Friday, March 9, 2012

Core Shroud of Mühleberg Nuclear Power Plant Was Found with a Huge Crack in 2009, Operator and Swiss Government Hid the Fact, Says Japan's Mainichi

(UPDATE) According to Switzerland's Beobachter (in German), the cracks are along the horizontal weld of the shroud, not "top to bottom" as Mainichi describes. The core spray system was also found with cracks. (H/T Atomfritz)


More on Mühleberg Nuclear Power Plant in Switzerland, whose license to operate will be withdrawn in June 2013 by the court order (see my previous post).

Japan's Mainichi Shinbun (3/8/2012; link goes to a message board with full copy of the article) reports that the plant operator BKW Energy and the nuclear regulating agency of the Swiss government hid the discovery in 2009 of a huge crack in the core shroud inside the Reactor Pressure Vessel.

From Mainichi Shinbun article (part):


However, the local media reported in June last year in the wake of the Fukushima I Nuclear Power Plant accident that the 9-meter high stainless-steel core shroud inside the Reactor Pressure Vessel at Mühleberg Nuclear Power Plant [there is only one reactor] had a crack from top to bottom. The federal nuclear safety regulation agency denied the risk, saying "Even if there is a crack, [the shroud] meets the safety standard, and there is no problem."


Anti-nuclear groups criticized the comment, saying "The core shroud is an very important structure that surrounds nuclear fuel rods and control rods. The damage may cause the fuel rods to shift." The crack had been discovered in 2009 but it was not disclosed. The anti-nuclear group(s?) filed a suit in the Federal Administrative Court demanding the withdrawal of the operation license issued by the federal government in 2009. With the ruling [on March 7], the Federal Administrative Court upheld the complaint from the group.

The crack in the core shroud was found in 2009, in the same year that the government granted the operator an open-ended (indefinite) operation license. I wonder which came first.

Mainichi also reports that BKW Energy plans to appeal to the Swiss supreme court.


Atomfritz said...

The operator BKW refused to publish the 2009 safety report, the authority accepted this.

The calming message of the utility was that the core shroud is still "72 percent intact".

The growth of the Muehleberg core shroud cracks was known since 1990.
The cracks of the core spray system are known since 2007.
See this Beobachter 03/2009 article (where you also can download the secret reports):

You can also see the Swiss nuclear authority page here: (nice illustration and charts)

By the way, the above ENSI report explicitly mentions that, such common core shroud cracks are no regulatory issue in the USA, as there the NRC accepts brackets as a fix. ;-)

Atomfritz said...

@ Crackett Brackett

"most important question is of course what caused the crack to begin with?"

Causes of shroud cracking are:
-suboptimal welding
-neutron embrittlement
-high thermal stress (hot inside, cold outside)
-high acoustic stress (=mechanical stress through shockwawes of boiling water bubbles popping)

In BWRs core shroud cracking is just normal and increases over time.
Usually plants worn down so much that the core shroud is in danger to fall apart get decommissioned in most countries.
Japan is one exception. Core shroud replacement was in progress at Fuku I-4 when tsunami stroke.

Anonymous said...

"The federal nuclear safety regulation agency denied the risk, saying 'Even if there is a crack, [the shroud] meets the safety standard, and there is no problem.'

??? How do they figure that? Does it get checked constantly? How do they know when a crack changes from "no problem" to "a serious problem"?

While there is no room in my average Joe brain for understanding reactor design and function in detail, common sense seems to suggest that a crack in whatever that contains highly dangerous material and/or potentially water can simply not be good news.

Looked around to understand this better and came across this interesting site (among others) and thought I'd share:

Apparently, a crack IS bad news, and it can only get worse, as Atomfritz has already pointed out. Shame on the plant operator and, even more so, the regulatory commission. Kudos to the people who succeeded in getting the courts involved.

arevamirpal::laprimavera said...

