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

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.

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: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: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.

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.

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.

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.