How would electricity be generated from a nuclear fusion reactor?

[cmb]

You can water-cool a solid blanket.

Of course, but then you don't get tritium to keep the thing running.

There has to be at least one new recoverable tritium atom for every neutron released in a deuterium-tritium fusion reactor. This is a completely integral scientific and technical requirement to generating electricity from those neutrons. Each neutron has to both deliver its 14MeV of energy to the coolant and also generate the tritium. It's a big ask.

Tritium generation is part of the same question 'how would electricity be generated'.

This is possibly a bigger scientific hurdle than creating a plasma that's hot enough. At least JET generated Q=0.6 for half a second. Has anyone ever generated recoverable tritium from a fusion reactor before?

It has to generate tritium. It can't buy the stuff for electricity generation. If it did, the costs work out like this;

Price of tritium from fission reactor production = $30,000/g

Total number of possible DT reactions per gramme of tritium at 100% fuel utilisation = (6E23/mol)/(3g/mol) = 2E23/g of reactions

Total neutron energy released = 2E23/g * 14MeV * 1.6E-19J/eV = 448GJ = 125MWh

Fuel cost per electricity unit (tritium cost only, ignoring over-night and operating costs) = $240/MWh

 

[mfb]

ITER will test some breeding concepts but it doesn't need to produce its own tritium. It is a scientific experiment, not a power plant. DEMO is expected to breed its own tritium after an initial supply.

 

[cmb]

ITER will test some breeding concepts but it doesn't need to produce its own tritium. It is a scientific experiment, not a power plant. DEMO is expected to breed its own tritium after an initial supply.

Of course this is the case.

But if I were to propose an experiment in which I aim to generate tomorrow's energy by burning gold, wouldn't the first (not second) question be where to get the gold from? If I said that'd be from transmuting base metals, wouldn't the scientific community ask for evidence that is possible, before putting much credence in gold as a source of future energy?

Tritium generation is a totally integral requirement to fusion power, and so the thread question, how to generate electricity from it, requires an answer to both absorbing neutron power and generating tritium from it. I don't think the OP's question was about ITER (it couldn't be, because ITER won't make electricity).

The additional dimension to the question is that if a future fusion power station were to operate in a pulsed mode, how long is the pulse/cycle time and what is the impact of that on generating power from it? If the future for a fusion power station is not a pulsed mode, then ITER can't really scientifically conclude much about continuous operation. So I don't think we know an answer to the OP's question, yet, and it's unclear if anyone really has a good idea about it.

 

[etudiant]

I do not have the actual data on the neutron economy, but afaik, the idea was to breed tritium from the lithium blanket around the tokamak. Afaik, the tritium supply has not been seen as an item of concern, as the expectation was that the operations would yield a surplus of tritium.

Re the power generation, I believe that the idea is to use the thermal inertia of the blankets to insure a continuous supply of steam even though the actual reactor operations are intermittent. Obviously one could rail at the idea of using fusion to boil water, but we are still a long ways from any direct fusion to electricity hardware, even if the concepts are pretty clear.

 

[PeterDonis]

Tritium generation is a totally integral requirement to fusion power, and so the thread question, how to generate electricity from it, requires an answer to both absorbing neutron power and generating tritium from it.

And you already have the answer to how tritium will be generated. The nuclear reactions involved in breeding tritium from lithium are well understood, so the expectations about being able to breed tritium from lithium in an actual power reactor are much better grounded than your hypothetical about making gold by transmutation of elements.

 

[mfb]

@cmb: Don't confuse "I don't know how it is done" with "it is unknown how it is done". Just because you are unaware of the research doesn't mean the research wouldn't exist. The tritium yield if you shoot neutrons into lithium is well-studied. How to extract the tritium efficiently is one of the things ITER will study. It doesn't need to produce all its tritium for that aspect, or even a significant fraction. If it can show that it could produce 8% of its tritium demand using 5% of the blanket area that is perfectly fine.

I don't think the OP's question was about ITER

It wasn't about tritium breeding either.

The additional dimension to the question is that if a future fusion power station were to operate in a pulsed mode, how long is the pulse/cycle time and what is the impact of that on generating power from it? If the future for a fusion power station is not a pulsed mode, then ITER can't really scientifically conclude much about continuous operation. So I don't think we know an answer to the OP's question, yet, and it's unclear if anyone really has a good idea about it.

ITER aims at 10 minutes, DEMO at 2 hours. Tokamaks have to be pulsed, but the time between pulses can be very short if the magnets can ramp fast enough. Short enough and you can produce electricity continuously. A bit longer and you want some short-term on-site energy storage. The impact on the cost per kWh would be negligible. And it doesn't impact the way electricity is generated from fusion.