Information Notice 2003-06, Failure of Safety-Related Linestarter Relays at San Onofre Nuclear Generating Station
| ML031700033 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/19/2003 |
| From: | Beckner W NRC/NRR/DRIP/RORP |
| To: | |
| Hodge, CV, NRR/DRIP/RORP, (415-1861) | |
| References | |
| +sunsimjr=200611, -RFPFR IN-03-006 | |
| Download: ML031700033 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001
June 19, 2003
NRC INFORMATION NOTICE 2003-06:
FAILURE OF SAFETY-RELATED LINESTARTER
RELAYS AT SAN ONOFRE NUCLEAR
GENERATING STATION
Addressees
All holders of operating licenses or construction permits for nuclear power reactors, except
those that have permanently ceased operations and have certified that fuel has been
permanently removed from the reactor.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform
addressees of recent failures of safety-related valves due to linestarter relay degradation. The
degradation was caused by past use of excessive amounts of trichloroethane-based cleaners
during preventive maintenance. It is expected that recipients will review the information for
applicability to their facilities and consider actions, as appropriate, to avoid similar problems.
However, suggestions in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
San Onofre Nuclear Generating Station utilizes reversing linestarters manufactured by Square
D to operate the motors on safety-related motor-operated valves. The linestarter consists of
two relays that provide 480 volt power to the motor and contain auxiliary contacts associated
with interlock and seal-in functions. The interlock function provides a means to avoid
energizing both open and closed relays at the same time. The seal-in function keeps the relay
energized until the valve has completed its stroke. All reversing linestarters have interlock
auxiliary contacts. San Onofre has 172 Square D linestarters associated with safety-related
motor-operated valves, 86 in each unit.
On August 30, 2002, a Unit 3 low-pressure safety injection (LPSI) pump mini-recirculation valve
failed to open during surveillance testing. Subsequent analysis determined that the plastic
housing on an auxiliary contact in the associated linestarter was degraded. The licensee
determined that the auxiliary contact housing degradation was caused by the past use of
excessive amounts of Inhibisol, a cleaning solvent based on trichloroethane (TCE). The
cleaning solvent caused the plastic to break down. Over time, small amounts of the plastic
came loose and interfered with the electrical contacts, resulting in the valve failure.
In response to the LPSI pump mini-recirculation valve failure, San Onofre developed a plan to
inspect a sample of other safety-related linestarters installed in Units 2 and 3. In October 2002, San Onofre completed the inspection of 19 additional linestarters. This sample inspection
identified two auxiliary contacts that showed signs of chemical attack (i.e., cloudy plastic contact
housing); however, both were found to be functional. Subsequently, the licensee developed a
risk-informed plan to inspect all safety-related linestarters and replace all auxiliary contacts
showing signs of chemical attack. The linestarter inspections were scheduled into online and
outage maintenance windows, and will be completed by the end of the Unit 2 outage in 2004.
On January 18, 2003, during a Unit 3 refueling outage, the quench tank sample containment
isolation valve failed to open during surveillance testing. Examination of the contact revealed
that a similar chemical attack had occurred and caused the valve failure.
On February 10, 2003, during an inspection of Unit 3 LPSI header stop valve linestarters, an
auxiliary contact failed on the 20th cycle of the auxiliary contact test. The linestarter inspections
included a test to cycle each auxiliary contact 20 times. This auxiliary contact cycle test was
performed to determine the functionality of the auxiliary contacts in the linestarter.
On Unit 3, all 86 linestarters have been inspected with two surveillance test failures noted and
one maintenance test failure. The licensee replaced 42 auxiliary contacts from the linestarters
due to evidence of chemical attack on the plastic auxiliary contact housing. On Unit 2,
33 linestarters have been inspected as of May 2, 2003, with no failures noted; however, four
auxiliary contacts showed signs of chemical attack on the plastic contact case.
Discussion
As a result of the valve stroke failure on August 30, 2002, the licensee initiated a laboratory
analysis of the suspect auxiliary contact from the linestarter. The contact was coated with a
plastic residue from the deterioration of the plastic switch bodies. The licensee concluded that
excessive use of cleaning solvents during previous preventive maintenance activities had
caused the failure of the contacts.
