A New Class of Nuclear Reactors

prunedude tips this quote from a post at Freakonomics about Japan's nuclear crisis: "The folks over at IV Insights, the blog associated with Nathan Myhrvold's Intellectual Ventures, point out that it was the complete loss of power that disabled the cooling systems protecting the plant's reactors. Which raises the question: Is there nuclear technology that could withstand such a catastrophe? Possibly. TerraPower, an Intellectual Ventures spin-off that also boasts Bill Gates as an investor, is working on a new reactor design called a traveling wave reactor that uses fast reactor technology, rather than the light water technology used at the Fukushima Daiichi plant. The two biggest advantages of the fast reactor design is that it requires no spent fuel pools and uses cooling systems that require no power to function, meaning the loss of power from the tsunami might not have crippled a fast reactor plant so severely."

Comments

Um, don't safe reactors already exist?

[DurendalMac]

My understanding is that breeder reactors and pebble bed reactors wouldn't have had the problem that hit the plant in Japan. That and breeder reactors have the added benefit of eating nuclear waste over and over until whatever is left might make you sneeze. Maybe I'm completely off on that, but why do we need a new design on this kind of reactor unless it's relatively simple to retrofit older reactors?

Re:Um, don't safe reactors already exist?

[Surt]

Indeed, this was what came to mind immediately to me as well.
http://en.wikipedia.org/wiki/Pebble_bed_reactor

Re:Um, don't safe reactors already exist?

[Anonymous Coward]

Germany ran a pebble bed reactor at the Nuclear Research Facility at Juelich. The Juelich post-mortem report concluded that pebble bed reactors have severe problems in practice (at least some of them base design flaws), in the specific case of the Julich AVR reactor leading to Strontium-90 contamination of the soil and aquifer beneath the reactor.

The post-mortem report is posted here http://www.eskom.co.za/content/AVR-Report-Press.PDF

Some interesting bits from the report:

The AVR primary circuit is heavily contaminated with metallic fission products (Sr-90, Cs-137) which create problems in current dismantling. The amount of this contamination is not exactly known, but the evaluation of fission product deposition experiments indicates that the end of life contamination reached several percent of a single core inventory, which is some orders of magnitude more than precalculated and far more than in large LWRs.
[...]
It leads to the conclusion that the AVR contamination was mainly caused by inadmissible high core temperatures, increasing fission product release rates, and not - as presumed in the past - by inadequate fuel quality only.

From the conclusions:

As outlined above there exist unresolved safety problems in pebble bed reactors for design basis accidents, as for beyond design basis accidents like severe air ingress with graphite burning. Previously a superior safety behaviour of pebble bed reactors was claimed compared to other nuclear systems including an allegedly catastrophe free design. According to the above presents arguments there are doubts, whether this depicts reality.

So while pebble bed reactors have some advantages over traditional designs, they are by no means the silver bullet that some people make them to be.

Re:Um, don't safe reactors already exist?

[Martin Blank]

Fukushima Daiichi was built to withstand a 5.7m tsunami, as required by Japanese regulators. It was hit with a 10m tsunami, though, which is why the generators were knocked offline.

Re:Um, don't safe reactors already exist?

[Mspangler]

"One big tank on that big hill behind the plant,"

(Pardon my English Engineering units)
Let's see, 2.3 feet per psi, 1000 psi steam pressure (According to wikipedia, sounds a bit high to me) so we are looking at a 2300 foot high hill. If it's 600 psi steam, at least after shutdown, then it's only about 1700 feet of hill.

And the big tank has to still be there after the 9.0 earthquake. There is more complication in "All they needed" than you think.

The basic design is supposed to have a steam powered feed pump with a source of makeup water. Whether it broke, was never there, or the source of makeup water was a condenser that was mudded out by the tsunami, I don't know. And I would like to know. I used to serve on an SSN, so I have a certain professional curiosity.

