05000333/LER-2006-001
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| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3332006001R00 - NRC Website | |
FACILITY NAME (1) � DOCKET (2) ' LER NUMBER (6) 1 � PAGE (3) 06�001� 00� 1James A. FitzPatrick Nuclear Power Plant 05000333
BACKGROUND
The function of the reactor building-to-suppression chamber vacuum breaker assemblies [BF] is to relieve vacuum when the suppression chamber [NH] depressurizes below reactor building [NG] pressure. If the suppression chamber depressurizes below reactor building pressure, the negative differential pressure is mitigated by flow through the reactor building-to-suppression chamber vacuum breaker assemblies. The design of the reactor building-to-suppression chamber vacuum relief system [BF] consists of two 100% capacity vacuum breaker assemblies each consisting of a (check valve type) vacuum breaker (VB) and an air operated (AOV) butterfly valve, located in series in each of two branch: lines from a single penetration through the reactor building to a common line that penetrates the suppression chamber airspace. The vacuum breaker is self actuating. The butterfly valve is actuated by pressure differential or can be remotely operated by a control switch in the control room. Both the butterfly valve and the vacuum breaker valve must be closed (except during testing) to maintain a leak tight primary containment [NH] boundary. The safety analyses assume the vacuum breaker assembly valves are closed initially and start to open at less than or equal to 0.5 pounds per square inch differential (psid).
Additionally, of the two vacuum breaker assembly valves, one is assumed to fail in a closed position.
The reactor building-to-suppression chamber vacuum breaker isolation valve (27A0V-101A) is a twenty (20) inch air operated Fisher series 9200 butterfly valve with a Bettis air actuator located on one end of the valve shaft and a manual operator located at the opposite end of the valve shaft. The air and manual valve actuators are coupled to the valve shaft, at opposite ends, by means of manual external keys and keyways. When the valve is in automatic operation, the air actuator is coupled to the valve shaft and rotates the shaft. The manual side coupler is uncoupled and stationary while the valve shaft rotates approximately eighty (80) degrees back and forth as the valve is cycled. With proper alignment between the manual output shaft and valve shaft, there is no load bearing contact between the shaft and manual side coupling block when disengaged.
EVENT DESCRIPTION
On March 6, 2006, at approximately 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />, with the plant operating at 100 percent power, it was determined that the reactor building-to-suppression chamber vacuum breaker isolation valve (27A0V-101A) was not fully closed (seated) although remote position indication showed the valve was in the closed position. This condition was discovered during troubleshooting activities to determine the cause of rising oxygen concentration levels in the suppression chamber. Over approximately an eleven (11) day period prior to this discovery, oxygen concentration levels in the suppression chamber had increased from approximately two (2) percent volume to three (3) percent volume, well within the Technical Specifications (TS) limit of four (4) percent.
The suppression chamber oxygen concentration increased following the performance of Instrument Surveillance Procedure (ISP) -89, Suppression Chamber/Reactor Building Vacuum Breaker Quarterly Functional Calibration. The oxygen increase is typical following this ISP because the vacuum breaker isolation valve is cycled allowing reactor building air, containing oxygen, to flow into the suppression chamber. After a period of time, the oxygen level typically decreases.
However, the oxygen level continued to trend upward prompting troubleshooting activities.
As part of the troubleshooting activities, plant operators checked 27A0V-101A to confirm the valve was fully closed.
During this check, plant operators noted slight movement of the valve shaft while trying to manually move the valve to the closed direction, providing evidence that the valve disc was slightly disengaged from its seat.
71111 in hI FACILITY NAME (1) DOCKET (2) LER NUMBER (6 PAGE (3) 06 001 00James A. FitzPatrick Nuclear Power Plant 05000333 , 1 TEXT llf more space is required, use additional copies of NRC Form 366A) (17) EVENT DESCRIPTION (continued) Operations concluded that 27A0V-101A had remained in the not fully closed position since the valve was last stroked during performance of ISP-89. This functional calibration started at approximately 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br /> on February 23, 2006.
