05000278/LER-2009-003
| Docket Number Sequential Revmonth Day Year Year Month Day Year 05000Number Na | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2782009003R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 3 was in Mode 1 and operating at 100% of rated thermal power when this event occurred.
The 3D Residual Heat Removal (RHR) Pump was considered inoperable for planned motor operated valve (MOV) diagnostic testing of the RHR Pump Suppression Pool Suction Isolation Valve (MO-3-10-013D). Since the MO-3-10-013D is a Primary Containment Isolation Valve (PCIV), containment penetration N-226B was isolated in accordance with Technical Specifications (TS) to allow for testing of the PCIV. The TS actions to allow for testing on the PCIV were entered on 3/26/09 at approximately 0036 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
As a result of extent-of-condition testing being performed due to grease deficiencies discovered on motor-operated valves (MOVs), it was discovered, on 3/26/09 at approximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />, that the 3D RHR (EIIS: BO) Pump Suppression Pool Suction Isolation Valve (MO-3-10-013D) was degraded. The discovery was made as a result of planned diagnostic testing being performed by Maintenance personnel. Once the condition was discovered, the concern was promptly reported to Licensed Operations personnel. Maintenance personnel identified MOV grease hardening and degradation of the motor-operator stem nut.
Repairs were initiated promptly to resolve the MO-3-10-013D deficiencies and the PCIV was returned to an operable condition on 3/27/09 by approximately 0430 hours0.00498 days <br />0.119 hours <br />7.109788e-4 weeks <br />1.63615e-4 months <br />.
Engineering personnel subsequently determined that this condition was prohibited by Technical Specifications (TS) since this valve was inoperable for containment isolation purposes for a time period longer than allowed by TS. TS 3.6.1.3, Primary Containment Isolation Valves (PCIVs), requires that each PCIV be operable or if a PCIV is inoperable, Condition C of TS 3.6.1.3 requires that the penetration be isolated within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of the PCIV becoming inoperable. As a result of the discovered degraded condition of the MO-3-10-013D, it is reasonable to conclude that this PCIV was inoperable for a time period longer than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> prior to the initiation of testing and repairs on 3/26/09. Therefore, the degraded condition of the MO-3-10-013D prior to the testing and repairs on 3/26/09 is considered as a condition is prohibted by TS.
This report is being submitted pursuant to:
10CFR 50.73(a)(2)(i)(B) — Condition Prohibited by TS — This occurrence is reportable under this criterion since there was evidence that MO-3-10-013D was in a degraded condition for a time period greater than allowed by TS 3.6.1.3, Condition C.
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Analysis of the Event
There were no actual safety consequences associated with this event.
The 3D RHR Pump Suppression Pool Suction Isolation Valve (MO-3-10-013D) is the isolation valve that is in the suction flow path for the 3D RHR pump. The 3D RHR pump provides a variety of functions including supplying water for the following modes of RHR: Low Pressure Coolant Injection (LPCI), Suppression Pool Cooling (SPC), Suppression Pool Spray, Containment Spray and Shutdown Cooling (SDC).
The diagnostic test data obtained on 3/26/09 indicated that the as-found thrust of the valve at the point of torque switch actuation was less than the required thrust value. This condition may have resulted in the valve prematurely stopping motion in the closed direction under design basis demand conditions.
The MO-3-10-013D is a normally open valve and the valve does not have any automatic open or close signals. It can be remotely-closed by use of a key-locked switch in the main control room. The conditions for which the valve must be closed include the following functions:
- SDC Mode Alignment
- Containment Isolation for Primary Containment (Suppression Pool) Penetration N-226 Engineering has determined that for the SDC mode of RHR, there were no concerns with the ability of this valve to close in its degraded condition. However, for its containment isolation function to isolate containment penetration N-226, the ability of the valve to close during design basis conditions involving an elevated pressure in the Suppression Pool (e.g., Loss-of-Coolant Accident conditions), the valve may not have been able to perform its design function to close.
