ML12138A361
| ML12138A361 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/17/2012 |
| From: | Matthews T FirstEnergy Nuclear Operating Co, Morgan, Morgan, Lewis & Bockius, LLP |
| To: | William Froehlich, Kastenberg W, Nicholas Trikouros Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| References | |
| RAS 22472, 50-346-LR, ASLBP 11-907-01-LR-BD01 | |
| Download: ML12138A361 (131) | |
Text
Timothy P. Matthews Partner 202.739.5527 tmatthews@morganlewis.com Morgan, Lewis & Bockius LLP 1111 Pennsylvania Avenue, NW Washington, DC 20004
Tel. 202.739.3000 Fax: 202.739.3001 www.morganlewis.com May 17, 2012 William J. Froehlich, Chair Nicholas G. Trikouros Dr. William E. Kastenberg Atomic Safety and Licensing Board
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
Docket: FirstEnergy Nuclear Operating Company, Davis-Besse Nuclear Power Station, Unit 1, Docket No. 50-346-LR Re: Notification of Filing Related to Proposed Shield Building Cracking Contention
Dear Licensing Board Members:
The purpose of this letter is to provide notification that FirstEnergy Nuclear Operating Company (FENOC), applicant in this proceeding, sent the enclosed letter to the Nuclear Regulatory Commission (NRC) on May 16, 2012, attached to which is FENOCs Revision 1 of the Root Cause Analysis Report (Report) for the cracking first identified in the Davis-Besse Shield
Building in October 2011.
FENOC is notifying the Board of the enclosed letter because it is relevant to the proposed contention that was filed by Intervenors on January 10, 2012 in this proceeding. This document
is a revision to the February 27, 2012 version of the Report, which FENOC provided to the Board in a February 29, 2012 notification. The revisions are identified and discussed in a
Revision Summary on pages 5-7 of the Report and are identified by italics throughout the
Report. The revisions include additional or clarifying information in response to observations made during a recent NRC inspection of the Report. The revisions do not invalidate the methodology, assessment and analysis, or conclusions of the Report.
Atomic Safety and Licensing Board
May 17, 2012
Page 2 Respectfully submitted, Executed in Accord with 10 C.F.R. § 2.304(d) Signed (electronically) by Timothy P. Matthews Timothy P. Matthews Counsel for FENOC Enclosure cc: Service List
Root Cause Analysis Report, CR 2011-03346 Table of Contents Page 2 Table of Contents
_____________________________________________________________________
Table of Contents......................................................................................................................2List of Acronyms........................................................................................................................4RevisionSummary....................................................................................................................51 Abstract.................................................................................................................................8 2 Introduction..........................................................................................................................11 2.1 Problem Statement................................................................................................11 2.2 Cons equences.......................................................................................................11 2.3 Self-Identification Information.................................................................................11 2.4 Root Cause Team Members..................................................................................11 3 Data Analysis.......................................................................................................................13 3.1 Met hodology..........................................................................................................13 3.2 Sequence of Events...............................................................................................14 3.3 Discussion..............................................................................................................15 3.3.1 Initial Problem Solving.........................................................................................18 3.3.2 Impulse Response Testing and Core Bores.........................................................19 3.3.3 Petrographic and Destructive Examination..........................................................24 3.3.4 Surface Examination............................................................................................29 3.3.5 Design..................................................................................................................3 2 3.3.6 Construction.........................................................................................................37 3.3.7 Operational Phase...............................................................................................41 3.3.8 Shield Building Modeling and Analysis.................................................................45 3.3.9 Failure Modes Analysis........................................................................................50 3.3.10 Hardware Disposition.........................................................................................53 4 Safety Culture Evaluation....................................................................................................54 5 Latent Organizational Weakness Evaluation.......................................................................55 6 Generic Implications............................................................................................................56 6.1 Plant and Industry Experience...............................................................................566.2 Extent of Condition.................................................................................................596.3 Extent of Cause.....................................................................................................60 Root Cause Analysis Report, CR 2011-03346 Table of Contents Page 3 6.4 Data Analysis Conclusions......................................................................................61 7 Root and Contributing Causes.............................................................................................64 8 Corrective ActionPlan.........................................................................................................66 9 Effectiveness ReviewPlan..................................................................................................72 10 References.........................................................................................................................73 10.1 Developmental References...................................................................................7310.2 Other References..................................................................................................75 11 Attachments........................................................................................................................77Attachment 1, Shield Building Exterior Developed Elevation........................................78Attachment 2, Shield Building Impulse Response Average Mobility Values.................79Attachment 3, Shield Building Core Bore Summary......................................................80Attachment 4, Shield Building Concrete Material Properties.........................................84Attachment 5, Shield Building Surface Visual Inspection History..................................85 , Shield Building Milestones.....................................................................86Attachment 7, Shield Building Slip-Form Constr uction Sequence.................................89Attachment 8, Shield Building Concrete Compression Test Results.............................93Attachment 9, Shield Building Concrete Mixes.............................................................94Attachment 10, Shield Building Construction Deviations..............................................95 1, Fault Tree............................................................................................99Attachment 12, Failure Modes Analysis......................................................................100 3, Change Analysis................................................................................119Attachment 14, Barrier Analysis..................................................................................120Attachment 15, Event and C ausal Factors Chart........................................................121 6, Generic ImplicationsMatrix................................................................122 7, Corrective Action Matrix.....................................................................123 Root Cause Analysis Report, CR 2011-03346 List of Acronyms Page 4 List of Acronyms
_____________________________________________________________________ACI American Concrete Institute ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials CANDU Canadian deuterium uranium nuclear plants CARB Corrective Action Review Board CF Causal Factor CFD Computational Fluid Dynamics CR Condition Report CTE Coefficient of thermal expansion CTL Construction Technology Laboratory DCM Design Criteria Manual DBNPS Davis-Besse Nuclear Power Station ECP Engineering Change Package EDG Emergency Diesel Generator EPRI Electric Power Research Institute
F Fahrenheit FEA Finite Element Analysis FENOC FirstEnergy Nuclear Operating Company FM Failure Mode FMA Failure Modes Analysis IAEA International Atomic Energy Agency INPO Institute of Nuclear Power Operations IR Impulse Response NRC Nuclear Regulatory Commission PCAQ Potential Condition Adverse to Quality report PII Performance Improvement International Rebar Reinforcing steel SEM Scanning Electron Microscope USAR Updated Safety Analysis Report USBR United States Bureau of Reclamation Root Cause Analysis Report, CR 2011-03346 Revision Summary Page 5 Revision Summary
_____________________________________________________________________
The Nuclear Regulatory Commission inspection of this root cause analysis report on the week-ending March 16, 2012 observed several minor weaknesses which are resolved by
documentation added or clarified in revision 1. The observations do not invalidate the methodology, assessment and analysis, or conclusions of the root cause analysis report, but do identify areas for improvement. The actions to revise this root cause analysis report were
tracked via Condition Reports 2012-04177 & 2012-04178. Information added or clarified in this root cause report was identified by italics text. The following list describes the observed minor
weaknesses resolved by documentation added or clarified in revision 1: a. The root cause report did not document, or initiate a corrective action to determine why the shield building design did not include a requirement for a protective sealant as was
included in the other safety related buildings.
Information regarding why the shield building design did not include a requirement for an exterior protective sealant was added in section 3.3.5 - Design [page 33], and
- Shield Building Milestones [pages 86 & 88]. b. The root cause report did not document all the reviews and evaluations performed that evaluated slip forming induced cracking as a potential failure mode.
Information regarding slip-form induced friction forces resulting in laminar cracking as a potential failure mode were added to Attachment 12 - Failure Modes Analysis (2.12
Plumb) [page 109]. c. The root cause report did not document why 6 core-bores revealed evidence of multiple laminar cracks in the same area of the outside face reinforcement.Information regarding why several core bores revealed evidence of multiple laminar cracks in the same area of the outside face reinforcement was added in section 3.3.3 -
Petrographic and Destructive Examination [page 27], and Attachment #3 - Shield
Building Core Bore Summary [page 83]. d. The root cause report did not document that weather conditions prevented boroscope inspection of one core bore. The root cause report additionally did not discuss radial
cracking identified in numerous core bores.
Information regarding high winds that prevented boroscope inspection of core bores was added to section 3.3.2 - Impulse Response Testing and Core Bores [page 22], and - Shield Building Core Bore Summary [page 83]. Information regarding
the radial cracking identified in numerous core bores was clarified in section 3.3.2 -
Impulse Response Testing and Core Bores [page 22].
Root Cause Analysis Report, CR 2011-03346 Revision Summary Page 6 e. The root cause report did not document additional investigation that was completed on failure modes 1.5 and 2.11. The root cause report indicates that additional investigation
is required.Information regarding high density reinforcing steel and small reinforcing steel spacing failure modes was clarified by removing verbiage about the need for further
investigation from section 3.3.9 - Failure Modes Analysis [pages 50 & 51]. f. The root cause report has insufficient Impulse Response documentation to conclude that laminar cracking initiated in the shoulder regions and propagated to areas of high
density reinforcement, specifically in the areas of the Main Steam Line Penetrations.Information regarding the propagation of laminar cracking into areas of high density reinforcement was added to section 3.3.8 - Shield Building Modeling and Analysis [page
46].g. The root cause report did not document all the walk-downs completed, or reviews of investigations completed (Maintenance Rule Records) to assess the existence and
condition of coatings on other safety related buildings.
Information regarding the examination of the condition of coatings on other safety-related structures was added to sections 3.3.4 - Surface Examination [page 29], and
6.1.2 - Plant and Industry Experience Results [page 56]. h. The root cause report inadequately documented why the dome of the shield building was excluded from the extent of condition.
Information regarding the sealant of the shield building dome was added to sections 3.3.4 - Surface Examination [page 29], 6.2.2 - Extent of Condition Results [page 59],
6.3.2 - Extent of Cause Results [page 60], and Attachment 6 - Shield Building
Milestones [page 88].i. The root cause report did not document the depth of the core samples at which ettringite was present in samples that contained ettringite deposits.
Information regarding the core sample ettringite depth was added to section 3.3.3 -
Petrographic and Destructive Examination [page 25]. j. The root cause report did not address micro-cracking that was identified in PII Exhibit 2.
The root cause report contradicts this evidence, and states that micro-cracking was not
identified.
Information regarding micro-cracking contradictions was added to section 3.3.3 -
Petrographic and Destructive Examination [page 27].
Root Cause Analysis Report, CR 2011-03346 Revision Summary Page 7 k. The scope of Root Cause Corrective Action #3 is too narrow, and should also include Maintenance Rule inspections (EN-DP-01511) of all safety related exterior surfaces, and not just the exterior surfaces of the Shield Building.
Information regarding examination of the similar exterior coating on the other safety-related concrete structures was added to sections 8 - Corrective Action Plan for root
cause corrective action #3 (CA-2011-03346-8) [page 69], 6.3.3 - Extent of Cause
Conclusions [page 60], and was incorporated into Procedure EN-DP-01511 revision 1. l. Extent of Condition Corrective Action #1 for additional investigation of the Shield Building lacks detail, and need to be expanded to confirm the conclusions of the Root Cause Report. (That is, to perform Impulse Response Testing in other safety related structures not subject to the Root and/or contributing causes). Information regarding confirmatory examination of a safety-related structure with waterproof coating was added to sections 8 - Corrective Action Plan for extent of condition corrective action #3 (CA-2011-03346-14) [page 66], 6.2.3 - Extent of Condition
Conclusions [page 59], and Attachment 17 - Corrective Action Matrix [page 123].
Root Cause Analysis Report, CR 2011-03346 1 Abstract Page 8 1 Abstract
_____________________________________________________________________On October 10, 2011 a concrete crack was observed at the architectural flute shoulder region of a temporary access opening in the wall of the shield building at the Davis-Besse Nuclear Power Station. The temporary access opening was being cut by supplemental personnel
under the direction of FENOC using a hydrodemolition process to allow replacement of the reactor pressure vessel head. A concrete crack in the architectural flute shoulder region of a
temporary access opening in the shield building wall was unexpected and needs to be
understood to evaluate the impact on the shield building structural integrity currently, previously, or within the future viable service life of the plant. Previous visual inspections of
the shield building exterior surface performed over many years did not identify any unusual
surface defects or symptoms of distress that would have indicated the presence of the
subsurface concrete laminar cracking.A team of subject matter experts knowledgeable in concrete structure design, construction, examination, and modeling was assembled to perform an in-depth investigation utilizing visual
inspection, examination of shield building core bore samples, and extensive computer
modeling and analysis to determine the most likely failure scenario and the cause(s) of the observed condition. This root cause investigation is intended to determine "how," "when," and
"why" the concrete laminar cracking occurred in the shield building wall.
Acoustic sounding of the shield building exterior wall was performed using the Impulse Response testing method to locate areas with concrete laminar cracking. Confirmation of the
Impulse Response testing results was achieved by visual inspection of 70 core bores, including
crack characterization. The initial condition assessment determined that the shield building
concrete wall contained tight width laminar cracking near the outer face of structural reinforcing
steel. The majority of the shield building laminar cracking occurred in the concrete at the outer
face of structural reinforcing steel located behind the architectural flute shoulder region. Some
laminar cracking occurred beyond the architectural flute shoulder region as 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 southwestern exposure of the shield building wall was
observed with the most extensive concrete cracking. The initial condition assessment
determined that the shield building was functional, but non-conforming with the concrete
laminar cracking.Examination of 36 shield building concrete cores was performed to define possible failure modes for the laminar cracking, or quantify material properties of the concrete to support
computer modeling and analysis. Two laboratories performed petrographic examination of four concrete cores in order to determine the concrete condition, possible reasons for the
damage, and prediction of whether deterioration may continue. Four other laboratories
examined the shield building concrete cores for material properties and possible failure modes.
Root Cause Analysis Report, CR 2011-03346 1 Abstract Page 9 The external laboratory examination of the shield building concrete cores determined that the concrete was in good condition, consistent with the mix design, and revealed no unacceptable
or degraded material properties. There was no evidence of typical concrete time-dependent
aging failure modes. The examination found the outer surface of the cores was not water-
repellant, and the air voids were lined with secondary deposits of ettringite (crystal formation from sulfate reaction with calcium aluminates) and calcium hydroxide suggesting long-term
exposure to moisture migrating through the concrete. The integrity of the concrete narrowed the failure mechanism to those related to design or environmental issues versus construction.
Computer modeling of shield building loads under environmental conditions with extreme combinations of temperature and wind showed that those combinations were insufficient to result in laminar cracking of the concrete.Therefore, the forces involved with the laminar
cracking were beyond those anticipated with generally accepted design practices. The acute
freezing and expansion of moisture in the shield building concrete was the only scenario
capable of generating radial stresses large enough to initiate laminar cracking. The blizzard of
1978 was determined to be the only event during the life of the shield building that integrated
the moisture content, wind speed, temperature, and duration necessary for development of
radial stresses large enough to enable the concrete laminar crack initiation.
The reason for the shield building laminar cracking was the design configuration of the architectural flute shoulders coupled with a rare combination of severe environmental factors
associated with the blizzard of 1978.
The design configuration did not include an exterior protective sealant on the shield building which allowed moisture to migrate into the concrete, freeze, and expand.
The design configuration inherent stress concentration at the outer face of structural reinforcing steel behind the thickest section of the architectural flute shoulder enabled the radial stress from the freezing moisture to exceed the tensile strength of the concrete and initiate a crack. Other horizontal (hoop) and vertical stresses that adjoined the outer face of
structural reinforcing steel underneath the architectural flute shoulder region enabled the
laminar crack created by freezing moisture to propagate along the outer face of structural
reinforcing steel.
The design configuration did not include radial reinforcing steel ties or stirrups at intermediate spacing between each end of the architectural flute shoulder reinforcing steel connection with
the structural reinforcing steel which enabled the laminar crack created by freezing moisture to
propagate.
The design configuration density of structural reinforcing steel within the top 20 feet of the shield building, and at the main steam line penetration blockouts (spacing was less than or
equal to six inches) enabled laminar cracks created by freezing moisture to propagate.
The laminar cracking at the main steam line penetration blockouts is a result of the adjacent laminar cracking in the architectural flute shoulders that continued to propagate into the adjacent areas of higher density reinforcing steel. The laminar crack continued into the area at
the main steam line penetration blockouts until obtaining equilibrium and stopping. Note that
the bottom of the shoulders in this area is three feet above the auxiliary building roof and in the
area of higher density reinforcing steel.
The southwestern exposure of the shield building wall was observed with the most extensive concrete cracking. The prevailing wind direction occurs from the southwest for most of the
year, particularly during the winter and spring seasons, and was the path of the blizzard of
1978.
Root Cause Analysis Report, CR 2011-03346 1 Abstract Page 10 An analysis was performed of a shield building wall section with a simulated crack. This analysis evaluated the potential for extreme summer or winter temperature events to generate radial stresses sufficient to propagate the existing crack. This analysis concluded that the
extreme temperature events do not cause stress levels that exceed the tensile strength of the
concrete. Therefore, the existing laminar cracks are not expected to propagate. The conclusion of this investigation is that the cause of the concrete laminar cracking was the design specification for construction of the shield building that did not specify application of an exterior sealant from moisture. The action to prevent recurrence of the shield building concrete laminar cracking is to apply an exterior protective sealant as a barrier against
moisture migrating into the concrete. Therefore, with an effective exterior protective sealant
the shield building concrete laminar cracking will not repeat under the required combinations of
extreme environmental conditions such as the shield building experienced during the severe blizzard of 1978. The other nuclear safety-related structures on-site have a protective sealant
as a barrier against moisture migration into the concrete.
Root Cause Analysis Report, CR 2011-03346 2 Introduction Page 11 2 Introduction
_____________________________________________________________________
2.1 Problem Statement On October 10, 2011 a concrete crack was observed at the architectural flute region of a temporary access opening in the shield building wall at the Davis-Besse Nuclear Power Station (DBNPS). The temporary access opening was being cut by supplemental personnel under the
direction of FENOC using a hydrodemolition process to allow replacement of the reactor pressure vessel head. Various visual inspections of the shield building exterior surface
performed over many years did not identify any unusual surface defects or symptoms of
distress that would signify the presence of the subsurface concrete laminar cracking.
2.2 Consequences A concrete crack in the architectural flute region of a temporary access opening in the shield building wall was unexpected and an investigation was started to understand the condition of
the shield building and determine how and why the observed condition occurred. Additionally, the initial investigation evaluated the observed condition and determined that the shield
building was capable of performing its intended function prior to restart of the unit from the mid-cycle outage. The investigation described in this report determined the most likely failure
scenario, identified cause(s), and determined the corrective action(s) to ensure the shield
building structural integrity for the remaining service life of the plant including extended
operation in the license renewal period.
2.3 Self-Identification Information Previous inspections of the shield building exterior surface did not identify symptoms that
would signify the presence of the concrete sub-surface laminar cracking.
2.4 Root Cause Team Members A team of industry experts was contracted by FENOC to support the investigation and
determine the cause(s) and recommended actions. The team was selected based upon capability and prior experience in root cause investigation with particular emphasis on previous
industry experience in nuclear containment laminar cracking. Alfred J. Cayia, Director - Fleet Performance Improvement and Root Cause Team Lead
Kevin Browning, DBNPS Root Cause Evaluator Richard Bair, DBNPS Civil / Structural Engineer
Thomas Henry, DBNPS Civil / Structural Engineer Performance Improvement International (PII) was the prime contractor with prior industry experience in both root cause investigation and modeling and analysis capability of nuclear
containment structures.
Root Cause Analysis Report, CR 2011-03346 2 Introduction Page 12 Performance Improvement InternationalDr. Chong Chiu Dr. Avi Mor Dr. Mostafa Mostafa Dr. Ray Waldo Dr. Yunping Xi Joe Amon David Dearth Tyson Gustus Henric Larsson Doug Marx Luke Snell Doug Starck
Hany Helmy During the early stages of the root cause investigation, two additional firms with experience in civil structural evaluation of nuclear concrete structures and with root cause investigative expertise participated in the development of potential failure modes for the observed condition.
This approach ensured that a comprehensive list of failure modes was developed to be further
evaluated during the course of the investigation.
MPR AssociatesEdward Bird James Bubb Richard Stark Dave Werder Vatic Associates, Inc.
Steve Eisenhart Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 13 3 Data Analysis
_____________________________________________________________________3.1 Methodology A team of subject matter experts knowledgeable in concrete structure design, construction, examination, and modeling were assembled to review evidence and documentation associated
with the indication of a concrete crack in the architectural flute region of a temporary access
opening in the shield building wall. The observed cracking of the shield building wall was
unexpected and required rigorous investigation to be understood to ensure there is no impact
with its structural integrity for the future viable service life of the plant. This root cause investigation is intended to determine "how," "when," and "why" the concrete cracking occurred
in the shield build wall.
This root cause investigation was conducted using the guidance described in procedure NOP-LP-2001 (Corrective Action Program), business practice NOBP-LP-2011 (FENOC Cause
Analysis), and reference material NORM-LP-2003 (Analytical Methods Guidebook). A pre-job
brief was conducted with the owning Manager, and a task assignment was approved by the
sponsoring Director. The root cause investigation was performed using the TapRoot
methodology along with Problem Solving and Decision Making (procedure NOP-ER-3001),
Equipment Apparent Cause Evaluation (form NOP-ER-1001-01), Event & Causal Factors
Charting, Barrier Analysis, Change Analysis, and Fault Tree Analysis.
The primary contractor supporting the root cause investigation, Performance Improvement International, is a recognized expert in root cause analysis. The Performance Improvement
International methodology is one of the techniques endorsed by FENOC to perform root cause
investigations.
The following additional Condition Reports discovered during the initial problem review were rolled into this root cause investigation: 2011-04214, Core Bore Found Additional Crack in Architectural Flute Area (10/24/2011)
2011-04402, Fractured Concrete Found at 17M Shield Building at Main Steam Line Penetrations (10/26/2011) 2011-04648, Shield Building Impulse Response Indications Above Elevation 780 (10/31/2011)
2011-05475, Concrete Cracking at the Top of the Shield Building Wall (11/16/2011)
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 14 3.2 Sequence of Events 08/10/11 Approval to implement the Engineering Change Package for creation of a temporary access opening through the shield building. [ECP 10-0458] 09/29/11 Approval to commence work on the Order for creation of a temporary access opening through the shield building. [Order 200433294] 10/03/11 @1545 Completed etching the cut line for a temporary access opening through the shield building. [Outage Log] 10/07/11 @0215 Started the diesel engines to commence the hydrodemolition of concrete for a temporary access opening through the shield building. [Outage Log] 10/07/11 @0415 Shutdown the hydrodemolition process to clean out debris hoppers.
Approximate depth at six inches in quadrant 1 and four inches in quadrant
- 3. [Outage Log] 10/07/11 @1700 Resumed the hydrodemolition process through the architectural flute reinforcing steel. [Order 200433294] 10/08/11 @0430 Began reinforcing steel removal from architectural flute. [Order 200460515]
10/08/11 @0730 Inspected reinforcing steel for minimum coverage and identified 3/4 inch concrete coverage in some regions of the shield building exterior. [Outage
Log & Condition Report 2011-03232] 10/09/11 @1255 Resumed the hydrodemolition process. [Outage Log]
10/09/11 @1700 Continued reinforcing steel removal. [Order 200433294]
10/09/11 @1800 Resumed the hydrodemolition process to expose outer face of structural reinforcing steel on east side. [Order 200433294] 10/09/11 @2210 Continued reinforcing steel removal. [Outage Log]
10/10/11 @0430 Completed the hydrodemolition process phase 2. [Outage Log]
10/10/11 @0450 Continued reinforcing steel removal. [Outage Log]
10/10/11 @1600 Bechtel reported that they were writing a Condition Report for discovery of a concrete crack propagating along the outer face of structural reinforcing
steel (#11) across the top and down the side of the shield building
temporary access opening. [Outage Log] 10/10/11 @2021 Fractured concrete found at shield building construction opening. During hydrodemolition operations to create the shield building construction
opening, fractured concrete was found. The concrete fractures extend into
concrete not currently intended to be removed. [Bechtel Condition Report
25539-000-GCA-GAMG-00182 & FENOC Condition Report 2011-03346] 10/10/11 Nuclear Regulatory Commission (NRC) inspectors were immediately notified of the indications of potential fracture lines in the concrete and
closely monitored the plant's actions and analysis. [PNO-III-11-014]
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 15 3.3 Discussion On October 10, 2011, a concrete crack was observed at the architectural flute shoulder region of a temporary access opening in the shield building wall at DBNPS. The temporary access opening was being cut by supplemental personnel under the direction of FENOC using a hydrodemolition process to allow replacement of the reactor pressure vessel head.
The shield building is a reinforced concrete structure of right cylinder configuration with a shallow dome roof [Reference 10.1.1]. An annular space is provided between the steel
containment vessel and the interior face of the concrete shield building of approximately 4 feet
6 inches width to permit construction operations and periodic visual inspection of the steel containment vessel. The containment vessel and shield building are supported on a concrete
foundation set on a firm rock structure. With the exception of the concrete under the
containment vessel, there are no structural ties between the containment vessel and the shield
building above the foundation slab. The shield building has a height of 279 feet 6 inches measured from the top of the foundation ring to the top of the dome and is the tallest building in the power structure. The inside radius of the shield building is 69 feet 6 inches and the thickness of the shield building wall is
approximately 2 feet 6 inches. The shield building exterior has eight vertical architectural flute
reveals that are spaced 45 degrees apart [Reference 10.1.2]. The architectural flute reveals consist of shoulders that extend another 1 foot 6 inches outward and gradually taper back to
the outer cylindrical wall of the shield building while reaching a point of tangency 17 feet 11
inches from the centerline of the flute. West Elevation View of Plant Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 16 Plan View of Architectural Flute / Shoulders A temporary access opening approximately 25 feet 6 inches wide and 35 feet 6 inches high centered at approximately azimuth 323 degrees was cut through the shield building wall during
the 17 Mid-cycle outage at DBNPS [Reference 10.1.3 & 10.1.4]. The left side of the temporary
access opening was cut near the thickest section of the architectural flute shoulder located on
the north-northwest side of the shield building between elevations 603 feet and 638 feet six
inches. The temporary access opening through the shield building wall was necessary for
installation of a replacement reactor pressure vessel head. The existing reactor pressure
vessel head was installed in 2002 through a temporary access opening located within the
boundary of the original construction opening. The current temporary access opening
extended past the edge of the original construction opening into part of the previously
undisturbed shield building wall.
The shield building temporary access opening was being cut using a hydrodemolition process.
Hydrodemolition is a method of concrete removal using high pressure water jets directed
towards the surface to separate the course and fine aggregate from the cement paste.
Hydrodemolition of concrete was first developed in Europe in the 1970's and has become
widely accepted and utilized for concrete removal and surface preparation. Unlike
conventional impact methods, hydrodemolition does not result in vibration through the
structure or induce micro cracking of the remaining material [Reference 10.1.5].
Hydrodemolition is particularly effective in removing concrete from around reinforcing steel.
The temporary access opening made in 2002 for replacement of the original reactor pressure
vessel head was also created using a hydrodemolition process.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 17 Elevation View of Shield Building / Construction Opening & Temporary Access Openings American Hydro personnel performing the hydrodemolition of the shield building temporary access opening noted that towards the left side, between the architectural flute reinforcing
steel and the outer face of structural reinforcing steel, the concrete removed consisted of larger
chunks that sheared through the aggregate leaving a smooth flat surface. The concrete past (inward of) the outer face of structural reinforcing steel, and also on the right side of the
temporary access opening placed during the 2002, was more difficult to remove and the larger chunks were not present [Reference 10.1.6]. The American Hydro personnel observed these
conditions while using consistent parameters for the hydrodemolition equipment (water pressure, cut angle, nozzle stand-off, traverse speed, step distance). Therefore, the only
variable was determined to be the condition of the shield building concrete.The known extent of condition at the time of problem discovery was a concrete crack in the shield building wall that was visible on the entire 35 feet height of the temporary access
opening left face. The crack was adjacent to the outer face of structural reinforcing steel, and
it extended approximately eight feet into the left-top and approximately four feet into the left-
bottom region of the temporary access opening progressing from the outer face of structural
reinforcing steel towards the architectural flute reinforcing steel. The crack at the left-top of the
temporary access opening continued to the exterior surface at the edge of the opening and
extended about two and a half feet vertically upwards on the exterior surface of the shield
building concrete [Reference 10.1.7]. The crack width was initially indeterminate, due to the
effect of the hydrodemolition process, resulting in disintegrating the concrete aggregate and cement paste at the crack location. The hydrodemolition process was incomplete at the time of crack discovery and had been stopped to allow removal of the outer face of structural
reinforcing steel.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 18 3.3.1 Initial Problem Solving FENOC promptly originated a Condition Report and assembled a Problem Solving Team to investigate the unexpected concrete crack within the shield building temporary access opening
[Reference 10.1.8]. Members on the Problem Solving Team consisted of Davis-Besse and Beaver Valley engineering staff as well as concrete material experts and structural engineering specialists from Bechtel and Sargent & Lundy to assist with the investigation. The Problem Solving Team on October 12, 2011 performed an initial examination of the concrete crack
within the shield building temporary access opening that was confined to the bottom region adjacent to the architectural flute. During this initial examination, the temporary access
opening was covered with grit and hydrodemolition residue which obscured the crack details.
