Information Notice 2013-04, 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 RIII/DRS/Branch 1 RIII/DRS/Branch1 OFFICE NRR/DE/EMCB Tech Editor
NAME MHolmberg:ls DHoang JDougherty DEHills
DATE 1/29/13 via email 2/13/13 via email 12/14/12 via
1/29/13 via email
BC/NRR/RASB/DL
D/NRR/DE
OFFICE RIII/DRS/DIRDRS BC/NRR/DE/EMCB R
NAME KGOBrien KAManoly PHiland MMarshall
DATE 1/30/13 via 2/11/13 2/11/2013 2/11/13 via email
BC/NRR/DPR/PRL PM/
OFFICE B 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