What are disadvantages of nuclear fusion?

[Nuke]

in an emergency yes they can shut down pretty quick (scram). i dont think its good for the reactor though, you dont want a lot of rapid thermal changes. for general maintenance and operation i think the preference is to shut it down slowly over the course of several days. in a grid setting i think nuclear is the last thing you throttle back.

[phoenix_ca]

in an emergency yes they can shut down pretty quick (scram). i dont think its good for the reactor though, you dont want a lot of rapid thermal changes. for general maintenance and operation i think the preference is to shut it down slowly over the course of several days. in a grid setting i think nuclear is the last thing you throttle back.

There are reactor designs that are ready to be built that allow for deep load following. Both the Canadian ACR-1000 and EC6 designs can do this (throttle back to 75% and 60% of output respectively, 50% using condenser bypass): http://www.nuclearfaq.ca/cnf_sectionA.htm#load-follow

Previously this wasn't even required, given the low fuel cost.

[Nuke]

once again i am impressed by canadian nuclearness.

[phoenix_ca]

once again i am impressed by canadian nuclearness.

I only talk about it because I know about it. I'd bet that other reactors also have load-following abilities.

Edit: Oh hey look, Wikipedia even has a page on it. https://en.wikipedia.org/wiki/Load_following_power_plant#Nuclear_power_plants

[peadar1987]

Uhhhh...nuclear power might be slow to get up to full power, but reactors are designed to be shut-down fast. Like seconds, and at most minutes.

They can be properly shut down very fast, but most (not all) have trouble changing power output quickly due to things like Xenon hold and various other fission products acting as poisons to the reaction.

They can probably be avoided by clever design (I was a fuel route engineer, not a reactor physicist), but it is true of the majority of current plants.

As for fusion reactions that release more than they take in, we've been able to do that since 1952:

[phoenix_ca]

They can probably be avoided by clever design (I was a fuel route engineer, not a reactor physicist), but it is true of the majority of current plants.

Um...yeah...it's already been done...see the link. The one in my post you were replying to... O.o

Edit: And here's another. http://www.neimagazine.com/features/featureload-following-capabilities-of-npps/

And another:

http://www.oecd-nea.org/ndd/reports/2011/load-following-npp.pdf

And another:

www.elforsk.se/Rapporter/?download=report&rid=12_71_

Edited June 3, 2014 by phoenix_ca

[Winter Man]

Well this is interesting. http://arxiv.org/abs/1406.0133 Looks like they've moved to a much smaller coil diameter (and chamber) than WB8 was intended to be to validate the 'high ß' ideas they've had floating around. Last I heard they were looking at 1.5m diameter coils, not 15cm.

[phoenix_ca]

Well this is interesting. http://arxiv.org/abs/1406.0133 Looks like they've moved to a much smaller coil diameter (and chamber) than WB8 was intended to be to validate the 'high ß' ideas they've had floating around. Last I heard they were looking at 1.5m diameter coils, not 15cm.

*yoinks the PDF*

Glad to see that polywell fusion is still alive and kicking, somewhere. These are experimental results, not theory, which is even more promising.

Also...that image of the plasma is beautiful. ... I'm tempted to ask them for a full-res image so I can print a poster of it.

Edited June 6, 2014 by phoenix_ca

[gamowin]

Here's a big problem, how will you extract energy from the reaction? The only way we currently have of doing this is heating fluid or gas to turn turbines connected to generators. But with fusion, a lot of the energy is expended as light. (This is also why I don't think cold fusion is feasible as a power source.)

[guto8797]

Here's a big problem, how will you extract energy from the reaction? The only way we currently have of doing this is heating fluid or gas to turn turbines connected to generators. But with fusion, a lot of the energy is expended as light. (This is also why I don't think cold fusion is feasible as a power source.)

Light produces heat upon hitting a surface. I guess the water thingy could be black, it would get cozy in an instant

[Aghanim]

Fortunately, most of the fusion energy is emitted in the form of charged particle, and some x-rays, and some visible light. You could decelerate the charged particle to recover its energy, and use metal foil to capture the x-rays.

[Nuke]

Well this is interesting. http://arxiv.org/abs/1406.0133 Looks like they've moved to a much smaller coil diameter (and chamber) than WB8 was intended to be to validate the 'high ß' ideas they've had floating around. Last I heard they were looking at 1.5m diameter coils, not 15cm.

i think the reason for the smaller scale device was to come up with operational procedures prior to integrating all the subsystems into the full scale device. of course this is all sourceless scuttlebutt.

[m4v]

Fortunately, most of the fusion energy is emitted in the form of charged particle, and some x-rays, and some visible light. You could decelerate the charged particle to recover its energy, and use metal foil to capture the x-rays.