@Atomfritz, is "Kernsprühleitung" core spray system? That's cracked, too?

The paper seems to say the crack is along the horizontal weld, not vertical as Mainichi article states. Can you confirm?

Anonymous said...

@laprimavera: don't know nuclear reactors, but Kern means core, Sprueh means spray, and Leitung means pipe - so I'm guessing yes.

Atomfritz said...

When reading through the archive news, I also found that Muehleberg has a rich history of accidents and near-catastrophes and frequently released radioactivity, contaminating its surroundings with Cesium, Cobalt and so on.

Just a small selection of incidents:
-Frequent substantial radioactivity releases into the environment due to damaged fuel cladding.
-While test operation of the NPP in 1971, a cable channel blaze originating from the turbine building was close to penetrate into the reactor building, producing a scenario close to that of Browns Ferry in 1973.
-Core feedwater system exchanged in 1974 due to parts broken and others cracked.
-In 1999 river water floods part of the reactor building basements. Plant area gets flooded again in 2005 and 2007.
-Multiple cracks in core spray system discovered in summer 2006, being reported in 2007.
-In 2007 a metal part of the fuel handling machine falls off, disappears in the reactor. Operator states that the lost part won't cause any problems.
-Also in 2007: maximum crack penetration of the core shroud reached 90%.
-2009 even a crack in the reactor pressure vessel was discovered.

Sources (including Muehleberg area contamination maps):

Atomfritz said...

Had to split the last post into two parts because of size. First one got apparently stuck in the spam filter.

Another note to people reading the Muehleberg report:
instead of "keine Anzeigen" (nothing found) there is often mentioned "keine registrierpflichtigen Anzeigen" (nothing which law demands us to report).
This actually can (and should) be interpreted as "the cracks found here are small enough so that we aren't required to report them to the authority".

Remember, the RPV lids in both reactors of another Swiss NPP, Beznau, get replaced "preventively", even there were "no cracks large enough to be obliged to report".
Why should the operator waste 100 million Franken if the cracks found are actually harmless?

Anyway in response to anon 4:39:
How do they figure that? Does it get checked constantly? How do they know when a crack changes from "no problem" to "a serious problem"?

At each revision (every 12-18 months) various measurements are done, by ultrasonic and/or dye checks.
Cracking to a particular threshold is tolerated, as long they don't become penetrating cracks.
But only a part of the vessel and the tubing can be checked with conventional methods because they are inaccessible.

As far as I understand from the ENSI statement in the USA non-penetrating cracks of any size are tolerated as long the core shroud gets secured by brackets. However, as these brackets probably cannot guard well against lateral forces, the Swiss nuclear authority didn't accept the brackets installed at Muehleberg 1995 as a remedial.

Japan has pioneered the technology of core shroud replacements.

Here is a 1999 document by Tepco describing its experience with core shroud replacements at Fukushima Daiichi:

I find particularly interesting how they describe the discovery of numerous tubing cracks at the reactor pressure vessel that could _only_ be found after removing the old, thoroughly cracked core shroud.

This again reminds how incomplete the inspections are. Only those parts that are easily accessible are being checked.
The rest just gets ignored and is supposed to be OK.

arevamirpal::laprimavera said...

@Atomfritz, thanks for info. Sorry about the SPAM filter. It filtered you out, even filtered me out, while letting in the spammers and trolls.

Checking the Japanese nuclear energy database, I found that after the discovery of a crack in this Swiss plant in 1990, Japanese electric power companies, two manufacturers (I suspect Hitachi and Toshiba) and GE started the joint development of technologies necessary to replace core shroud. The joint effort was complete by 1995, and the first shroud replacement was done on Fukushima Reactor 3 in 1997.

Looking at the before and after shroud schematics, it is possible that Muehleberg shroud had both vertical and horizontal welds.
(left side is "new", right side is "old")

Anonymous said...

I think it is possible to have a vertical crack on a horizontal weld.

Anonymous said...

