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Pebble Bed Nuclear Reactors are my Kind of Nukes!
Posted by: Dale Franks on Wednesday, September 27, 2006

Glenn Reynolds highlights the technology of pebble bed nuclear reactors.
Partly as a result of recent Congressional efforts to fund reactor research, and partly as a result of ongoing work in national laboratories and the nuclear power industry, things in the field are looking up. As a recent survey article in Popular Mechanics magazine makes clear, there are new approaches to nuclear power in the offing that promise cleaner and more efficient power production with far less risk of "all-out" (or even minor) nuclear war in the process. Of these, perhaps the most promising technology is the pebble bed reactor:

"A typical pebble-bed reactor would function somewhat like a giant gumball machine. The design calls for a core filled with about 360,000 of these fuel pebbles — "kernels" of uranium oxide wrapped in two layers of silicon carbide and one layer of pyrolytic carbon, and embedded in a graphite shell. Each day about 3000 pebbles are removed from the bottom as fuel becomes spent. Fresh pebbles are added to the top, eliminating the need to shut down the reactor for refueling. Helium gas flows through the spaces between the spheres, carrying away the heat of the reacting fuel. This hot gas — which is inert, so a leak wouldn't be radioactive — can then be used to spin a turbine to generate electricity, or serve more exotic uses such as produce hydrogen, refine shale oil or desalinate water.

"The pebbles are fireproof and almost impossible to use for weapons production. The spent fuel is easy to transport and store, though there still remains the long-term problem of where to store it. And the design of the nuclear reactor is inherently meltdown-proof. If the fuel gets too hot, it begins absorbing neutrons, shutting down the chain reaction. In 2004, the cooling gas and secondary safety controls were shut off at an experimental pebble-bed reactor in China — and no calamity followed, says MIT professor Andrew Kadak, who witnessed the test."
China, with a booming economy, a huge population, and air pollution problems that are already absolutely dreadful, is very interested in pebble bed reactors. And they would seem to promise a lot for the United States, too — plus a way to promote nuclear power in the Third World without the kinds of nuclear-weapons proliferation threats we face today.
For students, let's review:

1. No possibility of meltdown.
2. Only compact, solid waste.
3. No possibility for nuclear proliferation.
4. Eliminate thousands of deaths from coal-burning.
5. Eliminate global warming risks (if you believe in that sort of thing) from coal and natural gas-fired power plants.
6. Much less technically difficult to build, hence, much less expensive.
7. Can be built economically in varying sizes, unlike huge honkin' conventional reactors.

It's hard to argue against the pebble bed concept, either from the point of view of safety, proliferation, or environmental concerns. I would point out, though, that if you are environmentalist arguing against the pebble bed concept, then the only reasonable conclusion is that your objections lie in some other sphere than strictly environmental concerns. I think it's fair to presume your objections lie in the realm of ideological predispositions that exist separate from your environmental concerns.
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Previous Comments to this Post 

To the contrary, anyone arguing that PBMRs are completely safe are scientifically-challenged.

While PBMRs aren’t susceptible to meltdowns, a loss of coolant could produce catastrophic radiological consequences. Fire is a very real liklihood in the event of coolant loss; this would likely mean large releases of radioactivity.

Additionally, PBMRs use fuel that is more enriched; this means proliferation is a greater issue since PBMR fuel would require less effort to convert to weapons grade quality than conventional reactors.

WRT waste, there’s going to be a greater volume associated with PBMRs. That it is "compact and solid" is irrelevant. A clue: more nuclear waste is not a good thing no matter if it’s compact, solid, or smells like flowers.
Written By: jadegold
URL: http://
Amazing. I didn’t think it possible for even you to combine so many factual inaccuracies in a single comment.

Apparently, I was wrong.

Not that you’re interested, what with being a well-known Internet idiot and all, but your concerns have been exhaustively investigated, whether they are concerns about proliferation, safety, or waste.

Of course, no amount of scientific explanation is acceptable to morons or ideologues, who are, after all, immune to rational argument.
Written By: Dale Franks
PBRs may or may not be the way to go. We’ll see.

I’ve worked in the nuclear industry over twenty years. One of my primary concerns when our energy future is discussed is that the public at large doesn’t understand our energy present. Nor, unfortunately, do most of the media "experts" on the issue, who have never tried to squeeze electricity out of coal, uranium, or sunlight. It’s hard. The real world of nuclear power in particular is much different than that portrayed by advocates and opponents alike.