Same as it ever was

[drsmack1]

Of course any new reactors designed will have safeguards against any previous disaster - it's the ones that never happened before that fuck us.

Re:Same as it ever was

[ColdWetDog]

See above for the comments on Pebble Beds. It appears that even after decades of research and engineering into nuclear reactors, we still don't know enough to be confident that any particular design or implementation will behave the way the designers expect. Not exactly surprising since anything more complicated than a paper towel seems to have those same issues but it does mean that any progress will have to come slowly and hopefully carefully.

Just because it looks good in Autocad doesn't mean it will actually work correctly.

What about Thorium, Molten Salt Reactors

[Anonymous Coward]

From: http://en.wikipedia.org/wiki/Thorium

Some of the benefits of thorium when compared with uranium as fuel:
  * Weapons-grade fissionable material (U-233) is harder to retrieve safely and clandestinely from a thorium reactor;
  * Thorium produces 10 to 10,000 times less long-lived radioactive waste;
  * Thorium comes out of the ground as a 100% pure, usable isotope, which does not require enrichment, whereas natural uranium contains only 0.7% fissionable U-235;
    * Thorium can not sustain a nuclear chain reaction without priming, so fission stops by default.

Re:What about Thorium, Molten Salt Reactors

[ColdWetDog]

Rebuttal from Physicians for Social Responsibility

Weapons-grade fissionable material (U-233) is harder to retrieve safely and clandestinely from a thorium reactor

Thorium is not actually a “fuel” because it is not fissile and therefore cannot be used to start or sustain a nuclear chain reaction. A fissile material, such as uranium235 (U235) or plutonium239 (which is made in reactors from uranium238), is required to kickstart the reaction. The enriched uranium fuel or plutonium fuel also maintains the chain reaction until enough of the thorium target material has been converted into fissile uranium233 (U 233) to take over much or most of the job. An advantage of thorium is that it absorbs slow neutrons relatively efficiently (compared to uranium238) to produce fissile uranium233. The use of enriched uranium or plutonium in thorium fuel has proliferation implications. Although U235 is found in nature, it is only 0.7 percent of natural uranium, so the proportion of U235 must be industrially increased to make “enriched uranium” for use in reactors. Highly enriched uranium and separated plutonium are nuclear weapons materials.
In addition, U233 is as effective as plutonium239 for making nuclear bombs. In most proposed thorium fuel cycles, reprocessing is required to separate out the U233 for use in fresh fuel. This means that, like uranium fuel with reprocessing, bombmaking material is separated out, making it vulnerable to theft or diversion. Some proposed thorium fuel cycles even require 20% enriched uranium in order to get the chain reaction started in existing reactors using thorium fuel. It takes 90% enrichment to make weaponsusable uranium, but very little additional work is needed to move from 20% enrichment to 90% enrichment. Most of the separative work is needed to go from natural uranium, which ahs 0.7% uranium235 to 20% U235.

Thorium produces 10 to 10,000 times less long-lived radioactive waste;

Proponents claim that thorium fuel significantly reduces the volume, weight and longterm radiotoxicity of spent fuel. Using thorium in a nuclear reactor creates radioactive waste that proponents claim would only have to be isolated from the environment for 500 years, as opposed to the irradiated uraniumonly fuel that remains dangerous for hundreds of thousands of years. This claim is wrong. The fission of thorium creates longlived fission products like technetium99 (halflife over 200,000 years). While the mix of fission products is somewhat different than with uranium fuel, the same range of fission products is created. With or without reprocessing, these fission products have to be disposed of in a geologic repository.

Thorium comes out of the ground as a 100% pure, usable isotope, which does not require enrichment, whereas natural uranium contains only 0.7% fissionable U-235

Compared to uranium, thorium fuel cycle is likely to be even more costly. In a oncethrough mode, it will need both uranium enrichment (or plutonium separation) and thorium target rod production. In a breeder configuration, it will need reprocessing, which is costly. In addition, as noted, inhalation of thorium232 produces a higher dose than the same amount of uranium238 (either by radioactivity or by weight). Reprocessed thorium creates even more risks due to the highly radioactive U232 created in the reactor. This makes worker protection more difficult and expensive for a given level of annual dose.

