NRC – Keep language professional, avoid extreme opinion, careless hyperbole

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From: Thorp, John
Sent: Friday, April , 2011 2:36 PM
To: Thompson, John; King, Mark; Thomas, Eric; Garmon, David
Cc: Sigmon, Rebecca; NRRDIRS_IOEB Distribution
Subject: RE: More on hardened vents, etc. – as discussed in this week’s Inside NRC – FYI
Importance: High

I deeply appreciate the passion and desire for action you all have as nuclear professionals on operating experience topics and issues including the significant events unfolding in Japan. What is happening in Japan is of great concern to us, our agency and our fellow citizens.


I caution everyone to consider the potential for mis-interpretation of any comments you make in e-mail that are not based in fact, and, with respect to any e-mail you write, including e-mail regarding this significant event, I urge you to keep the language professional and objective, and avoid the use of extreme opinion, speculation or careless hyperbole. Some informal words and phrases such as “mis-information” and “half-truths” in reference to other organizations, licensees, etc., may be seen later by various audiences as inflammatory and may lead to lots of mis-understanding and unnecessary staff effort to respond to concerns that arise from such words.


Please meet with me if my message to you is not clear, and we can discuss.


-O-r-ig-in-a l Message —–
From: Thompson, John
Sent: Friday, April 01, 2011 10:35 AM
To: King, Mark; Thorp, John; Thomas, Eric; Garmon, David
Cc: Sigmon, Rebecca
Subject: RE: More on hardened vents, etc. – as discussed in this week’s Inside NRC – FYI


Very interesting story. I am sure there will be more to this that plays out in the public down the road.

I read the statement from the news report given by GEH, and remain skeptical (that is my nature) regarding its accuracy.

A Direct Torus Vent System (DTVS) was the focus of GL 89-16. I am not sure what the TEPCO official (who didn’t want to be identified) was refering to by stating that the Fukushima units used a “direct release line” to the atmosphere.

What is even more intriguing is the statement by the GEH that Fukushima I plants all had hardened vents.

If this was true, why didn’t this information come out earlier from GE?

The GE website doesn’t discuss this important fact (

Or better yet, given that GEH has been part of the NRC RST information exchange, and they were in consultation with NRC during our effort to compile the RST data on the status of the Fukushima units, why was this information withheld from NRC regarding the status on hardened vents?

Something seems amiss here.

Regardless, a DTVS is more than just a hardened vent line to the plant stack. It bypasses the SBGT system and is designed to withstand accident pressures and remain intact. The GL’s description of an acceptable DTVS design also contains isolation valves that are outfitted to use DC control power.

So, just installing hard pipe doesn’t necessarily meet the intent of the GL.

Given the “mis-information” and half truths coming out of Japan, we don’t really know what system was used by the Japanese when they vented containment.

It may have been a different system than what was the focus of the GL. Also, given that TEPCO waited so long to vent, with pressures building in excess of 100 psig in primary containment, maybe having and using a DTVS would not have prevented the explosion anyway. I just don’t know.

But, given that a DTVS bypasses secondary containment, and the fact that secondary containment was apparantly full of hydrogen, something doesn’t add up, as Mr. Marion asserts.

Given that the inerted atmosphere was lost, and our knowledge of gaseous parameters inside the reactor building and wetwell/drywell prior to the explosion was ifffy, we may have a hard time figuring out what caused the detonation.



It may be the seismic event damaged the vent piping and cause the leak directly into secondary containment, or some other crack allowed hydrogen to escape into secondary containment. But, if they did have a DTVS installed, and it remained intact, use of it should not have set off the explosions within the reactor building.



So, for the time being, this remains a mystery.


From: King, Mark
Sent: Friday, April ,2011 9:06 AM
To: Thorp, John; Thomas, Eric; Thompson, John; Garmon, David
Subject: More on hardened vents, etc. – as discussed in this week’s Inside NRC – FYI

FYI…. Industry highlights safety upgrades at US Mark I BWRs story starting on page 1 110328. pdf
more on … Hardened Vent

NRC staff undertook a study in the 1980s “to determine if any actions should be taken … to reduce the vulnerability of BWR Mark I containments to severe accident challenges,” according to an NRC generic letter, GL 1989-16, issued to Mark I licensees in 1989.

“The staff identified a number of plant modifications that substantially enhance the plants’ capability to both prevent and mitigate the consequences of severe accidents,” the letter said.

The commission, the NRC staff said in the letter, concluded that each licensee should evaluate most of the staff’s recommended safety improvements based on plant specific information. But with regard to “the hardened wetwell vent capability,” the letter said the commission directed the staff to “initiate plant-specific backfit analyses for each of the Mark I plants … Where the backfit analysis supports imposition of that requirement, the staff is directed to issue orders for modifications to install a reliable hardened vent.”

The original Mark I design came with a so-called standby gas treatment system, or SGTS, to channel steam from the torus, also known as the wetwell, to the atmosphere if pressure in the containment becomes too high.

The SGTS uses duct work to channel steam, which is susceptible to leakage because the duct work is neither airtight nor designed to withstand significant pressures, to channel steam, said Helwig. The NRC said in GL 1989-16 that agency staff “believes that the available information provides strong incentive for installation of a hardened vent,” which uses hard pipes to channel steam from the torus.

Bill Borchardt, NRC executive director for operations, said at a March 21 commission briefing that all US Mark I reactors had installed the hardened vents.

Alexander Marion, vice president of nuclear operations for NEI, said in an interview March 22 that the hardened vent – “an explosion-proof pipe or high-pressure” system – is a “key area of improvement.”

Marion said it was not clear if Japan’s Fukushima I units had installed hardened vents. “We’re assuming that they did not, because somehow they were releasing hydrogen into the secondary containment, but we just don’t know,” he said.

