[ RadSafe ] Pebble Bed Modular Reactor accident

[Maury Siskel]

Please accept my apology for the paucity of source information here. The 
accident description below fits my recall (becoming increasingly flawed) 
Part of this seems to come from NIRS which I think is an anti-nuc zealot 
group. ?? Anyway for what it is worth I got this by exercizing search 
engines. Also think Jaro had posted some excellent info some time ago 
about PBMRs
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x48109
Best,
Maury&Dog
================================
Democratic Underground

Original message
Pebble Bed Modular Reactors - German reactor closed down after accident

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.
~~
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.
~~
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 [isn't NIRS an anti-nuc 
group? --maury&dog]

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.

~~

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.
~~
~~
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.


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Replies to this thread
Hey, I like this technology Tommy_J Mar-30-06 05:52 PM #1
I like this technology too jpak Mar-31-06 12:12 PM #5
The Reactor was Shut Down in 1988 !?! GDAEx2 Mar-30-06 06:09 PM #2
Good question Tommy_J Mar-30-06 06:56 PM #3
Don't you have any info other than from anti-nuclear advocates? 
Pigwidgeon Mar-31-06 04:50 AM #4

Tommy_J Donating Member (382 posts) Click to send private message to 
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Mar-30-06 05:52 PM
Response to Original message
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.


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jpak Donating Member (1000+ posts) Click to send private message to this 
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Mar-31-06 12:12 PM
Response to Reply #1
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...

:)
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GDAEx2 (137 posts) Click to send private message to this author Click to 
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Click to add this author to your Ignore list Thu Mar-30-06 06:09 PM
Response to Original message
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.
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Tommy_J Donating Member (382 posts) Click to send private message to 
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Mar-30-06 06:56 PM
Response to Reply #2
3. Good question



All I've heard lately is that China is investing heavily in the 
technology but have no other details.
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Pigwidgeon (1000+ posts) Journal Click to send private message to this 
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Mar-31-06 04:50 AM
Response to Original message
4. Don't you have any info other than from anti-nuclear advocates? 
Updated at 7:31 PM

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.




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