05000440/LER-2003-005, For Perry Technical Specification Violation/Loss of Safety Function Due to Air Bound Water-leg Pump
| ML040070073 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 12/29/2003 |
| From: | Kanda W FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PY-CEI/NRR-2757L LER 03-005-00 | |
| Download: ML040070073 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 4402003005R00 - NRC Website | |
text
FENOC FirstEnergy Nuclear Operating Company Perry Nuclear Power Plant 10 Center Road Perry, Ohio 44081 illiarn R. Kanda 440-280-5579 Vice President - Nuclear Fax:440-280-8029 December 29, 2003 PY-CEI/NRR-2757L United States Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Perry Nuclear Power Plant Docket No. 50-440 LER 2003-005 Ladies and Gentlemen:
Enclosed is Licensee Event Report (LER) 2003-005, Technical Specification Violation/Loss of Safety Function Due to Air Bound Water-leg Pump. This LER was written to document conditions identified during LER 2003-002-001 preparation.
There are no regulatory commitments contained in this letter. Any actions discussed in this document that represent intended or planned actions, are described for the NRC's information, and are not regulatory commitments.
If you have questions or require additional information, please contact Mr. Vernon K. Higaki, Manager - Regulatory Affairs, at (440) 280-5294.
--Very truly-yours for William R. Kanda Enclosure: LER 2003-005 cc: NRC Project ManagE NRC Resident Inspei NRC Region
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Abstract
- - On September 1, 2003, it was determined that the division 1 feedwater leakage control system (FWLCS) piping and the low pressure core spray (CPCS)6re sidui heat-removal (RHR) A-crossover piping contained air. This condition resulted in air binding of the LPCS/RHR A water-leg pump on loss of power.
This condition was previously reported in LER 2003-002. On October 31, 2003, it was determined that sufficient air had accumulated in the FWLCS line such that it would have prevented the division 1 FWLCS and the RHR A suppression pool cooling mode from performing their function. This condition was determined to be a piping design error that caused air bubbles to be stripped out of solution and migrate into the FWLCS. Procedures to periodically vent the affected piping were not in place. The condition is believed to have existed since initial plant operation. The air in the piping was estimated to take about 31 days following a refuel outage to reach the amount required to impact operability. Since the FWLCS and RHR A suppression pool cooling mode were inoperable longer than the required action completion time, this condition is reportable per 10CFR50.73(a)(2)(i)(B), as a condition prohibited by Technical Specifications.
Also since the redundant division 2 equipment had been inoperable for maintenance on several occasions during this time, this condition is also reportable per 1 OCFR50.73(a)(2)(v)(B) and (C). Procedures to periodically vent the affected piping have been established. Design modifications are being initiated to reduce the accumulation of air in the FWLCS.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Fonn 366A) (17)
EVENT DESCRIPTION
At 1610 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.12605e-4 months <br /> on August 14, 2003, the Perry Nuclear Power Plant (PNPP) experienced a loss of offsite power (LOOP) event and a subsequent reactor SCRAM. Events associated with this condition were reported as required via the Emergency Notification System (ENS) and in Licensee Event Report (LER) 2003-002. As a result of the LOOP event, power to low pressure core spray (LPCS) / residual heat removal (RHR) A water-leg pump, RHR B/C water-leg pump, Reactor Core Isolation Cooling (RCIC) [BN] water-leg pump, and High Pressure Core Spray (HPCS) [G] water-leg pump, was momentarily interrupted. All four water-leg pumps restarted after the emergency diesel generators (EDGs)fEK] began supplying power to their respective electrical busses. At the same time that the water-leg pumps restarted, aarms were received for "RHR PUMP A DISCHARGE PRESSURE HI/LO" and "LPCS PUMP DISCHARGE PRESSURE LO." As a result of the alarms, RHR A and LPCS ware made inoperable at 1847 hours0.0214 days <br />0.513 hours <br />0.00305 weeks <br />7.027835e-4 months <br /> when the Unit Supervisor placed them in secured status as directed by plant procedures. At 2145 hours0.0248 days <br />0.596 hours <br />0.00355 weeks <br />8.161725e-4 months <br />, plant operators completed venting the LPCS/RHR A water-leg pump by opening the pump casing vent valve. An abnormal amount of air/gas was noted during the venting evolution. Following venting, the LPCS/RHR A water-leg pump was started and developed normal discharge pressure. The LPCS and RHR A systems were then filled and vented. Since the low pressure alarms cleared and the venting was completed, the RHR A system was declared operable at 2002 hours0.0232 days <br />0.556 hours <br />0.00331 weeks <br />7.61761e-4 months <br /> on August 15, 2003. LPCS was subsequently declared operable at 0318 hours0.00368 days <br />0.0883 hours <br />5.257936e-4 weeks <br />1.20999e-4 months <br /> on August 16, 2003.
