ENS 42714
ENS Event | |
|---|---|
21:15 Jul 18, 2006 | |
| Title | Potential Flooding Common Mode Failure of Service Water Pumps |
| Event Description | At 1715, it was determined that current plant configuration does not match the assumptions of the Service Water Pump House flooding design calculation. The calculation assumes that a leak developing in the discharge valve bay would cause the water level to rise to the level of the system piping and then stabilize due to leakage out of the valve bay through the area where the piping penetrated the wall. This level is below any electrical equipment and therefore would have no adverse impact on the system. The area around the piping where it was assumed the water would escape was found to be sealed with a fire barrier material. Since the water could not escape, it would continue to rise until it impacted the pump discharge valve (motor operated valve). This would potentially render the Service Water train inoperable.
A second issue with the design calculation was discovered in that it assumed the pump discharge bays for the other two pumps were physically isolated from each other. This is not the case. The discharge piping for the three pumps are cross-connected via a line which penetrates all three bays. The area between the cross connect piping and the bay walls is not sealed. Any leakage in one bay will be communicated to all three bays. This results in the potential for a leak in any of the bays to possibly impact the operability of both trains of Service Water. The licensee has put compensatory measures in place to maintain equipment operability. The licensee has determined that by putting either of the two following compensatory measures in place equipment operability will be maintained: 1. They will provide a continuous watch of the areas to detect water leakage that may cause a flooding concern and close service water pump discharge valves within 15 minutes and secure the affected service water pump, or 2. They will remove the fire seals causing the potential flooding concern in rooms 25-01, 25-02 and 25-03 of the service water pump house. The licensee notified the NRC Resident Inspector.
The following retraction was submitted by licensee: EN#42714 was submitted by South Carolina Electric & Gas Company based on the potential loss of both trains of V.C. Summer Nuclear Station Service Water due to leakage/flooding in the pump discharge valve bays (pits). South Carolina Electric & Gas company retracts EN#42714 based on the following discussion. Engineering has performed a more rigorous evaluation of the subject scenario utilizing existing calculations and analyses. Any flood or spray event in the Service Water Pump House operating floor or any one discharge valve pit will eventually propagate to all three pits through the open areas around the pipe penetrations. The pits will fill up to the pipe level and would conceivably continue to fill to the operating floor level. The discharge motor operated valve and the control panel above the floor of each valve pit in this scenario would be submerged and would become disabled. The control panels would be shorted to ground, and would fail the discharge motor operated valves in the as-is open position which would not affect the service water supply of either train. Since the motor operated valves fail as-is, this subject scenario would not result in the loss of both trains of service water. The licensee will notify the NRC Resident Inspector. Contacted R2DO (K. Landis) |
| Where | |
|---|---|
Summer  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+1.25 h0.0521 days <br />0.00744 weeks <br />0.00171 months <br />) | |
| Opened: | Arnie Cribb 22:30 Jul 18, 2006 |
| NRC Officer: | Pete Snyder |
| Last Updated: | Aug 10, 2006 |
| 42714 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 427142006-07-18T21:15:00018 July 2006 21:15:00
[Table view]10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat Potential Flooding Common Mode Failure of Service Water Pumps 2006-07-18T21:15:00 | |