Depends of the fuel, with D-T reactions most of the energy goes into those nasty fast neutrons that eventually convert the reactor into a radioactive pile of junk.

[phoenix_ca]

With these polywells from EMC2 the goal is to use p+B11 fuel which means minimal radiation that's easy to deal with (don't stand next to it while it's on and about eight hours after turning it off). The goal with polywells is also to use them primarily as a heat source to heat water and run a turbine, which is actually a really good thing, as it gives a relatively easy path to retrofitting fossil-fuel burning power plants into fusion power plants.

Dense plasma focus can harness the charged particles effectively because they are better controlled and go in a straight line (mostly; the x-rays get captured by metal films) which can be used to induce a current. Polywells make more of a soupy plasma of awesome, but it's a very big soup by comparison (target of 100MW with polywells versus 5MW from the Focus Fusion guys).

Edited June 7, 2014 by phoenix_ca

[Idobox]

I thought the maint point of p-B11 fusion was that almost all the energy is in the form of alpha radiation, which won't make your reactor radioactive, and can be used to directly charge a spheric capacitor with a few mV DC, ditching the steam turbine and heat exchangers.

[phoenix_ca]

I thought the maint point of p-B11 fusion was that almost all the energy is in the form of alpha radiation, which won't make your reactor radioactive, and can be used to directly charge a spheric capacitor with a few mV DC, ditching the steam turbine and heat exchangers.

The main point is that it doesn't make your reactor radioactive, full stop. In a polywell, those alpha particles will bump into other matter and thus transmit thermal energy.

[Nuke]

i think a direct conversion scheme for polywells exists, but you wont see it on first generation devices.

[Winter Man]

The main point is that it doesn't make your reactor radioactive, full stop. In a polywell, those alpha particles will bump into other matter and thus transmit thermal energy.

That and it's a lot smaller, with all those neutrons you don't have to block.

i think a direct conversion scheme for polywells exists, but you wont see it on first generation devices.

It's integral to the design. The shell of the device is the direct conversion. Something to do with decelerating the particles by charging the shell to a voltage equivalent to whatever the particle energy is (4.2MeV?). I can't quite remember, I'm kind of drunk.

[Nuke]

i read an article awhile back on direct conversion specifically in reference to polywells. ive yet to find the thing again. i know a couple times i wanted to use it as a source now and just drew a blank.

[m4v]

But the projects getting all the funding aren't polywells.

[phoenix_ca]

Meh. Polywells and DPF are getting enough funding to press on. If you're referring to ITER, the researchers behind EMC2 and Focus Fusion are all well aware of the political climate and are instead working around it entirely, getting funding elsewhere.

[Aghanim]

Polywell are funded by Department of Defense: http://arxiv.org/pdf/1406.0133v1.pdf

DPF are funded by some crowdfunding, but it will fail as everyone thinks that this is a scam

[phoenix_ca]

Polywell are funded by Department of Defense: http://arxiv.org/pdf/1406.0133v1.pdf

Funny, I searched that entire paper for "department", "funding", and "defence", and nadda. I must conclude you are making that up and citing an irrelevant document to lend superficial support to your statement. In fact their own website states clearly that they are a "charitable research and development organization". DoD contracts don't fall under "charity" by any stretch of the imagination.

DPF are funded by some crowdfunding, but it will fail as everyone thinks that this is a scam

"Everyone thinks" isn't an argument for anything.

In fact, Focus Fusion openly admits their project may fail. That's why they can't give shares in their company to just anyone.

And a scientific review concluded exactly the opposite of what you are saying.

Edited June 8, 2014 by phoenix_ca

[Nuke]

Funny, I searched that entire paper for "department", "funding", and "defence", and nadda. I must conclude you are making that up and citing an irrelevant document to lend superficial support to your statement. In fact their own website states clearly that they are a "charitable research and development organization". DoD contracts don't fall under "charity" by any stretch of the imagination.

"Everyone thinks" isn't an argument for anything.

In fact, Focus Fusion openly admits their project may fail. That's why they can't give shares in their company to just anyone.

And a scientific review concluded exactly the opposite of what you are saying.

not the dod, the navy. they want polywells on all their ships so that they can have unlimited propulsion and power left over for lasers and railguns.

polywells are funded for the current phase, they still need 200m to build a demo reactor. they better impress some admirals.

Edited June 8, 2014 by Nuke

[phoenix_ca]

not the dod, the navy. they want polywells on all their ships so that they can have unlimited propulsion and power left over for lasers and railguns.

polywells are funded for the current phase, they still need 200m to build a demo reactor. they better impress some admirals.

Then one should cite sources that actually support the statement instead of just asserting it.