Information Notice 2013-04, Concrete Subsurface Laminar Cracking Caused by Moisture Intrusion and Freezing

Concrete Subsurface Laminar Cracking Caused by Moisture Intrusion and Freezing

ML12352A052
Person / Time
Issue date:	03/07/2013
From:	Laura Dudes, Kokajko L Division of Policy and Rulemaking, Division of Construction Inspection and Operational Programs
To:
Klos L, NRR/DPR, 415-5136
References
IN-13-004
Download: ML12352A052 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NEW REACTORS

WASHINGTON, DC 20555-0001

March 7, 2013

NRC INFORMATION NOTICE 2013-04:

SHIELD BUILDING CONCRETE SUBSURFACE

LAMINAR CRACKING CAUSED BY MOISTURE

INTRUSION AND FREEZING

ADDRESSEES

All holders of an operating license or construction permit for a nuclear power reactor under Title 10

of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and

Utilization Facilities, except those who have permanently ceased operations and have certified that

fuel has been permanently removed from the reactor vessel.

All holders of an operating license for a non-power reactor (research, test reactor, or critical

assembly) under 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities, except those who have permanently ceased operations.

All holders of and applicants for a power reactor early site permit, combined license, standard

design certification, standard design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform

addressees of the occurrence of laminar subsurface cracks in the reinforced concrete shield

building (SB) of the containment system at the Davis-Besse Nuclear Power Station caused by

moisture intrusion and freezing. The NRC expects that recipients will review the information for

applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this IN are not NRC requirements; therefore, no specific action

or written response is required.

DESCRIPTION OF CIRCUMSTANCES

On October, 10 2011, the shield building (SB) of Davis-Besses containment was cut open to permit

removal of the old reactor vessel head and installation of the replacement vessel head. At that

time, the licensee discovered subsurface cracking located near the outer rebar mat, which extended

to adjacent areas of the SB that have not been modified since original construction. A manual

chipping process was applied to the cracked area in an initial attempt to determine the extent of the

cracks. Using this method, crack indications along the vertical edge of the containment access

opening essentially disappeared, but a crack at the top horizontal cut for the opening did not

disappear. The licensee investigated and confirmed, through the use of impulse response (IR)

mapping and core boring samples (CBS), that subsurface laminar cracking had occurred along the

outer rebar mat in the SB flute shoulder areas and at the top of the SB near the junction with the

ML12352A052 roof and at specific SB penetration openings. Specifically, CBS results confirmed that the SB walls

contained a concrete crack that had a laminar orientation located near the outer rebar mat and

passed through the coarse concrete aggregate.

The crack widths were found to be generally tight, less than or equal to 0.03 centimeters (0.012 inches), with one crack measuring 0.033 centimeters (0.013 inches).

Additional flute shoulders were inspected using IR mapping, and the results showed that all

shoulders inspected had indications of laminar cracking between the ends of the horizontal

reinforcing steel. It was determined that the southern and western portions of the SB wall, had the

most extensive cracking.

Based on the licensees initial condition assessment of the subsurface laminar cracking, it was

determined that the SB could not meet technical specifications, operability requirements. After

performing additional engineering analysis, the licensee concluded that the SB remained

structurally adequate for the controlling design-basis load cases (i.e. was operable). However, the

SB areas with the laminar subsurface cracking were nonconforming with respect to the SB design

and licensing bases.

The licensee subsequently chartered a Root Cause Team (RCT) supported by vendor subject

matter experts knowledgeable in concrete construction, design, examination, and modeling to

review evidence associated with the discovery of subsurface laminar cracking. The licensees RCT

evaluated IR results, concrete tests of CBS (including petrographic examinations), and results of

computer modeling to identify the causes of the SB laminar cracking. The RCT determined that the

direct cause for the SB concrete laminar cracking was the integrated effect of moisture content, wind speed, temperature, and the duration of these conditions created during the blizzard of 1978.