The Problem Solving Team requested that the temporary access opening be cleaned of the
grit and residue for follow-up visual examination to be performed on October 13, 2011.
Excavation of the left side of the temporary access opening commenced with an electric chipping hammer to remove the material influenced by the hydrodemolition process. The
chipping revealed that the concrete crack terminated from the bottom left corner to
approximately 18 feet above the opening bottom, and a 2 foot section at the top left corner.
After examining the region where chipping was performed, the exposed concrete was found to
be sound and tightly adhered to the reinforcing steel, and a crack was no longer apparent
along the left side of the shield building temporary access opening. Inspection of the
reinforcing steel visible at the temporary access opening, and the reinforcing steel already
removed from the outer face and architectural flute shoulder region, revealed that the
reinforcing steel corrosion was acceptable and there was no evidence of material loss.
Engineering Change Package 10-0458-001C was created to allow excavation beyond the design cut-line in the region at the top-left corner of the temporary access opening. Further
chipping at the top-left corner of the temporary access opening resulted in a section excavated upward approximately 23 inches. As a result of the chipping, the overall crack length had been reduced from the initial 8 feet to approximately 5 feet long. The crack in the region at the top-left corner of the shield building temporary access opening remained evident, tight, and
confined to the architectural flute shoulder region.
The Problem Solving Team developed an initial work plan to obtain 2 inch diameter core bores to define the extent of a concrete crack at the top-left corner of the temporary access opening in the shield building [Reference 10.1.9].A core bore approximately five feet above the
excavated section at the top-left corner of the temporary access opening was selected to
determine if the concrete crack was influenced by either the hydrodemolition process or
redistribution of stress adjacent to the opening. If a crack was evident in this original core
bore, then the CTL Group would commence Impulse Response testing to further define the crack characteristics followed by additional core bores. The initial core bore was performed
and it included the laminar crack identified below.
A grid pattern, 6 feet wide by 15 feet high with one foot intervals, was laid out to perform Impulse Response testing on the shield building exterior oriented about two feet from the edge
of the architectural flute and six inches above the temporary access opening. Engineering
Change Package 10-0458-001D and Order 200478731 were created to perform five 2-inch
diameter core bores along with the corresponding Impulse Response testing.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 19 3.3.2 Impulse Response Testing and Core Bores Nondestructive examination techniques for concrete have been slow to develop primarily because concrete is an inherently heterogeneous material with constituent materials that can
vary widely, depending on geographical region. As a consequence, material in concrete
structures tends to be unique and more difficult to characterize nondestructively than other
materials.
The Impulse Response testing method [Reference 10.1.10 & 10.1.11] is a direct descendent of methods for evaluating the integrity of concrete piles developed in France in the 1960's. The
Impulse Response testing method consists of generating a stress pulse in a structure by a
mechanical impact. The force-time function of the impact is monitored using an instrumented
hammer to generate the impact, a transducer (geophone) to monitor the dynamic response of
the structure to the impulse load, and a computer to acquire, process, and record data. The
time records for the hammer force and the geophone velocity response are processed using
Fourier transforms of the measured data to obtain the frequency spectra. The resulting velocity spectrum is divided by the force spectrum to obtain a transfer function, referred to as the mobility of the element under test. The test graph of mobility plotted against frequency
contains information on the condition and integrity of the concrete tested. When a crack or discontinuity is present within a structural element, the response behavior of the outermost layer controls the Impulse Response test result. The basic theory of dynamic mobility has
been utilized for a range of applications such as cracking in concrete and delamination of concrete around steel reinforcement in slabs, walls, and large structures such as dams, chimney stacks, and silos. Impulse Response testing has been demonstrated to detect
significant voids and other defects in concrete, and it can be used to survey relatively large
areas in a reasonably short time frame.
Experience with Impulse Response testing at Crystal River Unit 3 in 2009 with delamination cracking in the concrete containment structure previously demonstrated that a direct
correlation exists between the test results and evidence or absence of a crack in the core
bores [Reference 10.1.12]. The Impulse Response testing method was primarily used at the
DBNPS to determine whether a crack exists at a given measurement location and for mapping
regions of the shield building concrete that contains a crack. The Impulse Response testing
method utilized has a limitation such that anomalies existing at depths greater than
approximately ten inches may not be detected.
Validation for the Impulse Response testing method consists of taking a core bore from a location where testing shows a concrete crack and then visually confirming the existence of a
crack within the bore / core sample.
A numbering scheme was created for identifying the shield building architectural flutes designating them by number one through eight clockwise starting at 22 degrees 30 minutes. A
similar scheme was created for identifying the architectural flute shoulders designating them by
number one through 16 clockwise starting from the zero degree (North) azimuth. Impulse
Response data was taken systematically on a one foot grid pattern starting approximately 24
inches from the architectural flute edge horizontally. Ground penetrating radar was used to
define the reinforcing steel layout relative to the intended core bore location. Core bores were
labeled based upon the shoulder or flute number, the elevation, and the horizontal grid number. Results from the Impulse Response testing and core bores were compiled into a
comprehensive report [Reference 10.1.13].
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 20 The core bores were inspected internally using a boroscope to document the depth of the crack, and the crack width was established using an optical crack comparator in accordance
with Procedure EN-DP-01512, "Shield Building Concrete Examination."The results of the Impulse Response test data above the temporary construction opening indicated the presence of a concrete crack vertically within the central portion of the architectural flute shoulder region. The edge of the architectural flute extends approximately
18 inches and indicated no cracking. On October 18, both 2-inch diameter core bores S15-645.5-3 ("A") and S15-653.5-3 ("D") confirmed a concrete crack in the architectural flute
shoulder region that extended approximately 7 feet and 15 feet directly above the top-left
corner of the shield building temporary access opening. Both of these cores were sent off-site
for further independent petrographic examination. The Impulse Response testing pattern was expanded horizontally to include a grid 10 feet above the entire temporary access opening. Impulse Response testing established that the
concrete crack was confined within the architectural flute shoulder 15, as confirmed by core bore S15-646.5-8 ("E") on October 21. Next, increasing the height of the Impulse Response
testing pattern vertically to include a grid 40 feet high total and 10 feet wide established the top of the concrete crack as confirmed by core bore S15-674.5-3 ("G"). The concrete crack in
shoulder 15 had a laminar orientation located near the outer face of structural reinforcing steel
in the architectural flute shoulder region, bounded within an area 8 feet wide by 38 feet above
the temporary access opening on the northwest side of the shield building, with a crack width
measured at less than 0.010 inches.
The Impulse Response tests were then expanded horizontally to determine if similar conditions existed elsewhere at adjacent architectural flute shoulders 1 and 16 above the emergency
diesel generator building roof facing northward and shoulder 13 at the top-right of the original
construction opening facing westward. Engineering Change Packages 10-0458-001E, 10-0458-001F and Order 200479708 were created to perform additional 2-inch diameter core
bores.A concrete crack in shoulder 16 and also a crack in shoulder 1 have Impulse Response test data characteristics and orientation similar to the laminar crack originally identified in shoulder 15, on a substantially smaller scale. Condition Report 2011-04214 was originated on October 24, for the discovery of an additional concrete crack in the core bore taken from the
architectural flute region of shoulder 16. Core bores S16-613.0-46 and S16-613.0-42
confirmed that the concrete crack in shoulder 16 had a laminar orientation located near the outer face of structural reinforcing steel in the architectural flute shoulder region with a width
measured at less than 0.010 inches.
Cracking was identified in shoulder 13 that had similar Impulse Response test data characteristics and orientation to the laminar crack originally identified in shoulder 15. Core
bores S13-633.08 and S13-633.0-11 established that the concrete crack terminated prior to
the tie-ins and lateral hooks at each end of the architectural flute reinforcing steel. The
termination of the concrete crack in shoulder 13 was consistent with the termination of the
crack along the left side of the temporary access opening in shoulder 15 that was previously
confirmed by chipping back the concrete.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 21 Impulse Response testing and cores bores taken using man-lifts from the ground and scaffold from building roofs across 15 of the 16 architectural flute shoulders confirmed that a similar
concrete crack phenomenon in the architectural flute shoulders exists in other regions around the perimeter of the shield building. Examination of nine core bores (S3-650.0-9, S4-650.0-16, S5-666.0-8, S6-666.0-42, S6-666.0-44, S7-666.0-7,S8-666.0-41, S10-666.0-40, and S12-
666.0-4) revealed that each concrete crack had a laminar orientation located near the outer face of structural reinforcing steel in the architectural flute shoulder region. Therefore, the
shield building concrete crack phenomena were determined to be unrelated to hydrodemolition of the temporary access opening. Shoulder 14 was not accessible from the ground due to
interference with a start-up transformer.
A similar concrete crack also was detected in regions without architectural flutes between shoulders 6 & 7 and shoulders 10 & 11, unlike previous examples of the crack phenomena.
Condition Report 2011-04402 was originated on October 26, for a concrete crack adjacent to
one side of each main steam line penetration blockout at shoulders 6 & 7, and 10 & 11. Five
core bores (S7-656.0-6.5, S7-667.0-25, S9-653.0-11, S11-663.75-30, and S11-669.0-17)
confirmed that, adjacent to one side of each main steam line penetration blockout through the
shield building, there was a concrete crack with a laminar orientation located near the outer face of structural reinforcing steel. Impulse Response testing of a similar size blockout for a
containment purge line located one floor below the main steam line penetration blockout
determined there was no similar pattern of concrete cracking. Several cracked and un-cracked cores were sent off-site for further independent examination.
The Impulse Response testing data of the shield building also indicated that the concrete crack phenomena continued upward beyond the reach of the available scaffold and man-lifts.
Therefore, southward facing shoulder 9 was selected to determine the vertical extent of the
concrete crack while using a man-basket suspended from the shield building parapet. The
Impulse Response test data for shoulder 9 indicated three cracked sections that encompassed
the majority of the vertical distance of the architectural flute region from the roof of the auxiliary
building near elevation 665 feet to the top of the shield building near elevation 795 feet. The
concrete crack in shoulder 9 had similar Impulse Response test data characteristics and similar crack orientation originally identified in shoulder 15. Core bores S9-666.0-11, S9-680-3, and S9-785.0-22.5 confirmed that the concrete crack in shoulder 9 had a laminar orientation located near the outer face of structural reinforcing steel in the architectural flute shoulder region with a crack width measured at less than 0.010 inches.
The concrete crack near the top 20 feet of the shield building also continued into the region without architectural flutes between shoulders 8 & 9. Condition Report 2011-04648 was
originated on October 31, for a concrete crack outside the architectural flute shoulders located
within elevation 780 feet and 801 feet between shoulders 8 & 9. Additional Impulse Response
test data identified similar situations where the concrete crack continued into the region without
architectural flutes between shoulders 10 &11 and shoulders 12 & 13. Core bores S9-785.0-
22.5, S10-790.5-25, and S2-798.5-4.5 confirmed that the concrete crack, which continued into
the region without architectural flutes near the top of the shield building, had a laminar orientation located near the outer face of structural reinforcing steel with a crack width measured at less than 0.010 inches. Impulse Response testing of the spring line at the top 5 feet indicated a lesser extent of concrete cracking than the remainder of the top 20 feet of the
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 22 Condition Report 2011-05475 was originated on November 16, 2011 for additional assessment of the concrete cracking in the shield building wall above elevation 780 feet. Impulse
Response testing also identified a concrete crack across the approximate 5 foot 8 inch region
between both architectural flute shoulders 5 and 6 at the top of the shield building. Core bore
F5-791.0-4 confirmed that the concrete crack across the architectural flute near the top of the
shield building had a laminar orientation located near the outer face of structural reinforcing
steel with a crack width measured at 0.013 inches.Eight core bores were drilled deep into the shield building to ensure that the cracked concrete was confined to the outer face of structural reinforcing steel. Five core bores (S7-782.0-8.5, F2-790.0-4.5, F4-794.0-3.5, F4-791.0-2.5, and F5-791.0-4) confirmed that there was no similar concrete cracking inward from the outer face of structural reinforcing steel near the top of the
shield building wall.
Boroscope inspection of core holes for core bores F4-794.0-3.5 and F4-791.0-2.5 were not completed due to the weather (high wind conditions).
Three other core bores (S16-613.0-30, S16-613.0-42, and F7-633.08) confirmed that there was no similar
concrete cracking inward from the outer face of structural reinforcing steel in the lower half of the shield building wall. Additionally, visual examination of the entire perimeter of the temporary access opening did not reveal any laminar cracking at the inside face of structural
reinforcing steel.
Evidence of subsurface cracking, other than a laminar crack in the shield building concrete, was also identified on five core bores. Longitudinal / radial cracks, attributed to concrete shrinkage, were discovered in core bores F7-633.08 and F2-790.0-4.5 as described in
Condition Reports 2011-04507 and 2011-05648. Longitudinal / radial cracks of the material
extracted from core bores F4-794.0-3.5, and F5-791.0-4 were seen which was also attributed to concrete shrinkage. The concrete in the shield building was reinforced to limit the size and confine the longitudinal / radial cracking observed attributed to shrinkage during the curing
process. Another imperfection located approximately one inch below the surface was discovered in core bore S10-672.0-34 as described in Condition Report 2011-04507. Each of
these five cores, with indications other than laminar cracking in the shield building concrete, were sent off-site for further independent examination.
Four 3-inch and six 4-inch diameter core bores were collected to support destructive examination and the confirmation of material properties for the shield building concrete, in addition to samples from the 2-inch diameter cores collected while confirming crack locations.
Engineering Change Packages 10-0458-001H and 10-0458-001L Order 200478731 were
created to perform the 3-inch and 4-inch diameter core bores to support destructive
examination of the shield building concrete. The first 3-inch diameter core bore was extracted
from the passage to the emergency diesel generator rooms to provide a baseline sample that
was not exposed to environmental factors experienced by the shield building exterior walls.
The second 3-inch diameter core bore was extracted from the main steam line area to provide
a sample that experiences the worst chronic thermal factors. Two other 3-inch diameter core
bores were extracted from the northeast and southern facing sides, at approximately mid-span, to provide samples exposed to a differing magnitude of thermal factors experienced by the shield building exterior walls. Six 4-inch core bores were extracted to perform tensile, creep, freeze / thaw, and moisture testing of the shield building concrete.
Engineering Change Package 10-0458-001K was created to provide a sketch / drawing [Reference 10.1.14] showing locations of core bores. The shield building Impulse Response
average mobility values are provided in Attachment 1, and the shield building core bore
summary is provided in Attachment 2.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 23 Conclusion from Impulse Response Testing and Core Bores Core bore sample results confirmed that the shield building walls contained a concrete crack that had a laminar orientation located near the outer face of the structural reinforcing steel.
The crack widths were found to be generally tight, less than or equal to 0.010 inches, with one
crack measuring 0.013 inches. Inspection of the concrete cores indicates that the crack
passed through the coarse concrete aggregate.
Eight deep core bores were taken to confirm that the laminar cracking is only located near the outer face of the structural reinforcing steel. In addition, a thorough visual inspection of the
entire perimeter of the temporary access opening revealed no laminar cracking at the inside
face of the structural reinforcing steel.
Fifteen of the sixteen shoulders were inspected using the Impulse Response mapping.
Results indicate that all 15 shoulders inspected had indications of laminar cracking. The
cracks were well confined in the shoulder areas between the ends of the horizontal reinforcing
steel. The southwestern exposure of the shield building wall was observed to have the most
extensive concrete cracking.Impulse Response mapping identified a region of laminar cracking adjacent to the shoulder areas near the top 20 feet of the shield building. This area coincides with a higher density of
reinforcing steel (#11 horizontal bars at 6" c-c).
Impulse Response mapping also identified a region of laminar cracking adjacent to the main steam line construction blockout for penetration #39 and #40, located above and below the Auxiliary Building roof line. This crack is also located in an area of higher density horizontal
reinforcing steel.
As an extent of condition associated with the main steam line penetration line blockouts, Impulse Response mapping was conducted adjacent to a similar construction blockout (the containment purge outlet blockout for penetration #34) that also has a higher density of
reinforcing steel adjacent to this construction opening. This blockout is located one floor below
the main steam line penetration blockout. Impulse Response mapping in this area indicated no laminar cracking. This was the expected result considering this shield building penetration was not exposed to exterior environmental conditions, nor located near any of the architectural
flute shoulders.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 24 3.3.3 Petrographic and Destructive Examination The root cause team visually conducted examinations of a number of larger pieces of concrete removed from the shield building temporary access opening. These samples of concrete debris had fracture surfaces that propagated directly through the large and small aggregate
indicating that the bond between the aggregate and the cement paste was very strong.
Subsequent visual examination of the concrete cores also found similar transverse fractures
through the aggregate.
Thirty-six of the 70 cores extracted from the shield building concrete were subjected to either petrographic or destructive examination by external laboratories in order to quantify material properties for modeling and analysis, or to define possible failure modes. Some of the shield
building concrete cores were sectioned and subjected to more than one form of examination.
A shield building core bore summary is provided in Attachment 3.
Petrographic ExaminationFour of the 36 shield building concrete cores were submitted to two separate laboratories for petrographic examination per ASTM C856, "Standard Practice for Petrographic Examination of
Hardened Concrete." Petrographic examination of the mix design and the material properties of concrete were performed in order to determine the condition, possible reasons for damage, and prediction of whether deterioration may continue. Petrographic examinations with a
Scanning Electron Microscope are used to determine the physical and chemical characteristics of the concrete. This includes but not limited to; the relative amounts of constituents of the sample, presence of unstable minerals such as soluble sulfates, microcracks, and chemical or
physical deterioration. The four cores submitted for petrographic examination of the shield
building concrete included the initial 2-inch diameter cores bores collected (S15-645.5-3 &
S15-653.5-3), and two of the 3-inch diameter cores (F2-792.3-4.5 & F4-791.0-2.5). A point-count analysis was also performed of core F4-791.0-2.5 per ASTM C457, "Standard Test
Method for Microscopical Determination of Parameters of the Air-Void System in Hardened
Concrete."The CTL Group petrographic examination [Reference 10.1.15] of cores S15-645.5-3 ("A") and S15-653.5-3 ("D") determined that the shield building concrete is in very good condition and
that the limited carbonation at the fracture surface indicates that the laminar crack was not directly exposed to air. Transverse cracks in both cores, associated with those crack locations
identified in the core holes, pass through coarse aggregate. Fracture surfaces were clean, with no discoloration or debris and few deposits.While the concrete represented by the cores
exhibited some non-uniformity, the concrete was consistent with the mix designs provided in
terms of composition and quality.
The Wiss, Janney, Elstner Associates petrographic examination [Reference 10.1.16, Exhibit 26] of cores F2-792.3-4.5, and F4-791.0-2.5 determined that the concrete generally
corresponds to the mix design with moderate variability with respect to its consolidation, air-void system, and water-to-cement ratio. The specific surface and spacing factors of the air-void system in core F4-791.0-2.5 calculated by the point-count analysis did not meet industry requirements for freeze / thaw durability in moist conditions, but because of the increased
strength, no evidence of freeze / thaw deterioration was detected in either core F2-792.3-4.5 or
F4-791.0-2.5.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 25 The two separate petrographic examinations determined an estimated air content that ranged from 1 to 3 percent in core S15-645.5-3, from 1 to 3 percent at the outer end and 3 to 5 percent in the body of the core S15-653.5-3, and 5 percent in core F4-791.0-2.5. The concrete was air-entrained, but some air contents were lower than the 4.5 to 6 percent specified in the
original mix designs. The water-to-cement ratio for cores S15-645.5-3 and S15-653.5-3 was
estimated between 0.45 and 0.55, and 0.38 to 0.42 for core F2-792.3-4.5. Limited
petrographic examination of core F4-791.0-2.5 identified a variable water-cement ratio similar to core F2-792.3-4.5, but to a lesser extent. Core F2-792.3-4.5 had moderate amounts of thin, soft paste zones with an elevated water-to-cement ratio and air voids which represent areas of
weakness and increased potential for fluid penetration.
The outer surface of the cores was covered with a mortar coating of variable thickness that was not water-repellant, and the paste was highly absorbent along the outer surface. Cores
F2-792.3-4.5 and F4-791.0-2.5 contained some larger and abundant medium sized air voids
near the surface indicating less than optimal consolidation. The air voids of core F2-792.3-4.5
and F4-791.0-2.5 were lined with secondary deposits of ettringite (crystal formation from
sulfate reaction with calcium aluminates) and calcium hydroxide which suggests long-term
exposure to moisture migrating through the concrete.Core F2-792.3-4.5 was approximately 4-3/4 inches long and the secondary deposits thinly lined virtually all of the air voids throughout the concrete. Core F4-791.0-2.5 was approximately 4 inches long with both ends saw cut.
The air voids in core F4-791.0-2.5 contained secondary deposit linings in the same abundance
and pattern as those of core F2-792.3-4.5.
The near surface zone of core F2-792.3-4.5 was considered to be relatively poor. The paste along the outer surface (shield building exterior
wall) of cores S15-645.5-3 and S15-653.5-3 was fully carbonated to a depth of 0.2 to 0.3 inches, and typically 0.25 inches for core F2-792.3-4.5. These amounts of carbonation are
typical for a concrete surface exposed for 40 years.
The paste along the outer surface of cores S15-645.5-3 and S15-653.5-3 (exterior surface of the Shield Building wall) is fully carbonated to a depth of 5 to 8 mm. Carbonation in the body of
the cores exhibits a mottled pattern with small areas of carbonated and non-carbonated paste; however, this feature does not appear to affect the overall integrity and performance of the
concrete. Paste along the fracture surfaces of both cores, associated with those crack locations identified in the core holes, exhibits the same mottled carbonation pattern observed
in the body of the cores; however, the paste does not appear to have carbonated due to
exposure along the fracture surfaces.
The water soluble chloride in cores S15-645.5-3 and S15-653.5-3 ranged between 310 and 370 parts per million. No materials-related causes for the cracks and microcracks were
observed, and no evidence of chemical reactions involving aggregates and paste constituents (such as alkali aggregate reaction) was observed.
Destructive Examination Thirty-three of the 36 shield building concrete cores were submitted to four other laboratories for destructive examination in order to quantify material properties for modeling and analysis, or to define possible failure modes. The four locations examining the shield building concrete
cores were the United States Bureau of Reclamation (USBR), the University of Colorado -
Boulder, the Twining Laboratory, and the PhotoMetrics laboratory. A listing of the shield
building concrete material property tests performed for each core is provided in Attachment 3.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 26 Two shield building 3-inch diameter concrete cores (F4-791.0-2.5 and S7-782.0-8.5) were tested by the USBR for the material properties of thermal diffusivity, specific heat, thermal conductivity (calculated), and coefficient of linear thermal expansion [Reference 10.1.16, Exhibit 59]. Thermal diffusivity is the rate at which temperature changes take place in concrete and is measured per test procedure USBR 4909-92.Specific heat is the rate at which heat is
transmitted through a unit thickness of the concrete and is measured per test procedure USBR 4907-92. Thermal conductivity is the rate at which heat is transmitted through a unit thickness of material and is calculated from the thermal diffusivity, specific heat, and density of the concrete. The coefficient of linear thermal expansion is the change in unit length per degree of
temperature change of the concrete and is measured per test procedure USBR 4910-92.Two shield building 4-inch diameter concrete cores (S1-615-2 and S3-650-2) were tested by the Twining Laboratory for the material properties of modulus of elasticity, compressive
strength, and splitting tensile strength [Reference 10.1.16, Exhibit 3]. The modulus of elasticity
provides the stress to strain ratio and a ratio of lateral to longitudinal strain in hardened
concrete and is measured per ASTM C469. The compressive strength provides a basis for
determination of compliance with concrete proportioning, mixing, and placing specifications and is measured per ASTM C39. The splitting tensile strength evaluates the shear resistance
of concrete and is measured per ASTM C496.
Eight shield building concrete cores were tested by the University of Colorado - Boulder consisting of three 3-inch diameter cores (S9-680-3, EDG passage, and Main Steam line
room), and five 4-inch diameter cores (S2-616-14, S3-650-2, S4-649-22, S6-665-47, and S8-
665). The material properties tested by the University of Colorado - Boulder were internal relative humidity, compressive strength, splitting tensile strength, coefficient of thermal expansion, and accelerated creep [Reference 10.1.16, Exhibit 60].A freeze / thaw resistance
test per ASTM C666 was aborted due to test equipment malfunction which inhibited
completion of the test within the time available. Petrographic examination had already shown
no evidence of freeze / thaw deterioration. The internal relative humidity is important for
evaluating potential shrinkage and freeze / thaw damage in concrete. The accelerated creep test measures the load-induced time-dependent compressive strain of the concrete per ASTM
C512.None of the material properties for the shield building concrete were found to be unacceptable relative to typical results from the test standards. The specific heat and thermal diffusivity of
the shield building concrete were greater than typical ranges of thermal properties for normal
concrete, but the thermal conductivity calculated from these values was within the typical range for normal concrete. The coefficient for thermal expansion and concrete creep were also within the typical range for hardened concrete.The internal relative humidity test result
was typical of the annual value in the environment. The compressive strength was greater
than minimum design value, and the modulus of elasticity test result was greater than the
calculated design value. The splitting tensile strength was nearly double the value calculated
from the design compressive strength. A tensile strength of 600 pounds per square inch was
established as a material property for the shield building concrete based upon 10 percent of
the average 28-day compressive strength (6000 pounds per square inch) as shown in . The examinations found no evidence of chronic thermal factors in the concrete
cores collected at the various diverse orientations of the shield building wall.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 27 Twenty-two of the shield building concrete cores were examined by PhotoMetrics Laboratories using a scanning electron microscope for characteristics such as aggregate size, void fraction, concrete-to-reinforcing steel interaction, carbonation, and fracture analysis.
A methodology similar to ASTM C457 determined the void fraction for the concrete cross-sections and areas with reinforcing steel contact were not substantially different. Two core
samples with reinforcing steel interaction had iron oxide transfer to the concrete and one had
an imprint from the reinforcing steel deformation ribs.The carbonation measured on the exterior surface of the cores was consistent with the depth measured by the petrographic examination from other laboratories. The carbonation measured on both transverse and longitudinal crack surfaces was minimal (average 0.62 millimeters) and inconsequential.These trace amounts of carbonation do not adversely affect
the reinforcing steel or the capacity of the structure. The fracture analysis found no evidence
of microcracks with magnifications up to 500 times on virtually all the samples.The micro-cracks observed in the CTL Group petrographic examination are not representative of the areas examined by PhotoMetrics Laboratories from locations exposed to repetitive loading versus near surface concrete. The core bores with evidence of multiple laminar cracks in the same area of outside face reinforcement were considered part of a single delamination
process.Reinforcing steel samples taken from the shield building temporary access opening were also examined by PhotoMetrics. These reinforcing steel samples did not exhibit excessive
corrosion or material loss and were representative of the minor amount of corrosion expected
during staging for the shield building construction. There was no evidence of extensive
corrosion or deterioration that would be expected if the reinforcing steel had been exposed to
moisture during plant operation after the shield building had been constructed.