To provide an inside look at the US nuclear industry that’s also entertaining, I’ve written a thriller novel on the topic that covers all the bases - the technology, the politics, the weirdness. "Rad Decision" is available at no cost to readers at - and they seem to like it, based on their homepage comments.

I may have mentioned this before. If so, please forgive the redundancy.

"I’d like to see Rad Decision widely read." - Stewart Brand, internet pioneer, founder of "The Whole Earth Catalog", co-founder of The Global Business Network.
Written By: James Aach

factual errors:

Coollent Leaks: are not a problem. It’s HELIUM, you know periodic table #2, top of the nobel gasses. It reacts with *almost nothing. Certainly nothing found in nature. More over it is lighter than our atmosphere so in the event of a leak it litteraly just floats out into space.

More Enriched: Yes but also encased in some dificult materials. One of the biggest practical problems with PBRs is that recycling the fule (re-enrichment) is more difficult than conventional fule rods. Translation, you gotta crack the nut first, and it’s a hard shell. The fule it’s self is manufactured in secure locations, and can be distributed to, shall we say less ideologicaly safe places, without major fear of refinement into a weapon of an signifigant capacity. (say more dangerous than low grade uranium)

Waste: Solid waste that can be stacked in nearly unlimited volumes in close proximity is a good thing! One of the things that makes nuclear waste (especially Plutonium) so dangerous is that it can have run away melt-downs all on it’s own. All that is required is a critical ammount of fissable material and time; it slowly heats up and expands into a liquid and then, G_d help us, a gas. So solid waste that is thermaly stable is a really good thing.

Nuclear waste beats the heck out of most industrial waste, mostly because we understand it. And it’s regulated. Contrast the waste ’treatment’ solutions for say a Steel Mill (you need this to make windmills), a silicon wafer facility (photoelectrics), or a coal fire plant? In all cases the shear volume and amorphous nature of the wast makes it nearly imposible to deal with. Nuclear wast is nasty stuff, true. But it’s compact, and for the most part recylable (given some regulatory changes).

Written By: TheLoneCabbage
URL: http://
I have no idea about this stuff but it sure sounds like it would take alot of the energy produced from these plants to create the fuel for the plants. You would have the mining of all the different ingredients then the processing and everything.Thats alot of energy used.
Written By: SkyWatch
URL: http://

What you claim to be my factual errors are yours. In the event of a coolant loss, helium, as you correctly note will float away. It will be replaced by air which will then likely permit the graphite to catch fire. Further, fire is also a distinct possibility if a coolant breach occurs between the helium and water circuits.

Again, there is no real dispute that it would be easier (still difficult) to produce weapons grade quality material from PBMR fuel than light water reactors.

Waste: More waste simply isn’t a good thing no matter how you slice it.


Frankly, you’re not qualified to discuss this matter cogently. You claim that all concerns have been "exhaustively investigated."

In fact, they haven’t.

Written By: Jadegold
URL: http://

Frankly, you’re not qualified to discuss this matter cogently
And you are exactly why?
Again, there is no real dispute that it would be easier (still difficult) to produce weapons grade quality material from PBMR fuel than light water reactors.
I need citations please. Plenty of other studies say otherwise
The first main non-proliferation advantage of pebble bed reactors is the high proportion of fuel burnt. This fuel (90,000 MWd/MTHM) has proven to be bad weapons material because it would be expensive and difficult to get fissionable material from inside the spent pebbles. For example, the necessary steps to be able to gain 10 kg of plutonium 239 would be:

1. Diversion of 10^6 fuel elements (despite of international control)
2. Head end for 10^6 fuel elements (technology today not available)
3. Destruction of 1*10^10 coated particles (technology not available)
4. Reprocessing of the Pu-U-mixtures