The environmental conditions created by the blizzard of 1978 enabled moisture to penetrate the SB

concrete, freeze, and expand, which created radial stresses that exceeded the tensile strength of

the concrete and initiated the subsurface laminar cracking. The root cause for the SB concrete

laminar cracking was due to the design specification for construction of the SB, which did not

require application of an exterior moisture barrier. Additionally, the RCT identified three contributing

causes for the SB concrete laminar cracking:

the stress concentration behind the thicker section of the architectural flute shoulder added

to the radial stress caused by freezing and expansion of the moisture inside the SB wall

creating a radial stress that exceeded the tensile strength of the concrete and initiated a

crack.

the design that did not include radial reinforcing steel ties or stirrups at intermediate spacing, which enabled the laminar crack created by freezing moisture to propagate.

the density of the structural reinforcing steel that was less than or equal to 15.24-centimeter

(6-inch spacing). Once a crack originated in the shoulder region, it continued to propagate

into adjacent areas if a higher density of reinforcing steel was present, such as at the top

610 centimeters (20 feet) of the SB and the mainsteam line penetration blockouts. The

greater density of structural reinforcing steel enabled the laminar crack created by freezing

moisture to propagate into these areas.

The licensees corrective actions included establishing a test program to investigate the steel

reinforcement capacity adjacent to structural discontinuities (e.g., cracking), development of an

engineering plan to reestablish design and licensing bases for the SB, development of a procedure

for long-term monitoring of the SB laminar cracking, and installation of an exterior sealant system

on the SB. Additional information appears in the FirstEnergy Nuclear Operating Company (FENOC) root cause analysis report, Concrete Crack within Shield Building Temporary Access

Opening, Condition Report (CR) No. 2011-03346, Revision 1, dated May 8, 2012, an extent of

condition review. The report is located on the NRCs public Web site in the Agencywide Documents

Access and Management System (ADAMS) under Accession No. ML12142A053. The NRC

dispatched an inspection team to evaluate the root cause and corrective actions for this event as

documented in the Davis-Besse Inspection Report 05000346-46-12-009, dated June 21, 2012, (ADAMS Accession No. ML12173A023).

BACKGROUND

General Design Criterion 2, Design Bases for Protection against Natural Phenomena, of

Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50, states, in part, that structures, systems, and components important to safety shall be designed to withstand the

effects of natural phenomena, including, tornadoes, hurricanes, floods, tsunami, and seiches

without loss of capability to perform their safety functions. The design bases for these structures, systems, and components (SSCs) shall reflect: (1) appropriate consideration of the most severe of

the natural phenomena that have been historically reported for the site and surrounding area, with

sufficient margin for the limited accuracy, quantity, and period of time in which the historical data

have been accumulated; (2) appropriate combinations of the effects of normal and accident

conditions with the effects of the natural phenomena; and (3) the importance of the safety functions

to be performed.

In the 10 CFR 50.65, Requirements for Monitoring the Effectiveness of Maintenance at Nuclear

Power Plants (the maintenance rule), the NRC requires that licensees monitor the performance

or condition of SSCs against licensee-established goals in a manner sufficient to provide

reasonable assurance that such SSCs are capable of fulfilling their intended function. The

regulations in 10 CFR 50.65 require that these goals be established commensurate with safety and, where practical, take into account industrywide operating experience.

In Section C of Regulatory Guide 1.160, Monitoring the Effectiveness of Maintenance at Nuclear

Power Plants, the NRC provides guidance for monitoring structures. Specifically, in accordance

with10 CFR 50.65, the structural monitoring programs must provide reasonable assurance that

in-scope structures are capable of fulfilling their intended functions. An acceptable structural

monitoring program for the purposes of the maintenance rule should have the attributes discussed

in Section 9.4.1.4, Structure Level, of NUMARC 93-01, Industry Guideline for Monitoring the

Effectiveness of Maintenance at Nuclear Power Plants. Structures monitored in accordance with

10 CFR 50.65(a)(1) would continue to be monitored until the degradation and its cause have been

corrected. For these structures, there would be additional degradation-specific condition monitoring

and increased frequency of assessments until the licensees corrective actions are completed and

the licensee is assured that the structure can fulfill its intended functions and will not degrade to the

point that it cannot fulfill its design basis.

