05000269/LER-2011-007-01, Regarding Inoperable Containment Isolation Valve
| ML12136A242 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/14/2012 |
| From: | Gillespie T Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 11-007-01 | |
| Download: ML12136A242 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2692011007R01 - NRC Website | |
text
Duke T. PRESTON GILLESPIE, JR.
Vice President Energy Oconee Nuclear Station Duke Energy ONO] VP / 7800 Rochester Hwy.
Seneca, SC 29672 864-873-4478 864-873-4208 fax May 14, 2012 T. Gillespie@duke-energy.com U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555
Subject:
Duke Energy Carolinas, LLC Oconee Nuclear Station, Unit 1 Docket No. 50-269 Licensee Event Report 269/2011-07, Revision 1 Problem Investigation Program Nos.: 0-11-0218 and 0-11-8854 Gentlemen:
Pursuant to 10 CFR 50.73 Sections (a)(1) and (d), Duke Energy Carolinas, LLC (Duke.
Energy) submitted Licensee Event Report (LER) 270/2011-07, Revision 0 dated September 26, 2011. Attached is LER 270/2011-07 Revision 1 which includes the final cause analysis and corrective actions which were not available at the time Revision 0 was submitted.
The LER documents an inoperable containment isolation valve for a period of time which exceeded the completion times allowed by Technical Specification (TS) 3.6.3, "Containment Isolation Valves." Also, Oconee Nuclear Station violated TS 3.0.4 when exiting the forced outage caused by the initial identification of the inoperable isolation valve. Unit 1 changed modes on January 14, 2011, with an inoperable containment isolation valve.
Duke Energy is submitting this report in accordance with 10 CFR 50.73 (a)(2)(i)(B).
There are no regulatory commitments contained in this report.
Any questions regarding the content of this report should be directed to Oconee Regulatory Compliance, Sandra N. Severance, at 864-873-3466.
Sincerely, T. reston Gillespie, Jr.
Vice President Oconee Nuclear Station Attachment www. duke-energy, corn
Document Control Desk May 14, 2012 Page 2 cc:
Mr. Victor McCree Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, GA 30303-1257 Mr. John Boska Project Manager U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Mail Stop 8 C2 Washington, DC 20555 Mr. Andrew Sabisch NRC Senior Resident Inspector Oconee Nuclear Station INPO (Word File via E-mail)
NRC FOkM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Oconee Nuclear Station, Unit 1 05000-0269 1 OF 5
- 4. TITLE Inoperable Containment Isolation Valve
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED S R FACILITY NAME DOCKET NUMBER SEQUENTIAL REV I
MONTH DAY YEAR YEAR NUMBER NO MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 01 14 2011 2011 07 01 05 14 2012
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[]
20.2201(b) 0 20.2203(a)(3)(i)
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50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii) 1 E
20.2201(d)
[-
20.2203(a)(3)(ii)
E] 50.73(a)(2)(ii)(A)
E] 50.73(a)(2)(viii)(A)
[] 20.2203(a)(1)
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20.2203(a)(4)
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50.73(a)(2)(ii)(B) El 50.73(a)(2)(viii)(g) 20.2203(a)(2)(i)
[
50.36(c)(1)(i)(A)
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50.73(a)(2)(iii)
[
50.73(a)(2)(ix)(A)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
F] 50.36(c)(1)(ii)(A)
F] 50.73(a)(2)(iv)(A)
[
50.73(a)(2)(x)
[] 20.2203(a)(2)(iii)
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50.36(c)(2)
[-] 50.73(a)(2)(v)(A)
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73.71 (a) (4) 100 FD 20.2203(a)(2)(iv)
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50.46(a)(3)(ii)
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50.73(a)(2)(v)(B) E 73.71 (a)(5)
D 20.2203(a)(2)(v)
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50.73(a)(2)(i)(A)
[
50.73(a)(2)(v)(C) E OTHER D 20.2203(a)(2)(vi)
Z 50.73(a)(2)(i)(B)
[
50.73(a)(2)(v)(D)
Specify in Abstract below or in
Abstract
On January 8, 2011, Oconee Unit 1 containment isolation valve, 1 HP-5, was declared inoperable, and Unit 1 initiated a shutdown. Investigation identified galling between the gland ring and valve body of 1 HP-5. Corrective actions included replacement of the valve gland ring with one made from material that is less susceptible to galling and increasing the clearance between the gland ring and valve body. After successfully completing post-maintenance valve stroke testing, Unit 1 was returned to service on January 14, 2011.
However, further analysis identified that a valve seat material change in 2003 resulted in a reduction in actuator margin such that valve 1 HP-5 could not be assured of closing. On June 2, 2011, inadequate actuator sizing was confirmed. Therefore, 1 HP-5 was inoperable, and in a condition prohibited by Technical Specifications, from January 14, 2011, until Unit 1 entered Mode 5 for the planned refueling outage, April 2, 2011. Also, because 1 HP-5 remained inoperable following the forced shutdown, TS LCO 3.0.4 was violated since Unit 1 was unintentionally returned to service with 1 HP-5 still inoperable.
