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Questions Shadow Nuclear Cracking

Monday, October 15, 2012

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The discovery of cracks last year in an uncoated nuclear shield structure raised questions among federal regulators that were not publicly disclosed at the time, according to newly released documents.

One Nuclear Regulatory Commission official questioned the structural integrity of the Shield Building at the Davis-Besse Nuclear Power Station near Toledo, OH, and questioned the NRC’s own staff conclusions on the damage, according to agency documents recently released under a Freedom of Information Act request.

‘Extensive Cracking’

The 2.5-foot-thick, 250-foot-tall, reinforced concrete shield building was the only above-grade structure at Davis-Besse that did not receive a white Thoroseal finish before the facility went online in 1970. The project’s builder, Bechtel, says no coating was required at the time.

 The Shield Building at the Davis-Besse Nuclear Power Station

 Photos: NRC

The Shield Building at the Davis-Besse Nuclear Power Station was the only building in the complex that received no protective exterior coating before the facility went online in 1970.

However, cracks in the shield structure were discovered last year during an unrelated major repair. Facility owner FirstEnergy Nuclear Operating Co. (FENOC) and the NRC have said that the blizzard of 1978 and moisture penetration over time caused the cracking in the uncoated structure.

FirstEnergy has called the cracks superficial and says a new coat of weatherproofing now being applied over the building’s 100,000 square feet of surface area will address all of the problems.

The anti-nuclear group Beyond Nuclear, which made the FOIA request, contends that the integrity of the Shield Building has been compromised.

‘Greatly Downplay the Issue’

NRC documents show that internal questions were raised about the damage in the wake of last year’s revelations.

In an email Nov. 4, 2011, Pete Hernandez, of NRC’s Office of Nuclear Reactor Regulation, submitted detailed questions to colleagues about a report on the cracking prepared by NRC’s Division of Operating Reactor Licensing.

Hernandez writes that the staff description “seems to greatly downplay the issue.”

Capturing the Problem

“This description makes me think that they are looking at a single crack going in a circle,” Hernandez writes.

“From what I understood, the crack is pervasive along the entire surface, spidering in all directions, similar to a pane of tempered glass breaking. The description in Attachment B addresses only the crack at the opening and assumes that the crack is right along the rebar line.

“The core bores have shown that the cracks are at different depths, so this doesn’t seem to capture the current situation. Throughout the calculation, the word Crack, singular, is used. They also mention that the extent of the crack is only 10’-12’. This seems to greatly downplay the issue.”

The staff report notes “(#1) Extensive cracking in the shoulder region, (#2) Cracking in the structural region outside the flute shoulder region near the main steam piping penetrations, (#3) Cracking indication via Impact Response (IR) mapping in the cylindrical portion of the building near the top of the building at the interface between the domed roof and the cylindrical wall.”

‘Ignoring All That Concrete’

Questioning a calculation used to quantify the problem, Hernandez writes: “At this point, core bores of only the shoulders have been taken. So the only crack widths we are aware of are those in the shoulders, which are not being addressed. How can an analysis be done on the structurally credited concrete if no data from that area, in the form of core bores, has been taken? Shouldn’t the structural integrity of the shoulders be calculated as well?”

 NRC photos taken in late 2011 show the laminar subsurface cracking (left) at the Shield Building and core bore samples from the building.
Nuclear Regulatory Commission photos taken in late 2011 show the laminar subsurface cracking (left) at the Shield Building and core bore samples from the Shield Building.

Regarding the methodology for a staff calculation that “focuses on the structural integrity of the reinforced concrete ... once it is restored,” Hernandez asks:  “This seems to say that they are just doing calculations for the new concrete that is and ignores the rest of the building altogether. Is that right?”

The staff report also notes that “the vertical reinforcement next to each flute (i.e., in a vertical strip approximately 10 ft wide) is conservatively ignored for evaluating the structural integrity of the SB [Shield Building] under mechanical loads.”

To which Hernandez replies: This says to me, that they are ignoring the shoulders, if they are ignoring all that concrete, it seems to be the opposite of conservative for evaluating the mechanical loads.”