Or horizontal crack on vertical weld

Atomfritz said...

I see now that some mishap happened when splitting/copying/pasting posts.

The first part of text got lost, I copy it here from the editor (hope it doesn't get filtered again...)
Here it is:

@ LaPrimavera 4:48

Yes, you understood correctly, as anon 7:28 already said.

Re-reading the German-language articles and the study, I can only confirm that there is no mention of any _contiguous_ vertical crack that Mainichi has reported of.
However, it cannot be excluded with certainty that Mainichi was right.

There are horizontal _and_ vertical cracks in the core shroud, as the ENSI page shows clearly.
However, the older measurements (up to 2007) indicated they were not _contiguous_ yet. When a crack becomes contiguous the danger of breaking apart is imminent.

Regarding the confidential report released by the "Beobachter" in 2009, I looked more carefully again.
It is the 2007 and not the 2009 report.

These cracks were known for long and get measured at each revision.
However, we actually cannot exclude the possibility that Mainichi was right with stating that the 2009 report talks of a continuous up-down crack at Muehleberg.

It is very well possible that in the international information exchange of the nuclear industries all over the world Japanese nuclear insiders were confidentially told of findings that are still kept secret by the Swiss authorities.

So such information about vertical cracks could have got leaked to Mainichi because some Japanese informant of Mainichi carelessly "talked a bit too much" about non-Japanese nuclear affairs.
This wouldn't be the first time a scandal gets public due to such kind of information leak.

So potentially the reason for shutting down Muehleberg by the strictly pro-nuclear Swiss regulatory agency was actually the development towards a contiguous crack.

One has to keep in mind that the published measurement results of cracks strangely varied from revision to revision.
After the 2010 revision Muehleberg operator BKW even stated there were no shroud cracks at all, after they modified their measuerement method and claimed that all previous measurements were flawed.
This sounds so familiar when looking at Tepco's falsifications' history.

Remember, after some environmental groups sued, Swiss courts have ruled that secret studies done by the industry-owned German TUeV (Technischer Ueberwachungsverein, about "technical supervision association" in english) which detail the crack growth in Muehleberg must not be released to the public.
And the substantial information in the reports that get released to the public are partly being blackened out, like the Tepco emergency manual.

Atomfritz said...

@ LaPrimavera 10:52

"Looking at the before and after shroud schematics, it is possible that Muehleberg shroud had both vertical and horizontal welds."

Yes, all the core shrouds have vertical welds too.
Their relative positions are well recognizable on this ENSI drawing:

The vertical welds are not contiguous, but offset by either 90 or 180 degrees, so that cracks cannot so easily propagate vertically.
This is also visible in this detailed image of crack locations:

By the way, the picture you linked to is really interesting.
It indicates that the new core shrouds are quite different than the original GE ones.
More water in the outside, less water in the inner (core) side.
I guess this modification possibly could rather speed up meltdowns instead of slowing them.

Anonymous said...

Thanks to Atomfritz (and, of course, laprimavera) for all the interesting and helpful information.

It's actually pretty damn sad that it takes a court order to ensure NPP safety. Bad enough that the operator doesn't seem to care about it, though - while not excusable - relatively understandable given the financial interest. It is beyond comprehensible, however, that the federal regulators don't do their job in that respect close or no close ties to the nuclear industry.

And then there is still surprise or even contempt by some that people are concerned about or downright afraid of nuclear power?

Anonymous said...

@Atomfritz: Thanks for clarifying how and when the shrouds can be checked and pointing out the limitations.

I guess, my thinking was, what if some cracks turns into a problem ... let's say in month 8, i.e., before a refueling cycle finishes and checks, however limited to begin with, can be performed?

Atomfritz said...

FYI: Old core shroud of Reactor 4 was already removed when tsunami stroke.

Current shroud configuration: see last page of

Unknown said...

Any truth is better than indefinite doubt. See the link below for more info.


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