The licensee believes that all damage to the auxiliary contact housings occurred prior to 1989 and is showing up in the recent safety-related valve failures. The original linestarter preventive
maintenance procedure was issued in April 1984, and required the use of cleaning solvents on
linestarters, but had no caution regarding the potential for damage to plastic components within
the linestarter. Also, the procedure did not require visual inspection of internally mounted
auxiliary contact assemblies. As a result, Inhibisol was used liberally, which allowed the cleaner
to come in contact with plastics that were susceptible to chemical degradation. In April 1989, the licensee recognized that TCE-based cleaners were being used improperly and that controls
needed to be implemented to prevent future damage to equipment containing plastics. The
licensee revised the consumables controls manual to restrict the use of TCE-based cleaners on
plastics, and provided guidance on the approved method for use of the cleaner (i.e., spray on
cloth, then wipe component). Additionally, the linestarter preventive maintenance procedure
was revised to caution that cleaning solvents should be used sparingly to avoid damage to
plastic components. In response to the recent valve failures, the licensee took action on
March 7, 2003, to prohibit the use of all TCE-based cleaners for electrical maintenance
applications. The licensee missed several opportunities from plant and industry experience to recognize the
need for an extent-of-condition review. An extent-of-condition review could have identified any
equipment degradation that occurred throughout the plant due to improper use of cleaning
solvents. One of these prior opportunities was the review of Information Notice 93-76, Inadequate Control of Paint and Cleaners for Safety Related Equipment, which the licensee
performed in February 1994. The review determined that the programs in place were sufficient
to avoid problems similar to those discussed in the notice. The licensee focused on the TCE-
based cleaner controls in place at the time of the information notice review, but overlooked the
fact that safety-related equipment could have been damaged prior to the implementation of the
controls in April 1989. This oversight was a missed opportunity to correct the equipment
deficiency that has been revealed by the recent linestarter failures and the discovery of
degraded contacts.
The San Onofre linestarter experience emphasizes the need to perform an extent-of-condition
review to determine equipment impact when an improper maintenance practice is recognized
and corrected. Further, the root cause analysis revealed that past improper use of corrosive
cleaners could result in degraded plant equipment that could remain undetected for a
considerable length of time before showing up in equipment failures.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/
William D. Beckner, Program Director
Operating Reactor Improvements Program
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical Contacts:
Gregory G. Warnick
Vern Hodge
623-386-3638
301-415-1861 Email: gxw2@nrc.gov
Email: cvh@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
031700033 DOCUMENT NAME: G:\\RORP\\OES\\Staff Folders\\Hodge\\san_line inf.wpd
OFFICE
OES:RORP:DRIP
Tech Editor
RIV
EMCB
NAME
CVHodge
PKleene
GWarnick
KParcszewski
DATE
06/10/2003
06/09/2003
06/12/2003
06/10/2003 OFFICE
SC:OES:RORP:DRIP
PD:RORP:DRIP
NAME
TReis
WDBeckner
DATE
06/18/2003
06/19/2003
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit
Attachment LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information
Date of
Notice No.
Subject
Issuance
Issued to
_____________________________________________________________________________________
2003-05
Failure to Detect Freespan
Cracks in PWR Steam
Generator Tubes
06/05/2003
All holders of operating licenses
or construction permits for
pressurized-water reactors
(PWRs).
2002-15, Sup 1
Potential Hydrogen
Combustion Events in BWR
Piping
05/06/2003
All holders of operating licenses
for light water reactors, except
those who have permanently
ceased operations and have
certified that fuel has been
permanently removed from the
reactor.
2002-21, Sup 1 Axial Outside-diameter
Cracking Affecting Thermally
Treated Alloy 600 Steam
Generator Tubing
04/01/2003
All holders of operating licensees
for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2003-04 Summary of Fitness-For-Duty
Program Performance Reports
for Calendar Year 2000
02/06/2003
All holders of operating licensees
for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2003-03 Part 21 - Inadequately Staked
Capscrew Renders Residual
Heat Removal Pump
01/27/2003
All holders of operating licenses
or construction permits for
nuclear power reactors.
Note:
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command in the message portion:
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