Pebble Bed Modular Reactors - German reactor closed down after accident

[JohnWxy]

http://www.tmia.com/industry/pebbles.html

What's Wrong With the Modular Pebble Bed Reactor?

The pebble bed reactor is being touted as nearly "accident proof." It is being hailed as the savior of the nuclear industry. Three Mile Island Alert opposes this reactor design because of its inherent dangerous safety defects.


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.

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2. The uranium is covered by a layer of graphite. The graphite is covered by several other layers of materials including a silicon carbide. The graphite could burn if defects in the fuel defeat the outer coverings. The industry acknowledges that there is approximately 1 defect per pebble associated with these layers. There are approximately 370,000 pebbles in a pebble bed reactor. One tennis ball sized pebble comes out the bottom of the reactor every 30 seconds. It can be returned to the top of the reactor for additional use.
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4. The industry acknowledges that "fuel pebble manufacturing defects are the most significant source of fission product release." Recent history shows that some companies have falsified fuel quality. In fact, there have been instances of fuel sabotage and tampering over the last few decades. Germany and Japan have shut down plants or refused fuel shipments once the problems were discovered. The industry can't produce "defect-free" fuel and therefore it is a certainty that a pebble bed reactor will experience an accident. The industry acknowledges that there is approximately 1 defect per pebble associated with these layers.

http://www.nirs.org/factsheets/pbmrfactsheet.htm

THE PBMR: "OLD WINE IN A NEW BOTTLE"

The Pebble Bed Modular Reactor (PBMR) is being re-introduced in an industry effort to revive an all-but-moribund nuclear power technology. The PBMR’s basic design concept, the high-temperature gas-cooled reactor (HTGR), has been commercially abandoned time and again without tangible benefit over the past thirty years in England, France, Germany and with the 1967 and 1989 closures of the Peach Bottom Unit 1 and Fort St. Vrain reactors in the United States. Small HTGR non-power research reactors currently operate in Japan and China. For as many years, the concept has been offered as an "inherently safe" design.

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NO REACTOR CONTAINMENT BUILDING AND REDUCED SAFETY SYSTEMS CUT PBMR COSTS

Unlike light water reactors that use water and steam, the PBMR design would use pressurized helium heated in the reactor core to drive a series of turbine compressors that attach to an electrical generator. The helium is cycled to a recuperator to be cooled down and returned to cool the reactor while the waste heat is discharged to the environment. Designers claim there are no accident scenarios that would result in significant fuel damage and catastrophic release of radioactivity.

These industry safety claims rely on the heat resistant quality and integrity of the tennis ball-sized graphite fuel assemblies or "pebbles," 400,000 of which are continuously fed from a fuel silo through the reactor "little by little" to keep the reactor core only marginally critical. Each spherical fuel element has an inner graphite core embedded with thousands of smaller fuel particles of enriched uranium (up to 10 %) encapsulated in multi-layers of non-porous hardened carbon. The slow circulation of fuel through the reactor provides for a small core size that minimizes excess core reactivity and lowers power density, all of which is credited to safety.

However, so much credit is given to the integrity and quality control of the coated fuel pebbles to retain the radioactivity that no containment building is planned for the PBMR design. While the elimination of the containment building provides a significant cost savings for the utility—perhaps making the design economically feasible—the trade-off is public health and safety.

The protective containment building also is nixed because it would hinder the design’s passive cooling feature of the reactor core through natural convection (air cooling). Exelon also proposes a dramatic reduction in additional reactor safety systems and procedures (i.e. no emergency core cooling system and a reduced one-half mile emergency planning zone as compared to a 10-mile emergency planning zone for light water reactors) to provide for further reducing PBMR construction and operation costs.

To date, however, Exelon has not submitted to the Nuclear Regulatory Commission descriptions of challenges that could lead to a radiological accident such as a fire that ignites the combustible graphite loaded into the core. Fire and smoke then become the transport vehicle for radioactivity released to the environment from damaged fuel.

In addition, the lack of containment would require 100%-perfect quality control in the manufacture of the fuel pellets—an impossible goal. Imperfections in fuel pellet manufacture could lead to higher radiation releases during normal operation than is the case with conventional reactors.
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In 1985, the experimental THTR-300 PBMR on the Ruhr in Hamm-Uentrop, Germany was also offered as accident proof--with the same promise of an indestructible carbon fuel cladding capable of retaining all generated radioactivity. Following the April 26, 1986 Chernobyl nuclear reactor accident and graphite fire in Ukraine, the West German government revealed that on May 4, the 300-megawatt PBMR at Hamm released radiation after one of its spherical fuel pebbles became lodged in the pipe feeding the fuel to the reactor. Operator actions during the event caused damage to the fuel cladding.

Radioactivity was released with the escaping helium and radioactive fallout was deposited as far as two kilometers from the reactor. The fallout in the region was high enough to initially be blamed on Chernobyl. Government officials were then alerted by scientists in Freiburg who reported that as much as 70 % of the region’s contamination was not of the type of radiation leaking hundreds of miles away in Ukraine. Dismayed by an attempt to conceal the reactor malfunction and confronted with mounting public pressure in light of the Chernobyl accident only days prior, the state ordered the reactor to close pending a design review.