Conclusion from Petrographic and Destructive Examination The external laboratory examination of the shield building concrete core samples determined that the concrete was in good condition and consistent with the mix design. One core did not
meet industry requirements for freeze / thaw durability, however the higher apparent
compressive strength of the concrete provides resistance which is the key component to freeze / thaw deterioration. Long term exposure to moisture is clearly evident in the core
bores.General properties of concrete that may promote cracking include, by are not limited to, high volume of paste, elevated water-cement ratio and unsound aggregate. The overall volume of
paste in the DBNPS concrete is not considered to be high. The overall estimated water-
cement ratio of the concrete is considered to be low. The crushed limestone aggregate
appears to be chemically and physically sound. In general, variability in concrete may lead indirectly to cracking if areas of poor consolidation, elevated water-cement ratio, or
concentration of air void are extensive; however, this does not appear to be the case in the
concrete represented by the cores removed from the shield building.The exposed concrete surface had carbonation typical for a concrete structure of 40 years. In addition the thickness of the concrete cover is much larger (3-inches) than the carbonation
depth (<1/2-inch) and thus the current carbonation does not reduce the concrete's ability to
protect the reinforcing steel.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 28 The interior cracked concrete surfaces had trace amounts to no indication of carbonation which indicates that the cracked surfaces do not affect the concrete's ability to protect the
reinforcing steel.
The lack of microcracks on the fracture surfaces eliminates a progressive aging failure or fatigue mechanism. There was no evidence of typical concrete time-dependent aging failure modes such as chemical attack including reinforcing steel corrosion, physical attack, chronic
freeze / thaw, and vibration / fatigue. The integrity of the concrete narrowed the failure
mechanism to those related to design or environmental issues versus construction. The
observed extent of laminar cracking in the shield building together with the core examination
results indicated that the mechanism was most likely caused by an acute and large radial force
as opposed to gradual degradation over time due to smaller cyclical forces.
The examination found the outer surface of the cores was not water-repellant, and the air voids were lined with secondary deposits of ettringite and calcium hydroxide which suggests long-
term exposure to moisture migrating through the concrete.
The physical properties of the concrete were obtained and used as input to shield building modeling and analysis described later in this report.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 29 3.3.4 Surface Examination A surveillance test and a maintenance rule structural inspection procedure govern the periodic surface visual inspection of the shield building at DBNPS. Procedure DB-PF-03009, Containment Vessel and Shield Building Visual Inspection, satisfies the surveillance
requirement of Technical Specification 3.6.1.1 for performing the required visual examination
of the shield building in accordance with the Containment Leakage Rate Testing program, and also for maintenance or modification testing.Personnel who perform the shield building visual
inspection via procedure DB-PF-03009 meet the requirements for a general visual examiner.
The accessible interior and exterior surfaces of the shield building are examined for evidence of flaking, spalling, discoloration, voids, cracks, or other signs of distress. Any conditions that may affect structural integrity, or otherwise not meet the acceptance criteria, are documented on a Condition Report. Other insignificant scratches, dings, chips, or abrasions may at the
discretion of the inspector be documented on a Notification.Procedure EN-DP-01511, Design Guidelines for Maintenance Rule Evaluation of Structures, satisfies the criteria for evaluation of safety-related structures that are relied upon to mitigate an accident or transient or whose failure could prevent safety-related structures, systems or
components from performing their safety-related function. Personnel who perform the shield
building visual inspection via procedure EN-DP-01511 are degreed engineers with a minimum
of 5 years experience in civil structural engineering activities, with the ability to judge
deficiencies potentially affecting the structural adequacy of the respective structures. Concrete cracks less than 1/16 inch width need not be evaluated unless they have developed through the entire thickness. Any conditions that impair the structure capable of performing its intended function, or could deteriorate to an unacceptable condition are identified on a
Condition Report.
A shield building surface visual inspection history is provided in Attachment 3. The Maintenance Rule Structure Evaluation from June 1999 and November 2005 identified surface
cracks, but since they were all less than 1/16 inch, the cracks were found to be acceptable.
Since May 1996, the surface visual inspections of the shield building exterior have identified
concrete spalling above the original construction opening. The concrete spalling above the original construction opening coincides with the location of the various grout tubes used for
closing the blockout as shown on drawing C-112 detail 1.On August 15, 1976 the Toledo Edison Company construction superintendent documented an examination of the shield building dome parapet that found a cracked and broken architectural flute shoulder corner at approximately 292 degree azimuth. There were also other hairline shrinkage cracks in the dome parapet at both corners of each architectural flute shoulder, at mid-width of each flute, and vertical around the periphery of the parapet that should not affect the structural integrity of the shield building dome parapet. One small area of the latex coating at approximately 315 degrees mid-way up the shield building dome was found peeling and chipping from being applied too heavily (~1/4 inch). That coating was identified for removal with the area reapplied using a thinner layer of the same latex. None of the inspections of the shield building exterior surface identified any symptoms that would signify the presence of the concrete laminar cracking. None of the inspections of the
other safety-related structures such as the auxiliary building or intake structure exterior identified any symptoms that would signify the presence of concrete laminar cracking or
waterproof coating degradation.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 30 Three other Condition Reports initiated during the 2011 mid-cycle outage describe localized concrete surface distress consisting of surface cracks, spalling, and exposed reinforcing steel on the shield building. These three conditions were discovered subsequent to the original
crack at the left-top of the temporary access opening which continued to the exterior surface.
The other concrete surface distress conditions were evaluated separately from this root cause analysis and determined to not impact the structural integrity of the shield building.
Condition Report 2011-04190 was originated on October 23, 2011 for several instances observed from the roofs of the auxiliary building and emergency diesel generator rooms of
concrete surface cracking on the shield building exterior. The shield building exterior surface concrete cracks varied in length, and were tight with the greatest width measured at 0.025
inches. The surface cracks are not a structural concern due to their tightness.
Condition Report 2011-04507 was originated on October 28, 2011 and describes several minor tight concrete surface cracks on the shield building exterior near an anomalous
indication from Impulse Response testing and core bore S10-672.0-34. These surface cracks
were less than three feet in length and had depths of approximately one inch from the surface.
Another approximately one square foot area with minor concrete surface cracks was located
on shoulder 15 in close proximity to a second anomalous indication identified by Impulse Response testing. There was no spalling or signs of staining associated with either of these
locations having concrete surface cracks on the shield building exterior. The surface cracks
were determined to not be a structural concern due to their tightness.
Condition Report 2011-05648 was originated on November 18, 2011 for exposed reinforcing steel and spalling on the shoulder 4 corner located above the emergency diesel generator
room roof, and a horizontal shrinkage crack extending from flute 2 to the face of shoulder 4 at
approximately 797 feet elevation. The spalling condition on shoulder 4 originated from
reinforcing steel which was exposed to the environment and subjected to localized corrosion.
This exposed reinforcing steel and associated spalling is confined to the corner of
architectural shoulder 4, and therefore is not of a structural concern nor will it impact the ability
of the Shield Building to perform its design function.
After returning DBNPS to service in December 2011, thermal imaging was performed at the concrete near the main steam line penetration blockouts of the shield building with the unit at
100 percent power. The thermal imaging determined that concrete above main steam line
penetration 39 is about 107 degrees Fahrenheit, and about 101 degrees Fahrenheit at the
adjacent core bores (S7-652.0-6.5 & S7-652.0-6.5). The thermal imaging determined that
concrete above main steam line penetration 40 is about 122 degrees Fahrenheit, and about 108 degrees Fahrenheit at the adjacent core bores (S9-650.0-9 & S9-653.0-11). These
readings on the surface of the concrete at the main steam line penetration blockouts of the
shield building are substantially less than the general 150 degree or localized (penetration) 200
degree Fahrenheit temperature recognized as the threshold for a reduction of strength and
modulus due to elevated temperatures. Additional description of the potential impact from a
high temperature environment is provided in Attachment 12 (failure mode 3.7).
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 31 Conclusion from Surface ExaminationVarious visual inspections of the shield building exterior surface performed over many years did not identify any unusual surface defects or symptoms of distress that would signify the
presence of the subsurface concrete laminar cracking. The items identified were localized
surface conditions unrelated to the shield building concrete laminar cracking. As described above, the shield building is inspected by visual examination of the concrete surface. This inspection is specifically reviewing the structure for cracks, concrete spalling, and scaling (loss of cement and fine aggregate at the concrete surface). These may be
indications of a structural concern requiring further investigation.
This method of inspection, by definition, can not detect subsurface cracks. The visual method of inspecting concrete structures is the standard for nuclear power plant structures. The
corrective actions section of this report detail the DBNPS plan for the long term monitoring of
the shield building laminar cracks.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 32 3.3.5 Design The original concept for DBNPS included a post-tensioned concrete containment with steel liner similar to other plants with a nuclear steam supply system from Babcock & Wilcox. A
post-tensioned concrete containment consists of steel wire tendons that are installed, tensioned, and then anchored to the hardened concrete forming the structure. The tendons counteract tensile loads by subjecting the concrete to high compressive forces to prevent or
minimize cracking and also improve resistance to shear forces that could develop during
accident conditions.
In April and May 1969, the Chicago Bridge and Iron Company submitted proposals for a free-standing steel containment vessel with a reinforced concrete shield building at DBNPS. The
Chicago Bridge and Iron Company would subcontract for construction of the shield building, but the design would be the responsibility of the Bechtel Corporation. On May 22, 1969 the
Toledo Edison Company instructed Bechtel to proceed with a containment system for the station utilizing a free-standing containment vessel surrounded by a reinforced concrete shield
building instead of the post-tensioned concrete containment with steel liner.
The shield building is designed to provide biological shielding during normal operation and from hypothetical accident conditions [Reference 10.1.1]. The shield building provides
radiation shielding, a means for collection and filtration of fission product leakage from the
containment vessel following a hypothetical accident, and environmental protection for the
containment vessel from adverse atmospheric conditions including extreme winds, tornadoes, and tornado-borne missiles. Besides the emergency ventilation system, the shield building
also interfaces with station lightning protection, and station drainage.
The shield building is a structure consisting of concrete, and reinforcing steel, with other minimal miscellaneous embedded material. The shield building was designed in accordance
with American Concrete Institute (ACI) 307-69, Specification for the Design and Construction
of Reinforced Concrete Chimneys, and checked by the Ultimate Strength Design Method in
accordance with ACI 318-63, Building Code Requirements for Reinforced Concrete.
The design of the shield building considered the structure dead load, live load, earthquake load, wind load, tornado load, external missiles, thermal load, and a loss of coolant accident.
The dead load considered the density of the shield building concrete and reinforcing steel.
The live load considered 40 pounds per square foot on the shield building dome. The
earthquake load considered a horizontal ground acceleration of 0.15g acting concurrently with
a vertical ground acceleration of 0.10g.
The wind load considered 90 miles per hour at 30 feet above grade which represents the highest wind speed expected for a hundred year period. The tornado load considered a pressure drop of 3 pounds per square inch in 3 seconds which represents twice the greatest pressure drop ever reliably measured. The tornado load also considered a lateral force based
upon a funnel with a tangential velocity of 300 miles per hour. Objects of low cross-sectional
density such as boards, metal siding, and similar items may be picked-up and carried at the maximum wind velocity of 300 miles per hour. The external missiles considered include a 12 foot long piece of wood 8 inches in diameter traveling on end at a speed of 250 miles per hour, a 4000 pound automobile traveling through the air at 50 miles per hour not more than 25 feet
above ground, and a 10 foot long piece of pipe of 3.4 inches outside diameter traveling on end
at a speed of 100 miles per hour.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 33 The thermal load considered a temperature of negative 17 degrees Fahrenheit in the winter on the outside of the shield building, with an annulus temperature of 110 degrees Fahrenheit.
The loss of coolant accident load considered a temperature of negative 17 degrees Fahrenheit in the winter on the outside of the shield building, with an annulus temperature of 152 degrees
Fahrenheit. The design basis thermal load calculations for the shield building did not take any
structural credit for the mass of the architectural flute.
Load combinations specified in ACI 307-69 provide the design basis of the shield building. The smallest safety margin is greater than the ACI 318 code requirements by 3 percent and located
on the vertical reinforcement at the base of the shield building. The smallest safety margin
applies to the combination of dead load, live load, earthquake, and thermal load. The concrete for the shield building is a dense durable mixture of coarse aggregate, fine aggregate, cement, and water. An air-entrainment admixture and a water-reducing & retarding
admixture were added to improve the quality and workability of plastic concrete during placement and to retard the set of the concrete. The air-entrainment admixture increases the resistance to freeze / thaw cycles in the concrete by creating air voids which allow water to move to the void during freezing. The water-reducing & retarding admixture were utilized to
reduce the shrinkage and creep of the shield building concrete. Type II cement was used
below-grade for its greater resistance to aggressive chemical attack from sulfates in the fill
material placed against the structure. The concrete for the shield building has a design
compressive strength of 4000 pounds per square inch at 28 days for the wall, and wall below
grade. A waterproofing membrane is used around the below-grade portion of the shield
building exterior.No exterior protective sealant other than the waterproofing membrane below-grade was specified as a barrier against moisture migrating into the shield building structure from the environment. A Bechtel project meeting held on September 5, 1969 to review and estimate protective coatings for DBNPS determined that there would be no painting required on the inside or outside concrete walls of the shield building. Neither the Field Service Contract for field painting (FSC-21), the specification for field painting (A-24), or the specification for the
shield building (C-38) describe application of an exterior protective sealant on the shield building. An exterior protective sealant on the shield building was not identified in industry standards for protective coatings for reactor containment facilities or the nuclear industry such as ANSI N5.9-1967, ANSI 101.2-1972, or ANSI N101.4-1972. Therefore, the design codes at the time of construction did not require the application of a protective coating on the exterior of
the shield building. On November 11, 1970 Bechtel revised the site architectural elevation drawings (A-20 through A-23) to specify a waterproof finish applied to the reinforced concrete exterior surfaces of various buildings, excluding the shield building. On September 7, 1976 Bechtel requested the
field painting contractor to proceed with the application of a waterproof finish to the reinforced concrete exterior surfaces of various structures as shown on the architectural elevation drawings, excluding the shield building. A sprayed-on waterproof finish of Thoroseal plaster mix (white) was applied in accordance with Thoro System specification S-1-H. The American Concrete Institute standard for coating of concrete for protection against chemical attack (ACI 515.1) was subsequently updated in 1979 to provide guidance for use of water-proofing and damp-proofing barrier systems.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 34 As described above, the shield building wall contains concrete with a minimum compressive strength of 4000 pounds per square inch. Reinforced concrete principles dictate that the
concrete carries the compressive loads and the provided reinforcing steel carries the tension loads. This arrangement is due to the inherently low tensile strength of concrete. The tensile strength of concrete is a more variable material property than the compressive strength. The
tensile strength typically ranges between only 10 to 15 percent of the compressive strength of
the concrete, which is the reason that concrete is not designed to carry tensile loads. The structural reinforcing steel in the shield building consists of deformed billet steel bars. The reinforcing steel is placed in the concrete walls, dome, and foundation for tensile strength to
control cracking due to concrete shrinkage and temperature gradients. The design of the
shield building ensures an elastic behavior of the reinforcing steel during a maximum possible
earthquake which controls cracking of concrete and impairment of leak tight integrity. Major
openings and penetrations through the shield building are designed such that, the anticipated
loads are carried by frame action around the openings. This frame action is achieved by
adding sufficient reinforcement around the perimeter of the openings and adding diagonal bars at each corner of the openings to provide tension and shear capacity. Corrosion protection for
the reinforcing steel in the shield building is provided by a minimum of two inches of concrete
cover at either face of the wall.
The radial cracking effect of reinforced concrete is considered for thermal load as suggested by ACI 307-69. This cracking is limited by using a relatively large amount of reinforcing steel.
Based upon ACI publication SP-20, "Causes Mechanism and Control of Cracking in Concrete,"
under the operating conditions the maximum width of cracks is 0.009 inch, which is less than
the allowable (0.01 inch) permitted by the ACI Standard Building Code.
The primary pattern for the outside face structural reinforcing steel is #11 at 12-inch on-center in the horizontal and vertical direction as shown on Drawing C-110. Exceptions to this reinforcement pattern exist in areas of increased loading such as sections below grade, at the
top 20 feet / spring line, and at openings or penetrations. The architectural flute shoulder
horizontal reinforcing steel is #8 at 12-inch centers. The architectural flute shoulder has radial reinforcing steel that interfaces with the outer face of structural reinforcing steel adjacent to the
tangential end, and interfaces with the inner face of structural reinforcing steel at the thickest part of the shoulder. No other tie-bars or stirrups connect the outer face of structural
reinforcing steel to the architectural flute shoulder region besides that at the tangential end and
the thickest part of the shoulder.The original design of the shield building is robust as demonstrated in the following discussion of the calculations performed to evaluate the laminar cracking observed.
The assessment of the concrete cracking resulted in the development and approval of three new calculations to establish reasonable assurance that the shield building can perform its
intended design functions [Reference 10.1.19]. In addition to establishing reasonable
assurance that the shield building can perform its intended design functions, these calculations also identify several areas of additional margin where credit is not taken such as with tornado
design and damping criteria, and actual strength of reinforcing steel and concrete tested as greater than the minimum design basis. These calculations are not credited as design basis
analysis as they were performed to establish reasonable assurance that the shield building can
perform its intended design functions, and not performed to support full licensing compliance with all design basis loads, load combinations, and allowable stress requirements.
Direct Cause Corrective Action #2 re-establishes design and licensing basis conformance for the shield building with the observed concrete cracking.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 35 The first new calculation [Reference 10.1.20] analyzed the shield building with the vertical outer face of structural reinforcing steel considered ineffective in the sixteen architectural flute shoulder regions and adjacent to the main steam line penetration blockouts based on the extent of concrete cracking found by impulse response testing and core bores. This analysis evaluated the building for the applicable load combinations described in USAR Section 3.8.2.2.
This analysis evaluated the structure considering the reinforcing steel discussed above as
being ineffective for the accident loading combinations. The analysis evaluates the shield
building using several approaches to ensure that the overall structure remains adequate with
the ineffective reinforcing described above. The calculation concludes that the limiting design condition for the vertical reinforcement occurs towards the top of the structure. The analysis
concluded that the structure has a demand to capacity ratio of 0.90 which is less than the limit of 1.0. This calculation also identifies additional conservatisms that were not explicitly used in the evaluation. These conservatisms include potential use of the revised tornado design
criteria of Regulatory Guide 1.76, Rev. 1, increased seismic damping ratio of Regulatory Guide 1.61, Rev. 1, actual material strengths as documented in test reports. This analysis concluded that the shield building, as evaluated, remains adequate to perform its design basis functions.
The second new calculation [Reference 10.1.21] analyzed the shield building reinforcing steel to determine if the sixteen architectural flute shoulder regions remain adequately anchored for
seismic conditions. The analysis considers the reinforcing steel to carry all loads due to the identified cracking in the architectural flute shoulder area for the dead and safe shutdown earthquake (SSE) load combination. This analysis concluded that the architectural flute
shoulder regions will remain anchored by the reinforcement to the shield building and do not
present a seismic II/I or missile hazard.
The third new calculation [Reference 10.1.22] analyzed the horizontal outer face of structural reinforcing steel based on the extent of concrete cracking found by impulse response testing
and core bores. This analysis calculated the hoop stresses at the critical locations of the
spring line area between elevations 780 & 800 feet, the main steam line penetration blockout
areas, and at a critical location on the architectural flute shoulder region. This limiting portion of this analysis is the main steam line penetration blockout area where two-thirds of the
horizontal hoop reinforcement is considered to be ineffective. The analysis has determined
that the stresses in the remaining horizontal hoop reinforcement are approximately 73% of the
allowable stress limit. This analysis did consider the reduced tornado differential pressure loading of Regulatory Guide 1.76, Rev. 1 to calculate this reinforcement stress ratio. The use
of the regulatory guidance is acceptable for this functionality review type of calculation. The
calculation concludes that the shield building, as evaluated, remains adequate to perform its
design basis functions.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 36 Conclusion from Review of Shield Building Design The shoulder area was considered an architectural (cosmetic) feature of the shield building and no credit for the shoulders was taken in the design of the structure. The shoulder
horizontal reinforcing steel was based upon standard practices and tied back only at the sides
of the shoulder area.
As described above, the shield building was analyzed for the appropriately conservative design basis loadings and load combinations described in the USAR. The structure was designed for
these loads in accordance with the ACI 307-69 and 318-63 concrete codes and the allowable stress limits of the Davis-Besse USAR. This provided a robustly designed structure.
The robustness of this structure is further demonstrated by the functionality Calculations C-CSS-099.20-054 and C-CSS-099.20-056. These two calculations were performed to evaluate
the affect of the identified laminar cracks. The two analyses evaluated the structure on the basis that a large percent of the steel reinforcement was considered to be ineffective. The
analyses concluded that even with the "ineffective reinforcement," the shield building remains
adequate to perform its design basis functions.
In conclusion, the original Davis-Besse shield building was appropriately designed for the identified loadings and code requirements. The effects on the identified laminar cracking have
been evaluated and the shield building remains adequate to perform its safety functions.
However, there was no application of a sealant on the exterior concrete surface of the shield building to protect against moisture migrating into the structure.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 37 3.3.6 Construction The actual DBNPS site construction was accomplished through twelve major construction contracts and a number of other smaller contracts. The shield building wall was built by Fegles
Power Service under construction contract CC-18 and Purchase Order 1221. Bechtel Power
Corporation was retained to provide construction management services. Specification C-38
governed the construction of the shield building along with several of the C-100 series of drawings. The concrete forming, placing, finishing, and curing were in accordance with
Specification C-26. The reinforcing steel furnishing, detailing, fabricating and delivering were
in accordance with Specification C-29. Nicholson Concrete and Supply Company operated the
central concrete mix plant in accordance with Specification C-25, and on-site materials testing
services was performed by the Pittsburg Testing Laboratory in accordance with Specification C-27. The A. Bentley & Sons Company performed general station structural work including
construction of the shield building dome and closure of shield building blockouts that were
open after the initial construction for access, and mechanical or electrical penetrations.
The Fegles Power Service proposed construction of the shield building wall using the slip-form method of concrete construction based upon experience from three other similar containment
structures. The proposal was based upon revision 0 of the C-100 series of drawings for a
shield building wall 139 feet inside diameter, 256 feet 6-1/2 inches high, and 2 feet 6 inches
thick that was estimated to contain 10,881 cubic yards of concrete, and 1715 tons of
reinforcing steel.
The shield building specification [Reference 10.1.23] required Type II cement for use in slip-form construction of the shield building below grade, and Type I cement above grade. The
Type I cement had earlier strength gain which facilitates the speed of the slip-form
construction. Specification C-38 also required shield building construction tolerances for
thickness, roundness, plumb, and azimuth / elevation of embedded items and blockouts. Work
not included in the shield building construction contract was installation of waterproofing
membrane on the exterior of the shield building wall below-grade, or sealant of the shield
building wall.
The historical central concrete mix plant specification (C-25) required C-2 class concrete for foundations and walls over 12 inches thick. The C-2 class concrete required a 1-1/2 inch
maximum aggregate size, 5 inch slump working limit at the point of placement for slip-formed
concrete, a compressive strength of 4000 pounds per square inch at 28 days, and an air content of 3 to 6 percent by volume. The concrete mixes for the shield building slip-form
construction were developed by Fegles Power Service and approved by Bechtel Power
Corporation. Concrete mix C-2-SF-2 was used below grade for the shield building wall and
concrete mix C-2-SF-4 was used above grade.
Slip-form construction enables continuous structures that are based upon the quick-setting properties of concrete, but require a balance between the quick-setting capacity and
workability. The concrete form is surrounded by a platform used for workers pouring the concrete, placing reinforcing steel into the form, and staging of materials. The concrete form
and working platform are periodically raised together by means of hydraulic jacks. The slip-form rises at a rate which permits the concrete to harden by the time it emerges from the bottom of the form. Concrete used in slip-form construction needs to be workable enough to
be placed into a form and packed, yet quick-setting enough to emerge from the form with sufficient strength to permit the form to slip upward and also support additional concrete
poured above.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 38 The slip-form method was used in the early 20 th century for construction of concrete silos and grain elevators. Other applications for the slip-form construction method include concrete
chimneys and stacks, storage tanks, communication towers, bridge foundations, buildings such as the Canadian National (CN) Tower, and containment buildings at nuclear power
plants. Slip-form construction continues to be used for construction of the concrete
containment walls with the Canadian deuterium uranium (CANDU) nuclear plants.
The major advantages of the slip-form method are a shortened construction schedule, and the ability to complete the project with a single concrete pour with no joints. The slip-form method
for construction of CANDU concrete containment walls takes 13 to 20 days versus 6 to 9
months for conventional construction methods. Disadvantages of the slip-form method of construction are increased planning and coordination of resources, very few contractors with
slip-form capability, and mistakes are difficult to correct.
The slip-form construction used for the DBNPS shield building consisted of a form four feet high on the inside and outside of the wall with working decks eight feet wide on the inside and
six feet on the outside [Reference 10.1.24]. A cement finisher's platform was suspended at
both the inside and outside wall faces approximately 9 feet 6 inches below the working deck.
This platform was carried on the bottom of the pre-fabricated deck supports. Eighty pairs of 1-1/8 inch diameter mild steel jacking rods equally spaced around the circumference of the wall were used to lift the slip-form as the shield building was constructed. Lifting of the slip-form
was accomplished by means of pneumatic jacks that climb the rods and push against the
yokes which are attached to the top and bottom of each segment of the slip-form. The yokes hold the form to its proper width and batter.All of the jacks were connected to one control
board and operated at the same time to lift the form.After the first four feet of reinforcing steel was placed for the shield building wall, the moving form was erected and all concrete apparatus, jacks, and hoisting equipment was inspected
and approved by the Bechtel Quality Assurance Engineer prior to commencing the first concrete pour. The first four feet of wall was poured with the form standing still, but was
poured in the same manner as when the form was being raised to help train crews and to
balance the concrete level all around the circle. The concrete was placed directly into the
forms from a specially designed round concrete bucket in approximately 9 inch layers evenly
around the form, and then worked with electric vibrators. The bucket was hoisted to the deck by means of an electrically controlled, free-standing tower crane after being loaded from a
charging hopper. At the foundation level, the charging hoppers were fed by concrete
conveyers loaded from the ready-mix trucks. Once the first concrete in the four foot slip-form had attained the proper set, the jacking operation was started. Thereafter, the rate of the forms vertical movement was controlled by
the Slip-Form Superintendent, based on the setting rate of the concrete, placing of reinforcing bars, placing of inserts and openings. A minimum of 18 to 20 inches of firm concrete was
maintained in the lower part of the forms to provide support at all times for fresh concrete.
Roundness of the slip-form was controlled using an 8 inch channel rolled to a pre-determined radius placed on the top cross member of the jacking yoke to help maintain the required
circular configuration. A system of 16 adjustable cables was installed between the inside form
and a prefabricated steel hub located around the tower crane mast. This system provided horizontal adjustment necessary to maintain the circular configuration of the slip-forms. These
cables were attached to the form segments and their length was adjusted by manually
operated one-ton chain hoists.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 39 The form configuration was checked by the job engineer by eight direct diametric measurements across the inside of the wall at approximately the same times as the plumb
readings are made. The wall plumb was measured at 16 equally spaced stations on the moving forms at the inside face of the wall.The readings were taken at eight-hour intervals
during the slip-form operation. If deviations from plumb indicated that corrective measures
were necessary, the slip-form and working platform level were adjusted to bring the whole structure back to its original position.These adjustments were made through control of
individual jacks by the jacking crew and/or use of a telescoping leg and guide wheel system
mounted on the jacking yoke. A freeze / thaw test of the slip-form concrete mix was completed on January 8, 1971, prior to commencing construction of the shield building. A total of 32 cylinders 6 inches diameter by
12 inches long were cured, subjected up to 14 freeze / thaw cycles between 0 and 40 degrees
Fahrenheit, and compression tested at intervals up to 28 days. None of the specimens
subjected to the freeze / thaw cycles showed any surface defects such as spalling, and all had
compression test results greater than 4000 pounds per square inch.
Construction of the shield building commenced on January 25, 1971, and was interrupted on February 4, 1971, at elevation 583 feet 6 inches. This completed the below grade work which
was allowed by an Atomic Energy Commission exemption obtained on September 10, 1970.
Construction permit CPPR-80 was then issued on March 24, 1971, and shield building construction re-commenced with the second concrete pour on April 26, 1971. Construction of
the shield building wall was completed on May 19, 1971, at elevation 801 feet 6 inches. The
shield building milestones and shield building slip-form construction sequence are described in
Attachments 4 and 5.