For other lower pressure conditions other than the design event, the MO-3-10-013D was capable of performing its closure function. Additionally, for any design basis conditions involving no flow through the penetration, the valve would be capable of performing its design function to close.
Penetration N-226 (i.e., 3D RHR suction from the Suppression Pool) is isolated by the MO-3 10-013D. The water level in the Suppression Pool serves as the second barrier for containment atmosphere fission product releases. Therefore, there were no concerns with containment atmosphere isolation capability due to the presence of the water level in the Suppression Pool.
In the very unlikely case of a failure of an active mechanical device (e.g., RHR pump failure causing a seal leak) coupled with a design basis event Suppression Pool pressure condition (e.g., Loss-of-Coolant Accident conditions), the MO-3-10-013D may have not been able to be fully closed. For most seal leaks, however, the leak rate would be minor and well within the capability of the reactor building sump system. For larger leaks, the 3D RHR room water level alarm would alert Operations personnel to the condition. Operations personnel would remotely actuate the MO-3-10-013D to terminate the leak. The valve would begin to close, but might � Analysis of the Event, continued stop travel during the valve stroke as the pressure differential across the valve increases. The valve would stop motion, as a result of torque switch actuation. Based on conservative assumptions, the valve would travel approximately 82% closed, thereby isolating approximately 87% of the flow. Other manual actions could also be pursued to remotely close the valve.
However, as a result of internal flood design requirements of the Reactor Building, the affect of any un-isolated water leakage would preserve operability of redundant emergency core cooling or containment cooling subsystem subsystems.
This event is not considered as risk significant.
Cause of the Event
The cause of the MO-3-10-013D degradation is due to damage to the motor-operator actuator stem nut threads as a result of identified grease hardening. The stem nut is the device in the motor-operator actuator that interfaces with the threaded valve stem. The motor-operator actuator turns the stem nut resulting in movement of the valve stem. The damage to the stem nut threads included broken threads and the loss of some thread pieces. There was no significant degradation to the valve stem threads.
A root cause investigation was performed to examine the underlying reasons for the valve condition. This investigation focused on MOV actuator stem lubricant performance and the preventive maintenance program frequencies and actions for MOVs.
The Limitorque Corporation supplied the motor-operator (Model SMB 2-40). The grease was manufactured by Exxon (Nebula EP-1).
Corrective Actions
The MO-3-10-013D valve was repaired and returned to service on 3/27/09. An extensive extent-of-condition evaluation for other susceptible MOVs on both Units 2 and 3 was performed.
This included inspection, testing, cleaning, and/or re-lubrication as appropriate for more than 20% of the MOV population.
A root cause investigation was completed. Appropriate corrective actions will be performed to upgrade the MOV program as necessary including upgrading the preventive maintenance feedback process, adjusting preventive maintenance and diagnostic testing intervals, and revising appropriate procedures to address procedural weaknesses.
_NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER 5 Previous Similar Occurrences There were no previous LERs identified relating to inoperable MOVs resulting from greasing deficiencies.
However, two previous prompt notifications were recently made to the NRC regarding MOVs with similar greasing deficiencies. On 3/12/09, the Unit 2 High Pressure Coolant Injection (HPCI) Suppression Pool Suction Inboard Isolation Valve (MO-2-23-058) experienced degradation during valve stroking in preparation for routine surveillance testing. On 3/21/09, the Unit 3 High Pressure Coolant Injection (HPCI) Suppression Pool Suction Outboard Isolation Valve (MO-3-23-057) was also identified to have some degradation during surveillance testing.
Both of these valve degradation occurrences were evaluated and it was determined that neither valve was inoperable or had a loss of safety function. Therefore, the prompt notifications were retracted. However, these occurrences were similar in nature to the concerns that existed with the MO-3-10-013D. The MO-3-10-013D concerns were identified as a result of extent-of condition testing performed as a result of these previous degradations of the MO-2-23-058 and MO-3-23-057.
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