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I went a-Googling to rebut this -- after all, there had been a similar chain of events at Davis-Besse 18 months earlier -- but I didn't find anything that answers the questions that http://www.tmia.com/old-website/tmisab.html points out.

The best argument against sabotage is that there was no way for a saboteur to know that it would work. Theoretically, even a complete loss of feedwater should have led to a scram and activation of one of the multiple emergency core cooling systems, disruptive but not destructive.

Pebble beds have significant problems to overcome.

They have problems with full sphere jams and collisions between pellets (compromising their integrity).
Several of the world's worst nuclear incidents involved the oxidation (burning) of a Graphite moderator.
Care to guess what type of moderator pebble bed reactors use?

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In general, land based Nuclear reactors are ALL WAYS considered to be a primary target by any enemy combatant.

They are fixed, easy to destroy (with a minimal nuke) targets with a high collateral damage multiplier.
(Concentration of medium decay rate isotopes, (incorporated into the food chain), equal to 100's of nuclear weapons.)

Operational Utility scale reactors(1GWe/3GWt) have even larger concentrations of those isotopes(==1000's of N-weapons).
A significant release of these isotopes will remove a large area of land from human and/or agricultural usage for 100's of years.

Truly Chernobyl is an extreme and ill-fitting example...

Those who forget the past are doomed to repeat it.

The RBMK-1000 reactor specifically is known to have design flaws which creates safety issues.

The pebble bed reactor has known design flaws. These are valid issues.

All of the pebble bed reactors either in operation or planned are significantly smaller, on the order 100~200 MW of electric power and 200~400 MW of thermal energy (note the increase in efficiency)

Pebble bed reactors are designed to be modular. Source Reactor sites lack containment building for this exact reason. A fully equipped reactor would have to supply a comparable amount of electricity to be economically feasible, hence would need several pebble beds per facility. Extra beds alone increases risk.

So to make the blanket statement any fission reactor has the potential to create a catastrophe equal to the Chernobyl incident is to simultaneous ignore the design improvements in both safety & efficiency since the RBMK was designed, some 60 some odd years ago and to ignore the implementation details of existing and planned reactors.

Most likely, Chernobyl is not going to happen again. But a Chernobyl type accident is certainly on the cards if nuclear energy becomes popular. Safety and efficiency will only be as good as human fallability, and there is always room for error. Worst case scenario at a nuclear power plant is still orders of magnitude worse than worst case scenario at any other power generation station with the exception of a major dam. The west won't be the only place where these reactors might be built.

I've looked at the evidence. From what I've seen, pebble bed reactors are not some magic wand that can wave away the danger of a nuclear incident. It is fundamentally the same game, with more advanced technology. I believe that it is possible to use nuclear energy safely, but I am yet to be convinced of the competance of those responsible to do so, with the possible exception of those in France.

To cap it all off, there are questions on whether fission is really all that cost efficient by comparision to other methods, paticularly hydroelectric power.

I just don't think fission is ready for the big time.

1. It has no containment building.
   
2. It uses flammable graphite as a moderator.
   
3. It produces more high level nuclear wastes than current nuclear reactor designs.
   
4. It relies heavily on nearly perfect fuel pebbles.
   
5. It relies heavily upon fuel handling as the pebbles are cycled through the reactor.
   
6. There's already been an accident at a pebble bed reactor in Germany due to fuel handling problems.

The plant came within 30 minutes of a full meltdown. The reactor vessel was destroyed, and large amounts of unmonitored radiation was released directly into the community.

The company has informed us that from about 11 a.m. until about 1:30 p.m., Three-Mile Island discharged into the air, steam that contained detectable amounts of radiation.

On October 25, 1979, the NRC issued a Notice of Violation (NOV) to Met Ed for causing the accident. The Commission also recommended the maximum fine, $155,000, permitted under law Met Ed denied all NRC charges, but agreed to pay the NRC fine on December 15, 1979.

"Research into breeder technology was cancelled after 1986 mainly because of the chernobyl incident"

Thanks for your post, it was interesting to read.
pebble bed

From the linked site:
5. & 6. There was a pebble bed reactor accident at Hamm-Uentrop West Germany nine days after the Chernobyl accident. On May 4 1986, a pebble became lodged in a feeder tube. Operators subsequently caused damage to the fuel during attempts to free the pebble. Radiation was released to the environs. The West German government closed down the research program because they found the reactor design unsafe.

The accident at Chernobyl probably had a BIG impact on the desicion for closing down, but the main reason was the design had flaws. The German program would still be going if it hadn't of had this accident. (And the reactor would still be operating). I think it was intelligent of the German Government to do what they did for two reasons.
1. They learned from Chernobyl. (Something a lot of the humans in the world don't do. An accident occurs, and they think it won't happen to them, so they continue.)
2. They realised if they continued with the design they had, and more accidents occurred (which was most likely), the bad PR would sink them.

Like most of us I think in the future a design might come into being which is meltdown proof. I'm still waiting for it. Another link on the Pebble Bed reactor - this one showing that they chose to close it down in 1988. Two years after Chernobyl:
Factsheet
Just my two cents. Cheers.

Here is a source with some known down sides to Pebble beds I posted last time we debated this and it does discuss the manufacturing and shielding in some depth. Since there have been Pebble manufacturing problems in the past so its not like it can't happen.

There has been an accident with a pebble bed reactor at Hamm-Uentrop West in 1986 in which pebbles were damaged and radiation released.