The DBNPS shield building wall was constructed 139 feet inside diameter, 256 feet 6-1/2 inches high, and 2 feet 6 inches thick containing 11,028.5 cubic yards of concrete. Data readily available from two structures at other nuclear sites built using the slip-form method describes
similar construction. The Pickering vacuum building built in 7 days 10-1/2 hours in the late
1960's using slip-form construction was 168 feet diameter, 159 feet high, and 3 feet thick
containing 9,310 cubic yards of concrete and 952 tons of reinforcing steel. The St. Lucie Unit
2 reactor containment building built in 16-1/2 days in the late 1970's using slip-form
construction was 132 feet diameter, 192 feet high, and 3 feet thick using 10,000 cubic yards of
concrete. The target climb rate for the slip-form was 9 inches per hour at DBNPS, 9 inches per
hour at Pickering, and 6 inches per hour at Saint Lucie Unit 2. The DBNPS shield building remained uncovered until August of 1973. On August 9, 1973, a pour for the construction of the Shield Building dome ring girder was completed. A series of
pours were conducted for the parapet and the dome top slab was completed on October 2, 1973. Closure of the original construction opening commenced on August 6, 1975, and the
final pour was completed on December 1, 1975. Specification C-25 required D-1 class
concrete for foundations and walls less than 12 inches thick and / or congested reinforcement
steel. The D-1 class concrete required a 3/4 inch maximum aggregate size, 3 inch slump working limit at the point of placement, and a compressive strength of 5000 pounds per square inch. The A. Bentley & Sons Company used D-1-4P (no fly-ash) for the shield building dome
and D-1-3 (no fly-ash) for closure of the original construction opening. The shield building
concrete compression test results and mixes are described in Attachments 6 and 7.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 40 In August 2002, a temporary access opening for replacement of the original reactor pressure vessel head was created using a hydrodemolition process within the area of the original
construction opening [Reference 10.1.25]. The temporary access opening was restored in
September 2002, with replacement concrete that had a specified compressive strength of 4000 pounds per square inch at seven days to expedite achieving the original shield building design compressive strength results of 4000 pounds per square inch at twenty-eight days [Reference
10.1.26]. The concrete strength for the approved mix design was maintained by limitations to
the water/cement ratio. The concrete slump was controlled using a high-range water-reducing admixture to enable increased workability without an increase in the established water/cement ratio of the mix. This ensured that the quality and strength of the hardened concrete was not
adversely affected by a permitted slump range of 2 to 6 inches at point of placement.
Noteworthy deviations during construction of the shield building walls were issues such as concrete with the wrong water to cement ratio, concrete with smaller coarse aggregate size, concrete with the wrong type of cement, exceeding shield building wall tolerance for plumb, installation of reinforcing steel, embeds, or reglets, and omission of blockouts. The shield
building construction deviations are described in attachment 8.Three Quality Assurance audits of the Fegles Power Service jobsite were conducted on 2/18/1971, 5/11/1971, and 11/22/1972. These audits concluded that all drawings and
documentation were of the latest issue and bearing the necessary Bechtel approval.Other recently discovered issues involving concrete cover and/or spacing for reinforcing steel at the shield building temporary access opening are identified in Condition Reports 2011-
03232, 2011-04973, and 2012-00071. Condition Report 2011-03232 identifies locations where
the reinforcing steel at the shield building temporary access opening did not have the minimum
3 inches of concrete cover specified on the design documents. The concrete cover is required
by the American Concrete Institute to protect the reinforcing steel from environmental conditions and to provide sufficient embedment. The shield building concrete cover condition
was reviewed and a rework disposition specified to obtain the proper depth. Condition Report
2011-04973 identified additional locations at the shield building temporary access opening
where the 3 inch concrete cover over reinforcing steel was not provided, and locations where
the as-found spacing of reinforcing steel did not conform to the design documents. This
condition for reinforcing steel cover and spacing was reviewed and a Repair disposition was
specified to revise the design document requirements. Engineering Change Package 10-0458
was revised to provide the modified installation requirements and document the technical basis
for the changes to the shield building temporary access opening. Condition Report 2012-
00071 was initiated to identify that the evaluation of reinforcing steel spacing at the temporary
access opening only considered a maximum concrete aggregate size of 1 inch in lieu of the
specified 1-1/2 inch maximum aggregate used in the Shield Building slip-form concrete mix
design. The conclusion was that the reinforcing steel spacing was acceptable with the
specified 1-1/2 inch maximum aggregate used in the Shield Building slip-form concrete mix
design.Conclusion from Review of Shield Building Construction The deviations during construction were localized and minor in nature such that there was no evidence that construction methods or materials contributed to the laminar concrete cracking in
the shield building walls.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 41 3.3.7 Operational Phase Twenty-one events were identified in the Operational Phase that could have or did occur during the life of the station that could have initiated the laminar cracking in the shield building.
These 21 items can be categorized into the three main groups consisting of Construction
Activities, Long Term Events, and Acute Events.
Construction Activities The failure modes associated with the Construction Activities consist of installation of a shield building opening, modification activities that could adversely impact the structure, and
penetrations through the shield building. These failure modes were investigated and
eliminated since the location of the laminar cracks do not coincide with any of these activities.
In addition, settlement was also ruled out since the shield building foundation bears directly on
bedrock.Long Term Events The failure modes associated with the Long Term Events such as chemical attack, reinforcing steel corrosion, concrete/reinforcing steel creep, physical attack and vibration were investigated and were eliminated based on the results of the testing performed on the concrete cores. These tests show that there is no evidence of chemical attack, active reinforcing steel corrosion, chronic freeze / thaw or cyclic conditions and physical attack.
There is however, supporting evidence that indicates that the south-west quadrant of the shield building, which is typically at a higher temperature due to solar heating, is more prevalent than other locations of the shield building. Therefore, a detailed finite element analysis was
performed [Reference 10.1.16, Exhibit 64] to determine the effects of long term thermal stress
cycles with seasonal changes.
The possibility of thermal fatigue damage can be assessed by 1) Stress level caused by temperature gradient, 2) Damage, such as cracking, due to thermal strain variation, and 3)
Damage, due to elevated temperature.These items are addressed as follows:
- 1) Stress level caused by temperature gradient The finite element thermal stress analysis showed that the maximum radial stress in the structure is about 300 pounds per square inch during a record hot summer day. This is
well below the tensile strength of the concrete and well below the fatigue limit of
concrete under cyclic loading. Therefore, thermal stress due to cyclic solar loading can
be ruled out.
- 2) Damage, such as cracking, due to thermal strain variation The surface strain of concrete under solar heating is a combination of thermal expansion and drying shrinkage. Thermal expansion creates compressive stress in the
surface of concrete. The stress level is well below the compressive strength of the concrete [Reference 10.1.16, Exhibit 56, and 64]. The drying shrinkage creates tensile
stress of concrete, which could generate cracking in concrete. Petrographic
examination results [Reference 10.1.16, Exhibit 26] showed that the depth of shrinkage cracking is not more than one inch after 40 years of exposure to the environment. This
depth is relatively small compared to the depth of concrete cover (3 inches). More importantly, the internal surfaces of many concrete samples were examined by
microscopes [Reference 10.1.16, Exhibit 68], and there is no significant amount of
micro-cracking in the concrete. This indicated that the small surface shrinkage cracks Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 42 did not coalescence to form discrete large cracks. Therefore, thermal strain and shrinkage cracking can be ruled out.
- 3) Damage, due to elevated temperature.
Concrete properties can change under elevated temperatures where phase changes take place (vaporization of water, decomposition of calcium hydroxide, etc). In the case
of solar heating and cooling, the temperature level and the rate of temperature variation
are not sufficient to generate significant phase transformation and spalling damage in
concrete. Therefore, elevated temperature due to solar heating can be ruled out.
The conclusion of all of these analyses is that the radial stresses due to seasonal changes, thermal gradients, gravity, and wind loads are not high enough to cause laminar cracking in the
structure. In addition, based on the analysis performed and the concrete core test results, there is no accumulative aging affects or cyclic events that would indicate on going
degradation issues. Therefore, all long term operational phase issues can be ruled out.
Acute Events Several of the acute events failure modes were eliminated based on the event either not occurring (earthquake), or further evaluation/inspection showed that these were not of a
concern (lightning and electrical potential), or the crack locations did not match the activity (hydrodemolition).
Extreme weather related acute events were also considered. Emergency declarations and Licensee Events Reports were reviewed to identify the range of environmental conditions
experienced by the Shield Building that could be potentially relevant to the concrete laminar
cracking. The site has experienced several of these events, specifically, blizzard like
conditions and tornados.
The top three blizzards in recent recorded Ohio history in terms of temperature, wind and duration, occurring near the site were determined to be the 1977, 1978, and the 1994
blizzards. There three blizzard were researched and it was determined that the 1978 blizzard was the most significant of the three. The 1978 blizzard had wide spread rain two days prior to
the event, wind speeds up to 105 mph, low temperature of -5 o F, snowfall of 12 inches, and duration of 3 days. The 1977 blizzard was the second worst to have occurred at the site.
Blizzard of 1978 The blizzard of 1978 was preceded by warmer than normal weather and precipitation. At 4:30 PM on Wednesday, January 25, 1978, the National Weather Service issued heavy snow
warnings, which was subsequently upgraded to a blizzard warning at 9 PM, including the area
surrounding DBNPS. A moisture laden low pressure system moving northward from the Gulf of Mexico and a polar low pressure system descending from the Arctic were converging over
Ohio and would subsequently pass over the plant.
Early Thursday morning, with temperatures slightly above freezing, and rain / fog, the temperature dropped to near zero within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> at the onset of the Arctic air and remained near 10 degrees Fahrenheit throughout the day. Winds increased to greater than 50 miles per
hour with a wind chill of -50 degrees Fahrenheit. The wind gusts of 82 miles per hour at
Cleveland Hopkins airport were the strongest ever measured, and an ore carrier J. Burton
Ayers on Lake Erie, measured sustained winds of 86 and gusts of 111 miles per hour. At DBNPS, the plant was at 75 percent power in start-up testing when the switchyard breakers for
one transmission line opened at 0516 AM on Thursday, January 26, 1978, followed an hour
later by a loss of all meteorological instrumentation during the blizzard.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 43 The barometric pressure of 28.28 inches mercury at Cleveland Hopkins airport during the blizzard was the lowest in the 48 contiguous states in the 20 th century except for during a hurricane. In southern Ontario a barometric pressure of 28.05 inches mercury was measured, with record low barometric pressures also measured at Toledo, Columbus, Akron, and Detroit.
Snow accumulated between 5 and 10 inches over the two day duration of the blizzard with snow drifts of 15 to 20 feet. The combination of duration, wind speed, visibility, and
temperature rank the storm on January 26 & 27, 1978 as a severe blizzard. The blizzard of
1978 was examined further as a specific case in the modeling and analysis of the shield
building. [Reference 10.1.16, Exhibit 61]
Blizzard of 1977 The blizzard of 1977 was also evaluated to determine its affects on the shield building.However, the blizzard of 1977 was not as severe of an acute event in terms of the key
parameters consisting of moisture preceding the event, temperature, wind speed, and duration. The stresses produced from this analysis are significantly less then those produced
from the 1978 blizzard. The results show that the radial stresses do not exceed the tensile
capacity of the concrete and therefore most likely could not have contributed to the observed
crack. [Reference 10.1.16, Exhibit 61]
Tornado of 1998 On Wednesday June 24, 1998, a storm cell was tracking southeast from Michigan and then eastward along Lake Erie, until suddenly shifting southeast, making landfall directly adjacent to the DBNPS site. The DBNPS site was near the center of the storm cell, where cloud elevation
and wind-speed were the greatest. The rapidly upward moving air feeding the center of the storm spawned several funnel clouds. At approximately 2044 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.77742e-4 months <br />, a tornado touched down
onsite in the vicinity of the cooling tower with damage to the switchyard that resulted in a
complete loss of offsite power. The turbine building roof sustained a large hole estimated to be
8 feet by 20 feet, along with several turbine roof vents ripped off. The strong winds also
resulted in a loss of 9 out of 12 meteorological instruments, plus loss of the fiber-optic and
copper communication lines.
The storm cell experienced at the DBNPS site on June 24, 1998, was categorized by the National Weather Service as an F2 tornado, exhibiting winds between 113 and 157 miles per
hour. The force of this storm was well within the wind and tornado load design basis for the shield building (300 mile per hour wind and 3 pounds per square inch differential pressure).
Licensee Event Report 1998-006 documents the tornado damage to the switchyard causing
loss of offsite power.
An analysis was performed for the maximum wind speed from the blizzard of 1978, [Reference 10.1.16, Exhibit 62] using a wind speed of 105 miles per hour. This analysis concluded that the wind velocity of 105 miles per hour resulted in stresses of less than 1 pound per square
inch around areas where laminar cracking was observed. Scaling the peak wind velocity up to
157 miles per hour for a F2 tornado would not create stresses significant enough to create the laminar cracking observed. The tornado of 1998 was examined further as a specific case in
the modeling and analysis of the shield building [Reference 10.1.16, Exhibit 63].
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 44 Conclusions from Review of Operational PhaseTwenty-one different failure modes were reviewed that were associated with events that did or could have occurred during the operational phase of the plant (post design and construction).
Testing and research of the design documents ruled out the majority of these failure modes.
Extensive computer analyses were performed to develop an understanding of the affects the
various load combinations would have on the Shield Building stresses.
All scenarios analyzed produced stresses below the tensile strength of the concrete and as such they could be discounted. However, only one extreme environmental event, the blizzard
of 1978 which lasted three days, had the individual characteristics that could produce significant stresses. The analysis for the 1978 blizzard concluded that moisture driven into the outer layers of the shield building followed by near zero temperatures could cause freezing of
the water resulting in high radial stresses at the shoulder areas.
The blizzard of 1977, which had less moisture, lower wind speed, and lasted only one day, was also investigated and analyzed. The stresses associated with this condition were less
than the 1978 blizzard and could not have caused the laminar cracking.
The tornado of 1998 was investigated and it was concluded that the associated wind was clearly below the threshold to create the laminar cracking observed.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 45 3.3.8 Shield Building Modeling and Analysis Performance Improvement International (PII) analyzed the shield building for the loading conditions that could not be refuted in the Failure Modes analysis, such as Appendixes V, VI, and VII of Reference 10.1.16. As noted in the PII report, several potential load cases were
refuted including; seismic (Failure Mode 3.1), snow/ice (Failure Mode 3.13), dead weight of
dome (Failure Mode 1.7). Performance Improvement International used concrete stress and
fracture analysis modeling techniques originally developed as part of the Crystal River Unit 3
containment concrete delamination cracking root cause investigation. The modeling and
analysis was updated to reflect the design characteristics of the DBNPS shield building. The
material properties and failure criteria used in the analysis and modeling were based upon the
results of the DBNPS shield building concrete laboratory tests and examinations. The values
used for the material properties are presented in Attachment 4 of this report.
The following exhibits from the PII report document the analyses performed to evaluate various loading conditions for the potential to develop stresses that could cause the identified laminar cracks in the shield building. In addition to the PII analyses described below, PII performed
other analyses that provide input to these analyses or that are not pertinent to the root cause.
The five relevant PII analyses are summarized below:
Reference 10.1.16, Exhibit 51 - Freezing Failure and Rebar Spacing Sensitivity Study
Reference 10.1.16, Exhibit 56 - Structural and Thermal Analysis Investigation
Reference 10.1.16, Exhibit 61 - Stress State during 1978 and 1977 Blizzards
Reference 10.1.16, Exhibit 62 - Stress Analysis Due to 105 MPH Wind Load
Reference 10.1.16, Exhibit 73 - Laminar Cracking Due to 1978 Blizzard PII developed a detailed three dimensional Finite Element Analysis (FEA) model using the Abaqus software for the structural analysis of the Shield Building. The model included the shield building shoulders so that an accurate representation and analysis of this shield building
feature of interest could be completed. This model was used to evaluate various loadings on
the structure described in the PII exhibits below.PII also developed a three dimensional finite element model using the Fluent software. The model included the major structures adjacent to the shield building to allow for the accurate
assessment of their affects on this structure. This model was developed for computational
fluid dynamics analyses and it was used to evaluate various wind and thermal conditions acting on the shield building. This model was used in several PII analysis exhibits.
The NASTRAN analysis software was used to develop a three dimensional finite element model of the shield building. This finite element model was used to evaluate transient thermal
temperatures for the various environmental conditions.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 46 Reference 10.1.16, Exhibit 51 - Freezing Failure and Rebar Spacing Sensitivity Study A FEA model was developed to evaluate the potential for laminar cracks to propagate within the top 20 feet of the shield building cylindrical wall and at each of the main steam line
penetration blockouts. These areas of the shield building were designed with the horizontal
hoop reinforcing steel spaced at approximately 6 inches (center to center). The actual distance is further reduced in locations of the lap splices for the horizontal hoop reinforcement.
This spacing of the reinforcement results in approximately 3 inches of concrete between the
reinforcing steel. The analysis evaluated the potential for the concrete between the horizontal
reinforcing steel to crack during a condition of saturated concrete and below freezing
temperatures. The analysis was based upon a 0.6 and 1.0 percent void fraction under the
horizontal reinforcing steel and a 7 percent expansion of the void due to ice freezing. These
values are conservative based on testing of the shield building core bores. Testing measured an actual void fraction of approximately 6 percent which is consistent with the air entrainment
requirements for the shield building concrete and the 9 percent expansion of water when it
freezes. With a given motivating force, such as elements under horizontal reinforcing steel
treated as freezing ice, all of the models of the shield building exterior with 6-inch spacing
showed the development of some laminar cracks. The analysis for the 1% void fraction and 7% water expansion model indicates that cracking can occur over a significant area of the
shield building cylindrical wall.
This same analysis evaluated reinforcing placed at 12 inch spacing (both horizontal and vertical reinforcing steel) which is typical for most of the remaining exterior surface of this
structure. The 12 inch spacing analysis determined that laminar cracks would not propagate
with this amount of concrete between the reinforcing steel. Therefore, the tighter spacing of the outer face of structural reinforcing steel such as in the top 20 feet of the shield building and
adjacent to openings or blockouts can facilitate propagation of laminar cracking as evident at the main steam line penetration blockouts. This analysis also supports the results of the shield
building physical investigation cylindrical shell wall where cracking was not found in the areas
with the larger reinforcement spacing. The presence of laminar cracking in the main steam line room does not contradict the freezing mechanism. In places where there exists a very high density of reinforcing steel in a single plane (and therefore a very low density of concrete in that plane, like a perforated paper towel)
it is possible for a crack to propagate due to initiation of cracking in an adjacent region. Based upon the Impulse Response test results, the cracking in the concrete adjacent to the main steam line penetration blockouts coincides with regions of very high density reinforcing steel
and have arrested near the boundary of these regions.
Reference 10.1.16, Exhibit 56 - Structural and Thermal Analysis Investigation An analysis was also performed to evaluate the seasonal temperature and wind effects associated with the summer solstice, autumn equinox, winter solstice, and vernal equinox.
The analysis evaluated the two solstice cases and the two equinox cases in order to study the affects of solar radiation on this structure.The analysis identified two bounding cases: the summer solstice and winter solstice with an extreme combination of temperature and wind
conditions. The prevailing wind direction occurs from the southwest for most of the year, particularly the winter and spring seasons. The temperatures were based upon the
atmospheric heat sink surrounding the shield building based upon meteorological data.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 47 The case for the summer solstice (time 7:30 PM, no wind, & daytime temperature 104 degrees Fahrenheit) results in a radial tensile stress of less than 100 pounds per square inch starting at the outer face of structural reinforcing steel behind the thickest section of the architectural flute shoulder. The case for the winter solstice (time 5:00 AM, 105 mile per hour wind, &
temperature -24 degrees Fahrenheit) results in a tensile stress of approximately 190 pounds per square inch starting at the outer face of structural reinforcing steel behind the thickest
section of the architectural flute shoulder. These forces are not sufficient to cause cracking, as
the tensile failure stress of the shield building concrete is 600 pounds per square inch, as
detailed in Attachment 4 to this report.This exhibit also documents a finite element analysis that was performed to investigate the potential propagation of the existing laminar cracks in the shield building cylindrical shell area.
This analysis considered the summer solstice load case and a postulated 30 foot by 30 foot
area laminar crack within the top 20 feet of the shield building wall. This analysis evaluated
the southwest portion of the shield building where the laminar cracking was found to be most
prevalent. The analysis concluded that for the southwest side of the structure that there was
only a marginal increase in the magnitude of radial stress, less than 100 psi. Since the shield
building concrete has a tensile failure stress of 600 psi (Attachment 4 of this report), there is
insufficient radial stress to propagate cracking in the summer and winter bounding cases.
Reference 10.1.16, Exhibit 61 - Stress State during 1978 and 1977 Blizzards The blizzards of 1978 and 1977 presented a unique combination of environmental conditions acting on the shield building. In 1978, the actual blizzard was preceded by several days of
rain. The shield building was evaluated for the potential to introduce moisture into the shield
building shell as described Reference 10.1.16, Exhibit 72.
The analysis describes the use of computational fluid dynamics analyses to calculate the surface temperature of the shield building during the blizzard. The calculated temperatures were used as an input to the Abaqus model for the structural evaluation of the building.
The Abaqus analysis evaluated the structure for the affects of freezing of the entrapped moisture. The analysis model used a subsection of the structure that spanned between the centers of adjacent cylindrical wall panels.This model included two shoulders and the flute
area between the shoulders. The shield building model considered the extreme combination of
temperature and wind conditions of these blizzards. Additionally, the analysis included the
subsequent freezing of the moisture laden concrete using the coefficient of thermal expansion.
The case for the blizzard of 1978 results in a radial stress of approximately 550 pounds per square inch behind the thickest section of the architectural flute shoulder. The case for the blizzard of 1978 also results in a hoop stress of approximately 1200 pounds per square inch adjacent to the outer face of structural reinforcing steel behind the architectural flute shoulder, and a vertical stress of approximately 920 pounds per square inch in the same region.
This analysis concluded that the very high stresses are developed in all three directions. This indicates the damage was likely to have occurred. The analysis shows that the locations of high radial stress from the blizzard of 1978 coincide with the observed laminar crack locations
under the thick sections of the architectural shoulders and not in the thinner sections the shield
building wall.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 48 In order to evaluate the size of the postulated laminar crack a separate analysis was performed as documented in Reference 10.1.16, Exhibit 73. The 1977 blizzard was also evaluated in this exhibit of the PII report. A similar analysis was performed for the moisture, wind, and temperature conditions for this blizzard. The analysis for this less severe blizzard resulted in stresses that were insufficient to cause the laminar
cracking observed.
Reference 10.1.16, Exhibit 62 - Stress Analysis Due to 105 MPH Wind Load An analysis was performed for the maximum wind speed during the 1978 blizzard of 105 MPH.
Reference 10.1.16, Exhibits 67 and 62, describe the computational fluid dynamic and finite
stress analysis used to evaluate the 105 mile per hour (MPH) wind force of the shield building.
The results of these analyses determined that the calculated radial stress was less than 1 psi
for the 105 MPH wind. The 1998 tornado had a wind speed of approximately 157 MPH, Ref.
Failure Mode 3.3 of the PII report. By comparison, the tornado wind could not have generated
sufficient stress to cause the laminar cracking based on the radial stress values from the 105 MPH wind analysis. Therefore, neither the 105 MPH wind nor the 1998 tornado caused the
identified laminar cracks.
Reference 10.1.16, Exhibit 73 - Laminar Cracking Due to 1978 BlizzardThe analysis contained in this exhibit expands on the blizzard analysis presented in Exhibit 61.
This analysis was performed to determine if laminar cracks would actually develop in the high
stress areas predicted developed in Reference 10.1.16, Exhibit 61.
A detailed finite element submodel was created to analyze the probability for laminar cracks to develop under the previously discussed blizzard conditions. The submodel used the calculated temperature distribution in the shield building discussed in Reference 10.1.16, Exhibit 61. The material properties used in this analysis were derived in a sensitivity study that
determined that strength parameters of 600 psi for the concrete tensile strength and fracture
toughness of 0.18 in-lb/in
- 2. These parameter values are well within the expected ranges for these parameters.
The analysis also describes the coefficient of thermal (CTE) expansion of high moisture concrete used in this evaluation. The CTE is described in Reference 10.1.16, Exhibit 57 and it
is used as an input for this finite element analysis.
The finite element submodel spans an approximate width of 23 degrees in the circumferential direction and it includes one flute, one shoulder, and one-half of the adjacent cylindrical shell panel. The blizzard conditions were applied to this model and predictions on the development
of laminar cracks was determined.This analysis concluded that laminar cracks developed mostly at the outer reinforcing steel mat under the thick shoulder regions and not in the thinner sections of the flute and shell. This
cracking pattern was determined to have been caused during the 1978 blizzard. The 1977
blizzard determined that damage was significantly less likely to have occurred.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 49 Conclusion from Shield Building Modeling and Analysis None of the analyses that evaluated the dead, live, seismic, wind, tornado, or historical average or extreme combination of temperature and wind conditions developed sufficient
radial stress to cause laminar cracking of the shield building concrete. Therefore, the forces
involved with the laminar cracking were beyond those anticipated with the design practices
used for the shield building.
The prevailing wind direction occurs from the southwest for most of the year, particularly during the winter and spring seasons, and was the path of the blizzard of 1978.
The postulated acute freezing of moisture adjacent to the outer face of structural reinforcing steel behind the thickest section of the architectural flute shoulder in conjunction with the
blizzard of 1978 was the only scenario capable of producing large stresses. These stress levels would indicate that damage was likely in the shoulder areas where the principle laminar
cracking has been identified, Reference 10.1.16, Exhibit 61.
Reference 10.1.16, Exhibit 73 was performed to determine if laminar cracks would actually develop in the high stress areas identified in Reference 10.1.16, Exhibit 61. This analysis
documents a detailed finite element submodel of the shield building that was evaluated for the 1978 and 1977 blizzard conditions. This analysis concluded that laminar cracks formed in the
shoulder regions during the 1978 blizzard. The analysis concluded that cracking was
considerably less likely to have occurred during the 1977 blizzard. Reference 10.1.16, Exhibit 51 of the PII report describes the analysis of the outer face of structural reinforcing steel for the potential of crack propagation. This analysis determined that a 6 inch or less (center to center) reinforcement spacing would facilitate laminar crack propagation. This analysis is applicable to the laminar cracks found within areas such as
within the top 20 feet of the building wall and the areas adjacent to the main steam line
penetration blockouts. Reference 10.1.16, Exhibit 56 also documents an analysis of the shield building cylindrical wall for a postulated 30 foot by 30 foot area laminar cracking within the top 20 feet of the shield
building wall. This analysis evaluated a reinforcing steel spacing of 12 inches (center to
center) to determine if cracks could propagate. The analysis concluded that there is
insufficient radial stress to overcome the tensile strength of the concrete and that no propagation would occur under conditions such as summer and winter extreme temperatures.
Based on this analysis, there is no expectation that the existing laminar cracks will propagate.
In summary, the analyses discussed above concluded that the laminar cracks formed in the shield building shoulders during the blizzard of 1978 and that these cracks propagated into the
top 20 feet of the shell wall and main steam line penetration blockouts due to the greater
density of horizontal hoop reinforcing steel.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 50 3.3.9 Failure Modes Analysis A fault tree of potential failure modes for the shield building concrete laminar cracking was developed collegially among root cause team members from FENOC, VATIC Associates, MPR, and Performance Improvement International. A list of 45 possible failure modes that
could potentially contribute to the laminar cracking, either individually or in concert were
identified based upon characteristics of the shield building laminar cracking and other
operating experiences with concrete issues.
All 45 failure modes were grouped in three major categories consisting of Design, Construction & Fabrication, and Operational. Each of these failure modes was evaluated during the root
cause investigation. In general, each failure mode was either refuted or supported by
laboratory tests and examinations or by state of the art analysis. Some failure modes were
refuted by deductive reasoning based on existing evidence to either support or refute their mode of failure. Potential failure modes were not eliminated unless there was positive refuting evidence against a given failure mode. Attachment 11 identifies the Fault Tree. Attachment 12details the supporting and refuting evidence for each failure mode.
Completion of the Equipment Apparent Cause Evaluation form (NOP-ER-1001-01) did not identify any additional failure modes.
