PowerSwitch

I have a question regarding fusion, I hope it hasn't been asked already.

I have a fairly basic understanding of the fusion reaction and process. What I don't understand is how it will be powered.

• How much power will be required to get the fusion reaction going?
  
  How much power will be needed to sustain the reaction or is it self sustaining once the process is underway? If one had enough power to get the reaction going and then all other energy sources became extinct would the fusion reactor in itself be enough to keep itself going?
  
  Can you feed fuel into a fusion reactor once it's up and running?

son of ballard wrote:I have a question regarding fusion, I hope it hasn't been asked already.

I have a fairly basic understanding of the fusion reaction and process. What I don't understand is how it will be powered.

• How much power will be required to get the fusion reaction going?
  
  How much power will be needed to sustain the reaction or is it self sustaining once the process is underway? If one had enough power to get the reaction going and then all other energy sources became extinct would the fusion reactor in itself be enough to keep itself going?
  
  Can you feed fuel into a fusion reactor once it's up and running?

It takes quite a lot of power to get the thing up to temperature - but not so much that it is hard to do. JET regularly get up to temperate these days.

Once a large enough one is built (ITER should be the first one large enough) the process should create enough energy not only to maintain temperature and containment so the reactions can be sustained but also have a bit left over to boil our kettles. So yeah a useful 'reactor' will generate more than enough energy keep itself going. Good point about all other energy sources becoming extinct though... might not be able to jump start it again!

There is only a very small amount of fuel in the 'reactor' at any one time (one of the factors that improves safety) so yeah the fuel is fed in second by second as it's needed. We're only talking grams of hydrogen here.

Paul Mobbs said something about ITER which I was not aware of - a big part of it is to test new materials that won't decay so quickly. Apparently steel for example buckles after 4 years of exposure to that radiation. If I remember correctly.

Yeah, the radioactive waste from fusion comes from the surrounding material becoming radioactive - helpfully we can choose what material to use so the hunt is on for materials with suitable physical properties and the property of very rapid decay once radioactive. The point being that any radioactive waste from fusion should be very short lived - decades rather than millennium.

In the mid 1970s I met someome who worked at Culham. He gave me the data on radioactive waste that would be produced. I passed it on to FoE at the time. The quantities were really very significant, the copper windings in the magnets the for the magnetic containment 'vessel' being the main problem. The magnets would be made in sections that could be removed and replaced a section at a time. This would have to be done about monthly with several tons of medium level waste produced at each go. In the last thirty years I havn't been convinced that this problem has been solved.

clv101 wrote:Yeah, the radioactive waste from fission comes from the surrounding material becoming radioactive - helpfully we can choose what material to use so the hunt is on for materials with suitable physical properties and the property of very rapid decay once radioactive. The point being that any radioactive waste from fission should be very short lived - decades rather than millennium.

Did you mean fusion there (twice)?


Peter.

Ah, yeah! I was talking about fusion, not fission (will edit).

biffvernon wrote:In the mid 1970s I met someome who worked at Culham. He gave me the data on radioactive waste that would be produced. I passed it on to FoE at the time. The quantities were really very significant, the copper windings in the magnets the for the magnetic containment 'vessel' being the main problem. The magnets would be made in sections that could be removed and replaced a section at a time. This would have to be done about monthly with several tons of medium level waste produced at each go. In the last thirty years I havn't been convinced that this problem has been solved.

I think the magnets used are superconducting these days, so the coils may not be made of copper any more - most superconductors are weird ceramics I think.

It seems to me that nuclear fission and other energy technologies such as photovoltaics and wind turbines are top of the food chain technologies. They are like the big cats; top of the pyramid and utterly dependent on the rest of the energy, resource and technology pyramid below them.

From their inception to construction, maintenance and eventual decommission they seem utterly dependent on fossil fuels. I just cannot imagine or understand how these technologies will continue to be viable in a world of depleting and increasingly expensive oil.

Can anyone enlighten me?

son of ballard wrote:Can anyone enlighten me?

Erm, no. You're right. At least until we learn how to harness concentrations of quintessence* using kelp-derived dimension inversion turbines. Or something.

* Quintessence being one of the proposed theoretical forms of dark energy in this context; I'm not talking about the late '60s Jazz/Rock/Hari Krishna fusion band from North London. Although the propsects for harnessing energy from a bunch of erstwhile hippie rockers is of course far more promising...