This event is associated with the failure of 1HP-5 previously reported under LER 269/2011-02 and is similar to the failures of 2HP-5 and 3 HP-5 reported under LER 270/2011-01. There were no actual adverse consequences to the health and safety of the public as a result of this event.
NRC FORM 366 (10-2010)
BACKGROUND 1HP-5 is a containment isolation valve [EIIS:ISV] in the Oconee Unit 1 Letdown System [EIIS:CB].
This air operated valve (AOV) has an instrument air operated piston actuator and goes to the closed position on loss of air. The valve is normally open when High Pressure Injection (HPI)
[EIIS:BG] is in service to allow letdown flow from the Reactor Coolant System (RCS)[EIIS:AB]. The valve serves as the outside containment isolation valve and is automatically closed by an Engineered Safeguards (ES)[EIIS:JM] signal. ES channel 2 automatically de-energizes a solenoid valve to bleed off air, allowing HP-5 to close by spring force.
For Technical Specification (TS) Operability, 1 HP-5 is credited to close during Large Break Loss of Coolant Accident (LOCA), Small Break LOCA, and Rod Ejection Accident events. The inability of 1 HP-5 to fully close in all design basis accident scenarios from January 14, 2011, to April 2, 2011, constitutes an inoperable containment isolation valve for a period of time which exceeded the completion times allowed by TS 3.6.3, "Containment Isolation Valves." Therefore, this issue is reportable per 10 CFR 50.73(a)(2)(i)(B), operation prohibited by Technical Specifications.
Additionally, because 1 HP-5 remained inoperable following the forced shutdown, TS LCO 3.0.4 was violated since Unit 1 was unintentionally returned to service with 1 HP-5 still inoperable.
Prior to this event Unit 1 was operating at 100 percent power with no safety systems or components out of service that would have contributed to this event.
EVENT DESCRIPTION
On January 8, 2011, during performance of ES logic testing for Unit 1 ES digital channel 2, the wiring jumper intended to prevent travel of letdown line containment isolation valve 1 HP-5 became dislodged. The signal to close the valve became active, but 1 HP-5 did not fully close as expected.
Upon investigation of the unintended valve closure, 1 HP-5 was found to be approximately 25 percent open. When the jumper was reinstalled, 1 HP-5 returned to the fully open position.
However, because the valve did not fully close, it was declared inoperable.
TS 3.6.3 Required Action A.1 entry conditions were met at 0148 hours0.00171 days <br />0.0411 hours <br />2.44709e-4 weeks <br />5.6314e-5 months <br /> on January 8, 2011, for an inoperable containment isolation valve. LER 269/2011-02 (ADAMS Accession No. ML110690973) documents this event. Unit 1 was shut down to investigate and galling was identified between the gland ring and valve body of 1HP-5. Corrective actions included replacement of the valve gland ring with one made from material that is less susceptible to galling and increasing the clearance between the gland ring and valve body. After successfully completing post-maintenance valve stroke testing, Unit 1 was returned to service, entering Mode 4 on January 14, 2011.
As the root cause investigation continued, it was determined that valve seat material changes from the original seat material of ethylene propylene diene monomer (EPDM) to ARLON 1260, in 2003, represented an increase in seat coefficient of friction (COF) of 2.5 times the original seat COF used in the sizing calculation. Oconee personnel, working with a vendor, identified that the sizing analyses used in the 2003 time frame under predicted required valve torque. On June 2, 2011, the vendor calculation revealed that the actuator margin for 1 HP-5 was negative; thus, containment
isolation valve 1 HP-5 would not have been able to perform its required function from the time of the seat material replacement in 2003 until Unit 1 was shutdown for a refueling outage in April 2011.
Thus, Unit 1 was returned to service on January 14, 2011, with 1HP-5 still being unable to perform its design function in all required design basis event scenarios. This continued inoperability was not recognized. The corrective actions to replace the valve gland ring with one made from material that is less susceptible to galling and increasing the clearance between the gland ring and valve body were not sufficient to ensure proper valve performance. When the low margin concern was first identified, actions were initiated to replace the valve spring with a stronger spring during the Unit 1 refueling outage. When the negative actuator margin for 1 HP-5 was confirmed, the stronger valve spring had already been installed.
The event date for this LER is documented as January 14, 2011. It was on this date that Oconee Unit 1 entered Mode 4 from the forced outage, unknowingly with an inoperable containment isolation valve. Although the apparent cause of the inoperability had been addressed, the lack of actuator margin issues had not yet been identified or addressed. On April 2, 2011, Oconee Unit 1 entered Mode 5 for a scheduled refueling outage. It was not until June 2, 2011, that the continued valve inoperability was identified. Focus was then applied to extent of condition determinations (LER 270/2011-01 (ADAMS Accession No. ML11215A196) for 2HP-5 and 3HP-5), restoring 1 HP-5 to an operable status, and completing the cause investigation. It was not until July 26, 2011, that Oconee personnel recognized that 1 HP-5 inoperability for the period from January 14, 2011 to April 2, 2011 should be reported separately since this was an additional violation of the requirements of TS 3.6.3 and a violation of TS 3.0.4.