DISCUSSION

For the Davis-Besse SB, the applicable construction and design standards were American

Concrete Institute (ACI)-307-69, Design and Construction of Reinforced Concrete Chimneys, and

ACI-318-63, Building Code Requirements for Reinforced Concrete. For the Davis-Besse SB, an

external moisture barrier was not required by the applicable construction/design standards. The SB

design also was consistent with recommendations identified in ACI-201.2R-01, Guide to Durable

Concrete, but these measures were not effective at preventing the moisture intrusion associated

with the 1978 blizzard event. In practice, for concrete structures, application of 10 CFR 50.65 requirements usually translates into

periodic visual inspection, which would not be effective in identification of subsurface laminar

cracking developed by conditions of moisture intrusion and freezing. Site technical specifications

contain requirements for maintaining the containment systems operable and the site Corrective

Action Program, Criterion XVI of Appendix B 10 CFR Part 50, would require identification of and

correction of deficiencies adverse to quality, as noted in this IN. Therefore, if a licensee identifies

environmental and design vulnerabilities that could produce subsurface cracking (e.g., a lack of

adequate waterproof barrier or a design configuration that creates inherent stress concentrations),

nondestructive examination such as IR mapping with confirmatory CBS are techniques that have

identified subsurface laminar cracking.

The environmental effects on nuclear power plant concrete structures and related operating

experience are discussed in NUREG/CR-6927, Primer on Durability of Nuclear Power Plant

Reinforced Concrete Structures. Recommendations in this NUREG include radial reinforcement of

concrete structures to enhance concrete durability and this design element should prevent or limit

concrete problems similar to those discussed in this IN. Further, some of the causes for concrete

degradation identified included improper design specifications or violations of construction

specifications. Thus, for new reactors, preventative measures can be taken in the design and

construction phase to ensure the effect of moisture intrusion in concrete will be mitigated. For

example, the application of waterproofing material (e.g., sealant or coating) on the outer surface of

the containment combined with an effective maintenance program for the waterproofing material

should preclude moisture induced subsurface laminar cracking.

CONTACT

S

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below or to the appropriate Office of Nuclear Reactor

Regulation project manager.

/RA/

/RA/ by SBahadur for

Laura Dudes, Director

Lawrence E. Kokajko, Director

Division of Construction Inspection

Division of Policy and Rulemaking

and Operation Programs

Office of Nuclear Reactor Regulation

Office of New Reactors

Technical Contacts: Melvin S. Holmberg, Region III

E-mail: mel.holmberg@nrc.gov

CONTACT

S

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below or to the appropriate Office of Nuclear Reactor

Regulation project manager.

/RA/

/RA/ by SBahadur for

Laura Dudes, Director

Lawrence E. Kokajko, Director

Division of Construction Inspection

Division of Policy and Rulemaking

and Operation Programs

Office of Nuclear Reactor Regulation

Office of New Reactors

Technical Contacts: Melvin S. Holmberg, Region III

E-mail: mel.holmberg@nrc.gov

Note: NRC Generic Communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections

ADAMS Accession No: ML 12352A052 TAC ME9779 OFFICE

RIII/DRS/Branch 1 NRR/DE/EMCB

Tech Editor

RIII/DRS/Branch1 NAME

MHolmberg:ls

DHoang

JDougherty

DEHills

DATE

1/29/13 via email

2/13/13 via email

12/14/12 via

email

1/29/13 via email

OFFICE

RIII/DRS/DIRDRS

BC/NRR/DE/EMCB

D/NRR/DE

BC/NRR/RASB/DL

R

NAME

KGOBrien

KAManoly

PHiland

MMarshall

DATE

1/30/13 via

email

2/11/13

2/11/2013

2/11/13 via email

OFFICE

BC/NRR/DPR/PRL

B

PM/

NRR/DPR/PGCB

LA/PGCB/DPR

BC/PGCB/DPR

NAME

PIsaac

JKlos

CHawes

DPelton

DATE

1/30/13 via email

2/13/13

2/14/13

2/27/13 OFFICE

D/NRO/DCIP

DD/NRR/DPR

D/NRR/DPR NAME

LDudes

SBahadur

LKokajko

(SBahadur for)

DATE

3/5/13

3/7/13

3/7/13

OFFICIAL RECORD COPY