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Nuclear's next generation

economist.com

90 pointspg32 comments

One form of very high temperature reactor, the pebble bed reactor, was theorized in the 1950s and has been under development at various locations for more than a decade -- China begins commercial construction this year.

PBRs are one of several inherently safe designs wherein shutoff of circulating coolant raises core temperature and natural processes serve to choke criticality.

http://en.wikipedia.org/wiki/Pebble_bed_reactor

Pebble beds are also compatible with thorium, in case anybody was wondering.

The pebble bed reactor has inherently safe features concerning loss of coolant, but it is not inherently safe: There are other sever accidents not known in conventional reactors, like graphite fire (as it happened in Chernobyl, too) and water ingress into the core with subsequent explosions.

Another newer technology to keep an eye on: plasma gasification (http://www.slate.com/id/2181083/).

Although it produces paltry amounts of energy compared to nuclear facilities, it's a neat solution to the problem of waste management, capable of handling low-grade nuclear waste.

The current reactor designs are safe enough, let's build them now. Debating the pros and cons of advanced designs is dumb and accepts the enviros false claim that current BWR or PWR light water reactors are "unsafe". Moreover, significant real-world safety comes from operational experience on a fleet of the same or similar designs. It would be foolish to throw away 50 years of knowledge and experience on light water reactors to start over on sodium, fluoride, pebble-bed, etc.

It's also about efficiency. Nuclear power plants regularly live beyond their designed lifespan of 30-40 years. If a new reactor can be built with 45% efficiency rather that the 33% of existing light water reactors get, that alone will justify the delay.

u.s. nuclear reactors have always been safe: if a loss of coolant failure occurs the reaction is designed to slow down rather than speed up soviet cheronobyl style.

the concern is what to do with all the junk from processing\using fuel rods and depleted uranium besides dumping it on Iraqis via munitions.

That doesn't always seem to work though: http://en.wikipedia.org/wiki/Three_Mile_Island_accident

>In the aftermath of the accident, investigations focused on the amount of radiation released by the accident. According to the American Nuclear Society, using the official radiation emission figures, "The average radiation dose to people living within ten miles of the plant was eight millirem, and no more than 100 millirem to any single individual. Eight millirem is about equal to a chest X-ray, and 100 millirem is about a third of the average background level of radiation received by US residents in a year."[31][52]

Read a bit closer

IIRC the figures on TMI (not broken down into phantom per-capita exposures but to the environment) included millions of Curies released into the environment. Some credible researchers have found evidence that figure may be 10 to 100 times too small.

Not surprising; with all the money involved, the science gets 'adjusted'. The industry can afford the best PR.

I think the per-capita exposures figure was simply to give a sense of scale not to obscure the figures. Do you have a source that backs that claim?

In the case of TMI, the steam formation did slow down the reaction -- just not enough to prevent damage to the fuel rods. Of course, the reactor's pressure vessel acted as a passive heat sink once the fuel melted and easily prevented the fuel from escaping, but it was still costly and scary, and the response of the operators at the time can only be called a ridiculous clusterfuck.

This sort of thing is why I really like pebble bed reactors: you can just shut off the coolant and walk away, and they'll sit tight. (The operators of China's HTR-10 research reactor actually do this.) Everything is designed to withstand the maximum temperatures they could possibly achieve. Light water reactors have an impressive safety record, and the modern versions aren't susceptible to the problems that led to TMI, but inherently self-moderating reactors are just really aesthetically pleasant.

>the response of the operators at the time can only be called a ridiculous clusterfuck.

This is unfair to the operators. The accident revealed some reactor and control room design flaws plus some equipment out of service that left the operators in the dark re what state the reactor was in during the accident. They knew the info they were getting was bad and took heroic steps to get better data, including sending men down into radioactive zones to read thermocouples manually with a volt meter, among other things. It is the anti-nukes who perpetuate the myth that the reactor operators freaked out and just mindlessly started throwing switches, closing valves willy-nilly. Unfortunately, the operators did make the situation worse but it was not due to stupidity or incompetence. One problem for the operators was their training was based on some assumptions that were not true for this accident. TMI was a pressured water reactor and one of the cardinal sins taught in training was never let the primary coolant system "go solid", i.e., no steam void in the pressurizer. A solid piping system could easily be burst by even a mild pressure transient which was why they opted to drain more coolant from an already overheating reactor. Tragically, the pressurizer was going solid because a steam void had formed in the core, something their training did not adequately address and they could not infer from the info available at the time. For obvious reasons, they had to make critical decisions within the time constraints and the data actually at hand, not 6 months later in an academic study.

Thank you for clarifying my terse statement; I can see how it could be taken as knocking the operators, which was not what I meant at all. Of course, the operators weren't a bunch of dimwits -- they had seriously flawed information about what was going on in the reactor, and the error-reporting system wasn't designed to cope with the kind of cascading failure that they saw. I wasn't criticizing the operators, but rather their actions, and that wasn't their fault.

