What would make nuclear fusion viable?

Daffy Duck

Banned
It makes sense form a physics-geek perspective to finally resolve the three-cornered debate between relativity, quantum mechanics, and superstrings as explanations for how things work. In the long-view, far more important to figure that out far more thoroughly than we do now.

I couldn't agree more...Once the Grand Unified Theory is discovered and proven, our technological evolution will turn into a technological REVOLUTION. Too bad our psychological evolution (as a species) cannot keep pace...
 
It´s a common misconception, it it not the Thorium itself that it saver. Thorium is not fissile but decays into Uranium 233 which is. To have a meltdown or runaway proof reactor you need a Molten Salt Reactor (MSR) the Thorium/Uranium is solved in molten salts whichhave a high melting point and a boiling point over 1000 degress celsius . So no need to put the stuff under pressure like in PWR. So if the Reactor vessel is damaged will only cause a leak but not a steam explosion.

Which was my point. They are inherently much safer. It is also much harder to turn U233 into a nuclear weapon because U232 which is another product of the reaction "poisons" the reaction of U233.
 
Suffice it to say that Polywell and Focus Fusion are the most interesting fusion prospects but still at least three stages of development away from being viable power sources.

As to fissile technologies, how close do you think the newer flavors are to commercial scaling?

I know this seems silly, but how ASB are Atomic Age gadgetry proposed of miniaturizing nuclear reactors to stuff middle-class individuals owned and used possible/worthwhile? E.g. car engines, heat plants for buildings and so forth?
 
Suffice it to say that Polywell and Focus Fusion are the most interesting fusion prospects but still at least three stages of development away from being viable power sources.

As to fissile technologies, how close do you think the newer flavors are to commercial scaling?

I know this seems silly, but how ASB are Atomic Age gadgetry proposed of miniaturizing nuclear reactors to stuff middle-class individuals owned and used possible/worthwhile? E.g. car engines, heat plants for buildings and so forth?

The closest ones are Pebble Bed and Thorium Salt. Both have been done on pilot scales but imagine it will take at least a decade or two for them to scale up unless some research grant money is forthcoming. Much quicker than fusion which hasn't been successful even on a pilot scale.
 
Suffice it to say that Polywell and Focus Fusion are the most interesting fusion prospects but still at least three stages of development away from being viable power sources.

As to fissile technologies, how close do you think the newer flavors are to commercial scaling?

I know this seems silly, but how ASB are Atomic Age gadgetry proposed of miniaturizing nuclear reactors to stuff middle-class individuals owned and used possible/worthwhile? E.g. car engines, heat plants for buildings and so forth?

I'm pretty sure the Soviets deployed small nuclear reactors and nuclear batteries pretty widely. It didn't turn out well (very dangerous to decommission), but it's the Soviets were talking about...
 

Tusky

Banned
Throium fuelled molten salt reactors

Those interested in the details of the thorium MSR should go to "energyfromthorium.com" . This is Kirk Sorenson's site, and KS has pretty much single-handed resurrected Th MSR from obscurity. Everything is there, including a libary of old Atomic Energy Commission publications on the subject (engineering and research continued until 1975).

I know you guys all have plenty of reading, but for those with a genuine technical bent, go to Kirk's site and check out the Google TechTalk vid (http://www.youtube.com/watch?v=EHdRJqi__Z8). It's only 25 minutes long, well worth the time. Or if a nerd, there is a 75-minute vid that really gets into detail.

Here are the Th advantages:

  • Use all the Th, not 1% of the U in light water rx.
  • Th 4x as abundant as U, plus is used efficiently. One mine in Idaho (a known site) est to provide for US electricity for hundreds of years.
  • High temps, better Carnot efficiency.Well adapted to Brayton cycle gas turbines, an efficiency
  • High temps, less waste heat allow some designs can be air cooled. This eases siting considerations, perhaps can get away from NIMBY.
  • Makes only 1% of high level waste compared to KWR
  • High level waste decays to background in 300 yr, this number is 25 000 yr with LWR.
  • Hot heat transfer fluids are molten salts at atmospheric pressure. No chance of steam explosion. This danger is what mandates containment buildings for LWR, so here is another savings.
  • Negative heat coeff of reactivity...means runaway rx can't happen, thus no China Syndrome
  • Runs hot, can cheaply bust water and make H. This is a key to cheap coal-to-liquids.
  • Th MSR tech lends itself to small scale rx-ors, opens possibility of incremental build-out. Small scale means small parts, which can be factory buil and railed or trucked to site. Savings and quality result.
Heh, who will build them first? Kirk Sorenson's site suggests it will be the Chinese, capitalizing on the US R&D. Ai yi yi !