Following this functional calibration, the remote position indication of the valve indicated the valve was closed giving no indication to plant operators that the valve disc was slightly disengaged from its seat 27A0V-101A is equipped with position indication that remotely indicates, in the Relay Room, whether the valve is in the closed, open or intermediate position. In this case, the valve shaft rotated beyond the associated limit switch setpoint thereby actuating the limit switch and indicating remotely that the valve was in the closed position. The limit switch operated as expected and designed. The associated limit switch can not change state at the fully seated point as the limit switch requires valve shaft rotation to physically actuate the limit switch. When the valve is fully seated, the valve shaft rotation stops and therefore no motion is available to actuate the limit switch. Consequently, the limit switch is calibrated to actuate just prior to full seat contact which is consistent with industry standard practice.
As a result of 27A0V-101A being not fully seated, a small flow path across the valve seat was created. Due to containment pressure being less than reactor building pressure, a differential pressure existed across the associated vacuum breaker valve (check valve) VB-6 forcing VB-6 to open slightly, thereby allowing reactor building air to flow into the suppression chamber. This flow path caused the oxygen level in the suppression chamber to increase slightly over time, prompting the troubleshooting previously discussed. The oxygen level remained well within the TS limit of four (4) percent volume.
Inspection of 27A0V-101A showed that there was mechanical binding between the valve shaft and the manual actuator coupling block. The manual actuator coupling block was removed to preclude further mechanical binding (see cause section below) and the valve disc was confirmed to be fully seated. The valve was determined to be operable at approximately 0400 on March 7, 2006. The suppression chamber oxygen level subsequently returned to normal.
The plant's TS Limiting Conditions for Operation (LCO) 3.6.1.6, "Reactor Building-to-Suppression Chamber Vacuum Breakers", requires that each reactor building-to-suppression chamber vacuum breaker be operable in Modes 1, 2 and 3.
TS 3.6.1.6 also requires that a vacuum breaker that is not closed (Condition A) be closed within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and an inoperable vacuum breaker (Condition C) be restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If these Required Actions and associated Completion Times are not met, then the plant must be placed in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. As vacuum breaker 27A0V-101A was not fully closed and was inoperable for a duration of approximately 11 days and 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, which is in excess of the TS allowed out of service time (AOT), this report is submitted in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications.
There were no nuclear, radiological, or safety consequences associated with this event.
FACILITY NAME (1) DOCKET (2) LER NUMBER (6 PAGE (3) i James A. FitzPatrick Nuclear Power Plant 05000333� 06� 001� 00
CAUSE OF EVENT
The failure of 27A0V-101A to fully close was a result of mechanical binding due to dynamic adhesive wear (galling) between the valve shaft and manual actuator coupling block. Both the valve shaft and the manual actuator coupling block are constructed of type 410 stainless steel, which has poor dynamic adhesive wear properties, commonly identified as tendency to gall. Repetitive valve cycling combined with misalignment lead to eventual dynamic adhesive wear between the metal surfaces. The mechanism of adhesive wear involves the micro-welding of very small raised areas in the two surfaces that rapidly escalates to large wear scars and displacement of metal. This displaced metal fills the narrow space between the two subcomponents and leads to binding or seizing of the moving surface. [Cause Code B]
EVENT ANALYSIS
There were no nuclear, radiological or safety consequences associated with this event.
During the time period that 27A0V-101A was inoperable, the redundant alternate side vacuum breaker assembly was operable and continued to provide the depressurization function. In addition, the associated failure mechanism does not prevent 27A0V-101A from being operated manually.
The reactor building-to-suppression chamber vacuum breaker assemblies are not required to mitigate the consequences of any Design Basis Accident (DBA) since the maximum resulting negative differential pressure is below the design differential pressure limit of 2 psid. However, to ensure the resulting negative pressure is minimized, the reactor building- to-suppression chamber vacuum breaker assemblies are included in the design.
The reactor building-to-suppression chamber vacuum breaker assemblies serve a dual function, one of which is primary containment isolation. Since the depressurization function of the vacuum breakers would not be available if the normal TS 3.6.1.3 Primary Containment Isolation Valves (PCIV)" Required Actions were taken, the PCIV Operability requirements of TS 3.6.1.3 are not applicable to the reactor building-to-suppression chamber vacuum breakers. Similar surveillance requirements (SRs) in TS LCO 3.6.1.6, "Reactor Building-to-Suppression Chamber Vacuum Breakers," provide assurance that the isolation capability is available without conflicting with the vacuum relief function.