Hydrogen accumulation is suspected to be the cause of explosions at Fukushima I a few days after the accident began that tore open three secondary containment buildings.

An official from the Tokyo Electric Power Co., which operates Fukushima I, said the duct work SGTS was not used at Fukushima I for venting, “because the pressure of the containment vessel was high.” Instead, he said, the company used a different type of vent, called the direct release line, which can withstand high pressure, to blow off steam and reduce pressure inside the containments.

The direct vent line used after loss of cooling at the Fukushima I units to vent steam “is hardened pipe designed for severe accident case,” the Tepco official said. The official answered questions by email and requested anonymity as he is not authorized to speak to the press.

In an email response to questions, GEH spokesman Mike Tetuan said that “it is our understanding that Fukushima units 1-6 have hardened wet well vent arrangements.”

Hydrogen control

In 2003, NRC noted in a revision to regulations in 10 CFR 50.54 governing “combustible gas control for nuclear power reactors” that BWRs have smaller containment volumes, and in some cases lower design pressures, than do PWRs. As a result, said NRC, BWRs are more vulnerable to fire caused by combustible gas “during degraded core accidents because of the pressure loads could cause structural failure of the containment.”

“Also, because of the smaller volume of these containments,” the agency said, “detonable mixtures could be formed.”

As a result, NRC revised regulations to require all US BWRs with Mark I containments, or with the slightly modified Mark II containments, to inert the environment inside with nitrogen. “By maintaining an oxygendeficient atmosphere, combustible gas combustion that could threaten containment integrity is prevented,” said NRC.

Such a measure to fill the containment vessel with nitrogen to create an inert environment was also adopted for reactors at Fukushima I, the Tepco official said.

Unresolved issues

According to David Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, a test of a Mark I containment performed in the 1970s discovered a pathway for containment leakage under high pressure.

In a March 18 report, Lochbaum said workers at Brunswick-2, which has a Mark I containment, performed “a structural integrity test on the reactor” by pumping air into the containment vessel to raise the pressure inside beyond the designed maximum of 62 pounds per square inch to 71 psi.

But the pressure stayed constant at 70 psi, said Lochbaum. Workers subsequently discovered that the air had pushed up the metal containment head, which is bolted to the containment wall “with a rubber O-ring between the surfaces,” and seeped out into the refueling cavity above the primary containment, he said.



Lochbaum said the Brunswick test could explain “how a significant amount of hydrogen escaped from the primary containment into the reactor building” and caused explosions at Fukushima I after containment pressures exceeded designed limits.



Japan ‘s NISA reported that pressure in the containment of unit 1 at Fukushima I had exceeded 120 psi a day after the reactor had lost cooling.

The Tepco said the containment vessel pressure at unit 2 had surpassed 102 psi at some point after the accident began but did not say when that occurred.

Ryan Mosier, a spokesman for Progress Energy, which owns Brunswick, said in a March 22 email that the company “cannot find any documentation on our end that the test suggested by Mr. Lochbaum ever occurred at Brunswick.” In an email the next day, Mosier confirmed that the test did occur just before

Brunswick-2 went into service. Brunswick-2 began commercial operation in November 1975, according to NRC data.

The documentation Progress has on file about the test, however, “does not spell out in any detail the conclusions arrived at in the Lochbaum analysis,” Mosier said. Progress declined to release its information on the test.

Progress shared the test results with NRC but made no modifications to the containment “as a result of this test, as the containment performed as expected,” Mosier said.



“Hydrogen explosion is only one failure mode for the Mark I containments. There is also another failure mode, which is called containment liner melt-through, which is specific to Mark I’s,” Ed Lyman, senior nuclear scientist at the UCS, said during a March 20 press briefing.

“That’s because there’s an area of the containment shell that could come in contact with the molten core if it escapes the reactor vessel, and that’s also a significant [containment] failure mode,” Lyman said.


The melt-through risk was documented in an NRC study in 1990 on five containment designs, including Mark Is at Peach Bottom. The study concluded that the probability of a core melt was relatively low for a Mark Is, but the probability of containment breach is higher for Mark Is than for some other designs if a large core-melt were to occur.

In supplement 1 to GL 88-20, a generic letter sent to power reactor licensees regarding individual plant examinations for severe accident vulnerabilities, NRC staff recommended in August 1989 that plants install additional water supply for emergency cooling, enhance venting capabilities and improve emergency procedures and training.

According to NEI’s report, most Mark I units in this country have also made various other hardware changes to strengthen the containment and vent.

“The GE Mark I containment systems in US BWRs have undergone extensive testing and analysis and have been modified to meet NRC regulations. The Mark I pressure suppression containment is a proven technology that has been enhanced with confirmatory testing, enhanced knowledge and advanced analysis over time,” NEI said.

It is unclear what modifications Tepco has adopted for its Mark I reactors at Fukushima I. GEH’s Tetuan said in a March 24 email that information about the modifications made in the US “were communicated outside of the US,” but he did not say to whom they were sent.

“We understand that all of the BWR Mark I containment units at Fukushima Daiichi also addressed these issues and implemented modifications in accordance with Japanese regulatory requirements,” he said. Lyman said it is too early to draw conclusions about Mark I from the Fukushima I crisis, “but with regard the future of Mark I’s, we think that the safety assessment will have to be done, that all assumptions will have to be examined, and then the options will have to be laid out.

“One of those options could be shut-down,” he said.

-Yanmei Xie and Steven Dolley, Washington Inside NRC Copyright © 2011 The McGraw-Hill Companies

March 28, 2011 110328.pdf

See article: Industry highlights safety upgrades at US Mark I BWRs. Starts on Page 1

-a very interesting INSIDE NRC issue.

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