It is evident that this large diversion of elements and reprocessing cannot be done in an unobserved manner. Also, notice that the technology required for steps 2 and 3 is not available. Other ways of diversion of weapon-grade materials would need much less efforts. The low enriched uranium fuel is contained in half-millimeter sized particles of uranium dioxide encased in graphite and silicon carbide, which in turn is encased in the main graphite ball. Fuel balls are recycled through the reactor some 10 times. After each cycle they are extracted and analyzed to determine the amount of fissionable material left and either sent to depleted storage or returned to the reactor depending on the level. This process allows the fuel balls to be burnt to depletion leaving minimal fissile material to extract from them. Unlike conventional large fuel elements, the fuel balls cannot jam in reactor core housings allowing them be burnt to depletion without any fear of mechanical deformation causing handling problems in the core. Because of this, hundreds of thousands of balls must be stolen in order to retrieve enough fuel for weapons.
That sure as hell doesn’t sound "easier" to me. Sure, it’s not impossible, but there’d be weapons even without nuclear power.
Waste: More waste simply isn’t a good thing no matter how you slice it.
Depends on what you’re considering as waste. Pound for pound, yes there is more waste. But you’re talking about the pebbles themselves and not an apples to apples comparison of Uranium / Plutonium waste.

As far as fires go, good luck pushing that nonstarter!
If the reaction is not stopped by the graphite spheres or cooled by the helium, it will cool down naturally on its own in a very short time because the increase in temperature will make the chain reaction less efficient until it ceases to generate power. The peak temperature that can be reached in the reactor core is far below what would damage the fuel, because the ceramic materials coating the fuel—graphite and silicone carbide—are tougher than diamonds. Because of its shape—a high surface to volume ratio—the reactor will lose heat faster than the heat generated by the fuel in the core, so that the plant can never get hot enough for a meltdown of the fuel to occur.
This is what piqued my interest in PBMR in the first place. Again, not an impossibility, but definitely not a probability.

For someone who is so qualified to speak on this stuff, you sure are misinformed on a lot of things.
Written By: Robb Allen

Frankly, you’re not qualified to discuss this matter cogently. You claim that all concerns have been "exhaustively investigated."
And YOU are? My response is to say, that Jadegold is simply an idiot posting and is in no way qualified to discuss this issue, either. On what basis do I make that assertion? Well on the same basis Jadegold makes his/her assertions, out of the thin air. Jadegold IF you have a PhD in Nucler Phsysics and/or an extensive career in Nuclear Power by all means advance your credentials and then explain why Dale isn’t qualified, otherwise STFU.
In fact, they haven’t.
Well that’s debatable. IF you oppose Nuclear Power AND someone advances an argument in FAVOUR of a Nuclear Power, THEN obviously the issues have NOT been investigated sufficiently, because if they had YOUR position would be triumphant...on the other hand I’d bet if Helen Caldicutt advances an argument AGAINST Nuclear Power, then THOSE isssues HAVE been thoroughly investigated. Bottom-Line: I don’t trust your judgement on this as an "unbiased" observer and believe NO argument in favour of Nuclear Power is ever going to be sufficiently well-researched and investigated to overcome your opposition.
Written By: Joe
URL: http://
"It will be replaced by air which will then likely permit the graphite to catch fire. Further, fire is also a distinct possibility if a coolant breach occurs between the helium and water circuits."

That might be true if the PBR kernels weren’t also encased with an outer layer of silicon carbide. Not to mention high-density pyrolytic carbon doesn’t burn well:

This is not to say PBR tech is 100% safe, but it’s probably no worse than the tons of radioactivity we spray into the atmosphere each year burning coal. Caution is good, but this does appear to be a very promising tech. Wholesale signing it off as the doom and gloom anti-nukers do is silly.
Written By: Buddy
URL: http://
"Eliminate global warming risks"

On the contrary, my right-wingnut-tool-of-capitalist-environmental-rapists.
The very purpose, as you confessed, of this devilish machine is to GENERATE HEAT!! Hah! No doubt to be used by the wealthy countries generate electricity to hoard all the coolness with refrigeration and ice-making machines, inflicting even more warming on innocent third-world victims.
Written By: timactual
URL: http://
...inflicting even more warming on innocent third-world victims.
timactual, I find it useful to expand that, to include womyn, lesbians, gys, the transgendered and People of Colour...remember the forces of Darkness oppress all, not just some...You do want to be INCLUSIVE don’t you?
Written By: Joe
URL: http://
Dale, it’s great that pebble-bed reactors aren’t susceptible to meltdown, but nuclear waste is still nuclear waste. I’m not even pretending to be an expert, but if they store it in your town except buried under a mountain, significant fractions of the population get cancer. That’s the layman understanding. Sounds to me like the core environmental complaint - outputs cancer for 20,000 years or so - hasn’t really changed.