Tusky
 
Actually I would think the French would be right up there as well, seeing as 70% or so of their electricity generation is nuclear; they would suffer the most when uranium for LWR becomes scarce and expensive. Thorium breeders could be just what the doctor ordered.

There are two main challenges to overcome with thorium reactors:

1) Expense and complexity. Liquid metal and molten salt transfer fluids increase the cost and complexity of reactor designs. Safety is also an issue; both are corrosive and toxic, so coolant leaks would be environmental hazards. Granted they run at lower temperatures and pressures than LWR, so there is little to no risk of meltdown or explosion, but that does not make them perfectly safe.

(With some MSR designs meltdown is impossible; the fuel is a circulating solution rather than solid.)

2) Fuel recycling. Breeder reactors also produce neutron-absorbing isotopes as part of the breeding process, requiring periodic reprocessing of the fuel to remove these. In contrast LWR, at least as built in the US, are disposable; once the fuel runs out the reactor is decommissioned and abandoned.

Fuel reprocessing adds another level of complexity and expense to the process. With thorium reactors some of the decay products are strong gamma emitters, which will require the fuel to be remotely handled, further increasing the expense.

In any case it will be necessary to overcome the public's knee-jerk reactions to nuclear power in order to proceed with the development and construction of such reactors. That will be the biggest challenge of all.
 

Tusky

Banned
Reply dgharris

Hello!

I hope you will take the time to visit Kirk Sorenson's Energy from Thorium site.

But to quickly offer comment on your assertions:

Thorium MSRs (often liquid fluoride thorium rx, LFTR) are proposed to use LiF and BeF mixed salt. These have low neutron cross sections and are essentially inert in the rx. Since the coolant loops are only under atmospheric pressure plus pumping pressure, leaks very quickly congeal. There is no steam explosion as found with high pressure superheated water.

Emergency shutdown is done through a system drain, merely a section of frozen salt that is kept below freezing point by a refrigeration or cooling system. In an emergency the coolant is removed, the frozen salt plug melts, and the system drains to a tank. At Oak Ridge, an MSR ran with this system, draining the salt into a tank each weekend and restarting on Monday, for several years.

FYI, Li an Be F salts are not very toxic. Even so they are not sprayed about in case of an emergency.

By contrast, proposed breeders want to use liquid sodium as a primary coolant and water as a heat transfer fluid. Care to speculate what a heat exchanger failure might look like in this device?

LFTR is proposed to use a core and blanket. The core is where most of the fission occurs, and the neutrons travel into the blanket where they transmute thorium to protactinium, thence U. U233 is the gamma emitter of concern. But all the U is removed...by bubbling Fgas through a side stream, then the U is reduced which changes it from gas to solid, and it is fed to the core where it fissions. Also, this sidestream is available for replenishing Th as it is utilize, just dump it in...no fuel rods.

Continuous processing is a huge advance, as is doing all this work in the gas phase.

LFTR is a mighty clever system!

You might ask, can it process radioactive wastes or surplus atomic weapons. Yes, but there are technical differences in the reactor.
Theoretically it can be done...the option has been well considered and to me it appears to be practical.

Tusky
 
re: thorium, I'd imagine Canada or one of the other Candu operators will be the first since the reactors are already capable of it, perhaps prompted by a run-up in uranium prices.

p.s. you can pretty much shovel dirt into a heavy-water reactor and make energy ;)
 
So, do you have an opinion why ITER is pursued, then?

My understanding is that ITER is intended less as the direct forerunner of a future workable fusion reactor, and more as a means of collecting experimental data to refine our understanding of fusion and plasma physics. In principle, a lot of the information gathered could be useful in development of a practical fusion reactor built on different principles as well as contributing to our general understanding of high-energy physics.

I don't know how much of the focus on Tokamak reactors for this purpose comes from bureaucratic inertia and how much may come from some inherent suitability of the Tokamak for studying plasma physics.
 
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