Group 1 Failure Modes (Design)
A review of the initial design documents revealed the shield building was conservatively designed, considered all of the required loads and followed the code requirements. The Shield
Building design has a large margin when compared to the allowable loads. Except for the
reinforcing steel detailing associated with the shoulder area (FM 1.3, and 1.12), good design practices were used. As an example, the specified reinforcing steel to reinforcing steel lap splice (FM 1.4) is greater than specified per the ACI Code. FM 1.5 although acceptable per
the code, the area of high density reinforcing steel coincided with observed laminar cracking
and could not be refuted.
Group 2 Failure Modes (Construction & Fabrication)
A review of the construction drawing, specifications, and test records were evaluated with respect to the work preformed. Reviews of the historical testing records for concrete
compressive strength determined that the average compressive strength from 92 cylinder sets
exceeded both the 7-day, and 28-day design requirements (FM 2.1). In addition to compressive strength, a review of initial construction records and sample tests were completed
to evaluate aggregate strength and placement, cement type, air content (69 tests reviewed, and petrographic analysis), and durability. These evaluations determined there were no indications of reactive or weak inclusions in the aggregate, with relatively well distribution of aggregate in the concrete matrix. In conjunction with no evidence of micro-cracking, freeze /
thaw damage (air content evaluation) and confirmatory strength testing it can be concluded
that the materials contained no precursors to laminar cracking. (FM 2.1)
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 51 Mixing, conveying, placing, finishing, and curing of concrete for the shield building was governed under project specifications. The placement records were reviewed and determined
that the placement practices were within acceptable limits. These reviews did not identify any
segregation, temperature variations, concrete cover variations, or curing practices that would
contribute to the laminar cracking condition. From this review it can be determined that failure modes such as Concrete Mix (FM 2.1), Concrete Placement (FM 2.2) Drying Shrinkage (FM 2.4), and Concrete Construction (FM 2.5) were not the cause of the laminar cracking.Concrete core taken from the shield building in support of this root cause were also tested to obtain in-situ concrete physical and chemical properties. The test results from these concrete cores also confirm that the concrete is sound and many of the failure modes in this section can
be eliminated. Concrete core testing also confirmed that the exterior surface of the shield
building did not have a sealant to keep moisture out and examination of the cores revealed
evidence of secondary deposits which typically suggest long term exposure to moisture
migrating through the concrete (FM 2.7).
Consistent with the finding in Group 1, FM 2.11 Small Rebar Spacing could not be refuted.
Group 3 Failure Modes (Operational)
Review of events since the construction of the shield building was performed. The review encompassed items such as Earthquakes (FM 3.1), Tornados (FM 3.3), and Chemical Attack (FM 3.9).During the review of operational records it was determined that the site had no environmental loading such as seismic activity (FM 3.1), Lightning (FM 3.2), and vibrations (FM 3.14) that
would result in laminar cracking. In order to confirm that wind loading was not the initiating factor of the laminar cracking; the structure was evaluated against the most extreme wind event on record at Davis-Besse. This
condition was a category F2 tornado that passed in close proximity to the shield building in June 1998. A Finite Element Analysis model with the tornado conditions was generated to analyze this specific condition. This analysis concluded that wind loading did not generate
stresses of the magnitude to cause laminar cracking (FM 3.3).
Since initial construction, the shield building has been subjected to environmental conditions and weathering. The impact of this was analyzed in support of the root cause by conducting
examinations of the in-situ concrete structure, and testing of extracted samples. Specific
testing on 17 exterior face samples determined that the average exterior carbonation depth
was approximately 9 mm. This value represents very low levels considering the life of the
structure, and did not compromise the protective concrete cover on the reinforcement which has a nominal thickness of 3 inches (76 mm) (FM 3.9). Twenty-three concrete cores were also tested and inspected for carbonation on the interior crack surface. These inspections found
only trace amounts of carbonation and were found acceptable.
Other information gathered under visual in-situ and petrographic examinations indicated that there was no evidence of alkali-silica reactions, freeze / thaw micro-cracks, sulfate attack, leaching and efflorescence, acid degradation, or reinforcement corrosion. This information concludes that Operational Factors such as Chemical Attack (FM 3.9), Corrosion of Rebar (FM
3.10), Physical Attack (FM 3.15) and chronic Freeze / Thaw (FM 3.16) were not the cause of
the laminar cracking.
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 52 Long term thermal stress cycles (FM 3.7) conditions were investigated [Reference 10.1.16, Exhibits 56, 64, and 68]. The conclusions from these analyses are the radial stresses due to
seasonal changes, thermal gradients, gravity, and wind loads are not high enough to cause laminar cracking in the structure. In addition, based on the analysis performed and the concrete core test results, there is no accumulative aging affects or cyclic events that would
indicate on going degradation issues. Therefore, all the long term operational phase issues
can be refuted.Freezing near reinforcing steel in a Blizzard (FM 3.6) were also investigated and analyzed.
This extreme environmental event associated with the 1978 blizzard could produce high
stresses that could initiate laminar cracking in the locations observed.Conclusion from Failure Modes Analysis Finite Element Analysis of the shield building wall identified that there is a stress concentration located near the outer layer of reinforcing steel between the flute shoulder area and the shield
building shell directly behind the thick section of the architectural flute shoulder.
A review of the design drawings identified that the architectural shoulder horizontal reinforcing steel is connected only at the sides of the shoulders with an approximate 10 foot span. There
are no intermediate stirrups or radial reinforcing steel in this region to resist any radial stress in
this area should high radial stress occur. (Failure modes 1.3 and 1.12)
Finite Element Analysis of high density reinforcing steel spacing (#6 bar at 6" c-c) indicate that a laminar crack could propagate in this area for a specified motive force, while laminar cracking does not propagate when the reinforcing steel spacing is the normal 12" c-c spacing
for the identical motive force. (Failure modes 1.5 and 2.11)
A review of the design drawings and installation specifications revealed that an exterior sealant on the shield building exterior surface was not required. In addition, petrographic examinations of the concrete cores identified that the exterior surface did not have a sealant layer. In
addition, laboratory tests showed secondary deposits virtually in all air voids indicating the presences of long term exposure to moisture migrating through the concrete. (Failure mode
2.7)Finite Element Analysis identified that the acute freezing of moisture adjacent to the outer mat of reinforcing steel directly behind the shoulder areas could produce radial stress greater than
the concrete tensile strength when subjected to the environmental conditions associated with the blizzard of 1978. Finite Element Analysis was also done for the 1977 blizzard and the
stresses associated with the conditions experienced in this blizzard could not produce the high
stress needed to exceed the concrete tensile strength. Therefore, the 1978 blizzard was the
only scenario capable to producing radial stress to enable the laminar crack initiation. (Failure
mode 3.6)
Root Cause Analysis Report, CR 2011-03346 3 Data Analysis Page 53 3.3.10 Hardware Disposition The initial condition assessment determined that the shield building was functional, but non-conforming with the concrete laminar cracking. The initial condition assessment concluded
that no compensatory actions or operating restrictions were required due to the shield building concrete laminar cracking. Engineering analysis demonstrated that the shield building
remained structurally adequate for the controlling load case(s). However, the shield building
with the laminar cracking in its walls remains non-conforming to the current design and
licensing bases with regard to design stress analysis methodology, and the tornado allowable
stress values.
Direct Cause Corrective Action #2 re-establishes design and licensing basis conformance for the shield building with the observed concrete cracking.
Design stress analysis methodology USAR Section 3.8.2.2.5 and DCM Section II.H.2.5.1.5 specify the analysis methodologies used for the shield building design. These documents state that the shield building wall was
designed using the American Society of Mechanical Engineers (ASME) "Analysis of Spherical
Shells" from Section III of the 1968 code.
The initial condition assessment Calculations C-CSS-099.20-054 and 056 used the "ANSYS" computer analysis code to study the affect of the laminar cracks on the function of the shield
building. Any calculations used as the design for the shield building with the concrete laminar cracking will require conformance with the design & licensing bases.
Tornado allowable stress valuesUSAR Section 3.8.2.2.6 and DCM Section II.H.2.5.1.5 define the load combinations and allowable stresses for the shield building design. Study Calculation C-CSS-099.20-056
documents that the calculated stress for the tornado wind and differential pressure load
exceeded the allowable stress value in the design and licensing basis, but was within the
allowable limit using the alternate differential pressure design load of Regulatory Guide 1.76, Rev. 1.Disposition The primary disposition for the majority of the shield building laminar cracking is "Repair."
Design Engineering will prepare and track to completion a comprehensive plan to restore the
shield building to conformance with its design and licensing bases requirements.
Root Cause Analysis Report, CR 2011-03346 4 Safety Culture Evaluation Page 54 4 Safety Culture Evaluation The causal factors for the laminar cracking of the shield building concrete wall were primarily design related from about 40 years ago, so the evaluation of safety culture aspects is not
relevant to current performance.
Root Cause Analysis Report, CR 2011-03346 5 Latent Organizational Weakness Evaluation Page 55 5 Latent Organizational Weakness EvaluationThe causal factors for the laminar cracking of the shield building concrete wall were primarily
design related from about 40 years ago, so the evaluation of latent organizational weaknesses
is not relevant to current performance.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 56 6 Generic Implications 6.1 Plant and Industry Experience 6.1.1 Strategy The FENOC Corrective Action Program databases, Institute of Nuclear Power Operation (INPO) Plant Events Database, the Nuclear Regulatory Commission (NRC) website, and Electric Power Research Institute (EPRI) website were searched for similar symptoms of containment shield building concrete laminar cracking from at least the last five years using the
keywords Containment, Shield Building, Concrete, Crack, and Hydrodemolition.
A second search was conducted for plant and industry experience with concrete cracking to gain knowledge regarding similar potential failure modes, causes, corrective actions, and generic problems. Search terms (trend codes) from the direct and root causes included
blizzard, moisture, sealant, coating (0550), design interface (B04, F04, CM10), and design
specification (3900).
6.1.2 Results There was no previous DBNPS experience with shield building concrete laminar cracking. In 2002, a similar temporary access opening was created using hydrodemolition for the
replacement of the reactor pressure vessel closure head. The 2002 temporary access
opening was confined within the blockout used for the original construction opening and was not in an area exposed to similar regions where laminar cracks were found in 2011. There
were no symptoms of concrete distress observed on the exterior of the shield building that
would indicate laminar cracks were located below the surface.
None of the inspections of the other safety-related structures such as the auxiliary building or intake structure exterior identified any symptoms that would signify the presence of concrete laminar cracking or
waterproof coating degradation.The Perry Nuclear Power Plant has a similar configuration (without architectural features) of shield building as DBNPS, but there is no experience with similar laminar cracks. The Beaver Valley Nuclear Power Station units have a different containment system consisting of a reinforced concrete cylinder with a steel liner and there is no experience with similar laminar
cracks.A document from the NRC regarding containment liner corrosion operating experience
[Reference 10.1.27] lists 16 similar locations with a reinforced concrete shield building and a
freestanding steel containment vessel. The 14 pressurized water reactors with a reinforced
concrete shield building and a freestanding steel containment vessel are Davis-Besse, Kewaunee, Prairie Island 1 & 2, Saint Lucie 1 & 2, Waterford 3, Catawba 1 & 2, McGuire 1 & 2, Sequoyah 1 & 2, and Watts Bar 1. The 2 boiling water reactors with a reinforced concrete
shield building and a freestanding steel containment vessel are Perry 1 and River Bend 1.
None of these plants have reported experiencing similar laminar cracks. Davis-Besse and Saint Lucie have created temporary access openings in the shield building wall to replace major components. Sequoyah and Watts Bar have created temporary access openings in the
shield building dome to replace major components. Kewaunee, Prairie Island, Catawba, and
McGuire have performed their major component replacements through the equipment hatch.
Waterford has a major component replacement scheduled in the future.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 57 The majority of the nuclear power stations that have completed major component replacements through temporary access openings in containment systems are either post-
tensioned or reinforced concrete cylinders with a steel liner. The only other similar instance of
concrete delamination discovery associated with creating a temporary access opening in the containment structure occurred at Crystal River unit 3. The root cause of the Crystal River
containment concrete delamination was the design of the structure in combination with the type of concrete used, and the acts of de-tensioning and opening the containment structure. A study of the deterioration of concrete water storage tanks in the province of Ontario
[Reference 10.1.28] identified damage that ranged from heavy surface spalling and cracking to
delamination and eventual failure of some structures. The study concluded the prime factors
for the determining the rate of concrete structure deterioration were the number of freeze /
thaw cycles, temperature amplitudes and frequencies, concrete permeability, hydrostatic pressure, location, the effect of reinforcing steel, and internal ice formation. Remedial
solutions proposed included repair of joints and voids, applying waterproof coatings, insulation, and tank replacement.
An NRC document on the durability of reinforced concrete structures [Reference 10.1.29]
identified that water is the single most important factor controlling the degradation process of concrete apart from mechanical deterioration.This document was considered in the failure modes analysis. Also considered in the failure modes analysis were an ACI document on the
evaluation of nuclear safety-related structures [Reference 10.1.30], an EPRI document on concrete at nuclear power plants [Reference 10.1.31], and an IAEA document on assessment and management of aging of nuclear power plant components [Reference 10.1.32]. An ACI document on concrete cracking causes and restoration [Reference 10.1.33] identified methods of crack repair that may be applicable to the shield building concrete laminar cracking
include epoxy injection and additional reinforcement. Another ACI document describes the
use of waterproofing barrier systems for concrete [Reference 10.1.34]. These documents
were considered in the failure modes analysis and potential corrective actions.
6.1.3 Conclusions The laminar cracking of the shield building wall is unique with respect to reinforced concrete, but a much more severe symptom of laminar cracking occurred in a post-tensioned concrete
containment structure at Crystal River unit 3 due to a combination of design, materials, and the
act of de-tensioning.
Similar concrete laminar cracking has occurred in this geographical area with water tanks due to environmental conditions, concrete permeability, and the effect on reinforcing steel. Industry
resources identify water as the single most important factor controlling the degradation process of concrete apart from mechanical deterioration. Some solutions proposed included applying waterproof coatings and insulation. Past occurrences of similar conditions with concrete laminar cracking in water tanks, water as a controlling factor in concrete degradation, and applying waterproof coatings as solutions suggest that there may be a broader issue with moisture penetration. The extent of condition review addresses the broader issue with
moisture penetration other than the shield building exterior.
There were no similar issues with design specifications, coatings, or design interfaces to indicate a generic problem. There have been no similar previously identified events with concrete laminar cracking at DBNPS or within FENOC to judge the effectiveness of prior
corrective actions.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 58 There have been no similar previously identified events with concrete laminar cracking with conventionally reinforced concrete shield buildings to judge the effectiveness of operating
experience reviews.
Since the failure modes for the laminar cracking of the shield building concrete wall were primarily design related from about 40 years ago under a quality assurance program outside
the control of FENOC, then there is no basis to judge the effectiveness of training, self-
assessment, or oversight.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 59 6.2 Extent of Condition 6.2.1 Strategy The shield building concrete laminar cracking was reviewed for the extent of condition relative to other applicable programs / processes, equipment / systems, organizations, environments, and individuals.
6.2.2 Results The shield building was the only structure on site designed by Bechtel as a reinforced concrete right cylinder. The shield building was the only nuclear safety-related structure on site
constructed using the slip-form process by Fegles-Power Service. The shield building wall
laminar cracking was primarily located at the outer face of structural reinforcing steel under the
architectural flute shoulder regions due to the concentration of radial stresses. The shield
building wall laminar cracking was also across the top 20 feet and adjacent to the main steam
line penetration blockouts due to the density of reinforcing steel facilitating propagation. The
shield building wall laminar cracking is predominantly oriented to the southwest due to the
prevailing direction of severe storms, including the blizzard of 1978.
The shield building was the only above-grade nuclear safety-related structure on-site designed by Bechtel during original construction that did not have white cement Thoroseal finish applied for sealing of exterior concrete surfaces prior to the blizzard of 1978 [Reference 10.1.35]. A waterproofing membrane was installed below-grade on the shield building exterior. The shield building dome was coated in 1976. The shield building dome lacks susceptibility to the causal
factors for concrete cracking found in the architectural flute shoulders involving waterproof coating on the exterior surface, the discontinuity stress concentration factor, intermediate radial
reinforcing steel, and high density reinforcing steel.
Therefore, only the remainder of the accessible, above-grade, exterior wall of the shield building should be examined similar to
those areas previously examined.
The failure modes for the laminar cracking of the shield building concrete wall were primarily design related from about 40 years ago under a quality assurance program outside the control of FENOC. Therefore, the condition does not currently exist in other applicable programs /
processes, equipment / systems, organizations, environments, and individuals.
6.2.3 Conclusions The extent of condition was adequately bounded by the initial condition assessment
[Reference 10.1.19] based upon empirical data available at that time.
Extent of Condition Corrective Action #1:
Additional Examination of the Shield Building Exterior Wall.
Extent of Condition Corrective Action #2:
Issue Engineering Change Package for Additional Shield Building Core Bores. There is no broader issue with moisture penetration other than the shield building exterior since other above-grade nuclear safety-related structures were sprayed with a white cement finish for sealing the exterior concrete surfaces.
Extent of Condition Corrective Action #3: Confirmatory Examination of a Safety-Related Structure with Waterproof coating.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 60 6.3 Extent of Cause 6.3.1 Strategy The knowledge gained from the industry experience review regarding the causes of concrete cracking was used to develop the potential failure modes for the shield building laminar
cracking.The shield building concrete laminar cracking was reviewed for the extent of cause relative to other applicable programs / processes, equipment / systems, organizations, environments, and
individuals.
6.3.2 Results The shield building was the only above-grade nuclear safety-related structure on-site designed by Bechtel during original construction that did not have white cement Thoroseal finish applied for sealing of exterior concrete surfaces prior to the blizzard of 1978 [Reference 10.1.35]. A waterproofing membrane was installed below-grade on the shield building exterior. The shield building dome was coated in 1976. The shield building dome lacks susceptibility to the causal
factors for concrete cracking found in the architectural flute shoulders involving waterproof coating on the exterior surface, the discontinuity stress concentration factor, intermediate radial
reinforcing steel, and high density reinforcing steel.
The failure modes for the laminar cracking of the shield building concrete wall were primarily design related from about 40 years ago
under a quality assurance program outside the control of FENOC. Therefore, the extent of
cause was not reviewed in other programs / processes, equipment / systems, organizations, environments, and individuals.
6.3.3 ConclusionsThe accessible exterior concrete surfaces of the shield building should be sealed to prevent moisture penetration like the other nuclear safety-related structures on-site. The exterior of
other nuclear safety-related structures should be examined to ensure the protective coating
remains acceptable.
Root Cause Corrective Actions #1 & 2 design and implement a shield building exterior sealant system.
Root Cause Corrective Actions #3 update inspection procedure to include shield building exterior sealant system.
Also, the Maintenance Rule Structures evaluation procedure shall be updated to include examination of the similar exterior coating on the other safety-related concrete structures.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 61 6.4 Data Analysis Conclusions On October 10, 2011 a concrete crack was observed at the architectural flute shoulder region of a temporary access opening in the shield building wall. The temporary access opening was being cut by supplemental personnel under the direction of FENOC using a hydrodemolition
process to allow replacement of the reactor pressure vessel head. A concrete crack in the
architectural flute shoulder region of a temporary access opening in the shield building wall
was unexpected and needs to be understood to ensure there is no impact with its structural integrity currently, previously, or within the future viable service life of the plant. Previous inspections of the shield building exterior surface did not identify symptoms that would signify
the presence of the concrete laminar cracking.An acoustic sounding of the shield building exterior wall was performed using the Impulse Response testing method to locate areas with concrete laminar cracking. Confirmation of the
Impulse Response testing results was achieved by visual inspection of 70 core bores, including
crack characterization. The initial condition assessment determined that the shield building
concrete wall contained tight-width laminar cracking near the outer face of structural reinforcing
steel. The majority of the shield building laminar cracking occurred in the concrete at the outer
face of structural reinforcing steel located behind the architectural flute shoulder region. Areas
of the laminar cracking occurred beyond the architectural flute shoulder region as 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 southwestern exposure of the shield building wall
was observed with the most extensive concrete cracking.
The initial condition assessment determined that the shield building was functional, but non-conforming with the presence of the concrete laminar cracking. Engineering analysis demonstrated that the shield building remained structurally adequate for the case of the controlling loads. However, the shield building with the laminar cracking in its walls remains
non-conforming to the current design and licensing bases with regard to design stress analysis methodology, and the alternate tornado design criteria.
Direct Cause Corrective Action #2 re-establishes design and licensing basis conformance for the shield building with the
observed concrete cracking. Examination of 36 shield building concrete cores was performed to define possible failure modes for the laminar cracking, or quantify material properties of the concrete to support
computer modeling and analysis. Two laboratories performed Petrographic examination of 4 concrete cores in order to determine the concrete condition, possible reasons for the damage, and prediction of whether deterioration may continue. Four other laboratories examined the shield building concrete cores for material properties and possible failure modes.
The external laboratory examination of the shield building concrete core samples determined that the concrete was in good condition, consistent with the mix design, and no unacceptable
or degraded material properties. There was no evidence of typical concrete time-dependent
aging failure modes. The integrity of the concrete narrowed the failure mechanism to those related to design or environmental issues versus construction. The examination found the
outer surface of the cores was not water-repellant, and the air voids were lined with secondary
deposits of ettringite and calcium hydroxide which suggests long-term exposure to moisture
migrating through the concrete.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 62 Computer modeling of shield building loading under environmental conditions with extreme combinations of temperature and wind were insufficient to result in laminar cracking of the
concrete. Therefore, the forces involved with the laminar cracking were beyond those
anticipated with good design practices. The postulated acute freezing and expansion of
moisture in the shield building concrete was the only probable scenario capable of radial
stresses large enough to enable the laminar crack initiation. The blizzard of 1978 was the only identified event during the life of the shield building that integrated the moisture content, wind
speed, temperature, and duration necessary for development of radial stresses large enough
to enable the concrete laminar crack initiation. The most likely reason for the shield building laminar cracking was a lack of exterior protective sealant that allowed moisture to migrate into the concrete, freeze, and expand. The other
nuclear safety-related structures on-site have a protective sealant as a barrier against moisture
migration into the concrete.
The extent of condition was adequately bounded by the initial condition assessment based upon empirical data available at that time. The remainder of the accessible shield building
exterior walls should be examined using Impulse Response testing with confirmatory core bores to clearly define the extent of condition.The exterior concrete surfaces of the shield
building should be sealed as a barrier against moisture migration like the other nuclear safety-
related structures on-site.
Causal Factors Finite element analysis identified that the acute freezing of moisture adjacent to the outer face of structural reinforcing steel behind the thickest section of the architectural flute shoulder in
conjunction with the blizzard of 1978 was the only scenario capable of radial stresses to
enable the laminar crack initiation (failure mode 3.6). Petrographic examination of the concrete cores and review of the design records identified that the shield building exterior lacks a sealant and experienced long-term exposure to moisture
migrating into the concrete (failure mode 2.7).Finite element analysis of the outer face of structural reinforcing steel identified that a 6-inch or less spacing of reinforcement facilitated laminar crack propagation (failure modes 1.5 & 2.11).
Review of design records identified that although the architectural flute shoulder reinforcing steel included connections to the structural reinforcing steel at the ends approximately 10 feet apart, there were no middle stirrups or radial reinforcing steel to tie the reinforcement elements
together for crack mitigation (failure modes 1.3 & 1.12).
TapRootThe path through the TapRoot Root Cause Tree for the shield building concrete laminar cracking is Equipment Difficulty / Design / Design Specifications / Specifications Need
Improvement.
The reason for the shield building laminar cracking was that the design specification for construction (C-038) of the shield building did not specify application of an exterior sealant from moisture. The lack of exterior sealant enabled moisture preceding the blizzard of 1978 to
migrate into the concrete, freeze, and expand.
Root Cause Analysis Report, CR 2011-03346 6 Generic Implications Page 63 A contributor to the shield building laminar cracking was an inherent stress concentration at the outer face of structural reinforcing steel behind the thickest section of the architectural flute
shoulder. The stress concentration behind the thickest section of the architectural flute
shoulder enabled the radial stress from the freezing moisture to exceed the tensile strength of
the concrete and initiate a crack. A horizontal (hoop) stress and vertical stress that adjoined
the outer face of structural reinforcing steel underneath the architectural flute shoulder region
enabled the laminar crack created by freezing moisture to propagate.
A second contributor to the shield building laminar cracking was the design did not include radial reinforcing steel ties or stirrups at an intermediate spacing between each end of the architectural flute reinforcing steel connection with the structural reinforcing steel. The design
not including intermediate radial reinforcing steel ties or stirrups enabled the laminar crack
created by freezing moisture to propagate.
A third contributor to the shield building laminar cracking was a density of structural reinforcing steel less than or equal to six inch spacing. Once the crack originated in the shoulder region, it
continued to propagate into adjacent areas where the higher density of reinforcing steel was present such as at the top 20 feet of the shield building. The greater density of structural
reinforcing steel enabled the laminar crack created by freezing to propagate into this area.
The main steam line penetration blockout laminar cracks propagated due to the freezing in
adjacent shoulders located three feet above the auxiliary building roof and the higher density
reinforcing steel. This cracking continued until obtaining equilibrium and stopping at these
blockouts.
Root Cause Analysis Report, CR 2011-03346 7 Root and Contributing Causes Page 64 7 Root and Contributing Causes
_____________________________________________________________________
The Direct Cause for the shield building concrete laminar cracking is the integrated affect of moisture content, wind speed, temperature, and duration from the blizzard of 1978. [Cause
code T22]
The environmental conditions from the blizzard of 1978 enabled radial stresses from moisture to freeze and expand, creating radial stresses which then exceeded the tensile strength of the
concrete and initiated the cracking in the shield building exterior wall. The blizzard of 1978 was the only event identified during the life of the shield building that integrated the moisture
content, wind speed, temperature, and duration necessary for development of radial stresses
large enough to enable the concrete laminar crack initiation. In equipment failure analysis, a root cause is typically the main factor that leads to the damage of an engineered system. A root cause must possess the following characteristics to be
considered valid: 1) it can be eliminated to prevent recurrence, and 2) it is within the control of
management. This investigation has identified several factors that when combined resulted in
the laminar cracking observed. Specifically shoulder configuration, reinforcing steel details, environmental conditions, and no exterior sealant from moisture. Each of these factors can be eliminated as not under the control of management except one, and that is the root cause.
The Root Cause for the shield building concrete laminar cracking was due to the design specification for construction of the shield building (C-038) that did not specify application of an
exterior sealant from moisture. [Cause code DA1D]
The design specification for the shield building identified work that was not included in the slip-form construction such as backfill and installation of waterproofing membrane below grade, but
did not specify application of an exterior sealant from moisture. The other nuclear safety-
related structures on-site have a protective sealant as a barrier against moisture migration into
the concrete.
The examination found the outer surface of the cores was not water-repellant, and the air voids were lined with secondary deposits of ettringite and calcium hydroxide which suggests long-
term exposure to moisture migrating through the concrete.
Computer modeling of the shield building under environmental conditions with extreme combinations of temperature and wind were insufficient to result in laminar cracking of the
concrete. The acute freezing and expansion of moisture in the shield building concrete was
the only scenario capable of generating radial stresses large enough to enable the laminar
crack initiation.
A subsequent regulatory reference on the durability of reinforced concrete [Reference 10.1.29] from February, 2007 identified water as the single most important factor controlling the
degradation process of concrete apart from mechanical deterioration.
Root Cause Analysis Report, CR 2011-03346 7 Root and Contributing Causes Page 65 Contributing Cause #1 for the shield building laminar cracking was an inherent stress concentration at the outer face of structural reinforcing steel behind the thickest section of the
architectural flute shoulder. [Cause code DA1D]
The stress concentration behind the thickest section of the architectural flute shoulder enabled the radial stress from the freezing moisture to exceed the tensile strength of the concrete and initiate a crack. Other horizontal (hoop) and vertical stresses that adjoined the outer face of
structural reinforcing steel underneath the architectural flute shoulder region enabled the
laminar crack, once created by freezing moisture, to propagate along the outer face of
structural reinforcing steel.
Contributing Cause #2 for the shield building laminar cracking was the design did not include radial reinforcing steel ties or stirrups at intermediate spacing between each end of the architectural flute shoulder reinforcing steel connection with the structural reinforcing steel.