(The article goes into a bit more detail. One does have to keep in mind that PSR is generally quite anti nuclear - but I think these are fairly reasonable counterarguments)

Lastly, no one has actually made a commercial level thorium cycle reactor despite decades of trying. It MIGHT have some advantages and engineering and research efforts should continue, but it's hardly a viable solution as of yet.

Re:What about Thorium, Molten Salt Reactors

[KonoWatakushi]

Nice "fact sheet" by people who are clearly not experts in the field and obviously have an anti-nuclear agenda. Most importantly though, it is anything but objective; it is highly selective of the "facts", full of half truths and strawmen, and has a clear intent to deceive the reader. While I have little desire to sift through their drivel, I fully expect that they have similar "fact sheets" for many other competing energy sources. What we could use is a real fact sheet for fossil fuels, and especially coal...

Just to start with, anything with a half life of 200,000 years is so stable, that it is only technically "radioactive", and poses no health risk whatsoever, beyond possible issues of toxicity. Any residual radiation remaining after a few hundred years is below the background level; the only reason to point out things like this is to incite fear and induce hysteria.

Otherwise, while some hypothetical straw man reactor in once-through mode might suffer from some imaginary reprocessing problems, real designs such as the Molten Salt Reactor are conveniently ignored. There is no solid fuel to start with, no separation necessary, and the "reprocessing" is basically just removing the reaction products, and can be done online.

The amount of real waste from such reactors is so small, and the timeframes so short, that it is ludicrous to even begin talking about geologic storage. For a comparison of the waste and mining requirements, see this presentation. In terms of raw environmental devastation and heath effects, it would also be nice to see a comparison with coal.

CANDU

[andymadigan]

Since a CANDU (Heavy Water) reactor's fuel isn't naturally capable of going critical, couldn't that existing, tried and true design be used instead? We can fuel it with nuclear waste from American reactors, or use raw uranium ore, with no need for centrifuges or other tech that can be used to create nuclear weapons. If the cooling system fails, then you should have the backup of draining the heavy water from the reactor core, thus killing the reaction.

I'm not saying that's the only solution, I'm just saying that a known good solution that's been working for decades is probably better than a new one.

Is there nuclear technology?

[ShakaUVM]

"Is there nuclear technology that could withstand such a catastrophe? Possibly."

Yeah, as in all other modern designs.

Passive cooling has been the hot new thing since, you know, the 80s.

Dumb question...

[sideslash]

If nuclear power plants are used to power cities, why can't they power their own cooling? Seems like keeping the darn thing running would be safer than watching it sit there unpowered and on the verge of blowing up. (Don't get me wrong; I'm sure there's a good reason. I'm just curious.)

Re:Dumb question...

[XiaoMing]

I'm sorry, but that is one of the most misleading and misinformed sequence of words to get marked up regarding this whole issue.

First off, it should be noted that this reactor was in the middle of what can be considered by the general public as three chronological regimes of reactors:

1. Very unsafe reactors that have little or no passive safeguards (i.e. reactors reminiscent of Chernobyl or Simcity2k's 50 year kaboom)
2. Relatively safe reactors that have many passive safeguards (multiple layers of containment, and spill region with unfavorable fission geometry etc.) but that still rely on external containment measures (active cooling in the situation we're discussing now)
And finally
3. Very safe reactors that have many passive safeguards built in for every foreseeable (keyword, so no need to go thinking up magical exceptions to this category) circumstance (such as the capability to snuff themselves out via high concentrations of neutron absorbing daughters etc). As these reactors were being constructed and developed during a period of nonproliferation and disarmament, you see mixed results as many in operation were also once-off prototypes, but there are many places (Japan, France, Canada, etc.) where standarization and continued development/production means that most of the public fear is about as accurate as the tea party's propaganda regarding Kenyan birth records.

