Talk-Polywell.org

I have been reading up all little on the liquid flouride reactor.

The transuranics are to be removed by continuously distilling a fraction of the circulating liquid fuel stream.

Noble gasses and iodine will be taken away by letting them evaporate from the hot fuel in a spray chamber.

And U233 breeded from thorium will be circulated from the fertile fuel stream to the fissile stream by flourination to UF6 and then by reduction back to UF4.

Sounds really nice.

However, the fission product responsible for the bulk of the long lasting ground pollution in the event of an accident, cesium, will remain in the fuel in the form of flouride until a very high degree of burnup has occured.

In the event of major structural damage to the reactor (meteorite, terrorist bombing, crashing airplane and the like), can it be assumed that cesium discharges from a LFTR will be as large as those from a conventional reactor?

If not: Why?

Seems to me that if it won't come out in one of the reprocessing steps like most of the other elements it is because it is VERY stable in the salt solution. If so, won't it just turn to rock when it cools?

I think with major structural damage radiation release is inevitable no matter what kind of design you have. The advertized benifit I see in LFTR is that it is harder for there to be self inflicted damage: explosions, melting, etc. due to otherwise minor malfunctions (eg power outage)

KitemanSA wrote:Seems to me that if it won't come out in one of the reprocessing steps like most of the other elements it is because it is VERY stable in the salt solution. If so, won't it just turn to rock when it cools?

A rock very soluble in water then.

If I make a guess: You should be better of in the LFTR. Not because the boiling point of the CsF is lower than in the oxides present in a light water reactor, but because the temperatures are lower than in a melted solid core.

I think with major structural damage radiation release is inevitable no matter what kind of design you have. The advertized benifit I see in LFTR is that it is harder for there to be self inflicted damage: explosions, melting, etc. due to otherwise minor malfunctions (eg power outage)

Of course. But if the iodine is somewhere else than in the core the situation should, to some extent, be better.

Unless the truck bomb destroys the iodine tank too.....

All new nuclear reactors are designed to widthstand an airplane crashing into it. They have a very thick outer shell. I would be more worried about the hundreds of older reactors out there that are not only a less safe reactor design, but also a less safe building design.

LOPAs are way more prevalent than aircraft strikes. And yet reactors are less able to handle LOPAs.

TMI, Fukushima come to mind.

Munchausen wrote:
In the event of major structural damage to the reactor (meteorite, terrorist bombing, crashing airplane and the like), can it be assumed that cesium discharges from a LFTR will be as large as those from a conventional reactor?

If not: Why?

(1) dirty parts of system is not pressurised (is this right?)

(2) system is passively cooled/self-quenching

So in the event of major structural disturbance problems are likely to be less. If somone smuggled a bomb into the reactor housing big enough to breach all containment walls that would still help a little, since runaway would not be a subsequent problem.

Tom

Munchausen wrote:

KitemanSA wrote:Seems to me that if it won't come out in one of the reprocessing steps like most of the other elements it is because it is VERY stable in the salt solution. If so, won't it just turn to rock when it cools?

A rock very soluble in water then.

Yup, my bad. Most of the other FP salts are not very soluable.

But going back, I think your initial supposition is incorrect.

1. Extractions
2. Noble metals plate out.
3. Noble gasses and other gasses get sparged out.
4. U and TRU (and some FP) get fluoridated out. May be further distilled. Some elements get returned to the fuel salt..
5. Some FPs (including CsF) get distilled out.
6. The carrier salt gets distilled out.
7. The rest of the FPs remain behind in the still. Further seperation may occur.

Thus, the Cs SHOULD be removed fairly continuously. Whether it gets returned for transmutation depends.

Also, a lot of the Cs is formed by beta decay of the Xenon which is parged early, so a lot won't be there to begin with. No?

OMG this stuff is complicated!

KitemanSA wrote:OMG this stuff is complicated!

"Complicated" or a "no brainer". Make up your mind:)

My take, and probably what you are saying also, is that it is a no brainer to build it because the advantages are so enormous but it is really complicated and will take a lot of engineering.

Regarding the OP's post, the biggest advantage to LFTR in the event of a catastrophic failure is the lack of pressure and the passive cooling plan. In the event of a loss of power, the fluid passively drains into a drain tank. Plan is that in the event of a breach of the vessel, fluid drains out into drain pans which lead to the same passive cooling tanks. Fluid may also self plug the breach. Because their is no pressure, the fluid drains rather than explodes, which is a good thing.

As far as deliberate attacks, my take is that the containment building has the same structural requirements to prevent intentional attack. However, the LFTR is probably more secure because a specific attack on the power system is no longer an issue.

The biggest issue I see with a LFTR is in the area of all of the on line reprocessing. Once you start pumping around this nuclear fuel to various reprocessing steps, I have to imagine that the complexity of the plumbing creates opportunities for many kinds of additional accidents, relatively less serious, but potentially more common. Removing transuranics and fussion products is an area that may make the thing less safe in general even if it is more catastrophically safe.

LOPAs are way more prevalent than aircraft strikes. And yet reactors are less able to handle LOPAs.

TMI, Fukushima come to mind.

LFTRs wont have such problems and I think that newer reactor designs have less problems with that as well. Dont forget that the Fukushima plant was built in the 70ies.

Skipjack wrote:

LOPAs are way more prevalent than aircraft strikes. And yet reactors are less able to handle LOPAs.

TMI, Fukushima come to mind.

LFTRs wont have such problems and I think that newer reactor designs have less problems with that as well. Dont forget that the Fukushima plant was built in the 70ies.

Agreed.

The big problem is that people are so affraid of old nuclear reactors and their safety issues that they dont want any new nuclear reactors to be built to replace them. It defies all logic...

seedload wrote:

KitemanSA wrote:OMG this stuff is complicated!

"Complicated" or a "no brainer". Make up your mind:)

My take, and probably what you are saying also, is that it is a no brainer to build it because the advantages are so enormous but it is really complicated and will take a lot of engineering.

Yup. And it is a no-brainer for me cuz others have the brain-power to do it. I've met them!

Skipjack wrote:

LOPAs are way more prevalent than aircraft strikes. And yet reactors are less able to handle LOPAs.

TMI, Fukushima come to mind.

LFTRs wont have such problems and I think that newer reactor designs have less problems with that as well. Dont forget that the Fukushima plant was built in the 70ies.

And not updated like the US plants of that era have been.

Some FPs (including CsF) get distilled out.
The carrier salt gets distilled out.
The rest of the FPs remain behind in the still. Further seperation may occur.

No they don't. Have done some reading up on it. See page 590 in this document:

www.energyfromthorium.com/pdf/FFR_chap12.pdf

"Quite high burnups would be before a molten salt reactor could saturate its fuel with any of these fission products"

Let me guess: You still have a better situation than in the LWR in case of a major structural breakdown.

There are no volatiles and a substantially lower nuclear inventory per installed unit of power. Which result in less residual power needed to be cooled away.

You won't get a melting pile of fuel and rubble with ever rising temperatures that make the cesium fuming of to the surroundings.

But rather fuel salts splashing away in lumps that can be collected. Still a very nasty situation but limited to the immediate surroundings of the reactor.

No major evacuations due to fallout.

Is this right?