[Cause code DA1D]
The design not including radial reinforcing steel ties or stirrups at intermediate spacing enabled the laminar crack created by freezing moisture to propagate to the end connections.
Contributing Cause #3 for the shield building laminar cracking was a density of structural reinforcing steel less than or equal to six inch spacing. [Cause code DA1D]
Once the crack originated in the shoulder region, it continued to propagate into adjacent areas where the higher density of reinforcing steel was present such as at the top 20 feet of the
shield building, and the main steam line penetration blockouts. The greater density of
structural reinforcing steel enabled the laminar crack created by freezing moisture to propagate
into these areas.
Root Cause Analysis Report, CR 2011-03346 8 Corrective Action Plan Page 66 8 Corrective Action Plan
_____________________________________________________________________
Problem Statement On October 10, 2011 a concrete crack was observed at the architectural flute region of a temporary access opening in the shield building wall.
Extent of Condition Corrective Action #1:
Additional Examination of the Shield Building Exterior Wall.
Site Projects shall arrange access to the exterior face of the shield building wall. This access will be used to support further investigation of the structure. Engineering will specify the areas
of access required and the necessary work scope, such as additional Impulse Response and
core bores. Using an Impulse Response (IR) vendor and method approved by Design
Engineering identify potential cracked or un-cracked areas of the Shield Building as directed by
Design Engineering.
Provide the necessary ground and/or suspended man-lifts required to access the shield building wall exterior surface.
Perform confirmatory core bores as directed by Design Engineering.
Facilitate the examination of the core bores by Design Engineering.
Repair/Rework core drill holes as described in the ECP for the core bore.
Extent of Condition Corrective Action #2:
Issue Engineering Change Package for Additional Shield Building Core Bores.
Design Engineering to issue an Engineering Change Package (ECP) to allow for additional core bores, as required, in the exterior surface of the Shield Building.
This ECP shall identify the size, location, reinforcing steel cutting allowances (if any), and maximum number of core bores for this issue. This ECP shall also revise the applicable
design documents (drawings, calculations, etc.) to track the core bores, crack depths, crack
widths etc.
Extent of Condition Corrective Action #3: Confirmatory Examination of a Safety-Related Structure with Waterproof Coating Site Projects shall arrange access to the exterior face of a safety-related structure with waterproof coating in accordance with the corresponding Engineering Change Package.
Engineering will specify the areas of access required and the necessary work scope, such as additional Impulse Response and core bores. Using an Impulse Response (IR) vendor and method approved by Design Engineering confirm the absence of laminar cracking in a safety-related structure with waterproof coating as directed by Design Engineering. Provide the necessary ground and/or suspended man-lifts required to access the safety-related structure wall exterior surface. Perform confirmatory core bores as directed by Design Engineering.
Facilitate the examination of the core bores by Design Engineering.
Repair/Rework core drill holes as described in the ECP for the core bore.
Root Cause Analysis Report, CR 2011-03346 8 Corrective Action Plan Page 67 The Direct Cause for the shield building concrete laminar cracking is the integrated affect of moisture content, wind speed, temperature, and duration from the blizzard of 1978.
Direct Cause Corrective Action #1:
Testing Program to Investigate the Steel Reinforcement Capacity Adjacent to Structural Discontinuities.
Design Engineering will administer a testing program to be performed at a selected test facility.The test procedure will be developed and performed by the selected facility to determine the
effect on the steel reinforcement/ splices adjacent to structural discontinuities (i.e. laminar
cracks). This test program and the deliverable test report will be reviewed and approved by
Design Engineering.
Direct Cause Corrective Action #2:
Engineering Plan to Re-Establish Design & Licensing Basis for Shield Building.
Design Engineering to develop a comprehensive plan for re-establishing shield building conformance to the DBNPS design and licensing bases. Upon the completion of the corrective
action for inspection of the shield building, the extent of laminar cracking will be established.
Upon the completion of the corrective action for the Testing Program the capacity of the
reinforcing steel adjacent to the laminar cracking will be known. The steps for re-establishing
shield building design and licensing bases conformance will be finalized and additional
corrective actions will be initiated as required.
Direct Cause Corrective Action #3:
Issue a Site Specific Procedure for the Long-Term Monitoring of the Shield Building Laminar Cracking.
Design Engineering will develop procedural requirements for the long-term monitoring of the Shield Building laminar cracking condition. The procedural requirements will include the
following:1. The periodic monitoring of the shield building will begin with an annual inspection cycle starting in 2012. The schedule is outlined below:
2012 inspection shall be completed by 9/1/2012
2013 inspection shall be completed by 9/1/2013
If the inspection results remain unchanged after the first two inspection cycles (defined as no discernable change in crack width or the confirmation that no cracks have developed in
previously un-cracked core bores), the inspection cycle will change to two year cycles per
the schedule below:
2015 inspection shall be completed by 9/1/2015
2017 inspection shall be completed by 9/1/2017
2019 inspection shall be completed by 9/1/2019
The periodic monitoring will repeated every two years for a minimum of three cycles. If after three monitoring cycles, the results of the core bore and crack examinations remain
unchanged, the monitoring schedule may be changed to a five year cycle.
2024 inspection shall be completed by 9/1/2024
2029 inspection shall be completed by 9/1/2029
2034 inspection shall be completed by 9/1/2034 Root Cause Analysis Report, CR 2011-03346 8 Corrective Action Plan Page 68 If any adverse changes are identified (as defined in the acceptance criteria) during these examinations, a Condition Report shall be initiated to evaluate any required change to the
inspection schedule.2. A minimum of 6 core bores of each type (un-cracked & cracked) will be inspected during each inspection cycle. The approximate distribution of the core bore inspections is as
follows: 3 in shoulder regions, 1 in the steam line penetration areas, and 2 at the top of the
building outside the shoulders.3. The examination of the core bores will be performed by visual inspection and the use of a boroscope and optical crack comparator. Any identified cracks shall be measured using an
optical crack comparator and the boroscope.4. The acceptance criteria to be used for the examination of the core bores that did not contain a crack indication initially (as defined on Drawing C-111A) shall be that no new crack indication is identified. If a new crack is identified, a Condition Report shall be
initiated and the crack shall be measured as described above. The condition report will
determine any additional inspections or required changes to the monitoring. The previously identified core bores containing cracks shall be re-examined to determine the current width of the crack. The as-measured crack width shall be compared to the
initial crack width measurement as recorded on Drawing C-111A. If it is it determined that
the crack width has increased (a discernable change in width within the accuracy of the
measurement technique), a Condition Report shall be initiated to evaluate. 5. Chloride ion testing and carbonation testing will be carried out on a minimum of 2 core samples collected for examination. This testing will be performed during alternating
inspection cycles. The testing will be performed as detailed in the requirements. The procedural requirements will establish the acceptance criteria for these tests.
The Root Cause for the shield building concrete laminar cracking was due to the design specification for construction of the shield building (C-038) that did not specify application of an
exterior sealant from moisture.
Root Cause - Preventive Action #1:
Issue Engineering Change Package for a Shield Building Exterior Sealant System.
Design Engineering to issue an Engineering Change Package (ECP) to specify the required details and requirements for application of a sealant to the exterior of the shield building. The
selected system will preclude moisture migration into the reinforced concrete. As part of this
ECP, establish a preventive maintenance frequency once the specific product is selected for
the shield building exterior sealant system.
Root Cause - Preventive Action #2:
Implement Engineering Change Package for a Shield Building Exterior Sealant System.
Site Projects shall provide for the implementation of the shield building sealant system specified in the Engineering Change Package. This sealant system shall be applied to exterior
of the shield building, as specified in the Engineering Change Package.
Root Cause Analysis Report, CR 2011-03346 8 Corrective Action Plan Page 69 Root Cause - Corrective Action #3:
Update Inspection Procedure to Include Shield Building Exterior Sealant System. Design Engineering shall update the Maintenance Rule Structures evaluation procedure (EN-DP-01511) for inspection of the shield building exterior sealant system.
Also, the Maintenance Rule Structures evaluation procedure shall be updated to include examination of the similar exterior coating on the other safety-related concrete structures.
Contributing Cause #1 for the shield building laminar cracking was an inherent stress concentration at the outer face of structural reinforcing steel behind the thickest section of the
architectural flute shoulder.
Contributing Cause #1 - Corrective Action:
None required.
Basis for no action required: The stress concentration behind the thickest section of the architectural flute shoulder enabled the radial stress from the freezing moisture to exceed the
tensile strength of the concrete and initiate a crack. Other horizontal (hoop) and vertical
stresses that adjoined the outer face of structural reinforcing steel underneath the architectural
flute shoulder region enabled the laminar crack created by freezing moisture to propagate
along the outer face of structural reinforcing steel. The root cause preventive actions for an
exterior sealant system established a barrier against moisture migrating into the concrete. The
acute freezing and expansion of moisture in the shield building concrete was the only scenario
capable of radial stresses large enough to enable the laminar crack initiation. Computer
modeling of shield building loads under environmental conditions with extreme combinations of
temperature and wind were insufficient to result in laminar cracking of the concrete without
moisture migration and subsequent freezing. Therefore, the root cause preventive actions
nullify the impact of contributing cause #1.
Contributing Cause #2 for the shield building laminar cracking was the design did not include radial reinforcing steel ties or stirrups at intermediate spacing between each end of the
architectural flute reinforcing steel connection with the structural reinforcing steel.
Contributing Cause #2 - Corrective Action:
None required.
Basis for no action required: The design not including radial reinforcing steel ties or stirrups at intermediate spacing enabled the laminar crack created by freezing moisture to propagate to
the end connections. The root cause preventive actions for an exterior sealant system
establish a barrier against moisture migrating into the concrete. The acute freezing and expansion of moisture in the shield building concrete was the only scenario capable of radial
stresses large enough to enable the laminar crack initiation. Computer modeling of shield building loads under environmental conditions with extreme combinations of temperature and wind were insufficient to result in laminar cracking of the concrete without moisture migration
and subsequent freezing. Therefore, the root cause preventive actions nullify the impact of
contributing cause #2.
Root Cause Analysis Report, CR 2011-03346 8 Corrective Action Plan Page 70 Contributing Cause #3 for the shield building laminar cracking was a density of structural reinforcing steel less than or equal to six inches at the top 20 feet of the shield building, and at
openings or penetrations.
Contributing Cause #3 - Corrective Action:
None required.
Basis for no action required: The greater density of structural reinforcing steel enabled the laminar crack created by freezing moisture to propagate beyond the end of the architectural flute reinforcing steel connection with the structural reinforcing steel such as that evident at the
top 20 feet of the shield building and adjacent to the main steam line penetration blockouts.
The root cause preventive actions for an exterior sealant system establish a barrier against moisture migrating into the concrete. The acute freezing and expansion of moisture in the
shield building concrete was the only scenario capable of radial stresses large enough to
enable the laminar crack initiation. Computer modeling of shield building loads under
environmental conditions with extreme combinations of temperature and wind were insufficient to result in laminar cracking of the concrete without moisture migration and subsequent
freezing. Therefore, the root cause preventive actions nullify the impact of contributing cause
- 3.Confirmatory Action Letter Commitment - Corrective Action #1:
Root Cause Report Submittal.FENOC (Design Engineering) will provide the results of the shield building concrete laminar cracking root cause evaluation and corrective actions to the NRC, including any long-term
monitoring requirements, by February 28, 2012. Confirmatory Action Letter Commitment - Corrective Action #2:
Examine Four Un-Cracked Core Bores Following Restart.
FENOC (DBNPS Design Engineering) will examine four un-cracked core bores directly adjacent to locations that have been confirmed to be cracked with a boroscope to verify cracking has not migrated to these core bores located in solid (un-cracked) concrete, within 90
days following plant restart (Mode 2) from the October 2011 mid-cycle outage. a. adjacent to a flute shoulder [S9-666.0-12]
- b. in a flute area [F4-1-666.0-3]
- c. adjacent to main steam line penetration 39 [S7-652.0-6.5]
- d. adjacent to main steam line penetration 40 [S9-650.0-9] Confirmatory Action Letter Commitment - Corrective Action #3:
Main Steam Line Room New Core Bore & Examination Following Restart.
FENOC (DBNPS Site Projects) will perform a core bore in a known crack area within the main steam line room and Design Engineering will examine the crack interface to identify any
changes, within 90 days following plant restart (Mode 2) from the October 2011 mid-cycle
outage.
Root Cause Analysis Report, CR 2011-03346 8 Corrective Action Plan Page 71 Confirmatory Action Letter Commitment - Corrective Action #4:
Examine Six Un-Cracked Core Bores in 17RFO.
FENOC (DBNPS Design Engineering) will examine six un-cracked core bores directly adjacent to locations that have been confirmed to be cracked with a boroscope to verify cracking has
not migrated to these core bores located in solid (un-cracked) concrete, during the seventeenth refueling outage currently scheduled to commence in 2012. a. adjacent to a flute shoulder [S9-666.0-12]
- b. in a flute area [F4-1-666.0-3]
- c. adjacent to main steam line penetration 39 [S7-652.0-6.5]
- d. adjacent to main steam line penetration 40 [S9-650.0-9]
- e. in a flute area [F5-777.0-4]
- f. adjacent to a flute shoulder [S2-783.5-4.0] Confirmatory Action Letter Commitment - Corrective Action #5:
Examine Three Crack Interface Core Bores in 17RFO.
FENOC (DBNPS Design Engineering) will examine the crack interface to identify any changes by examining either existing core bore locations with known cracks or by performing a core
bore in a similar area during the seventeenth refueling outage currently scheduled to
commence in 2012. a. adjacent to a flute shoulder [S9-666.0-11]
- b. near the top of the shield building [S9-785-22.5]
- c. adjacent to main steam line penetration [S9-653.0-9] (core bore following restart)
Root Cause Analysis Report, CR 2011-03346 9 Effectiveness Review Plan Page 72 9 Effectiveness Review Plan
_____________________________________________________________________
Prerequisites for this effectiveness review:
After at least one operating cycle of implementing the site specific procedure for the long-term monitoring of the shield building laminar cracking and completion of the following corrective
actions.Direct Cause Corrective Action #1:
Testing Program to investigate the Steel Reinforcement Capacity adjacent to structural discontinuities (i.e. laminar cracks)
Direct Cause Corrective Action #2:
Engineering Plan to Re-Establish Design/Licensing basis for Shield Building Direct Cause Corrective Action #3:
Issue a site specific procedure for the long-term monitoring of the shield building laminar cracking Root Cause - Preventive Action #1:
Issue Engineering Change Package for a shield building exterior sealant system Root Cause - Preventive Action #2:
Implement Engineering Change Package for a shield building exterior sealant system Root Cause - Corrective Action #3:
Update Inspection Procedure to Include Shield Building Exterior Sealant System.
In accordance with NOBP-LP-2011 section 4.7.4:
Complete a Maintenance Rule Structures evaluation inspection of the shield building exterior sealant system per procedure (EN-DP-01511) to ensure the moisture barrier is still effective
with no areas of unacceptable degradation.
Root Cause Analysis Report, CR 2011-03346 10 References Page 73 10 References
_____________________________________________________________________
10.1 Developmental References 10.1.1 DBNPS Updated Safety Analysis Report - Section 3.8.2, "Containment Structures,"
revision 28, December 29, 2010. 10.1.2 DBNPS Drawing C-110, "Shield Building Roof Plan, Wall Section & Details," revision 6, June 3, 1976. 10.1.3 DBNPS Engineering Change Package 10-0458, "Install Shield Building Construction Opening."10.1.4 FirstEnergy Order 200433294, "Shield Building Construction Opening in Support of RVCH Replacement." 10.1.5 American Concrete Institute, "Concrete Removal Using Hydrodemolition," ACI RAP Bulletin 14. 10.1.6 American Hydro, "Hydrodemolition Parameter and Sequence (Davis-Besse),"
October 28, 2011. 10.1.7 Bechtel Condition Report 25539-000-GCA-GAMG-00182, "Fractured Concrete Found at Shield Building Construction Opening," October 10, 2011. 10.1.8 FENOC Condition Report 2011-03346, "Fractured Concrete Found at 17M Shield Building Construction Opening," October 10, 2011. 10.1.9 CTL Group, "Proposed Work Plan for Davis-Besse Nuclear Power Station," Revision 1, October 16, 2011. 10.1.10 American Concrete Institute, "Nondestructive Test Methods for Evaluation of Concrete in Structures," ACI 228.2R-98, June 24, 1998. 10.1.11 American Society for Testing and Materials, "Standard Test Method for Low Strain Integrity Testing of Piles," D5882 10.1.12 Performance Improvement International, "Root Cause Assessment - Crystal River Unit 3 Containment Concrete Delamination," August 10, 2010. 10.1.13 DBNPS, "Davis-Besse Shield Building Cracking Investigation and Assessment Report," Revision 1, November 23, 2011. 10.1.14 DBNPS Drawing C-111A, "Shield Building Exterior Developed Elevation" revision 2, December 5, 2011. 10.1.15 CTL Group, "Laboratory Evaluation of Shield Building Concrete Cores A and D,"
October 27, 2011. 10.1.16 Performance Improvement International, "Root Cause Assessment - Davis-Besse Shield Building Laminar Cracking," revision 0, February 23, 2012. 10.1.17 DBNPS Calculation VC02/B001-005, "Shield Building - Thermal Stress," revision 0, October 17, 1977.
Root Cause Analysis Report, CR 2011-03346 10 References Page 74 10.1.18 DBNPS Calculation VC02/B001-007, "Shield Building - Cylinder Walls," revision 0, October 17, 1977. 10.1.19 DBNPS, "Davis-Besse Shield Building Investigation and Technical Summary,"
revision 1, November 21, 2011. 10.1.20 DBNPS Calculation C-CSS-099.20-054, "Evaluation of Shield Building for the Permanent Condition with Outside Vertical Reinforcement Removed at Cracking
Areas," revision 3, December 1, 2011. 10.1.21 DBNPS Calculation C-CSS-099.20-055, "II/I Evaluation for Architectural Flute Shoulder," revision 0, October 31, 2011. 10.1.22 DBNPS Calculation C-CSS-099.20-056, "Evaluation of Shield Building Hoop Reinforcement with Observed Cracking," revision 2, December 5, 2011. 10.1.23 DBNPS Specification C-038, "Shield Building," revision 1, October 30, 1970.
10.1.24 Fegles Power Service, "Quality Assurance and Construction Procedures - Reactor Shield Wall Slip-Form Construction Method," 7749-C-38-3-1, September 8, 1970. 10.1.25 DBNPS Engineering Change Package 02-0146, "Containment Structure Access Opening for Reactor Pressure Vessel Head Replacement." 10.1.26 FirstEnergy Order 200008657, "Restore the Containment Shield Building."
10.1.27 Nuclear Regulatory Commission, "Containment Liner Corrosion Operating Experience Summary: Technical Letter Report - Revision 1," August 2, 2011. 10.1.28 Golder Associates and W. M. Slater & Associates Inc., "Deterioration and Repair of Above Ground Concrete Water Tanks in Ontario, Canada - Report to Ontario
Ministry of the Environment," September 1987. 10.1.29 Nuclear Regulatory Commission, "Primer on Durability of Nuclear Power Plant Reinforced Concrete Structures - A Review of Pertinent Factors," NUREG/CR-6927, February 2007.10.1.30 American Concrete Institute, "Evaluation of Existing Nuclear Safety-Related Concrete Structures," ACI 349.3R-02, June 17, 2002. 10.1.31 Electric Power Research Institute, "Program on Technology Innovation: Concrete Civil Infrastructure in United States Commercial Nuclear Power Plants," 1020932, May 2010. 10.1.32 International Atomic Energy Agency, "Assessment and Management of Aging of Major Nuclear Power Plant Components Important to Safety - Concrete
Containment Buildings," IAEA-TECDOC-1025, June 1998. 10.1.33 American Concrete Institute, "Causes, Evaluation, and Repair of Cracks in Concrete Structures," ACI 224.1R-07, March 2007. 10.1.34 American Concrete Institute, "A Guide for the Use of Waterproofing, Dampproofing, Protective, and Decorative Barrier Systems for Concrete," ACI 515.1R-79. 10.1.35 DBNPS Design Criteria Manual, Materials and Building Finishes, revision 4, August 18, 2004.
