Information Notice 2012-11, Age Related Capacitor Degradation
| ML120330272 | |
| Person / Time | |
|---|---|
| Site: | Hatch, Surry  |
| Issue date: | 07/23/2012 |
| From: | Laura Dudes, Mcginty T Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Alexion, T W, NRR/DPR, 415-1326 | |
| Shared Package | |
| 4 | List: |
| References | |
| FOIA/PA-2013-0030, FOIA/PA-2013-0139 IN-12-011 | |
| Download: ML120330272 (5) | |
ML120330272 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001
July 23, 2012
NRC INFORMATION NOTICE 2012-11:
AGE-RELATED CAPACITOR DEGRADATION
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 or applicants for an early site permit, standard design certification, standard
design approval, manufacturing license, or combined license issued 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 recent problems involving age-related degradation of capacitors. The NRC
expects that recipients will review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. Suggestions contained in this IN are not
NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
Surry Power Station Unit 1
On June 8, 2010, an automatic reactor trip occurred from full power because of an inadvertent
electrical contact made during maintenance activities. The plant conditions encountered and
system responses as a result of the trip were generally as expected, except as noted below.
Approximately 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> following the event, failure of a resistor/capacitor (RC) suppressor in a
nuclear instrument (NI) cabinet resulted in a small control room fire, which was extinguished by
the use of manual carbon dioxide fire extinguishers. Approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> later, another RC
suppressor failed in a second NI cabinet, causing a control power fuse to blow and the source
range NIs to become deenergized. The source-range NIs were restored in about 5 minutes.
(No power failures or blown fuses resulted from the RC suppressor failures in the first NI
cabinet.) The most probable cause of the RC suppressor failures was age-related hardening and
cracking of the RC suppressors epoxy insulation, which allowed degradation of the RC
suppressor capacitor. These RC suppressors were original plant equipment and had not been
replaced. The capacitor degradation allowed the RC suppressor circuit to draw excessive
current and overheat. The excessive heat caused the epoxy in the RC suppressor to ignite.
The older (date codes from 1969 to 1971) suppressors contained epoxy which is not flame
retardant. Subsequent to this event, the licensee opted to install newer RC suppressors which
use a flame retardant epoxy.
Additional information is available in NRC Special Inspection Report 05000280/2010006, dated
September 10, 2010, and can be found on the NRCs public website in the Agencywide
Documents Access and Management System (ADAMS) under Accession No. ML102560333.
Edwin I. Hatch Unit 2
Between March 2005 and February 2009, three loss-of-offsite-power/loss-of-coolant-accident
(LOSP/LOCA) loading timers associated with redundant plant service water pumps for the two
Unit 2 and swing emergency diesel generators experienced failures. After the failure in
February 2009, the licensee established a root cause team which determined the failures were
caused by age-related degradation of electrolytic capacitors.
Specifically, the power supplies for the LOSP/LOCA circuitry were exhibiting excessive voltage
ripple on their outputs. The root cause team attributed this to degradation of electrolytic
capacitors in the power supply circuits, which tend to exhibit increased noise toward the end of
life. These capacitors had been installed for 20 years, which was beyond their vendor- recommended service life of 10 years.
Additional information is available in NRC Inspection Report 05000366/2009005, dated
February 12, 2010, and can be found on the NRCs public Web site in ADAMS under Accession
No. ML100430494.
Additional Examples of Age-Related Degradation of Capacitors and Other Components
Additional examples of problems involving age-related degradation of capacitors can be found
on the NRCs public Web site in ADAMS under Accession No. ML12033A044.
NRC IN 2012-06, Ineffective Use of Vendor Technical Recommendations provides additional
insight on components that are left in service beyond the vendor-recommended service life.
IN 2012-06 can be found on the NRCs public Web site in ADAMS under Accession No.
DISCUSSION
Criterion XVI, Corrective Action, of Appendix B, Quality Assurance Criteria for Nuclear Power
Plants and Fuel Reprocessing Plants to 10 CFR Part 50 requires licensees to assure that
conditions adverse to quality are promptly identified and corrected and corrective actions are
taken to preclude repetition. Regulatory Guide 1.33, Quality Assurance Program Requirements (Operation) (ADAMS
Accession No. ML003739995), Section 9.b, states preventive maintenance schedules should
be developed to specify lubrication schedules, inspections of equipment, replacement of such
items as filters and strainers, and inspection or replacement of parts that have a specific lifetime
such as wear rings.
RC suppressors contain a capacitor and a resistor connected in series. Both components are
normally completely encased in a molded epoxy package with an electrical lead from one end of
the resistor and one end of the capacitor extending out. In a non-degraded condition, the epoxy
electrically insulates the RC suppressor's capacitor, resistor, and their conductive surfaces in an
encapsulated environment devoid of oxygen, moisture, and other air contaminants.
Aging adversely affects the capacitors in RC suppressors by causing the epoxy insulation to
harden and crack over time. This degrades the capacitor, allowing a high flow of current and
excessive heating. The excessive heat can then ignite the epoxy in the RC suppressor.
Although newer RC suppressors use a fire retardant epoxy, capacitor overheating can still
cause failure.
Capacitors also may exhibit tendencies to leak, drift, or make electronic noise, as a result of
varying environmental conditions (e.g., shifts in temperature, humidity levels, or both). Extreme
temperature conditions can be problematic for capacitors that contain aluminum electrolytes. At
lower temperatures, capacitance falls off rapidly. At higher temperatures, the electrolyte may be
lost through evaporation, thereby accelerating leakage. This may result in premature circuit
damage or malfunction.
Capacitors are energy storage devices that are widely used in electronic and electrical power
circuits. Operating experience has shown that capacitors have finite lifetimes. Placing these
capacitors in a periodic preventative maintenance program that accounts for both time in
storage and time in service can address the adverse effects of aging capacitors in equipment
circuitry and prevent equipment failures.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or to the appropriate Office of Nuclear Reactor
Regulation project manager.
/RA by SBahadur for/
/RA by JLuehman for/
Timothy J. McGinty, Director
Laura A. Dudes, Director
Division of Policy and Rulemaking
Division of Construction Inspection
Office of Nuclear Reactor Regulation
and Operational Programs
Office of New Reactors
Technical Contacts: Rossnyev Alvarado, NRR
301-415-6808
301-415-2621 E-mail: Rossnyev.Alvarado@nrc.gov E-mail: Robert.Bernardo@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
ML120330272 *via e-mail TAC No. ME7139 OFFICE
NRR/DIRS/IOEB
NRR/DE/EICB
Tech Editor
BC:NRR/DIRS/IOEB
NAME
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RAlvarado
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HChernoff (EThomas
Acting)
DATE
4/6/2012
4/17/2012
2/14/2012
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TJackson*
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6/26/2012
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DATE
7/05/2012
7/06/2012
7/17/2012
7/20/2012 OFFICE
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NAME
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DATE
7/23/2012