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Nuclear Cracks Tied to Lack of Coating

Thursday, March 1, 2012

More items for Quality Control

A decision decades ago to forego an exterior weatherproof coating on an Ohio nuclear containment building left it vulnerable to weathering that eventually caused the 2.5-foot-thick reinforced concrete structure to crack, a new analysis concludes.

Plant photos: ohiocitizen.org

A Nuclear Regulatory Commission inspector examines cracks at the Davis-Besse Nuclear Power Station Shield Building.

The Davis-Besse Nuclear Power Station Shield Building “was the only above-grade nuclear safety-related structure on site designed by Bechtel during original construction that was not sprayed with a white cement Thoroseal finish for sealing of exterior concrete surfaces,” FirstEnergy Nuclear Operating Co. reports in a Root Cause Analysis Report submitted this week to the Nuclear Regulatory Commission.

Cracking Described

The 119-page report follows FirstEnergy’s investigation into laminar cracking in the containment building in Northwest Ohio. The operator discovered the cracking Oct. 10, during hydrodemolition work being conducted to replace a reactor head.

FirstEnergy’s investigation revealed that most of the cracking occurred “in the concrete at the outer face of structural reinforcing steel located behind the architectural flute shoulder region,” the report said.

The cracks were discovered when a temporary access opening was cut into the structure to replace a reactor head in October.

Cracks were evident “across the top 20 feet of the shield building and in localized areas adjacent to one side of each main steam line penetration blockout,” the report said. The wall with a southwestern exposure showed the most cracking.

The shield building surrounds a 1.5-foot-thick steel containment vessel that encloses the reactor. The containment vessel and the shield are 4.5 feet apart.

Company Challenged

FirstEnergy contends that the building’s structural integrity remains intact. The NRC found no immediate safety concern and allowed the facility to return to service, pending FirstEnergy’s root cause review.

However, U.S. Rep. Dennis Kucinich (D-OH) has challenged the company’s description of the damage as “hairline” cracks in “decorative” concrete. In November, Kucinich asked the NRC to hold a public hearing on the matter. He said the cracks “appeared to follow the line of the rebar, are clearly visible, and run for 30 feet,” according to The Toledo Blade.

A FirstEnergy spokeswoman told the newspaper that there was no corrosion in the rebar.

Design Blamed

FirstEnergy’s analysis determined that the “failure modes” for the cracking were “primarily design-related from about 40 years ago, under a quality assurance program outside the control of FirstEnergy.”

Therefore, the report adds, “the extent of [the] cause was not reviewed in other programs/processes, equipment/systems, organizations, environments, and individuals.”

U.S. Rep. Dennis Kucinich (D-OH) accused FirstEnergy of concealing the extent of the damage.

The company said that the cracking apparently began with the blizzard of January 1978. The lack of a waterproof exterior coating allowed moisture from the blizzard “to migrate into the concrete, freeze and expand, causing tight, subsurface cracks in portions of the building,” FirstEnergy reported.

The cracking followed “the blizzard's combination of extreme weather conditions, which included three days of driving rain preceding a drastic temperature drop to around 0 degrees Fahrenheit and intense winds throughout the storm,” the company said.

The report notes an NRC document on the durability of reinforced concrete structures that identifies water as “the single most important factor controlling the degradation process of concrete apart from mechanical deterioration.”

However, “structural concrete and causal analysis experts” have determined that the building’s concrete “is sound and in good condition.”

Corrective Measures

FirstEnergy’s report outlines several corrective measures. The company says it will:

• Design and apply an exterior sealant system to the building;

• Perform additional inspections, to verify that the cracks have not spread; and

• Update inspection procedures to include the building’s new waterproof coating.

NRC Review

The NRC said it was initiating a “rigorous review” of FirstEnergy’s report and proposals, which are available through the agency’s ADAMS database, and would release its conclusions at a public meeting.

The NRC said four of its inspectors had been monitoring FirstEnergy’s investigation.

FirstEnergy Nuclear Operating Co. is a subsidiary of FirstEnergy Corp., which also operates the Beaver Valley Power Station in Shippingport, PA, and the Perry (OH) Nuclear Power Plant.

Comment from Ray Sams, (3/2/2012, 5:57 AM)

After over thirty years in the coatings industry it still amazes me that civil engineers do not believe concrete needs coating especially in exposed environments with reinforcing steel at risk from water ingress.

Comment from William Feliciano, (3/2/2012, 9:32 AM)

Can a storm crack a 2.5 foot thick reinforced concrete wall? If the cracks are parallel to the rebar, but the rebar "are not corroded", then what gives here? I would have thought that lack of coating would have caused a gradual freeze/thaw decay of the outer facing. Many home foundations are of poured concrete, are much thinner than 2.5 feet, and storms don't crack those. I sense there is more to this than meets the eye, e.g. good concrete construction practices.

Comment from peter gibson, (3/2/2012, 11:14 AM)

William ,you are obviously a concrete guy;not a coatings person. This is not a concrete issue, but concrete corrosion protection. Exposed concrete 150 ft tall.Not at ground level. Big difference !

Comment from William Feliciano, (3/2/2012, 1:59 PM)

Actually Peter, I am a coatings guy. I just put on my engineer hat and tried to understand the mechanism of failure. We own bridges with thick concrete abutments at 150 feet or higher, with rebar in them, and don't see this kind of failure that is traceable to one weather event. Just trying to understand the mechanism of failure, that's all.

Comment from Jim Haig, (3/5/2012, 2:47 PM)

It seems to me that there is too much data missing - perhaps it is simply that it hasn't been transmitted in the article - but one would expect core results with depth of carbonation at, away from, and along the crack; depth of the cracks; rebar cover; pH at the rebar; status of the cracks - live of stopped?; deformation of teh overall structure; etc. The nature of teh cracking smacks of structural movement to me - the concrete in tension will crack at its thinnest point - opposite the rebar. Why the tension? Inadequate reinforcement in the opposite direction to the cracks? It seems on the basis of teh article to be a case of "coat over and hope it will go away". My money, in the absence of better information, would say it won't.