CAUSAL FACTORS The technical cause for the inoperability of 1 HP-5 has been determined and addressed in LER 269/2011-02. However, this event report results from an incomplete root cause during initial failure investigative efforts. Because all aspects of the cause of the failure of 1 HP-5 had not been revealed during the initial cause evaluation, the inoperable valve was inappropriately returned to service. For completeness, the causal factors for this event include both the technical cause, as reported under LER 269/2011-02, and the human performance causes.
Root Cause:
- 1. The failure of the 1 HP-5 Air Operated Valve was due to a lack of actuator capability caused by changes in the seat material. An ineffective modification process combined with a lack of engineering analysis during the equivalency change that installed the ARLON 1260 seat material is the root cause of the failure of 1 HP-5 to fully close during normal operations. This cause is reported in LER 269/2011-02.
- 2. Failure Investigation Process and Root Cause Evaluation procedures lack the necessary guidance to ensure the facts used in the failure mode determination are verified.
Basis:
This root cause evaluation has concluded that the root cause was the lack of verification of the facts used in the Failure Investigation Process (i.e., the organizational response to equipment issues) and Root Cause Analysis for the initial failure causal analysis for the failure of 1 HP-5 to close. Numerous facts were used to support galling as the cause of the failure and to refute the failure mode of inadequate actuator sizing. The facts that were available were not verified and/or were used out of context to support or refute the associated failure mode. Both processes lack the necessary guidance to ensure that facts are verified adequately.
CORRECTIVE ACTIONS
Immediate:
No additional actions were required to restore 1 HP-5 to operability. When the negative valve actuator margin was determined, Oconee Unit 1 was in a refueling outage and not in a Mode of Applicability for TS 3.6.3. Prior to returning Oconee Unit 1 to service, an Engineering Change replaced the Bettis SR60 actuator spring with a stronger SR1 00 actuator spring on 1 HP-5 to restore margin.
Corrective Actions to Prevent Recurrence:
- 1. The Root Cause User's Guide was revised to incorporate the following process activities:
- Added source document identification for facts used to support the root cause conclusion to ensure that the information is verified.
Included guidance on establishment of system, structure, or component design basis at the start of the root cause evaluation.
" Provided guidance on the need to thoroughly review the inputs into a root cause evaluation from other cause evaluation processes.
- 2. Engineering Directives Manual (EDM) 240 "Failure Investigation Process" shall be revised to incorporate the following process activities:
Add preparer and verifier to the Fault Table to ensure the failure mode information is verified.
Add source document listing to the Fault Table to ensure that the source document is identified for the information listed for each failure mode.
Include allowances to address situations where source documentation or verifications cannot be obtained. The use of engineering judgment is allowable but must be identified in the Fault Table with a justification for the judgment and communicated to the Management Sponsor for the FIP Team.
Include guidance on establishment of system, structure, or component design basis at the start of the FIP.
SAFETY ANALYSIS
With respect to the inoperability of the valve, 1 HP-5 is normally open during unit power operation to allow letdown flow from the Reactor Coolant System. The valve serves as the outside containment isolation valve for penetration number 6 and is automatically closed by an engineered safeguards (ES) signal. ES channel 2 automatically deenergizes a solenoid valve to close 1 HP-5. The valve has an instrument air operated piston actuator that goes to the closed position on loss of air or if the solenoid valve loses power. 1 HP-5 also receives a close signal on high letdown temperature to terminate letdown flow; however, this function is provided to prevent damage to the Purification Demineralizers (equipment protection) rather than for nuclear safety.
The risk impact of 1 HP-5 failing to close on demand was evaluated using the Oconee PRA model and determined to have a conditional core damage probability of less than 1 E-06 and a conditional large early release probability of less than 1 E-07. Consequently, the inoperability of 1 HP-5 on Oconee Unit 1 did not have a significant risk impact.
ADDITIONAL INFORMATION
This event is directly related to the failure of 1HP-5 reported initially under LER 269/2011-02. That LER identified the technical cause of the valve failure whereas this event report is associated with an additional period of inoperability resulting from an incorrect cause determination. This event is also related to the failure of 2HP-5 and 3HP-5 reported under LER 270/2011-01. It was determined through the root cause extent of condition review that the condition described in this LER did not adversely affect any other similar valve and actuator combinations.
Also, a search of Oconee's Corrective Action Program data base for the previous five years of operation found one event similar to the documentation concern that resulted in an inadequate initial cause determination. For LER 269/2010-01, Standby Shutdown Facility Letdown Line Orifice Strainer Blocked by Valve Gasket Material, the failure to identify all of the failure mechanisms for the SSF Letdown line led to an incorrect Prompt Determination of Operability for Unit 2. This inaccuracy delayed entry into the operability process.
Energy Industry Identification System (EIIS) codes are identified in the text as [EIIS:XX]. The initial failure of 1 HP-5 was considered reportable under the Equipment Performance and Information Exchange (EPIX) program; however, this subsequent event is not an additional equipment concern and does not warrant reporting to EPIX. There were no releases of radioactive materials, radiation exposures or personnel injuries associated with this event.