my head

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so I wrote it down.

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What i wrote down is:

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If we want to cover the current global energy consumption

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- which is roughly 500 exajoule (5 * 10^20 Joule) -

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If we convert that in gigawatt-hours

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how much would we consume?

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That would be 45 thousand tons of Lithium consumed

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to cover the global energy consumption for one year.

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And to compare i looked up how much coal

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we burn in a coal power plant.

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We have one close to use, in Munich.

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There they burn 800 thousand tons of coal each year

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to cover a part of Munich,

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which is 20 times more than you need Lithium to satisfy the energy thirst of the whole world.

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And that is the answer to this questions, we can calculate all of these numbers

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they are vanishingly small.

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If we turn the calculation around and look how much Lithium is available

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how much of the Lithium 6 we need

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-  not even the Lithium 7 we need for the laptop batteries -

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then the result is a few thousand years.

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Only taking the Lithium reserves in account

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that can be mined easily - If we look at how much Lithium

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is evenly spread in rocks, how much is available there

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then the result is many hundreds of thousands of years.

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So i think that is not a problem we have.

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From the nuclear fission reactions we know that the result are radio active elements

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which unfortunately have high half-life periods, they radiate very long

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and are a long time environmental burden.

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So one question that came up frequently

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for example from the user "acidfreak"

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or also from - now i have to take a look for that

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It wasn't (Joba?), right, it was "Wardragon"

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"What about radioactivity?

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How long does it radiate?

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In the presentation it was talked about a few years."

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Can you quantify that a bit?

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So...

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First, we differentiate between

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the radioactivity of the fuels we use

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because we can't avoid those

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and then the radioactivity of the structure materials

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that surround the fuels, so the walls.

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For the fuels it's indeed the Tritium which is radioactive

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it has a half-life period of 12 years.

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So after 12 years there's half of it left, after another 12 years the half of the half, etc.

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So Tritium is something that can be considered as rare ressource

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which has to be processed and what you can't find a lot on earth.

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And we already addressed it earlier

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those are really low amounts that are used

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One gigawatt power plant would use 500g

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Tritium each day, so consume it.

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That is not a lot.

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I think more of a thing we have to adress

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are the walls and the structure materials.

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And there we can chose the materials by their half-life period

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A typical mix of materials we could use to build right now

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currently could be recycled after 100 years of buffer storage.

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So actually recycle it and use it again to build the next power plant.

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That means - and 100 years typically is where you say "I leave it where it is" -

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or even "I don't have to lock that away"

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These long half-life periods we have at nuclear fission

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that go into hundreds of thousands of years

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just don't exist for nuclear fusion if it's done correctly.

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I consider that as huge advantage.

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Because for me

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the accident hazard for a nuclear fission isn't that high either if it's built correctly

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- it's more about that we don't know how to permanently store the waste.

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Like where we burden generations of people

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not only today and tomorrow

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Neither you or me know what it'll be like in thousand years - god beware -

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and we don't want to bequeath that I think

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Good - The next question is from "Bob Tronexy" (?)

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"I don't understand the cooling of the plasma from the carbon sheets.

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How does such a discharge work?

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The plasma doesn't have direct contact with the surrounding

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in case of an accident. How can I picture that?"

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Ok, so first: There is no direct contact of the hot plasma in the centre

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and the wall, that's what the magnetic field is used for

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As the plasma particles are charged they are bound to the magnetic field.

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The plasma at the edge comes into contact with the surrounding material when it cooled down

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that is where the energy is discharged

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There we have to take care a bit

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the plasma still is very hot.

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When it recombines from plasma to neutral gas

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and then comes to the wall it still has around

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10.000 degrees if we measure the temperature of it.

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In another episode of "comment check" we already discussed

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that the density of the plasma is very low - 10^20 particles in one cubic metre

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which is one millions times less particles than it would be in one cubic metre of air

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And that leads to the result that the energy density is very low in the end.

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And what heats up the plasma at the edge

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for example where the wall comes into contact with the plasma

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is about the energy density, not so much about the temperature.

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And that is the part

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which is confusing a bit

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the amount of energy that is actually stored is not that high.

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For an accident that also means

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if the kinecic energy, the temperature, the thermal energy in the plasma is set free

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uncontrolled

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- the wall can't be destroyed.

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The first wall might melt by 1mm or so

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more can't happen because of the thermal energy

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It's also a bit about "What is the worst case scenario?"

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that also has been a user question from "acidfreak"

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There always is a worst case scenario

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That is a serious problem for the operator as the machine will be broken

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and he can't earn money with it after that

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- but it won't lead to the destruction of the facility.

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For an accident from inside we can calulate that the energy densities aren't high enough

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- a much higher energy density is used for the magnetic field than for the plasma itself

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With that you can destroy components

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but not let it explode, bust it, etc.

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In fact the accident scenarios we have to talk about

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are about "Where will what kind of material be released?"

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There are scenarios we have to consider, like a crashing plane

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and it falls right into the reactor - the worst place - and something is released

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And there the inventories that could be released are relatively low

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Then of course the machinery is broken

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and you probably don't want to stay at the power plant area

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But in fact you don't have to evacuate the people that are outside of the fence of the facility

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even in this case

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And if you can handle the worst case scenario like that

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and that it doesn't lead to the evacuation of the surrounding people

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as it for example was at Fukushima

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I consider that as a huge advantage

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of nuclear fusion compared to fission too.

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In a fission power plant  there are Cadmium rods that drop in when there's an emergency

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which intercept the neutrons immediately and the reaction stops

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Is there a similar process in a fusion power plant where something drops in

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or someone who has to push a button or something that happens automatically?

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You don't have to press the button

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We always need intervention and active control

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otherwise the reaction stops itself.

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As soon as there is wall material in the plasma

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which happens as soon as the plasma comes into contact with the wall

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the plasma will be poluted and it stops to burn.

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And the fuel supply in the container is depleted after 3 seconds

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if you don't resupply it actively

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Such a power plant has supplies stored for half a year or a year

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There is no chain reaction

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where it consumes all of its fuel supplies

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There's just not enough of that and also the fusion always has to be controlled actively, otherwise it stops.

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Then there are questions from "Tina Tiet" (?)

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"I didn't understand yet what is considered the advantage compared to the fission power plants.

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Which advantage does the fusion have compared to the fission

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- both is radioactivity as we already discussed -

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and what is the sustainability there for mankind?"

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Partially we already discussed it before

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Yes, we already discussed sustainability before a bit

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it is not regenerative by the meaning that we transform something

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but in fact we burn something.

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But it's not much

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That is a big advantage for sustainability

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If you're running a fission power plant with uranium

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you'll come to the point after a few hundred years where you have to use different

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and not so favored fission products

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If you replace that with nuclear fusion you have a relatively sustainable process

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as deuterium and lithium are commonly available

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One thing i believe is very good too

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is deuterium from sea water and lithium from rocks

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so it's not geograhically located and concentrated

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There won't be a "lithium sheik"

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someone who holds the monopoly for that

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as it's relatively accessible for everyone

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Very good

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As i see it, we addressed all the important questions now

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I hope you had fun and for the end I'd say we show our fine t-shirts

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As always, if you liked the video give it a thumbs up

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Comments are always welcome and if you liked the answers you're welcome to write that too

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Thank you a lot

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Thank you a lot too

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If we have to discuss more I'll be content to join

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If we have further questions, when interesting new questions emerge we didn't answer yet

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we can talk about nuclear fusion again with pleasure.

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Great, thanks a lot for the offer, we surely will need an update

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and we will contact you again - thanks again Hartmut

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With pleasure!