‘Will the Building Stay Standing’

Hernandez also challenged a staff goal to determine the seismic stability of what FirstEnergy has called decorative concrete on the structure.

“I think the greater concern is will the SB stay standing and not whether or not the decorative concrete will fall off,” he wrote. “Because the licensee has not performed core bores to see if there is cracking in the credited concrete, do they have a basis to say that the structural concrete will maintain a Seismic II/I condition?”

He adds: “This use of singular terminology also discounts this calculation because it seems that they are looking at only 1 crack and 1 shoulder or 1 flute. Because cracks have been found through multiple core bores, shouldn’t the appropriate calculations account for the combined effects of cracks in all the shoulders and not just one by the opening and not just individually?”

‘Must Be Validated’

Finally, he questions the use of Impulse Response testing to support the staff’s conclusion that “the actual crack length is 10 to 12 feet long.”

“From what I understand, IR mapping is only an indicator, but must be validated by core bores,” writes Hernandez.

“Does basing all the calculations on a length of a 12 foot crack discount the calculations altogether, because we have indications of cracks at distances greater than 12 feet. This also seems to assume that there is only 1 crack and not many as the core bores seem to prove. Isn’t IR mapping only useful at a limited depth too, so that using it to evaluate a 48” thick piece of concrete is not realistic?”

Almost two weeks later, in another email, Hernandez notes that FirstEnergy's own concrete/rebar bonding technical consultant has informed the operator “that with the assumptions they are making, no credit for the rebar impacted by the cracks is warranted. In light of this, the licensee has started to do more mapping and core bores to better analyze the SB.”

The NRC did not reply Monday (Oct. 15) to a request for more information. An email to Hernandez was returned Monday as undeliverable.

Licensing Issues

The documents, released in response to a Freedom of Information Act request, include pages of NRC emails, inspection reports, the Commission’s requests for additional information from plant owner FirstEnergy, and engineering reports on the cracks found in the containment structure.

The cracks have become an issue in the operator’s application for a 20-year extension on the plant’s license, which is due to expire in 2017.

The NRC says its license renewal staff is “evaluating the implications of” the cracking issue and developing an inspection protocol to ensure that FirstEnergy corrects the problems.


Tagged categories: Certifications and standards; Concrete; Concrete defects; Cracks; Exterior coatings; Facility Managers; Nuclear Power Plants; Protective coatings

Comment from Glenn Summers, (10/16/2012, 7:57 AM)

Cracks that are visible to the naked eye on a surface such as this is the "Kiss of Death" for the structure. There should have been a Quality penetrating sealer applied to the concrete surfaces when they were poured. This will create a No/Low moisture concrete interior with a higher ohms resistance. Corrosion does not ocurr in an environment starved of oxygen and moisture. Absent this type protection the concrete will absorb moisture and contaminates and ASR may be one of many conditions that will happen with age. Use of some sort of coating is not the answer. Coatings that are "Breathable" will demonstrate a limited life cycle and will be subject to internal concrete chemistry collecting at the substrate/coating interface causing a delamination and peeling of the coating. A penetrating sealer will stop moisture transfer in or out of the matrix. Left as it is, these cracks will become larger as they now offer even a larger path for moisture and contaminates to enter and react with internal chemistry of the matrix. Selection of the Penetrating sealer is the most important factor in protecting a concrete. Do Not Consider a product that provides for a Re-Application at a later date or one that cautions not to allow the product to come in contact with glass or metal! They Don't work !!

Comment from John Fauth, (10/16/2012, 8:17 AM)

Glenn, I'm curious as to what penetrating chemistries you might recommend.

Comment from peter gibson, (10/16/2012, 11:12 AM)

Come on Glenn,tell us which sealer to use.You are the expert on this project. Glass,metal - why even mention that.Stating the obvious. In the 70's the coatings industry was very rudimentary ;they thought unprotected concrete could do it all.