(I can't even conceive of a reactor operator who would just start randomly fiddling with valves. That's just so far removed from everything I know about them, it would be like a horse reciting Shakespeare.)

We can use the U-238 in breeder reactors. Or make a subcritical blanket of U-238 and some of the longer-lived radioactive elements in spent fuel rods, and put them around a fusion reactor. The fusion reactor doesn't have to generate a net positive amount of usable energy; it just has to provide a lot of neutrons, which it does. This is the basis for fusion-fission hybrid systems, which can be marketed as nuclear-waste annihilation systems.

I'm a fan of liquid fluoride thorium reactors (LFTR). The prevalence of Thorium is a big positive and the ability to process out existing nuclear waste is a tremendous boon.

We're not that far away from commercializing LFTR. It's a shame we can't find more research funds.

I like the sodium fast reactor: low pressure, moderate temperature, sodium is dirt cheap, high burn-up of non-uranium/plutonium products ("waste"), and plutonium need never be separated from other reaction products.

The article doesn't say, but because molten salt reactors use liquid fuel, they release the radioactive xenon gas produced by uranium fission. (In fact this is sold as a benefit, since xenon absorbs neutrons better used for the chain reaction.) Xenon is a noble gas and therefore volatile, so the reactor will need strenuous containment measures. Loss of the gas seal would result in significant radioactivity release.

Helium-cooled reactors may be constrained by shortages of helium, which is rather rare and difficult to extract on Earth. You'd hope that government program managers would have worked out the logistics of this, but they tend to not see things that would get their funding cut. (Argon is plentiful but might not be a substitute because it reacts with neutrons a lot more than helium does.)

> Xenon is a noble gas and therefore volatile

This must be some definition of "volatile" I'm not familiar with.

Evaporating easily. Xenon boils at -108 deg. C. Given the chance, it would tend to rapidly escape from liquid fuel at reactor temperatures.

We're probably both thinking of "prone to explode" vs. "prone to evaporate".

Well, if had said "nonvolatile" it would have been boring.

In the case of liquid fluoride thorium reactors, I don't think the xenon-135 is what you need to be worrying about; worry about the fluorine gas instead! It's very reactive. Xenon, on the other hand, is chemically stable because it's a noble gas. And it's larger than helium, so it's easier to contain.

Also, I'd like to point out that pebble-bed reactors, while usually cooled with helium, could also be cooled with nitrogen that we just pull out of the air. It's more reactive than helium and it forms carbon-14 when you expose it to neutron flux, but those issues are both fairly minor. I think they're going with helium now because they want to get something working as quickly as they can, and they don't want to go mucking with what works.

They use the relatively-nonvolatile fluoride ion (F-), not the gaseous molecular fluorine (F2). Fluoride is corrosive in higher concentrations, but nowhere near as dangerous as the oxidative toxicity of fluorine gas.

Re. nitrogen, the radiation would turn it into ionized nitrogen radicals. Any info on how much damage that would cause to the graphite and metals? Also, carbon-14 is preferentially concentrated into living things, so a release would provoke a political panic similar to strontium-90.

I like the idea, as long as it's very far away away from my house.

I don't mind at all having a nuclear power plant upriver not particularly far from my home. It makes the electricity rates here noticeably less expensive than in many other parts of the country. That plant has been operating harmlessly for about four decades now.

After edit: indeed, I prefer having a nuclear power plant (somewhat) nearby to having a coal-burning power plant equally upstream and nearby, and prefer both to living without inexpensive electricity.

As the other poster said, it's better than living next to a coal burning plant. The coal burning plant would actually release more radioactive material into the environment than a nuclear power plant would.

I’ve heard this before, but is there any reason to think that the issue goes beyond the fact that CO2 has a higher natural level of radiation than H2O?

incomplete combustion\plenty of other stuff in the ground in it(heavy metals etc.). The smoke is not just CO2.

Plus " sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. In the US, About 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal." http://www.policyalmanac.org/environment/archive/acid_rain.s...

and acid rain causes a number of environmental problems.

NOx also creates low level ozon when it breaks down, which has a number of nasty environmental and health side effects as well.

At least with nuclear power the byproducts are stored in nearly-indestructible containers. Where are the byproducts of coal-fired generation stored?

Actually that's not quite right. (I was just talking to an engineer who services nuclear reactors for a living about this.) Most of the spent fuel rods are left sitting in storage pools ("wet storage") next to the reactor. What you refer to, cask ("dry") storage, is the other option, but is not as prevalent due to cost and opposition to storing nuclear waste outside. Ironically wet storage is the less safe of the two, because mechanical failure could result in the coolant boiling off, at which point radiation would be released into the air. Apparently this scenario is outlined in one of those Discovery channel, "What would the world be like without humans" shows.

As I recall, wet and dry storage are not mutually exclusive. The usual scheme is to let the waste sit in wet storage until the shorter-lived isotopes have decayed away and the waste has become cool enough to move to dry cask storage.

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