TS SR 3.6.1.6.1 verifies each vacuum breaker is closed to ensure that a potential breach in the primary containment boundary is not present. Vacuum breakers that are open due to an actual differential pressure are not considered as failing this SR. As VB-6 was slightly open due to an actual differential pressure (due to slight leakage past 27A0V-101A), it was operating as designed and was not prevented from performing its primary containment isolation function.
The oxygen level in the suppression chamber remained well within the TS limit of four (4) percent volume.
All required safety functions were maintained and this event is of low safety significance.
FACILITY NAME (1) DOCKET (2) LER NUMBER (6) PAGE (3) 05000333 06�001�00�James A. FitzPatrick Nuclear Power Plant 1
EXTENT OF CONDITION
The alternate reactor building-to-suppression chamber vacuum breaker isolation valve, 27A0V-101B, was visually inspected. The shaft was confirmed to move freely (no binding) within the manual actuator coupling block.
As part of the Extent of Condition review performed following the 2005 similar event, a total of six (6) installed Fisher butterfly valves were identified with stainless steel coupling and valve shaft configurations. All have been evaluated, and corrective actions have been identified in the Corrective Action Program. Interim actions to lubricate the manual actuator couplings on the highest priority valves have been completed.
CORRECTIVE ACTIONS
Corrective Actions Completed by JAF Prior to this Report:
1. Removed the galled manual actuator coupling block from 27A0V-101A to allow free rotation of the shaft.
2. Verified that the reactor building-to-suppression chamber vacuum breaker VB-7 Isolation Valve 27A0V-101B shaft rotates freely within the manual actuator coupling block, showing no binding exists.
3. Lubricated the manual actuator coupling on the highest priority valves.
Actions not yet Completed:
1. Revise applicable procedures to require a visual verification of complete valve closure following the cycling of 27A0V- 101B, until the bronze bushing is installed or the manual actuator coupling block is removed.� ' (Due 05/12/2006) 2. Lubricate manual coupling block for Torus Purge and Inert Supply Valves 27A0V-115 and 116.
(Due 07/04/2006) 3. Lubricate manual coupling block for Reactor Building-to-Suppression Chamber Vacuum Breaker VB-7 Isolation Valve 27A0V-101B (Due 09/04/2006) 4. Install bronze bushings in the six (6) Fisher butterfly valves.
(Due 11/30/2006)
SAFETY SYSTEM FUNCTIONAL FAILURE REVIEW
A review of this event determined that a safety system functional failure as defined by NEI 99-02, Revision 4, did not occur.
SIMILAR EVENTS
A similar valve failure (different valve function) occurred in 2005. That failure was not reportable because the condition was immediately identified due to dual position indication being displayed rather than the expected closed indication. Although that failure did not result in a reportable condition, an equipment failure evaluation was performed. Contributing causes identified following the 2005 valve failure were a combination of poor design (use of 410 stainless steel), misalignment and valve cycling frequency, with the predominant contributor determined to be valve cycle frequency. Subsequent follow-up corrective actions were prioritized based on valves with a higher frequency exercise rate. Appropriate corrective actions were generated and scheduled for completion; however, the actions had not yet been completed on 27A0V-101A.
No other similar issues were identified in previous plant Licensee Event Reports.
FACILITY NAME (1) DOCKET (2) LER NUMBER (6 PAGE (3) 06�001�00James A. FitzPatrick Nuclear Power Plant 05000333
FAILED COMPONENT IDENTIFICATION
Manufacturer:� Fisher Model Number: Model # 9222 NPRDS Manufacturer Code:
� F130 NPRDS Component Code: VACB FitzPatrick Component ID:�27A0V-101A
REFERENCES
1. JAF Condition Report CR-JAF-2006-00979, Reactor Building-to-Suppression Chamber Vacuum Breaker VB-6 Isolation Valve 27A0V-101A Failure, dated 03/06/2006.
2. Apparent Cause Evaluation (ACE), JAF Condition Report CR-JAF-2005-00705, Failure of Torus Inner Isolation Valve 27A0V-117, dated 02/23/2005.