Continuing technical problems including a lack of quality control resulting in damage to unused fuel pebbles and radiation-induced bolt head failures in the reactor’s gas channels resulted in the unit’s closure in late 1988. Citing doubts about reliability, the government refused to further subsidize utility funding and instead approved plans for decommissioning the reactor.

[Tommy_J]

1. Hey, I like this technology

Theres a lot of scary sounding stuff listed there but the truth is this pebble bed technology is a great leap over existing reactors. It is intrinsically safe due to a negative reaction rate coefficient so that a melt down of the Three Mile Island type is actually not possible. Green minded folk might consider it as better than the the alternatives.

[jpak]

5. I like this technology too

The fuel has a high 235U content (~9% relative to ~3-4% for light water reactors).

The 235U content of the spent fuel is ~3%.

As these "pebbles" are extremely difficult to reprocess, the widespread use of PBMR's will accelerate depletion of global uranium supplies and...

**poof**

no more nukes...

:)

[GDAEx2]

2. The Reactor was Shut Down in 1988 !?!

What's been going on with this technology lately?

This is a low density (~9 grams of U/pellet)fuel that operates at temperatures below the flammability range of carbon.
Check out the MIT website:
http://web.mit.edu/pebble-bed/

<>

Actually pretty cool technology!
I'm a serious tree-hugger, employed in the environmental field within academia, and believe knee jerk, anti-nuclear responses are undeserved by the new MPBR technology.

[Tommy_J]

3. Good question

All I've heard lately is that China is investing heavily in the technology but have no other details.

[Dogmudgeon]

4. Don't you have any info other than from anti-nuclear advocates?

NIRS is the "Nuclear Information and Research Service Reactor Watchdog Project".

TMIA is the "Three Mile Island Alert". Here is their self-description:

Three Mile Island Alert is a non-profit citizens' organization dedicated to the promotion of safe-energy alternatives to nuclear power and is especially critical of the Three Mile Island nuclear plant. (Emphasis mine.)

They both share the problem common to all advocacy organizations, whether pro- or anti-nuclear -- they want you to believe in their cause and forsake all others.

It is extremely difficult to find information that simply analyzes a situation without injecting a political point of view -- but I don't think we can afford to play Culture Warrior anymore with any source of energy. I've been to both websites before, and they are major culture-war players. (You know ... "nukes are un-cool" ... "solar power is for hippies".) In addition, they make a number of sweeping assertions about nuclear energy that are doubful at best, and then simply expect their readers to believe them.

Yes, I've seen the same thing from pro-nuke sites; you don't have to remind me. It all sucks.

I'm pro-nuclear, but no, I'm NOT uncritical of it. I am also quite open to non-nuclear options. But I have been very disappointed from NOT being able to find the kind of large-scale alt-energy planning that will be required to replace oil and/or nuclear energy. We need a whole lot of power to do that -- about 500 EJ (the exajoules of which NNadir writes) or Quads (a nearly identical measure) per year. And we don't have a lot of time left to get to work on the actual generators, be they nuclear, wind, solar, or even cold fusion. The nuclear industry is further along in planning and development. We know that most of the problems with nuclear are very down-to-earth -- the incompetence and greed of their owners.

Yes indeed -- it sucks that all our energy supplies seem to be held by rat bastards who live to crack the whip over Humankind. But their political might can be checked, and the extra dangers their avarice brings to all energy generation can be greatly reduced by vigorous oversight and regulation. And you know that if they gain control over windplant, tidal generator, and/or solar panel production, they will muck it up just as they did with nuclear reactors. (Although I think the risks of nuclear energy are lower than you probably do, I recognize that there have been some truly heinous, dumb-ass mistakes made.)

But criticisms of both nuclear and non-nuclear energy must also be made in the context of ongoing, active global warming, and the possible deaths of 6.5 billion people. The risks and benefits of every kind of energy source are substantial, and will absorb most of our capital and labor over the next half-cenutry -- or more. We, as a world, are facing a number of nasty choices. There will be real dread, pain, and the frustration of the hopes of billions. None of us are likely to get our way, whatever we think "our way" is. The best we can hope for is to ride out the storm with as few deaths and as little damage as possible. That may include or exclude nuclear power. But unfortunately, for the "perplexed" (to use Maimonides' term), advocacy organizations are not helpful in figuring out what to do.

And I also know that most of us "pro-nuclear" DUers came to that position after long, sometimes agonizing, consideration. I can't speak for everyone, but my experience is probably common: I was anti-nuke for years, but as we wasted time and opportunities, the problem became increasingly imminent -- and threatening. In 1978, a purely non-nuke future was possible; in 2006, I do not think we will survive without a major effort that includes nuclear power generation. And it is not a pleasant conclusion for me by any means.

Of course, I could be wrong. But I've gone over this time and time again and come to the same conclusion -- nuclear might save us, but if we reject it entirely, we're doomed. No cogent plan for any renewable has yet emerged. With any mix of technologies, the transition will be extremely difficult. But give me a solid plan for the development of a 500 EJ/year energy infrastructure that uses renewables, and that can be built and come on-line by 2025, and sign me up.

Whether we have a mini-nuke on every block or a windplant on every building, it IS essential we have enough energy to prevent global catastrophe from taking place. And whatever solution(s) we opt for, we should demand popular control of all forms of energy under any regime. But rejecting any energy solution out-of-hand is a luxury we declined when we decided back in the early 1980s that there really was no problem after all. This loss of choice is merely the first price we will have to pay.

--p!