Tuesday, June 19, 2012

Faulty Steam Generators at San Onofre Nuke Plant in CA Caused by Mitsubishi Heavy Industries' Faulty Computer Modeling, Says NRC


The information was disclosed in a public hearing.

Mitsubishi Heavy Industry's computer modeling underpredicted the velocity of steam and water by a factor of 3 to 4.

According to the NRC who conducted the pressure test, it was "the first time in the history of the nuclear industry that more than one tube at a plant has failed". 8 tubes failed in the Unit 3's steam generators.

From LA Times (6/18/2012; emphasis is mine):

San Onofre's issues appear to be result of faulty computer modeling

The unusual equipment issues that have shut down the San Onofre nuclear power plant appear to be the result of faulty computer modeling by manufacturer Mitsubishi Heavy Industries, officials from the U.S. Nuclear Regulatory said Monday.

The agency used a public hearing in San Clemente to present the preliminary results of its inspection of the plant, which has been out of commission for more than four months after a steam generator tube sprang a leak, releasing a small amount of radioactivity. That led to the discovery that tubes were vibrating excessively and rubbing against each other, leading them to wear out more quickly than normal for equipment that had been operating for less than two years.

The NRC ordered plant operator Southern California Edison to keep the plant shut down until operators fully understand the wear and how to fix it.

Eight tubes in the plant's Unit 3 failed pressure testing, which NRC officials said Monday was the first time in the history of the nuclear industry that more than one tube at a plant has failed.

"This is a significant, serious safety issue," said NRC Regional Administrator Elmo Collins. "This is a very difficult technical issue, and to be honest, it's not one we've seen before."

NRC officials said it appears that simulations by Mitsubishi underpredicted the velocity of steam and water flowing among the tubes by a factor of three to four. The rate of flow caused the tubes to vibrate and knock against each other.

There were also issues with support structures intended to prevent vibration in Unit 3, but apparently not in Unit 2, officials said.

Mitsubishi did not have any representatives at the meeting and couldn't immediately be reached for comment. Collins said, however, that even though Mitsubishi did the computer modeling, the ultimate responsibility lies with Edison.

NRC and Edison officials did not give a timeline for restarting the plant, saying there are still unanswered questions and more inspections that need to be done.


19 comments:

Anonymous said...

Deeper and deeper the rabbit-hole goes. Mitsubishi Heavy was a contractor on the Fukushima build and they are now involved with the cleanup, no?

Beppe said...

Mtsubishi (the manifacturer) is not liable, only Edison (the operator); furthermore in the US the liability of the utility is capped (50 mil USD was it?).
How about we also waive liability for car manifacturers and cap the drivers liability to 5000 USD?

Quail said...

From what I remember, Mitsubishi warned that there may be something wrong with it before it was installed. Edison tested it and said it was good to go.
Why ship something knowing it may be faulty? Why install something after being warned? All to make money off of something the citizens are going to have to pay to clean up in the end.

Anonymous said...

"the first time in the RELATIVELY SHORT history of the nuclear industry that more than one tube at a plant has failed"
*fixed

They make it sound like nuclear industry tech has been around a long time. It hasn't even been a century yet, and this is just one fault. How many more possible fault/miscalculations AKA ticking time bombs are waiting to go off?

Nobody will know until it's too late...

Anonymous said...

Failure of the alloy 600 and 690 steam tubes has been know for a long time and has only gotten worse as the plants age.

http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/steam-gen.html

The NRC's Advisory Committee on Reactor Safeguards (ACRS) issued a report in February 2001.[2] The ACRS substantiated many of Dr. Hopenfeld's concerns. For example, the ACRS concluded:

"The techniques [used to look for cracked steam generator tubes] are not nearly so reliable for determining the depth of a crack, and in particular, whether a crack penetrates through 40% of the tube wall thickness." [NRC's regulations do not allow a nuclear plant to start up with any steam generator tube cracked more than 40 percent of its wall thickness, but the methods used to inspect the tubes for cracks cannot reliably determine the depth of cracks.]

"The NRC staff acknowledged that there would be some possibility that cracks of objectionable depth might be overlooked and left in the steam generator for an additional operating cycle." [Exactly what actually happened at Indian Point 2 to cause last year's accident.]

"Both the [NRC] staff and the author of the DPO [Dr. Hopenfeld] agree that the alternative repair criteria [used by the NRC staff to allow nuclear plants to continue operating with steam generator tubes known to be cracked] increase the probability of larger primary-to-secondary flows during the MSLB [main steam line break] and SGTR [steam generator tube rupture] accidents."

"The [ACRS] also finds that this contention of the DPO [namely, that an accident at a nuclear plant with cracked steam generator tubes could cause those tubes to completely break] has merit and deserves investigation."

"This seems to be a plausible contention [that an accident at a nuclear plant with cracked steam generator tubes could widen the cracks and result in larger leakage], and the staff has not produced analyses or test results to refute it."