As an aside, it's also a good time to note that nuclear power plants are still nothing more than a fancy way to boil water. I.e. after a few heat exchange processes, the steamy water from these reactions is still used to do what water flowing downhill is used for, to drive a turbine.

Now the important part: Shutting down the reactors was by far the correct thing to do here because cooling was necessary for the daughter isotopes.
That is, the stuff we've been cooling all this time is the result of decay from before the plant was shut down.

What does this mean? Now here comes the simple part: It means that if you took the exact same situation, but kept the reactors running critically (i.e. no full insertion of control rods), you'd not only continue to generate heat from the primary fission reaction itself, but ALSO continue to generate more heat from the fission of the daughter products.

So sure, you might have had a few hours, hell maybe a day to generate additional energy before the subsequent tsunami--that managed to wipe out: the national electrical grid, thirteen backup diesel generators; and backup batteries that last for eight hours--is now expected to leave your steam turbine energy generation system completely untouched and functional. (http://www.voximate.com/blog/article/1058/failover-backup-systems-redundant/)
And in the very very likely case that it doesn't? Well now you have all that additional heat as well as even more daughter products to take care of.

No manuals will be rewritten, if this shit happens again they'll shut down the plants just like they did this time, only get plugs that fit rather than risking a full blown meltdown while hoping that a damaged powerplant can supply its own cooling somehow.

And of-course, if these defunct cores are replaces with newer designs after this is all over, we'll be in much better shape regardless.

Re:Dumb question...

[CrimsonAvenger]

Now the important part: Shutting down the reactors was by far the correct thing to do here because cooling was necessary for the daughter isotopes.
That is, the stuff we've been cooling all this time is the result of decay from before the plant was shut down.

It should perhaps be noted that I'm a former reactor plan operator. I have a clue.

Yes, cooling the daughter isotopes is exactly the issue. You generate fewer of them when you reduce output from commercial levels to self-sustaining levels.

And when you reduce power (but not shutdown completely), the decay products begin to decay down toward the new steady-state level. Which is a LOT less than steady state when you're operating at 90%+.

Every minute that goes by with the reactor operating at a reduced output is another minute you don't have to find an external power source to cool things down. And another minute farther from a core meltdown.

As was, by doing a hard shutdown immediately, the reactor was placed into a position such that the only possible way for a "good" outcome would be for the national electrical grid to stay completely intact during the next few days. There's no way that the battery back-up they had could keep cooling that plant for the next couple days by itself.

Which leaves as your only real option to try to use the reactor's output to maintain cooling while you burn through the decay products for as long as possible. After all, you can always scram the reactor later, if things don't work out.

Re:Pebble Bed

[Anonymous Coward]

Actually, the pebble reactor in Julich, Germany (I'll assume that's what you are referring to) had severe problems leading to long half-life fission products contaminating the soil and water around the reactor.

The flaws are not based on the particular design of the AVR facility, but seem to be flaws in the whole pebble-bed idea. You can read the Julich Research Facilities own post-mortem here: http://www.eskom.co.za/content/AVR-Report-Press.PDF

Re:Pebble bed reactor

[Anonymous Coward]

These are only the size of a shipping container and are a self contained unit. They would be a great way to bypass the NIMBYism associated with nuclear power plants. They are also much safer. If these can be bought by people with a bit of cash in the attic and installed in the countryside unknown to the neighbours we can all enjoy cheap nucular energy while everyone is blisfully oblivious to the fact that the neighbours little 'storage' container is actually a nucular power plant

It turns out that pebble beds aren't quite so maintenance free. Although the helium used as a coolant doesn't become radioactive, the graphite in the pebbles absorb radioactive metals and spread it around in graphite dust particles. Both the the AVR and HTR reactors in germany had big problems with contamination of the reactors due to this and due to the inability of the pebbles to contain radioactive isotopes.