As Yucca mountain demonstrates, once the waste is headed to *your* state for storage, *everyone* suddenly becomes an environmentalist..
Written By: glasnost
URL: http://
As much as it pains me and may pain Glasnost I am with him on the waste issue. I have no in-depth knowldege of nuclear power or physics, but on the surface the pebbled reactor seems to deal well with safety and proliferation issues nicely, BUT there is STILL waste. The fuel pellets and the reactor STILL have to be disposed of...I just wonder if that’s practically possible? Yucca Mountain has divided my own party, as folks who vote reliably "my" way have been fighting the Glasnost says:
...once the waste is headed to *your* state for storage, *everyone* suddenly becomes an environmentalist.
Written By: Joe
URL: http://
Everything we do generates waste products. The key is to get the most benefit for the least waste. Fission accomplishes this. Are the waste products dangerous? Well duh! Driving is dangerous, flying is dangerous, bathing is dangerous, living is dangerous. I ride my bicycle to work. This is more dangerous than driving but I do it anyway. I get a benefit (exercise) that I feel outweighs the increased risk of injury or death. If we focus, concentrate, and pay attention, we can handle these dangerous waste products. Have any of you ever been in a foundry (a real metal one, not a chip one)? Sparks are flying, molten metal is flowing, there’s danger everywhere but somehow it’s all under control.
Written By: Paul
URL: http://
I’m not even pretending to be an expert, but if they store it in your town except buried under a mountain, significant fractions of the population get cancer.
Numbers? Links? Proof? Anything?

Please note that there are pollution problems with our current power generating technology.

As for the "omigod, it’ll be around for 20,000 years" theme, get real. 20,000 years. That’s the twice the time humans have been in the Americas. I cannot believe that we will find some use for or better way to handle nuclear waste long before then.
Written By: Mark A. Flacy
URL: http://
Pebble bed reactors are pretty neat, no doubt. Just don’t expect any significant electrical generation market penetration for decades. They are smaller and better suited for intermediate load generation. The core technology, the ceramic-coated fuel grains, is a spin-off of the nuclear rocket engine program back in the ’60s.

For the next 30 years, plan on using advanced light water reactor technology.

As a nuclear engineer, it is hysterical reading JadeGold’s postings. While I hate to play the "Me Expert" card, critics of nuclear power have reduced their arguments to either the illogical or the dishonest. Don’t these people have any mathematical training?

To JadeGold’s assertion "anyone arguing that PBMRs are completely safe are scientifically-challenged" - May I suggest a recent article about how the ancient Greek mathematicians would treat reactor safety:

Thankfully, the critics no longer command and monopolize the public communications pathways. I encourage my fellow citizens to dig into the topic a bit themselves and apply some critical thinking skills to what they read.

The owners of nuclear power plants have HUGE incentives to build and operate their multi-billion investments in a responsible and conservative manner.
Written By: Whitehall
URL: http://
This hot gas — which is inert, so a leak wouldn’t be radioactive
I don’t think so.
Helium being chemically inert does help with the problem of corrosion, but as for being radioactive, I doubt it. The good news though is that most isotopes of helium have very short half-lives, some as short as a few micro seconds. The down side is that the radiation emission will strong, but short.
Written By: Neo
URL: http://
"You do want to be INCLUSIVE don’t you?"
Oh. I missed last weeks meeting, so I thought they were all still included under "third-world". Thanks for the update. Power to the people!

" Don’t these people have any mathematical training?"

Sure. One, two three, many. See? I am a magma come loudly gradient.

"The down side is that the radiation emission will strong, but short."

And the upside is that, since helium risees, only the birds are at much risk.

Written By: timactual
URL: http://
Thanks Whitehall, that was a fascinating read.
Written By: Robb Allen
Pebble bed reactors are pretty neat, no doubt. Just don’t expect any significant electrical generation market penetration for decades. They are smaller and better suited for intermediate load generation.

Actually, this is the direction that electrical distribution systems are heading. In other words, PBRs are perfect in this regard.

As for the waste storage, I think people are missing the point of why the fuel is put into pebble form in the first place. Each one is essentially harmless by itself. Or even in a heap, once the moderator has been removed. Spent PBR fuel requires less space to store than does light water reactor spent fuel.

Don’t take my word for it, folks. Read some scientific research instead of environmental websites.
Written By: Wulf

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