Root Cause Analysis Report, CR 2011-03346 10 References Page 75 10.2 Other References Condition Reports 2011-03232, Shield Building Reinforcement Bar Concrete Cover Less Than Drawing Requirement 2011-03996, Extent of Condition for Shield Building Fracture Indications
2011-04190, Surface Cracks Identified on Fluted Areas of the Shield Building
2011-04214, Core Bore Found Additional Crack in Architectural Flute Area
2011-04402, Fractured Concrete Found at 17M Shield Building at Main Steam Line Penetrations2011-04507, Isolated Crack Indication Identified by Impulse Response Testing
2011-04648, Shield Building Impulse Response Indications Above Elevation 780
2011-04973, As-Found Concrete Cover and Spacing of Reinforcement Steel (Rebar) Do Not Meet Specified Design Requirements at the 17M Shield Building Construction
Opening 2011-05475, Concrete Cracking at the Top of the Shield Building Wall
2011-05648, Concrete Cracking in Shoulder 4 / Flute 2 Region of the Shield Building (Azimuth 67.5)Drawings C-100, Shield Building Foundation Plan & Details
C-109, Shield Building Roof Plan and Details
C-111, Shield Building Wall Development
C-112, Shield Building Details, Sheet 1
C-113, Shield Building Details, Sheet 2
C-114, Shield Building Dome Framing Plan and Details
C-115, Shield Building Blockout Details
E-401, Shield Building Lighting and Lightning Protection Licensee Event Reports 1978-017, Loss of Meteorological System 1998-006, Tornado Damage to Switchyard Causing Loss of Offsite Power Potential Condition Adverse to Quality Reports 95-0395, Shield Building Concrete Cracks and Spalling Root Cause Analysis Report, CR 2011-03346 10 References Page 76 Procedures DB-PF-03009, Containment Vessel and Shield Building Visual Inspection EN-DP-01511, Design Guidelines for Maintenance Rule Evaluation of Structures
EN-DP-01512, Shield Building Concrete Examination Purchase Orders 55113470, CTL Group 55113539, Performance Improvement International Specifications C-25, Central Concrete Mix Plant C-26, Forming, Placing, Finishing, and Curing of Concrete
C-27, Material Testing Services
C-29, Furnishing, Detailing, Fabricating, and Delivering of Reinforcing Steel Technical Specifications 3/4.6.1, Primary Containment
Institute of Nuclear Power OperationsINPO Event Report Level 4 11-4, Lessons Learned from Construction Projects Involving Concrete Placement Nuclear Regulatory Commission Information Notice 2008-17, Construction Experience with Concrete Placement Information Notice 2011-20, Concrete Degradation by Alkali-Silica Reaction Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 77 11 Attachments
_____________________________________________________________________1. Shield Building Exterior Developed Elevation 2. Shield Building Impulse Response Average Mobility Values
- 3. Shield Building Core Bore Summary
- 4. Shield Building Concrete Material Properties
- 5. Shield Building Surface Visual Inspection History
- 6. Shield Building Milestones
- 7. Shield Building Slip-Form Construction Sequence
- 8. Shield Building Concrete Compression Test Results
- 9. Shield Building Concrete Mixes
- 10. Shield Building Construction Deviations
- 11. Fault Tree
- 12. Failure Modes Analysis
- 13. Change Analysis
- 14. Barrier Analysis
- 15. Event and Causal Factors Chart
- 16. Generic Implications Matrix
- 17. Corrective Action Matrix Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 78 Attachment 1, Shield Building Exterior Developed Elevation Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 79 Attachment 2, Shield Building Impulse Response Average Mobility Values Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 80 Attachment 3, Shield Building Core Bore Summary Core Bore Number (alias)Core Diameter (inches)Core Depth (inches)Crack Depth (inches)Crack Width (inches)Comments S1-615-2 (S1)4 15 No crack Not applicable Twining Compressive
MOES1-786.5-17.5 2 9.75 No crack Not applicable S1-798.0-11 2 9 No crack Not applicable S2-616-14 (S2)4 15.75 No crack Not applicable Colorado CTE CreepS2-783.5-4.0 2 9 No crack Not applicable S2-798.5-4.5 2 10 5 <0.005 PhotoMetrics CarbonationF2-1-650.0-3 2 9 No crack Not applicable F2-790.0-4.5 3 25.5 No crack Not applicable PhotoMetrics Carbonation
Void size F2-792.3-4.5 3 4.5 No crack Not applicable WJE PetrographicS3-650.0-9 2 15.5 8 & 9 Inconclusive S3-650.0-11 2 12.75 No crack Not applicable S3-699.3-1 (S3-55)3 18 No crack Not applicable PhotoMetrics Carbonation S3-650-2 (S3)4 15.5 No crack Not applicable Twining/Colorado Split tensile S4-650.0-13 2 11.75 No crack Not applicable S4-650.0-16 2 15 6 0.009 S4-649-22 (S4)4 15.25 No crack Not applicable Colorado Compressive
CTE F3-1-666.0-3 (F3-1)2 8.5 No crack Not applicable PhotoMetrics Carbonation
Void size
Aggregate size S5-666.0-8 (S5-1)2 16 7 Inconclusive PhotoMetrics Carbonation
Void size S5-666.0-10 (S5-2)2 12.5 No crack Not applicable PhotoMetrics Carbonation
Void size S6-666.0-42 2 17 9 0.005 S6-666.0-44 2 19 9 Inconclusive S6-665-47 (S6)4 14 No crack Not applicable Colorado Relative humidity F4-1-666.0-3 2 8 No crack Not applicable Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 81 Core Bore Number (alias)Core Diameter (inches)Core Depth (inches)Crack Depth (inches)Crack Width (inches)CommentsF4-791.0-2.5 3 24 No crack Not applicable USBR/WJE Specific heat
CTE PetrographicF4-794.0-3.5 3 27.6 Not measured Not measured PhotoMetrics Carbonation S7-666.0-7 (S7-1)2 17.25 9.25 Inconclusive PhotoMetrics Carbonation
Void size
Aggregate size S7-666.0-9 (S7-2)2 15.5 No crack Not applicable PhotoMetrics Carbonation
Void size S7-667.0-25 (S7-3)2 6.5 6.5 0.007 PhotoMetrics Carbonation
Void size S7-782.0-8.5 3 26 No crack Not applicable USBR Thermal Diffusivity S7-652.0-6.5 2 8 No crack Not applicable S7-656.0-6.5 2 8 5 Inconclusive PhotoMetrics Carbonation
Void size
Aggregate size S8-666.0-38 2 12 No crack Not applicable S8-666.0-41 2 15 6 Inconclusive S8-665 (S8)4 14.75 No crack Not applicable Colorado Split tensile F5-1-666.0-4 2 8 No crack Not applicable F5-777.0-4 2 10 No crack Not applicable F5-791.0-4 2 25.5 6.5 - 7.5 0.013 PhotoMetrics Carbonation S9-666.0-11 (S9-1)2 13 5 0.005 PhotoMetrics Carbonation
Void size S9-666.0-12 (S9-2)2 10.5 No crack Not applicable PhotoMetrics Carbonation
Void size S9-782.5-22 2 7.5 No crack Not applicable S9-785.0-22.5 2 8 4 <0.010 PhotoMetrics Carbonation
Void size
Aggregate size S9-650.0-9 2 7.5 No crack Not applicable Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 82 Core Bore Number (alias)Core Diameter (inches)Core Depth (inches)Crack Depth (inches)Crack Width (inches)CommentsS9-653.0-11 2 6.5 6.3 Inconclusive PhotoMetrics Carbonation
Void size
Aggregate size S9-680-3 (S9)3 21.5 14.5 Inconclusive Colorado Compressive
Freeze / thaw S10-666.0-38 2 14 No crack Not applicable S10-666.0-40 2 5 5 Inconclusive S10-672.0-34 2 2.5 No crack Not applicable S10-780.0-19 2 8.75 No crack Not applicable S10-790.5-25 2 10 4.5 - 5.5 Inconclusive S10-799.5-22 2 10 No crack Not applicable F6-1-666.0-4 2 11.25 No crack Not applicable S11-663.75-30 (S11-1)2 8 5 0.005 - 0.010 PhotoMetrics Carbonation
Void size S11-663.75-32 (S11-2)2 7.5 No crack Not applicable PhotoMetrics Carbonation
Void size S11-669.0-17 2 8.25 5.5 0.005 S11-671.0-17 2 8.25 No crack Not applicable S12-666.0-2 (S12-1)2 21 No crack Not applicable PhotoMetrics Carbonation
Void size S12-666.0-4 (S12-2)2 16.5 5 0.005 PhotoMetrics Carbonation
Void size F7-633.08 2 25.5 No crack Not applicable S13-633.08 2 18.25 No crack Not applicable PhotoMetrics Void size S13-633.0-11 2 13 No crack Not applicable S13-633.0-12 2 4.5 No crack Not applicable S15-645.5-3
("A")2 15.75 15.75 Inconclusive CTL Group Petrographic S15-653.5-3
("D")2 25.5 14 Inconclusive CTL Group PetrographicS15-646.5-8 2 25.5 6.5 0.009 S15-674.5-3
("G")2 14.75 No crack Not applicable ColoradoS16-613.0-30 2 27.75 No crack Not applicable S16-613.0-42 2 30.00 8 <0.010 Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 83 Core Bore Number (alias)Core Diameter (inches)Core Depth (inches)Crack Depth (inches)Crack Width (inches)Comments S16-613.0-46 (S16-3)2 21.75 15 <0.010 PhotoMetrics Carbonation
Void size MS room 3 8 No crack Not applicable Colorado Freeze / thaw EDG passage 3 8 No crack Not applicable Colorado Compressive NOTES:Measurement of crack width was inconclusive in several bores due to the affect of the drilling equipment disturbing the crack surface in combination with the tight diameter of the hole
complicating use of a crack comparator and boroscope.Boroscope inspection of the holes from core bores F4-794.0-3.5 and F4-791.0-2.5 were not completed due to the weather conditions (high winds). The six core bores with evidence of multiple laminar cracks in the same area of outside face reinforcement were considered part of a single delamination process. The core bores with multiple laminar cracks include S3-650.0-9, F5-791.0-4, S10-790.5-25, S15-653.5-3, S16-
613.0-42, and S16-613.0-46.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 84 Attachment 4, Shield Building Concrete Material Properties Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 85 Attachment 5, Shield Building Surface Visual Inspection History 09/02/11 A DB-PF-03009 inspection identified minor concrete spalling on the shield building exterior in the area from the emergency diesel generator rooms south to the auxiliary
building. Condition Report 2011-01540 describes one small area of distressed
concrete (minor flaking/spalling) observed on the shield building exterior that has been identified in previous inspections and Condition Report 07-29203. Comparing
the pictures from the previous inspection to the current pictures shows no evidence of growth or change in the appearance of the affected area. Resolution of the
deficiency is being tracked by Order 200288911.10/25/07 A DB-PF-03009 inspection identified minor concrete spalling or flaking on the shield building exterior in the area from the emergency diesel generator rooms south to the auxiliary building. Condition Report 07-29203 describes two small areas of
distressed concrete 6 inch by 10 inch wide and 2 inch deep located on the northwest
side of the shield building at the adjacent to the temporary access opening from
2002 for the replacement of the reactor pressure vessel head. Resolution of the
deficiency is being tracked by Order 200288911. 10/17/05 A Maintenance Rule Structure Evaluation identified minor concrete spalling in concrete repairs on the Shield Building exterior surface similar to that identified in
the previous evaluation. Cracks were noted and judged to be acceptable. 11/22/02 A DB-PF-03009 inspection identified concrete spalling in four areas on the shield building exterior above the original construction opening that ranged from 2 to 6 inch
diameter. Resolution of the deficiency is being tracked by Order 200011687. 05/08/00 A DB-PF-03009 inspection identified concrete spalling with less than two inch depth on the northwest side of the Shield Building exterior between the west and northwest
architectural flutes.06/11/99 A Maintenance Rule Structure Evaluation identified minor concrete spalling mainly with past repairs located above the original construction opening, and various small
hairline cracks and in the shield building exterior concrete. 05/18/96 A DB-PF-03009 inspection determined there was no unacceptable degradation on the shield building exterior concrete surface. A grout repair from a previous problem
report (PCAQ 95-0395) was holding up well and all other areas were in good order. 10/23/91 A DB-PF-10309 / DB-PF-03009 inspection determined there was no unacceptable degradation identified on the shield building exterior concrete surface. 09/26/88 A DB-PF-03009 inspection determined there was no apparent change in the appearance of the shield building exterior concrete, and no indication of cracking, chipping or other unacceptable degradation.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 86 Attachment 6, Shield Building Milestones Date DescriptionMay 22, 1969 The Toledo Edison Company instructed Bechtel to proceed with a containment system for the station utilizing a free-standing containment vessel surrounded
by a reinforced concrete shield building instead of the pre-stressed, post-
tensional concrete containment. Aug 01, 1969 The Toledo Edison Company and Cleveland Electric Illuminating Company filed for the necessary licenses to construct and operate the Davis-Besse
Nuclear Power Station (DBNPS). Aug 25, 1969 The Bechtel Power Corporation established the shield building walls as 2 feet 6 inches thick with a 2 feet thick hemispherical dome. Sep 05, 1969 The Bechtel Power Corporation determined that there would be no painting required on the inside or outside concrete walls of the shield building. Jun 02, 1970 The Bechtel Power Corporation determined that the shield building will be changed to having a shallow dome versus a hemispherical dome. Jun 04, 1970 The Toledo Edison Company requested an exemption to 10CFR Part 50.10(b) from the Atomic Energy Commission to permit certain work at the site of
DBNPS prior to issuance of a construction permit. Aug 07, 1970 The Bechtel Power Corporation issued for detailing and material purchase construction civil drawings (C-110 through C-113) for the shield building wall. Sep 08, 1970 Fegles-Power Service Incorporated revised the procedure for slip-form construction of the DBNPS shield building wall. Sep 10, 1970 The Atomic Energy Commission granted an exemption to allow concrete and reinforcing steel placement for construction of the shield building and auxiliary
buildings up to grade level (583 feet 6 inch elevation). Oct 09, 1970 Fegles-Power Service Incorporated submitted revised proposal for construction of the shield building wall. Oct 13, 1970 Construction Contract CC-18 addendum #3 issued to Fegles-Power Service Incorporated for construction of the shield building wall. Oct 23, 1970 The Bechtel Power Corporation issued for construction civil drawings (C-110 through C-113) for the shield building wall. Oct 30, 1970 The Bechtel Power Corporation issued for construction the design specification (C-38) for the shield building wall. Nov 11, 1970 The Bechtel Power Corporation revised the site architectural elevation drawings (A-20 through A-23) to specify a waterproof finish applied to the
reinforced concrete exterior surfaces of various buildings, excluding the shield
building.Dec 07, 1970 Fegles-Power Service Incorporated accepted Construction Contract CC-18 for construction of the shield building wall.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 87 Date DescriptionDec 29, 1970 The Bechtel Power Corporation approved Fegles-Power Service Incorporated drawings for construction of the shield building wall. Jan 25, 1971 Fegles-Power Service Incorporated started concrete pours for construction of the shield building wall at the 545 feet elevation. Feb 04, 1971 Fegles-Power Service Incorporated curtailed concrete pours for construction of the shield building wall at the 583 feet 6 inch elevation. Mar 24, 1971 The Atomic Energy Commission issued Construction Permit number CPPR-80 for DBNPS. Apr 26, 1971 Fegles-Power Service Incorporated resumed concrete pours for construction of the shield building wall. May 19, 1971 Fegles-Power Service Incorporated ended concrete pours for construction of the shield building wall at the 801 feet 6-1/2 inch elevation. Jun 17, 1971 Fegles-Power Service Incorporated submitted "as-built" drawings for construction of the shield building wall. Dec 09, 1971 The Bechtel Power Corporation issued for construction civil drawing (C-109) for the shield building roof plan and details. Mar 02, 1972 The Bechtel Power Corporation issued for construction civil drawing (C-114) for the shield building dome framing plan and details. Dec 14, 1972 The Bechtel Power Corporation issued for construction civil drawing (C-115) for the shield building blockout details. Aug 09, 1973 The A. Bentley and Sons Company performed a concrete pour (P1714Q) for construction of the shield building dome ring girder. Aug 22, 1973 The A. Bentley and Sons Company performed a concrete pour (P1745Q) for construction of the shield building dome bottom slab. Aug 29, 1973 The A. Bentley and Sons Company performed the first concrete pour (P1758Q) for construction of the shield Building dome parapet. Sep 12, 1973 The A. Bentley and Sons Company performed the second concrete pour (P1786Q) for construction of the Shield building dome parapet. Sep 21, 1973 The A. Bentley and Sons Company performed the third concrete pour (P1809Q) for construction of the shield building dome parapet. Oct 02, 1973 The A. Bentley and Sons Company performed a concrete pour (P1827Q) for construction of the shield building dome top slab. Aug 06, 1975 The A. Bentley and Sons Company started the concrete pours (P2666Q) from elevation 579 feet to 594 feet 8 inches for closing the shield building
construction opening. Oct 06, 1975 The A. Bentley and Sons Company performed a second concrete pour (P2746Q) from elevation 594 feet 8 inches to 610 feet 4 inches for closing the
shield building construction opening.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 88 Date DescriptionDec 01, 1975 The A. Bentley and Sons Company finished the concrete pours (P2826Q) from elevation 610 feet 4 inches to 625 feet 6 inches for closing the shield building
construction opening. Aug 15, 1976 The Toledo Edison Company examined the shield building dome parapet area and found a small area of the latex coating at approximately 315 degrees mid-way up the dome that was peeling and chipping from being applied too heavily. Sep 07, 1976 The Bechtel Power Corporation requested the field painting contractor to proceed with the application of a waterproof finish to the reinforced concrete
exterior surfaces of various structures, excluding the shield building. Apr 22, 1977 The Nuclear Regulatory Commission issued Facility Operating License NPF-3, Docket 50-346 for the Davis-Besse Nuclear Power Station. Apr 27, 1977 Fuel loading completed. Aug 12, 1977 Initial criticality achieved. Aug 20, 1977 Zero power physics testing completed. Sep 02, 1977 15 percent power level achieved. Nov 14, 1977 40 percent power level achieved. Dec 21, 1977 75 percent power level achieved. Jan 26, 1978 A severe blizzard impacted power distribution and transportation in the region and rendered the meteorological monitoring system inoperable at the plant. Apr 04, 1978 100 percent power level achieved. Jul 07, 1978 Full commercial operation commenced. Jun 24, 1998 A tornado touched down onsite damaging the switchyard and resulting in a loss of offsite power. Aug 12, 2002 The American Hydro Company started hydrodemolition (Order 02-003545-010) of the shield building to create a temporary access opening for replacement of
the reactor pressure vessel closure head with one from the cancelled Midland
Unit 2. Aug 17, 2002 The American Hydro Company finished hydrodemolition (Order 02-003545-010) of the shield building. Sep 24, 2002 The Bechtel Power Corporation performed a concrete pour (Order 200008657) from elevation 601 feet 6 inches to 620 feet for restoring the shield building
temporary access opening. Oct 07, 2011 The American Hydro Company started hydrodemolition (Order 200433294) of the shield building to create a temporary access opening for replacement of the
reactor pressure vessel closure head with one constructed from Alloy 690. Oct 10, 2011 Unexpected concrete crack within the shield building temporary access opening.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 89 Attachment 7, Shield Building Slip-Form Construction Sequence Date Shift Deck Height Footage jacked Shift Concrete Total Concrete Comments1/25/71 1 4'0" 0 108 108 6 cubic yards concrete batch ticket DB-00219 rejected with 8-1/4 inch slump at 0945 am. 1/25/71 2 5'8" 1'8" 132 240 1/25/71 3 8'8" 3'0" 108 348 6 cubic yards concrete batch ticket DB-00266 rejected with 7 inch slump at 0130 am. 1/26/71 1 10'8" 2'0" 42 390 Pour stopped at 10 am due to high winds. 2/1/71 1 11'10" 1'2" 120 510 2/1/71 2 14'10" 3'0" 138 648 2/1/71 3 17'8" 2'10" 108 756 2/2/71 1 19'8" 2'0" 108 866 2/2/71 2 21'9" 2'1" 102 968 6 cubic yards dumped on 2 nd shift because of tower crane down time. 2/2/71 3 24'9" 3'0" 114 1082 2/3/71 1 28'8" 3'11" 162 1244 2/3/71 2 31'11" 3'3" 132 1376 2/3/71 3 34'2" 2'3" 90 1466 2/4/71 1 37'6" 3'4" 132 1598 2/4/71 2 38'6" 1'0" 66 1664 Pour stopped at 583'6" elevation. Waterstop inserted and key way poured. Below-grade work for Shield Building construction allowed to 583'6" by a September 10, 1970 Atomic Energy Commission exemption obtained prior to construction permit issuance on March 24, 1971. 4/26/71 1 43'4" 3'9" 150 1814 Interim Field Report #14/26/71 2 47'5" 4'1" 144 1958 Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 90 Date Shift Deck Height Footage jacked Shift Concrete Total Concrete Comments4/26/71 3 51'0" 3'7" 126 2084 4/27/71 1 55'0" 4'0" 138 2222 4/27/71 2 59'3" 4'3" 132 2354 4/27/71 3 63'6" 4'3" 150 2504 4/28/71 1 68'7" 5'1" 168 2672 4/28/71 2 73'6" 4'11" 156 2828 4/28/71 3 77'0" 3'6" 144 2972 4/29/71 1 81'7" 4'7" 168 3140 4/29/71 2 85'5" 3'10" 156 3296 4/29/71 3 90'0" 4'7" 204 3500 4/30/71 1 94'4" 4'9" 210 3710 4/30/71 2 99'8" 4'11" 198 3908 4/30/71 3 103'11" 3'5" 156 4064 5/3/71 1 108'6" 5'5" 216 4280 5/3/71 2 113'2" 4'8" 192 4472 5/3/71 3 117'6" 4'4" 192 4464 5/4/71 1 122'0" 4'6" 198 4862 5/4/71 2 126'6" 4'6" 204 5066 5/4/71 3 130'3" 3'9" 180 5246 5/5/71 1 135'0" 4'9" 228 5474 5/5/71 2 139'10" 4'10" 222 5696 5/5/71 3 143'6" 3'8" 180 5876 5/6/71 1 148'5" 4'11" 216 6092 Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 91 Date Shift Deck Height Footage jacked Shift Concrete Total Concrete Comments5/6/71 2 153'3" 4'10" 228 6314 5/6/71 3 158'4" 5'1" 228 6542 5/7/71 1 163'4" 5'0" 234 6776 5/7/71 2 167'10'` 4'6" 204 6980 5/7/71 3 171'10" 4'0" 204 7184 5/10/71 1 176'9" 4'11" 216 7400 5/10/71 2 181'3" 4'6" 198 7598 5/10/71 3 185'10" 4'7" 204 7802 5/11/71 1 189'5" 3'7" 180 7982 5/11/71 2 193'6" 4'1" 180 8162 5/11/71 3 197'10" 4'4 210 8372 6 cubic yards of concrete was sent back to the batch plant due to time factor (governed by the spec) due to
a break down in the tower crane.5/12/71 1 202'2" 4'4" 192 8564 5/12/71 2 205'11" 3'9' 174 8738 5/12/71 3 210'4" 4'5" 198 8932 5/13/71 1 214'5" 4'1" 180 9116 5/13/71 2 218'3" 3'10" 174 9290 Interim Field Report #3 5/13/71 3 222'6" 4'3" 192 9482 5/14/71 1 226'10" 4'4" 195 9677 5/14/77 2 230'9" 3'11" 180 9857 5/14/71 3 234'2" 3'5" 181.5 10,038.5 On 2 nd shift, truck #82 ticket DB02764 delivered 6 cubic yards of concrete with Type II cement instead of
Type I cement.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 92 Date Shift Deck Height Footage jacked Shift Concrete Total Concrete Comments5/17/71 1 238'8" 4'6" 192 10,230.5 5/17/71 2 242'6" 3'10" 156 10, 386.5 5/17/71 3 246'9" 4'3" 192 10,578.5 5/18/71 1 250'4" 3'7" 168 10,746.5 5/18/71 2 253'0" 2'8" 108 10,854.5 5/18/71 3 256' 61/2" 3'6 1/2" 108 10,962.5 On 5-18-71 about 9:30 pm the concrete mix was noted as being sticky and not as consistent a mix as it should
be. The slump was 3". The problem appeared to be
the cement - to try to correct the problem the mix was
changed to type II cement at about 11:30 pm 5-18-71.
Nonconformance Report #57 5/19/71 1 256' 61/2" 0'0" 66 11,028.5 Concrete struck off @ 256'0 1/2" & 256'6 1/2" water stop and keyway in place and water is being piped to the
top of the shield wall for curing the concrete for
required time.
Nonconformance Report #359 Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 93 Attachment 8, Shield Building Concrete Compression Test Results 0 2000 4000 6000 8000 10000Pourour2PoundsPerSquareInch7daysdaysdays Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 94 Attachment 9, Shield Building Concrete Mixes C-2-SF-2 C-2-SF-4 D-1 490A Specified Strength 4000 pounds per square inch
@ 28 days 4000 pounds per square inch
@ 28 days 5000 pounds per square inch
@ 28 days 4000 pounds per square inch
@ 7 days CementMedusa Type II 564 pounds Type I 588 pounds Medusa Type II 520 pounds Type I 490 pounds Fly ash Detroit Edison 91 pounds Fine aggregate Woodville Lime manufactured
sand 1475 pounds Woodville Lime manufactured
sand 1440 pounds Woodville Lime manufactured
sand 1380 pounds Roundlake#2 natural sand
1535 pounds Coarse aggregate Woodville Lime
- 67 limestone
930 pounds Woodville Lime
- 67 limestone
940 pounds Woodville Lime
- 67 limestone
1650 pounds STONECO#57 limestone
1741 pounds Coarse aggregate Woodville Lime
- 4 limestone
620 pounds Woodville Lime
- 4 limestone
620 pounds WaterPotable 36.0 gallons Potable 36.0 gallons Potable 35.2 gallons Toledo 28.5 gallons AdmixtureMaster Builders Pozzolith 200-N Master Builders Pozzolith 200-N Master Builders Pozzolith 200-N Master Builders Micro Air AdmixtureMaster Builders MBVR AEA Master Builders MBVR AEA Grace Daravair R Master Builders Rheobuild 1000 Slump4 inches 5 inches 4-1/2 inches 5 inches Air content 5.5 percent 5.7 percent 3.3 percent 4.5 percent Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 95 Attachment 10, Shield Building Construction Deviations Interim Field Report #1 Water cement ratio of mix C-2-SF-4 was exceeded for 48 cubic yards of concrete placed on 4-26-1971 at elevation 583 feet 6 inches in the shield building wall. Minimum temperature was
below the specified requirement of 70 degrees Fahrenheit as per the attached concrete cylinder test reports for cylinders 170, 171, 172 and 175. Reference Specifications C-38 & C-
- 25. The attached cylinder strength reports and mix plant inspection report indicate acceptable
compression strengths were attained.
Bechtel Engineering has reviewed the Interim Field Report and its attachments relating to an excess of water in concrete mix C-2-SF-4. All concrete breaks are considerable higher than the 4000 pounds per square inch specified. No other harmful effects have been noted in the subject concrete. Bechtel Engineering approves the Use As Is disposition for the structure as
it is constructed.
Interim Field Report #3 Fegles Power Services Incorporated placed 6 cubic yards of C-1-3 concrete in pour #2 on 5-13-1971 at deck height 215 feet 6 inches in the shield building wall. Reference Specifications C-38 & C-25. Fly ash was not used in the batch. The batch plant operator apparently did not
change the batch plant mix design punch card before producing the aforementioned concrete.
The mix design is approved for use in Q-list structures and for 4000 pounds per square inch
compression strength requirements. The concrete batch ticket was checked and reveals
acceptable quantities of all materials used to produce the concrete in question.
Pittsburg Testing Laboratory report on concrete cylinder numbers 275, 276, 277, and 278 compressive strength indicate that the concrete inadvertently placed in the shield building
meets the minimum strength of 4000 pounds per square inch with considerable margin. No
other concrete defects are discernible. Bechtel Engineering approves the Use As Is disposition for the concrete as it has been placed in the structure. No remedial action is
required.Interim Field Report #5The shield building concrete wall outside face is not within the plumb tolerance of 1 inch in any 25 feet. Reference Specification C-38.
Bechtel Engineering has reviewed the Interim Field Report and its attached plumb plots. Out of tolerance exceeds the 1 inch in 25 feet specified by 2-3/4 inches. The affect this has on the shield building structural integrity were found to be insignificant. Bechtel Engineering approves
the Use As Is disposition for the structure and recommends that all interface work be adjusted
to meet the as-built alignment of the structure.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 96 Nonconformance Report #57 Pittsburg Testing Laboratory reports for cylinder 295, 301, and 302 shows that 156 cubic yards of Type II cement was used in place of Type I in the shield building wall between deck height
253 feet 4 inches and 256 feet 6-1/2 inches on 5-18-1971. Reference Specifications C-38 &
C-26.Bechtel Engineering approves the Use As Is disposition for the concrete based on the acceptable 28-day concrete compression tests as reported. Both the 28-day and 90-day
concrete compression test results far exceed the specification of 4000 pounds per square foot
compressive strength indicating that the change in cement type did not adversely affect the
required strength characteristics.
Nonconformance Report #359 The concrete keyway at elevation 801 feet 6-1/2 inches at the top of the shield building wall second pour was constructed in an inverted position in order to not allow water to settle and
freeze. Reference drawing C-109.
Bechtel Engineering approves the Use As Is disposition for the keyway based upon the fact that it does not change the structural analysis.
Nonconformance Report #382Electrical blockouts at azimuth 82.8 degrees elevation 610 feet and 615 feet were not installed during shield building wall concrete placement. Reference drawing C-115. Concrete has been
chipped out and reinforcing steel bars cut to place the 1 foot 3 inch square boxes required by
the design drawings.
Bechtel Engineering approves the repair based on the fact it does not affect the structural integrity of the shield building. Place extra vertical reinforcing steel in the Purge line blockout to replace verticals cut by placement of the blockout. One horizontal bar of reinforcing steel
will be disturbed on each face by each blockout with no affect on the structural integrity since
many extra bars of horizontal reinforcing steel were added for the Purge line blockout at the
same location.
Nonconformance Report #407 Approximately twenty #5 dowels were omitted or broken off attempting to bend them out from transfer tube penetrations through the shield building. Reference drawing C-113.
Bechtel Engineering approves the repair to drill holes, place #5 dowels, and grout with Embeco 636 for missing or broken dowels.
Nonconformance Report #415 Embedded plates for the station vent stack supports were not placed at locations on the shield building wall. Reference drawing C-112. All embedded plates are within a usable tolerance
except for the embedded plate at elevation 625 feet 11-3/16 inches east of the station vent
stack center line.
Bechtel Engineering approves the Use As Is disposition for all embedded plates except the one at elevation 625 feet 11-3/16 inches. For the embedded plate at elevation 625 feet 11-
3/16 inches, cut plate which mounts to embed and weld as shown on sketches.
Nonconformance Report #451 Superseded by Nonconformance Report #479.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 97 Nonconformance Report #457 The pipe sleeve for penetration #39 through the shield building must be placed at a fixed distance from the flued head anchor. The pipe sleeve flanges do not align with the concrete due to out of roundness of the shield building. Reference drawing C-115.
Bechtel Engineering approves the repair to place the sleeve in its proper location in relation to the flued head and adjust concrete and reinforcing steel to match as shown on sketches.
Nonconformance Report #474Concrete was placed in the blockout for penetrations 33 and 40 at azimuth 237 degrees elevation 643 feet prior to approval of Nonconformance Report #451, therefore the flange cannot be moved as stated in the disposition.Reinforcing steel which extends into concrete
was not placed with 3 inch clearance. Reference drawing C-115.
Bechtel Engineering approves the Use As Is disposition with sleeve placement in accordance with Nonconformance Report #479.
Nonconformance Report #479 The pipe sleeve for penetration #40 through the shield building must be placed at a fixed distance from the flued head anchor. The pipe sleeve flanges do not align with the concrete due to out of roundness of the shield building. Reference drawing C-115.
Bechtel Engineering approves the repair to place the sleeve in its proper location in relation to the flued head and adjust concrete and reinforcing steel to match as shown on sketches.
Nonconformance Report #602The reglet in the shield building was not placed and maintained at a constant elevation.
Counter flashing cannot be placed due to the waviness of the reglet. Reference drawing C-
112.Bechtel Engineering approves the repair that places a continuous saw cut in the shield building concrete at elevation 662.25 feet in lieu of the reglet shown on drawing C-112.
Nonconformance Report #743 Two #11 dowels are missing on the horizontal face of penetration #80 and the spacing of #8 and #10 vertical dowels along the top of penetration #80 exceeds the 20 inch maximum.
Reference drawing C-115.
Bechtel Engineering approves the repair to place 2 grouted-in replacement dowels as shown on sketches, and a Use As Is disposition for the dowel spacing where jacking rods interfere
since it will not affect the design or stress distribution of the shield building.
Nonconformance Report #772 The shield building reinforcing steel was installed at elevations beyond the construction tolerances. Reference Specification C-38 and drawing C-110.
Bechtel Engineering approves the Use As Is disposition for the reinforcing steel elevation deviations based upon the fact that it does not affect the integrity of the structure.
Material Rejection Report, 1-25-1971 6 cubic yards concrete mix ticket DB-00219 rejected by Fegles Power Service for 7-1/2 inch slump. Concrete disposed at burrow pit.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 98 Material Rejection Report, 1-26-1971 6 cubic yards concrete mix ticket DB-00266 rejected by Fegles Power Service for 7 inch slump. Concrete disposed at burrow pit.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 99 Attachment 11, Fault Tree Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 100 Attachment 12, Failure Modes Analysis Failure Mode No. 1
==
Description:==
Design Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Initial laminar crack in the temporary access opening
was located at a vertical to horizontal rebar interface
within the architectural flute shoulder.
1.1)Rebar to rebar interaction None Review design records Drawing C-110
Calculation C-CSS-099.20-054
Calculation C-CSS-099.20-056
Ground penetrating radar survey Refuted.Rebar lap splice length is consistent or more conservative
than ACI 318-63 requirements.
Typically the stresses in the rebar and concrete are approximately 1/2
of the allowable values.
Initial laminar crack in the temporary access opening
was located at a rebar to concrete interface within the
architectural flute shoulder.
1.2)Rebar to concrete interaction None Review design records Drawing C-110
Calculation C-CSS-099.20-054
Calculation C-CSS-099.20-056 Refuted.Rebar lap splice length is consistent or more conservative
than ACI 318-63 requirements.
Typically, the stresses in the rebar and concrete are approximately 1/2
of the allowable values.
Initial laminar crack in the temporary access opening
was located at a rebar to concrete interface within the
architectural flute shoulder.
1.3)Rebar interaction with flute / shoulder Similar laminar cracks were subsequently located at areas beyond the architectural flute shoulders such as
near the top of the shield building, and adjacent to the
main steam line penetration blockouts.
Review design records Drawing C-110
Drawing C-111A Causal Factor.
The architectural flute vertical rebar are not tied to the outside
face rebar mat.
The architectural flute horizontal rebar are tied to the main rebar
only at the ends.
There is an approximately 10 foot horizontal span in which the
architectural flute shoulder
concrete is not connected to the
main rebar mat.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 101 Failure Mode No. 1
==
Description:==
Design Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Initial laminar crack in the temporary access opening
was located at a rebar to rebar overlap area.
1.4)Rebar to rebar overlaps Shield building designed for rebar lap splices.
Review construction photos Review design records
Drawing C-110
Calculation C-CSS-099.20-054
Calculation C-CSS-099.20-056
Ground penetrating radar survey Refuted.Rebar lap splice length is consistent or more conservative
than ACI 318-63 requirements.
Typically, the stresses in the rebar and concrete are approximately 1/2
of the allowable values.
Initial laminar crack in the temporary access opening
was located at an area with a high rebar density.
1.5)Density of rebar Additional rebar was added at the construction opening and other similar blockout areas to compensate for the
rebar interrupted by the opening.
Review construction photos Review design records
Drawing C-110
Drawing C-112
Finite element analysis Causal Factor.
A rebar spacing sensitivity study established that a higher density
of rebar could propagate laminar
cracking beyond the architectural
flute region with a given stress
condition.
Some laminar cracks extended beyond the architectural
flute shoulders such as those located near the top of
1.6)Building / dome weight Shield building designed for load from dome.