"The [ACRS] concluded that the issue of the possible evolution of severe accident to involve gross failure of steam generator tubes and bypass of the containment is not yet resolved … [and] that the issue needs consideration regardless of the criteria adopted for the repair and replacement of steam generator tubes."

http://epw.senate.gov/107th/loc_0508.htm

Anonymous said...

June 19,2012 7:05 am continued

"Data available to the [ACRS] suggest that the constant probability of detection [of cracked steam generator tubes] adopted by the NRC staff is nonconservative for flaws producing voltage signals less than about 0.7 volts." [In other words, the NRC staff assumes that methods used to find cracked tubes are much better than the data shows them to be.]

"The [ACRS] was unable to identify defensible technical bases for the [NRC] staff decisions to not consider the correlation of the iodine spiking factor with initial iodine concentration [when evaluating the potential offsite radiation dose consequences from accidents involving cracked steam generator tubes]."

"The [ACRS] found that the [NRC] staff did not have a technically defensible understanding of these processes to assess adequately the potential for procession of damage to steam generator tubes." [In other words, the NRC staff has no sound basis for arguing that one broken tube will not cascade and cause the failures of other tubes.]

"The [NRC] staff has not developed persuasive arguments to show that steam generator tubes will remain intact under conditions of risk-important accidents in which the reactor coolant system remains pressurized. The current analyses dealing with loop seals in the coolant system are not yet adequate risk assessments."

"In developing assessments of risk concerning these design basis accidents, the [NRC] staff must consider the probabilities of multiple tube ruptures until adequate technical arguments have been developed to show damage progression is improbable." [In other words, the risk studies to date, which only consider failure of a single tube, may understate the true risk and therefore should not be relied upon.]

The concerns raised by Dr. Hopenfeld are extremely important safety issues. As the ACRS stated:

"Steam generators constitute more than 50% of the surface area of the primary pressure boundary in a pressurized water reactor."

"Unlike other parts of the reactor pressure boundary, the barrier to fission product release provided by the steam generator tubes is not reinforced by the reactor containment as an additional barrier."

"Leakage of primary coolant through openings in the steam generator tubes could deplete the inventory of water available for the long-term cooling of the core in the event of an accident."

In the decade since Dr. Hopenfeld first raised his safety concerns, the NRC has allowed many nuclear plants to continue operating nuclear power plants with literally thousands of steam generator tubes known to be cracked. The ACRS concluded that the NRC staff made these regulatory decisions using incomplete and inaccurate information. After receiving the ACRS's report, the NRC staff considered Hopenfeld's concerns "resolved" even though it had taken no action to address the numerous recommendations in the ACRS report.

http://epw.senate.gov/107th/loc_0508.htm

CaptD said...

Computer modeling...

Yet another NEW excuse, that tries to deflect the fickle finger away from SCE, who tried to get away with "souping up" it's reactors...

Anonymous said...

All these plants are getting old, we should expect to see more failure and cascading failure as we see age related cracking trip off cascade failure.

Anonymous said...

It WAS NOT 8 tubes total out of all the tubes in the steam generator, NRC only TESTED 129 and 8 failed.

Anonymous said...

This failure was not age related in any way. It was new equipment that was poorly designed and improperly accepted into operation.

Anonymous said...

The Japanese to blame again, they cant be trusted with Nuclear, idiots,..

check this out, sums it up really.

http://www.japantimes.co.jp/text/fl20120612hn.html#.T-CecRce6o1

...

Beppe said...

Not only " the equipment was poorly designed and improperly put into operation": Edison replaced the steam generator saying that they were replacing the old one with a similar one but NRC found out that this was not the case. Why did Edison reported a simpler change than what they were actually performing?

Anonymous said...

Wasn't the Oi NPP rated good for restart based on the results of a computer model?

Beppe said...

@anon 4:53 kind of yes but ... the algorithms and the input data were determined by the utility and they are not public nor they have undergone independent third party review. This means that more than the simulations, Oi is being restarted on the good faith of its owner.
The good faith of that owner has promptly been confirmed today as it apologized for not reporting an accident until a day and a half after its occourrence (the level of the water in the tank of an electricity generator decreased until it set off an alarm).

Atomfritz said...

Thanks Ex-SKF and commenters for your insights.

This thing really smells foul.
Is there any data about the actual design differences between Onofre 2 and 3 reactor's steam generators?

Has the faulty SG been of a new, cheaper, but neither peer-reviewed nor certified design?
Any price data available that could point to substantially different designs?

Anyway, it is very very rare that a nuclear operator company doesn't press for permitting restart.
This could indicate that the operators themselves are actually too scared to put the NPP in its current shape into operation again.

arevamirpal::laprimavera said...

@Atomfritz,

What I know is the Mitsubishi SG at San Onofre has about 10,000 tubes each, whereas Mitsubishi SGs sold in Japan and in Europe usually has about 5,000 tubes. Custom-made for San Onofre, I'm guessing.

Anonymous said...

Thank you again for all your hard work on this blog.

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