The problem with you and most of the people who've pilloried me in this thread is you seem to lack the healthy dose of skepticism necessary when considering nuclear technology from an industry with a history of downplaying the dangers. You all seem to be saying its safe, prove its not. I'm saying prove it is. I'm not saying nuclear is inherently BAD but it is a technology with catastrophic results when there is failure so it DEMANDS inordinate scrutiny.

The two issues with PBMR relating to the coating:

A. A track record of manufacturing defects in the pebbles resulting in cracks and defects that may defeat the coating

B. A track record of damaging the pebbles in handling.

Here is a website with pictures of defective pebbles and some healthy skepticism.

"There was a pebble bed reactor accident at Hamm-Uentrop West Germany nine days after the Chernobyl accident. On May 4 1986, a pebble became lodged in a feeder tube. Operators subsequently caused damage to the fuel during attempts to free the pebble. Radiation was released to the environs. The West German government closed down the research program because they found the reactor design unsafe."

It simply isn't the infallible technology suckers like you are saying it is. Sure if they fix the problems or at least have a mechanism for rejecting manufacturing defects in pebbles then maybe it is a solvable problem.

But, PBMR's are still a pile of graphite in a reactor without a containment buildinb which means they could in fact be extremely dangerous if something unexpected happens.

Pebble bed reactors are also not the panacea that people are seeking. Before you stake your life on pebble bed reactors, perhaps you should read: http://www.tmia.com/pebbles.html TDz.

I beg to differ. Having lived within a ten mile radius of Three Mile Island all my life, I've become good at cutting through the BS most energy companies spit out. Take a look at these two sites and tell me if you still feel they are safe: http://www.tmia.com/pebbles.html http://www.nirs.org/factsheets/PBMRFactSheet.htm

I recently was sent this link by a friend. One of the witnesses says,

And I looked outside. It was so blue! It was so blue! I couldn't see ten feet ahead of myself! I got scared.

Yeah, sure. It's a non-event only if you realize how close they were to core meltdown which would have poisoned the water table across a large swatch of the east coast (lookup china syndrome), and ignore the fact that the reactor containment facility STILL (a quarter centyry later) has places too radioactivly hot to enter. And several years after the incident considerably more radiation was released:

For 11 days, in June-July, 1980, Met Ed illegally vented 43,000 curies of radioactive Krypton-85 (beta and gamma; 10 year half life) and other radioactive gasses into the environment without having scrubbers in place. In November 1980, the United States Court of Appeals for the District of Columbia ruled that the krypton venting was illegal.
link

He posted this one, in english and german
An American opinion!

.....and that is just the top of the list. If you want to know more try this place and do some research.

Suppose a nuclear plant has a problem, you contaminate 100's of square miles with radioactive emissions

This is bullshit. Cuba has been hydrogen-fuel-cell powered for decades.

I don't know if it was your meant to troll, but troll you did.

Cuba may have made some efforts to use clean, renewable energy sources (wind, wave, solar) but it's also made considerable effort to use dirty, finite sources as well, including nuclear power.

The nuclear power plant at Juragua has been under construction since 1983. It's not yet been completed, so it's not up and running, but Cuba is still trying to get the plant productive.

Unsurprisingly, for what it calls "safety concerns", the US isn't too keen to see that happen - apparently, it's OK for the US to have nuclear power plants all over the country, nuclear powered ships and submarines and even to launch nuclear powered satellites but God forbid that some communists 200 miles off the coast of Florida should want to use nuclear power too.

It's true that these concerns aren't totally unfounded as the type of reactor that the plant uses (the Soviet-designed VVER-440) doesn't have an exemplorary track record but let's remember that while the USSR had Chernobyl, the US had Three Mile Island.

By withholding its funding to the International Atomic Energy Agency - an overly-aggressive and short-sighted attempt to pressurise that body into abandoning all assistance that its giving Cuba to safely complete and operate the plant - the US is effectively shooting itself in the foot. By doing everything it can to make sure that the Cuban plant isn't built, the US is only ensuring that cost-effectiveness and completion at any cost are the paramount in Cuba's considerations, at the expense of safety.

Yet elsewhere, the US is spending millions to make sure that similar Soviet-designed plants are as safe as possible. Overall, a rather naive approach by US legislators - not the first time and it won't be the last either.

(So, in a way, there is a capitalist conspiracy, but not where you were looking.)

But I digress. Cuba obviously isn't 100 percent wave powered and, frankly, it's never likely to be. Wave power stations cost money too and, if you've got chronic power shortage problems like Cuba has, they're far less cost-effective than the alternatives.

On the other hand, Islay is hoping that its wave power station may soon provide all the energy that it ever needs - a noble goal, well worthy of our praise and good wishes.

Oh my, suburbia invaded by giant mutant dandelions, what a nightmare, or extremely low-maintenance lawn, depending on your approach to yard work. 8-) Except that these were found "in an area that was untouched since the days of the accident," leading me to suspect that these are just ordinary dandelions that got left along long enough to grow really big. I have no idea how big a dandelion can grow, do you? But you get enough people out looking for something weird and they are going to find something, because there's always something weird out there. Call it the Erin Brokovich effect.

I wouldn't have wanted to save that gas in a tank and breathe it all, but the way it was vented it would have spread over a wide area and raised the background radiation level a fraction of a percent. A coal-fired plant releases more radiation in the fly-ash. Your TV set and CRT computer monitor emit more radiation. It was nothing to worry about, except that the way this happened (a stuck valve undetected for hours) suggests that either the operators were incompetent or the control console was beyond human comprehension...