Review design records Drawing C-109
Drawing C-110
Drawing C-111A
Calculation C-CSS-099.20-054 Refuted.The dead weight load from the building & dome is substantially
less than the compressive
strength of the concrete.
Typically, the stresses in the rebar and concrete are approximately 1/2
of the allowable values.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 102 Failure Mode No. 1
==
Description:==
Design Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause.
Summarize review of data collected to confirm or disprove
cause.Some laminar cracks extended beyond the architectural
flute shoulders such as those located near the top of
1.7)Interaction between building / dome Shield building designed for load from dome.
Review design records Drawing C-109
Drawing C-110
Drawing C-111A
Calculation C-CSS-099.20-054 Refuted.The stresses in the rebar and concrete are approximately 1/2 of
the allowable values.
Typically, the amount of rebar in the top 7-1/2 feet is double the
ACI 307-69 requirements.
Some laminar cracks extended beyond the architectural
flute shoulders such as those located adjacent to the
main steam line penetration blockouts near the shield
building and auxiliary building interface.
1.8)Interaction between wall / buildings Most laminar cracks were situated away from building interfaces. Shield building and auxiliary building
designed for potential seismic loads.
Review design records Drawing C-110
Drawing C-111A
Drawing C-200 Refuted.No relevant seismic activity.
Shield building and auxiliary building both founded on bedrock.
Buildings isolated by an expansion joint.
Some laminar cracks extended beyond the architectural
flute shoulders such as those located adjacent to the
main steam line room penetration blockouts at shield
building and auxiliary building interface.
1.9)Structures dynamic interaction Most laminar cracks were situated away from building interfaces. Shield building and auxiliary building
designed for potential seismic loads.
Review design records Drawing C-110
Drawing C-111A
Drawing C-200 Refuted.No relevant seismic activity.
Shield building and auxiliary building both founded on bedrock.
Buildings isolated by an expansion joint.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 103 Failure Mode No. 1
==
Description:==
Design Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause.
Summarize review of data collected to confirm or disprove
cause.Operating experience documents indicate that rebar
location in structure had previously been a problem area
relevant to nuclear power plants. NRC IN 2008-17 &
NUREG/CR-6927 1.10)Rebar location in structure None Review design records Drawing C-110 Refuted.Rebar location was consistent with good engineering /
fabrication practices.
Initial laminar crack in the temporary access opening
was located in a uniform plane along the outer rebar
mat under the architectural flute shoulder cross-section.
1.11)Concrete tensile strength None Review design records Drawing C-111A
Destructive examination of concrete cores Refuted.Split tensile test results (>800 psi) were nearly double the ACI 318-
89 value based upon the design
minimum compressive strength.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 104 Failure Mode No. 1
==
Description:==
Design Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause.
Summarize review of data collected to confirm or disprove
cause.Initial laminar crack in the temporary access opening
was located at a rebar to concrete interface in the
architectural flute shoulder.
Operating experience documents indicate that lack of radial reinforcement had previously been a problem
area for concrete delamination at the Crystal River and
Turkey Point nuclear power plants. NRC NUREG/CR-
6927 1.12)Shoulder reinforcement detail Similar laminar cracks were subsequently located at areas beyond the architectural flute shoulders such as
near the top of the shield building, and adjacent to the
main steam line penetration blockouts.
Review design records Drawing C-110
Drawing C-111A Causal Factor.
The architectural flute vertical rebar are not tied to the outside
face rebar mat.
The architectural flute horizontal rebar are tied to the main rebar
only at the ends.
There is an approximately 10 foot horizontal span in which the
architectural flute shoulder
concrete is not connected to the
main rebar mat.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 105 Failure Mode No. 2
==
Description:==
Construction / Fabrication Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Operating experience documents indicate that concrete
mix had previously been a problem area relevant to
nuclear power plants. NRC IN 2008-17 & INPO IER L4-
11-4.2.1)Concrete mix Pittsburg Testing Laboratory independently verified each mix ticket.
Review design and construction records Specifications C-26 & C-38
Destructive examination of concrete cores Refuted.The concrete mix achieved material property requirements for
aggregate, cement type, concrete
strength, durability, air content, and workability.
Nonconformances were localized.
Operating experience documents indicate that concrete placement had previously been a problem area relevant
to nuclear power plants. NRC IN 2008-17 & INPO IER
L4-11-4.2.2)Concrete placement None Review design and construction records Specifications C-26 & C-38 Refuted.The concrete placement achieved material property requirements for
segregation, temperature, water
content, cover, curing and
placing.Nonconformances were localized.
Cold joints between hardened and fresh concrete occurred between the two major pours and other times
such as weekends.
2.3)Slip-form joints The laminar cracks were oriented perpendicular to the slip-form joints and also mostly on the southern
exposure versus circumferential.
Visual examination of the shield building exterior did not observe surface distress resulting from cold joints
allowing moisture movement.
Review design, construction, and operation records Drawing C-111A Refuted.The design specification addresses how to continue
placement beyond cold joints.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 106 Failure Mode No. 2
==
Description:==
Construction / Fabrication Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Operating experience documents indicate that concrete
shrinkage had previously been a problem area relevant
to nuclear power plants. NRC NUREG/CR-6927 2.4)Drying shrinkage Visual examination of shield building exterior concrete did not observe active surface distress resulting from
shrinkage allowing moisture movement. Review operation records Refuted.
Visual examination of shield building exterior concrete did not
observe active surface distress
resulting from shrinkage allowing
moisture movement.
Operating experience documents indicate that concrete
construction had previously been a problem area
relevant to nuclear power plants. NRC IN 2008-17 &
2.5)Concrete construction None Review design and construction records Specifications C-26 & C-38
Destructive examination of concrete cores Refuted.The concrete construction achieved process requirements
for vibration, pour timing, joints, forms, slip-form speed, and
jacking rod configuration.
The concrete material properties were acceptable.
Operating experience documents indicate that voids
near rebar had previously been a problem area relevant
to nuclear power plants. NRC NUREG/CR-6927 2.6)Voids near rebar Visual examination of shield building rebar at temporary access opening did not veal any substantial difference in voids adjacent to rebar or away from rebar Review operation records Destructive examination of concrete cores Refuted.Petrographic examination found no substantial difference in voids
adjacent to rebar or away from
rebar.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 107 Failure Mode No. 2
==
Description:==
Construction / Fabrication Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Industry documents indicate that moisture intrusion into
concrete had previously been a problem area above
grade due to hydrostatic pressure, water vapor gradient, capillary action, wind-driven rain, or any combination of
these forces. ACI 515.1 R-79.
2.7)Concrete sealant None Review design and construction records Specification C-38
Destructive examination of concrete cores Visual examination of shield building exterior Causal Factor.
Construction records indicate a sealant was applied to protect the
concrete only during curing.
There was no sealant specified to
mitigate moisture penetration.
Destructive examination of concrete cores identified that the
surface zone is not water-
repellant, and the presence of
deposits in air voids typically
suggests long-term exposure to
moisture migrating through the
concrete.
Initial laminar crack in the temporary access opening
was located at a rebar to concrete interface within the
architectural flute shoulder.
2.8)Concrete to rebar adhesion Visual examination of shield building rebar at temporary access opening identified numerous examples of
concrete strongly adhered to rebar.
Review design and operation records Drawing C-111A Refuted.Reinforced concrete design relies upon rebar deformation versus
adhesion to transfer the stresses.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 108 Failure Mode No. 2
==
Description:==
Construction / Fabrication Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Operating experience documents indicate that the
amount of rebar had previously been a problem area
relevant to nuclear power plants. NRC IN 2008-17 &
2.9)Amount of rebar in structure None Review design records Drawing C-110
Drawing C-111
Drawing C-112
Calculation C-CSS-099.20-054
Calculation C-CSS-099.20-056 Refuted.The amount of rebar was less than the global density for brittle
fracture.
The amount of rebar was greater than the strength needed for the
required loads.
Initial laminar crack in temporary construction opening
was located at rebar to rebar overlap area 2.10)Rebar lap splice None Review design records Drawing C-110
Calculation C-CSS-099.20-054
Calculation C-CSS-099.20-056
Ground penetrating radar survey Refuted.Rebar lap splice length is consistent or more conservative
than ACI 318-63 requirements.
Typically, the stresses in the rebar and concrete are approximately 1/2
of the allowable values.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 109 Failure Mode No. 2
==
Description:==
Construction / Fabrication Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove this cause Summarize review of data collected to confirm or disprove
cause Initial laminar crack in the temporary access opening
was located at an area with a high rebar density.
2.11)Small rebar spacing Additional rebar was added at the construction opening and other similar blockout areas to compensate for the
rebar interrupted by the opening.
Review construction photos Review design records
Drawing C-110
Drawing C-112
Finite element analysis Causal Factor.
A rebar spacing sensitivity study established that a higher density
of rebar could propagate laminar
cracking beyond the architectural
flute region with a given stress
condition.
Plumb tolerance was exceeded during the above-grade
pour.Friction forces from geometry changes and the slip-form not in level have resulted in concrete delamination.
2.12)Plumb Plumb tolerance issues oriented different than the laminar cracking locations.
The observed cracking through aggregate indicated the laminar cracking occurred after the concrete reached sufficient maturity and not during placement. Review construction records Refuted.
The effect of the out of tolerance plumb was insignificant to
structure integrity. The rate of slip-form movement was fast enough to minimize friction problems.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 110 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause A classifiable event from seismic activity occurred on
March 5, 1986.
3.1)Earthquake Shield building was designed for potential adverse environmental conditions including seismic loads.
Review operational records Unit log Event number 3837 Refuted.No relevant seismic activity.
Seismic system actuation attributed to movement of heavy
equipment near trigger.
A potential lightning strike of the shield building occurred
on May 10, 1995.
3.2)Lightning Shield building was designed for potential adverse environmental conditions including lightning strikes.
Review operational records Drawing E-401
Problem report 1995-0395 Refuted.No actual lightning strike damage found.Sufficiently grounded at the dome.
A classifiable event from a tornado occurred on June 24, 1998.
3.3)Tornado Shield building was designed for potential adverse environmental conditions including tornado loads.
Review operational records Licensee Event Report 98-006
Finite element analysis Refuted Insufficient radial stress from tornado loads to initiate or
propagate the laminar cracks.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 111 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Initial laminar crack in the temporary access opening
was located in an area observed with corrosion and rust
stains on the outer mat of rebar.
3.4)Electrical potential Visual examination of the shield building rebar at temporary access opening did not observe excessive
rebar corrosion or material loss.
Destructive examination of concrete cores Refuted.Destructive examination of concrete cores found no
accelerated rebar corrosion
produced from galvanic action
due to an unbalance in electric
potential.
Initial laminar crack in the temporary access opening
was located at the boundary of the hydrodemolition.
3.5)Hydrodemolition Similar laminar cracks were subsequently located at areas beyond the hydrodemolition boundary such as
near the top of the shield building, and adjacent to the
main steam line penetration blockouts.
Review operating experience Drawing C-111A Refuted.Similar laminar cracks were subsequently located at areas
beyond the hydrodemolition
boundary such as near the top of
the shield building, and adjacent
to the main steam line penetration
blockouts.
A severe blizzard occurred surrounding the facility on
January 26 & 27, 1978.
3.6)Freezing of water near rebar in blizzard Shield building was designed for potential adverse environmental conditions including wind and thermal
loads.Review operational records Unit log Licensee Event Report 78-017
Finite element analysis Causal Factor.
The wind load moisture intrusion into the unsealed concrete
followed by the thermal load from
the moisture freezing and
expanding were sufficient to
produce a radial stress to initiate
the laminar cracks Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 112 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Most laminar cracks were oriented on the southern
exposure of the shield building exterior.
Some laminar cracks were located at main steam line room interface with the shield building at the piping
penetration blockouts.
Operating experience documents indicate that prolonged exposure of concrete to elevated
temperatures results in decreased elastic modulus and
compressive rupture strength. EPRI-1020932.
3.7)Long term thermal stress cycles A general threshold limit for temperature exposure degradation of concrete is approximately 95 degrees
Centigrade / 203 degrees Fahrenheit.
Review design and operational records Drawing C-111A
Thermal imaging
Destructive examination of concrete cores Finite element analysis Refuted.No micro-cracks evident.
Insufficient radial stress from thermal loads (<1/2 tensile
strength) to initiate or propagate
the laminar cracks.
Insufficient thermal and shrinkage strains to cause cracking.
Insufficient temperature (<150 degrees Fahrenheit) for
temperature exposure
degradation adjacent to the main
steam line penetration blockouts.
No actual fires adjacent to the shield building.
Permafrost produces cracks parallel to the ground
surface 3.8)Permafrost Laminar cracks are located above grade.
Review design and operational records Drawing C-110
Drawing C-111A Refuted.The mean air temperature near the facility is greater than freezing
necessary for permafrost.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 113 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Operating experience documents indicate that chemical
attack had previously been a problem area relevant to
nuclear power plants. NRC NUREG/CR-6927, Information Notice 2011-20, and EPRI-1020932.
Leaching & efflorescence - water passing through cracks dissolves the constituents in cement paste.
Sulfate attack - magnesium and sulfates present in soil, groundwater, and acid rain can react with the cement
paste and cause swelling and irregular cracking.
Ettringite formation - reaction of sulfate with calcium aluminates resulting in expansion and cracking.
Carbonation - carbon dioxide in the atmosphere reacts with calcium hydroxide or other lime-bearing
compounds and results in a reduction in pH of the
cement paste which has the potential to cause
degradation to embedded steel reinforcement.
Alkali-aggregate reaction - reaction of alkali ions in cement with silica mineral aggregates forms a gel that
expands when it comes into contact with water and
manifests as small surface cracks in an irregular
pattern.Acids and bases - acidic aqueous solutions attack the cement paste leading to increased porosity. High
concentration bases can disintegrate concrete.
3.9)Chemical attack Visual examination of the shield building exterior did not observe excessive chemical attack.
Review operation records Destructive examination of concrete cores Refuted.Destructive examination of concrete cores found no evidence
of chemical attack producing the
laminar cracking. Only
inconsequential amounts of
ettringite formation and
carbonation were identified.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 114 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Initial laminar crack in the temporary access opening
was located in an area observed with corrosion and rust
stains on the outer mat of rebar.
3.10)Rebar corrosion Visual examination of the shield building exterior did not observe excessive cracking, staining or spalling.
Visual examination of the shield building exterior did not observe excessive rebar corrosion or material loss.
Review design, construction, and operational records Destructive examination of concrete cores Refuted.Sufficient barriers for minimizing rebar corrosion were established
including low water permeability
concrete mix design, and
adequate rebar cover.
Destructive examination of concrete cores found an
inconsequential carbonation
depth.None 3.11)Rebar creep NoneFinite element analysis Refuted.
Insufficient radial stress from thermal loads in the concrete to
affect the creep threshold for
rebar (>30,000 psi).
Strain that accumulates due to dead or live static loads
over long periods of time as a function of the loading
magnitude and history, environment, and material
properties of the concrete. EPRI-1020932.
3.12)Concrete creep Creep in those concrete structures not pre-stressed is not considered to be a significant degradation
mechanism, because cracking is generally not sufficient
to expose the steel reinforcement and has a minor effect
on structural integrity. EPRI-1020932.
Destructive examination of concrete cores Refuted.The measured concrete creep coefficient is in the normal range
and not sufficient to cause laminar
cracks.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 115 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Some laminar cracks extended beyond the architectural
flute shoulders such as those located near the top of the
3.13)Snow & ice loading to dome Shield building designed for live and dead loads from dome.Review design records Drawing C-109
Drawing C-110
Drawing C-111A
Calculation C-CSS-099.20-054 Refuted.The live & dead weight load from the building & dome is
substantially less than the
compressive strength of the
concrete.
Operating experience documents indicate that cyclic
loading in concrete structures from vibration or fatigue
initiates as microcracks in the cement paste adjacent to
aggregate particles, reinforcing steel, or stress
concentrations which in the later stages can manifest
itself as large, structurally significant cracks. EPRI-1020932.3.14)Vibration / fatigue Operating experience documents indicate that fatigue failure of concrete is unusual because of its good fatigue
resistance. IAEA TECDOC-1025.
Review design and operation records Destructive examination of concrete cores. Refuted.No rotating equipment located on or supported by the shield
building.No adverse vibration identified by monitoring major rotating
equipment inside containment.
Destructive examination of concrete cores found no
microcracks related to vibration /
mechanical fatigue.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 116 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Operating experience documents indicate that physical
attack had previously been a problem area relevant to
nuclear power plants. NRC NUREG/CR-6927 and
EPRI-1020932.
Abrasion or cavitation - loss of concrete material on concrete surfaces exposed to fluid flow, impingement, or
negative surface pressure.
Irradiation - dehydration of concrete and changes in mechanical properties when exposed to prolonged or
very high doses.
Salt crystallization - movement of salt solution by capillary action generating expansive forces that result
in the physical breakdown of the concrete.
3.15)Physical attack Visual examination of the shield building exterior did not observe excessive physical attack.
Review of design, construction, and operation records Destructive examination of concrete cores. Refuted.Destructive examination of concrete cores found no evidence
of physical attack producing the
laminar cracking.
Operating experience documents indicate that the
freeze / thaw cycle of entrained water has demonstrated
spalling at the surface and localized internal cracking.
EPRI-1020932.
3.16)Freeze / thaw The freeze / thaw cycle damage typically occurs in concrete in contact with water, such as on flat horizontal
surfaces.Visual examination of the shield building exterior did not observe excessive surface deterioration.
Review of operation records Destructive examination of concrete cores. Refuted.Destructive examination of concrete cores found no
microcracks related to freeze /
thaw thermal fatigue, or freeze /
thaw deterioration at the core
surface.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 117 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Initial laminar crack in the temporary access opening
was located adjacent to a previous temporary access
opening and the original construction opening.
3.17)Containment cutting Similar laminar cracks were subsequently located at areas beyond the hydrodemolition boundary such as
near the top of the shield building, and adjacent to the
main steam line penetration blockouts.
Review operating experience Drawing C-111A Refuted.No previous operating experience with laminar cracking caused by
hydrodemolition.
Literature review concluded that hydrodemolition poses less
damage to adjacent material than
mechanical impact alternatives.
Initial laminar crack in the temporary access opening
was located adjacent to a previous temporary access
opening.3.18)Modification activities Similar laminar cracks were subsequently located at areas beyond the hydrodemolition boundary such as
near the top of the shield building, and adjacent to the
main steam line penetration blockouts.
Review operating experience Drawing C-111A Refuted.Similar laminar cracks were subsequently located at areas
beyond the hydrodemolition
boundary such as near the top of
the shield building, and adjacent
to the main steam line penetration
blockouts.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 118 Failure Mode No. 3
==
Description:==
Operational Issues Existing data that supports this as the cause.
POSSIBLE CAUSE(S)
Existing data that tends to disprove this as the cause.
Data required to confirm or disprove cause Summarize review of data collected to confirm or disprove
cause Operating experience documents indicate that structures have a tendency to settle during construction
and early life that can lead to concrete cracking. IAEA
TECDOC-1025.
3.19)Building settlement Minimal settlement is expected for foundations situated on bedrock.
No laminar cracks were located adjacent to the inner face rebar mat.
Visual examination of the shield building exterior did not observe excessive surface distress.
Review of design and operation records Drawing C-100 Refuted.Shield building founded on bedrock.Some laminar cracks extended beyond the architectural
flute shoulders such as those located adjacent to the
main steam line room penetration blockouts at shield
building and auxiliary building interface.
3.20)Penetration translational stress Most laminar cracks were situated away from penetration blockouts.
Review of design records Drawing C-111A
Drawing M-284A
Drawing M-284B Refuted.The high energy piping penetration loads are structurally
isolated from the shield building.
Some laminar cracks extended beyond the architectural
flute shoulders such as those located adjacent to the
main steam line penetration blockouts at shield building
and auxiliary building interface.
3.21)Piping penetration loads Most laminar cracks were situated away from penetration blockouts.
Review of design records Drawing C-111A
Drawing M-284A
Drawing M-284B Refuted.The high energy piping penetration loads are structurally
isolated from the shield building.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 119 Attachment 13, Change AnalysisChange Analysis Current Condition Previous Condition Impact Since 10/1973 the dome has been in place on the shield building.
Prior to installation of the shield building dome, the walls had reinforcing steel /
jacking rods that were exposed to
environmental conditions Potential impact due to a broad pathway for moisture ingress to facilitate reinforcing steel
corrosion or freeze / thaw damage.
Since 12/1975 the original
construction opening has been
closed with a different mix of
concrete having smaller aggregate
than the shield building wall.
Prior to closure of the original construction opening, the perimeter
reinforcing steel were exposed to
environmental conditions Insignificant impact other than both a potential local pathway form moisture ingress to
facilitate reinforcing steel corrosion or freeze /
thaw damage, and a different concrete mix
with smaller aggregate for closure of the
original construction opening.
Since 08/1977 the reactor has been
critical except for refueling or
maintenance shutdowns.
Prior to start-up testing and reactor criticality there was lesser heat and
radiation on the annulus side of the
Insignificant impact as the radiation source on the shield building during normal operation
term is minimal, and the differential
temperature for thermal cycling is less severe
than during operation.
Since 09/2002 a temporary access
opening has been cut into the shield
building wall by hydrodemolition and
closed with a different mix of
concrete having smaller aggregate
than the shield building wall.
Prior to creating and closing the temporary access opening, the concrete
of the original construction opening had
not been disturbed.
Insignificant impact other than a different concrete mix with smaller aggregate for
closure of the temporary access opening.
Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 120 Attachment 14, Barrier Analysis Barrier Analysis Consequence / Adverse Effect Barrier that should have Precluded Consequence Barrier Assessment(Why the Barrier Failed) Lack of sealant on exterior Design basis Not in specification Rebar density in some areas Design basis Not concerned with amount of rebar Lack of radial reinforcement Design basis Not concerned with architectural elementsStress concentration behind flute Design basis Not concerned with architectural elements Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 121 5, Event and Causal Factors Chart Design of shield building 1969 - 1972 Construction of
shield building 1971 - 1975 Blizzard of 1978 Jan 26, 1978 Reactor pressure
vessel closure
head replacement Aug 2002 Concrete crack within shield building wall CF Concrete mix at construction
o p enin g Lack of radial
reinforcement CF Hydro-demolition Tornado of 1998 Jun 24, 1998 Concrete mix
at temporary
o p enin g Lack of sealant on
exterior Rebar density
in some areas Extreme severe environment CF CF CF Oct 10, 2011 Stress concentration
at shoulder Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 122 6, Generic Implications Matrix Item Original Scope Extent of Condition Program / Process Hydrodemolition of temporary access opening for replacement of reactor
pressure vessel closure head Slip-form construction of right cylindrical structuresPlant / System / Structure /
ComponentDavis-Besse shield building Nuclear reactor containment shield buildings Chimneys / Stacks
Storage tanks / Silos
Cooling towers OrganizationSupplemental personnel Construction Management / Oversight Architectural Engineer
Civil Engineer EnvironmentArchitectural flutes Outer reinforcing steel mat Southwestern exposure People / Group American Hydro Fegles Power Service / Chicago Bridge and Iron Bechtel Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 123 7, Corrective Action Matrix Corrective Action or Notification Number Cause Cause Code Corrective Action Description Corrective Action Type Group Responsible Due Date Safety Precedence SequenceCA-2011-03346-1 Extent of Condition CA1 T22 Additional Examination of the Shield Building Exterior Wall Corrective Site Projects 07/15/2012 N/A CA-2011-03346-2 Extent of Condition CA2 T22 Issue Engineering Change Package for Additional Shield Building Core Bores Corrective Design Engineering 04/30/2012 N/A CA-2011-03346-14 Extent of Condition CA3 T22 Confirmatory Examination of a Safety-Related Structure with Waterproof Coating.
Corrective Site Projects 08/31/2012 N/A CA-2011-03346-3 Direct Cause CA1T22 Testing Program to Investigate the Steel Reinforcement Capacity Adjacent to
Structural Discontinuities Corrective Design Engineering 08/01/2012 N/A CA-2011-03346-4 Direct Cause CA2T22 Engineering Plan to Re-Establish Design &
Licensing Basis for Shield Building Corrective Design Engineering 12/01/2012 N/A CA-2011-03346-5 Direct Cause CA3T22 Issue a Site Specific Procedure for the Long-Term Monitoring of the Shield
Building Laminar Cracking Corrective Design Engineering07/11/2012 4 - procedure CA-2011-03346-6 Root Cause CA1DA1D Issue Engineering Change Package for a Shield Building Exterior Sealant System Preventive Design Engineering05/01/2012 1 - design for minimum hazard CA-2011-03346-7 Root Cause CA2DA1DImplement Engineering Change Package for a Shield Building Exterior Sealant
System Preventive Site Projects10/01/2012 1 - design for minimum hazard CA-2011-03346-8 Root Cause CA3DA1DUpdate Inspection Procedure to Include Shield Building Exterior Sealant System Corrective Design Engineering10/01/2012 4 - procedure CA-2011-03346-9 CAL Commitment
CA1N/A Root Cause Report Submittal Corrective Design Engineering 03/02/2012 N/A CA-2011-03346-10 CAL Commitment
CA2N/A Examine Four Un-Cracked Core Bores Following Restart Corrective Design Engineering 03/05/2012 N/A Root Cause Analysis Report, CR 2011-03346 11 Attachments Page 124 Corrective Action or Notification Number Cause Cause Code Corrective Action Description Corrective Action Type Group Responsible Due Date Safety Precedence Sequence CA-2011-03346-11 CAL Commitment
CA3N/A Main Steam Line Room New Core Bore &
Examination Following Restart Corrective Site Projects 03/05/2012 N/A CA-2011-03346-12 CAL Commitment
CA4N/A Examine Six Un-Cracked Core Bores in 17RFOCorrective Design Engineering 06/15/2012 N/A CA-2011-03346-13 CAL Commitment
CA5N/A Examine Three Crack Interface Core Bores in 17RFO Corrective Design Engineering 06/15/2012 N/A UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD
)
In the Matter of )
) Docket No. 50-346-LR FIRSTENERGY NUCLEAR OPERATING COMPANY )
)
(Davis-Besse Nuclear Power Station, Unit 1) ) May 17, 2012
) CERTIFICATE OF SERVICE I hereby certify that, on this date, a copy of the Notification of Filing Related to Proposed Shield Building Cracking Contention was filed with the Electronic Information Exchange in the above-captioned proceeding on the following recipients.
Administrative Judge William J. Froehlich, Chair Atomic Safety and Licensing Board Panel U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001 E-mail: wjf1@nrc.gov
Administrative Judge Dr. William E. Kastenberg Atomic Safety and Licensing Board Panel
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001 E-mail: wek1@nrc.gov
Office of the Secretary
U.S. Nuclear Regulatory Commission Rulemakings and Adjudications Staff
Washington, DC 20555-0001 E-mail: hearingdocket@nrc.gov
Administrative Judge Nicholas G. Trikouros Atomic Safety and Licensing Board Panel U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001 E-mail: nicholas.trikouros@nrc.gov
Office of the General Counsel
U.S. Nuclear Regulatory Commission
Mail Stop O-15D21
Washington, DC 20555-0001
Brian G. Harris Megan Wright Emily L. Monteith Catherine E. Kanatas E-mail: Brian.Harris@nrc.gov; Megan.Wright@nrc.gov; Emily.Monteith@nrc.gov;
Catherine.Kanatas@nrc.gov
2DB1/ 69853620.1
Office of Commission Appellate Adjudication
U.S. Nuclear Regulatory Commission
Mail Stop: O-16C1
Washington, DC 20555-0001 E-mail: ocaamail@nrc.gov
Kevin Kamps
Paul Gunter
6930 Carroll Avenue, Suite 400 Takoma Park, MD 20912 E-mail: kevin@beyondnuclear.org;
paul@beyondnuclear.org
Michael Keegan Dont Waste Michigan
811 Harrison Street
Monroe, MI 48161 E-mail: mkeeganj@comcast.net
Terry J. Lodge
316 N. Michigan St., Ste. 520
Toledo, OH 43604 E-mail: tjlodge50@yahoo.com Signed (electronically) by Stephen J. Burdick Stephen J. Burdick Morgan, Lewis & Bockius LLP 1111 Pennsylvania Avenue, N.W.
Washington, DC 20004
Phone: 202-739-5059 E-mail: sburdick@morganlewis.com
COUNSEL FOR FENOC