Comment from Chuck Pease, (10/16/2012, 1:00 PM)


Comment from RICHARD SMITH, (10/16/2012, 3:17 PM)

The consern here is not surface cracking but structural cracking that was found in a tempory opening into the outer containment shell.[concrete]The pictures used in JCPL are part of a 46 page report issued by the NRC dated 6-21-12. The main consern of the NRC is if the Containment Shell is sound enough to withstand a Type II/I seismic event. If you look at the photo in the report of the core sample you can see a crack [Transverse fracture] located 4.5 inches into the core sample and another at 12 inches into the sample. This condition is somewhat more than a coatings repair issue.

Comment from Glenn Boos, (10/17/2012, 7:23 PM)

If it can be proved that the cracks are not structural cracks, the surface cracks should be treated with a High Penetrating, clear (not pigmented) 100% solids epoxy sealer. Afterwards, two coats of an elastomeric acrylic coating will prevent oxygen from penetrating the structure and will not copy the cracks even if they occure after the coating application.

Comment from Tom Schwerdt, (10/18/2012, 10:35 AM)

Glenn - if this were my structure, I would strongly consider starting with a nice silane/siloxane blend before using the epoxy sealer.

Comment from John Fauth, (10/19/2012, 8:39 AM)

Tom, wouldn't the silane/siloxane require periodic reapplication? The epoxy sealer would require removal to do so.

Comment from Glenn Summers, (10/19/2012, 1:25 PM)

My mention of the cautionary statements concerning "Re-Application and Glass or Metal contact " of some sealer products was done so to direct attention to these products basic chemistry and testing that has been done since the 70's as Peter mentions. Consider that the effects of Carbonation had not been thouroughly investigated until that same time period. The damning affect of carbonation is lowering of the pH to the depth of that carbonation! Cracks, be they from plastic shrinkage or movement afford a path for carbonation to reach even deeper into the matrix and possibly the depth of embedded steel. A steel member that maintains the passivating layer is protected from corrosion :At a Ph of 13.2, 8,000 ppm of chlorides are necessary for corrosion to commence but when the pH drops to 11.5 it now requires only 70 ppm!! A DRASTIC DIFFERENCE and if a crack, be it "surface or structural" is a contributing factor to lowering of the pH, the long term problems are just beginning. The product I use is a polymerized polyester polymer, the viscosity of water which penetrates into a crack and effectively waterproofs the crack interior as well as the surface. Cracks on vertical surfaces represent a challenge to reach the depth of the crack however gravity works wonders on a horizontal surface. StabelCrete, when applied to a new pour minimizes cracking as it stops evaporation. Application of this product ASAP does not allow carbonation of a surface and waterproofs the concrete with no change in surface profile. This will allow application of any coating to a treated surface as Glenn Boos recommends,with no fear of an internal chemistry migrating out to the surface to destroy a paint/coating bond. We consider the application of StableCrete and a coating as the "Belt & Suspenders' approach of total protection. Tom, the need for reapplication of a silane/siloxane usually presents adhesion issues and we find our approach more acceptable. When dealing with a large containment vessel we apply the product to the tank "Static" and then Re-Apply after it is taken hydraulic [filled]. In this fashion, if a new crack is opened on filling we want to reach the crack interior depth to preserve the high pH values closer to the steel. An elastomeric acrylic may then be applied to take into consideration any further movement in the future. The NRC would be well advised to look at other markets and at what is being done to protect concretes. Opps, I forgot, they know everything !!

Comment from John Fauth, (10/22/2012, 8:37 AM)

It's a miracle!

Comment from Tom Schwerdt, (10/22/2012, 11:47 AM)

Concrete treated with a silane/siloxane blend should not need any reapplication unless the treated surface layer of the concrete is physically abraded away. If the epoxy (or other coating) is intact, there would be no reason to reapply the silane/siloxane. Bridge decks treated with silane/siloxane are often re-treated every 10 years or so (in some states) because the surface layer of concrete has been physically worn or abraded away! I have no objection to using an elastomeric sealer over the silane/siloxane instead of an epoxy.

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