Also, the pebble bed itself can't be instrumented so it becomes a black box resulting in unexpected hot currents of gas that can be significantly (200+K) warmer than expected. This resulted in maintenance issues in the two reactors in Germany (I don't think there is information on other experimental or production reactors using a pebble bed design). These problems might be surmountable but right now they're pretty big issues.

Kind of off topic, borderline AC even, but..

[drfreak]

If Bill Gates' life was to flash before his eyes, would it be a blue flash?

THESE reactors should't have had a problem

[unassimilatible]

It can't believe nobody has mentioned this, but the reactor designs were not the problem. All of these cooling problems could have been solved by some sort of waterproof backup power, even if it had to be stored 50 miles away and delivered via an underground cable that comes up under the reactors. Some of these reactors' cooling systems failed because the battery backup power was in the farking basement for crissakes! Below sea level on an Island! Totally flooded. I'm a social science (excuse the contradiction of terms) and I know better than that.

How hard would it be to either 1) keep battery backup at a high point above a nuke plant* (I know, weight, whatever, engineer around it) or 2) the plan I mentioned above, the same redundancy that data centers have, redundant power located elsewhere. Either would have likely saved these reactors.

*Patent pending.

Problem with terra power

[mbkennel]

"the two biggest advantages of the fast reactor design is that it requires no spent fuel pools and uses cooling systems that require no power to function"

Let's translate what this means. The core of the reactor will be VERY radioactive as it will have decay products from many more gigawatt hours---yes it will transmute quite a bit of these but do not underestimate just how hot it will be.

The cooling systems use molten sodium. It has the wee problem that it is explosive in contact with water. Say from a flood. Or if the building catches on fire. (and it's probably quite radioactive in itself simply from activation from the neutron flux). Or suppose there's a leak in the roof and it rains.

And it's right next to an extremely radioactive core. And if the explosion results in something cracking open......

One huge problem at Fukushima reactors was the unappreciated dangers of flooding, combined with the hydrogen explosions. These explosions damaged other important machinery and structures---you get a 'blunder chain reaction'.

See some other comments about the TWR

http://theenergycollective.com/barrybrook/43928/terrapower%E2%80%99s-travelling-wave-reactor-%E2%80%93-why-not-use-ifr

Re:Problem with terra power

[Ihlosi]

how about having a huge chlorine bath under the sodium reactor,

Great idea. Let's build a huge potential bomb by placing a metal that reacts violently with pretty much anything else next to the substance that it reacts most violently with.

and if there's a reactor problem the barrier dividing the two is lowered resulting in radioactive NaCl being created?

The reaction between chlorine and sodium is hugely exothermic. What you propose basically amounts to blowing the reactor and its contents sky-high.

Also, you don't want chlorine anywhere near neutron radiation, since the Cl-36 created that way has a half-life of a few hundred thousand years. Short enough to make it a radiation hazard, and yet long enough to make disposal quite difficult.

Some might, but some wouldn't:

[Hartree]

That's not entirely true.

For example. Amory Lovins, one of the notables of the anti-nuclear movement was asked in an interview what he thought of a truly cheap clean energy source. He said it would be a disaster. Why? Because he believes that whenever humans are given concentrated sources of power, they use it to destroy nature. Thus humans need to be limited to diffuse and limited sources of energy.

Quite often the waste and radiation questions are arguments used against nuclear power, when some of the motivation would have problems with any concentrated source of energy.

Needless to say, I disagree with that viewpoint, but it is one that can be argued and is not totally without merit.

Re:Wikivertisement

[spun]

Good Lord. This looks like a total scam. This is all funded by a known patent troll. It appears to be some sort of viral marketing campaign to drum up customers, i.e. moronic investors willing to part with huge sums of money they will never see again. And now we're all part of it, they'll point at Slashdot and say, "Look! Nerds are talking about it. Smart people. See them talking about it? Now give me some money." I feel dirty now.