On September 11, the team that was investigating the air-binding of the water-leg pump, identified that the division 1 FWLCS piping and the LPCS to RHR A crossover piping contained significant amounts of air.
Approximately 7.5 standard cubic feet (SCF) of air was vented from the division 1 FWLCS high point vent.
This volume was determined by measuring the flow rate and monitoring the time that air flow existed. Air was also vented from the crossover piping for 3 to 4 minutes. The other water-leg pumps, RCIC, HPCS, RHR B/C and the fire protection system water-leg pumps were vented to ensure operability. No significant air was found in these additional systems. On September 17, ultrasonic testing was performed on the accessible division 2 FWLCS piping which verified it did not contain any significant air pockets.
After identification of the air, the investigators determined air bubbles were being stripped from the water by an industry known phenomenon called "Air Stripping" and Desorption" (Ref. SOER 97-01) and
- - accumulating in the piping-for the FWLCS,-Calculations confirmed that the-volume-of the FWLCSpiping, 8 cubic feet, was about the same as the volume of air that was vented, 7.5 cubic feet.
A corrective action to measure air volume, during periodic venting, was established to determine the rate that the air accumulates in the FWLCS piping. It was initially estimated that it took about 31 days for air to void the FWLCS piping. The current process requires the accumulation time between venting to be gradually increased. Currently the air accumulated, up to a period of 3 weeks, is small and does not impact operation of the system.
After identifying the manner in which the air accumulated in the FWLCS, it was determined that the FWLCS piping high point vent had not been included in the procedures to vent the piping.
An evaluation was performed to determine the impact of the air on FWLCS, LPCS and RHR A. On 10/31/03, it was determined that sufficient air had accumulated in the FWLCS line to cause air binding of the water-leg pump following a loss of power, which would have prevented the division 1 FWLCS from performing its function and that RHR A would have been inoperable for suppression pool cooling mode following a loss of power. Since LPCS and the low pressure coolant injection mode of RHR A start on power restoration with an initiation signal present, before the water-leg pump becomes air bound, operability (If more space is required, use additional copies of (f more space is required, use additional copies of (If more space is required, use additional copies of (f more space is required, use additional copies of NRC Form 366A) (1 7) water-leg pump. Due to the failure mechanisms, as discussed above, the LOOP/MSIV closure transient that requires operation of RHR in the suppression pool cooling mode is the transient of interest. This analysis provides a quantification of the risk in terms of the increase in the core damage frequency (CDF) associated with the added RHR A failure mode during a LOOP.
A version of the Perry PSA model that includes internal flooding was used to assess the increase in risk associated with the degradation of RHR A during a LOOP. Changes were made to the RHR A functional fault trees to emulate the vulnerability of RHR A during a LOOP. The increase in risk relative to the baseline configuration was used to determine the significance of the RHR vulnerability during a LOOP.
Fire assessmit riltsfrrn-iheEPR Firari-(uVed E)-eValutio6nin the Independent Plant Evaluation of External Events plus new conditional core damage probabilities computed with the PSA model were used to assess the impact to fire scenarios.
An estimation of the impact to seismic scenarios was made using data from NUREG-CR/1488.
The WinNucap Level 2 model was used to assess the impact to the large, early release frequency (LERF).
Results:
- 2. Including external events the increase in the CDF due to the additional RHR A failure mode is about 2.9E-06 per year.
This assessment includes an estimation of the seismic contribution and results extrapolated from the conservative FIVE analysis that was performed for the IPEEE. The increase in the CDP associated with seismic events due to the additional RHR A failure mode is about 7.8E-09. The increase in the CDP due to fires is about 2.OE-06. The contribution due to external flooding is considered to be non-significant.
In conclusion, the failure of the RHR A pump is considered to have a low to moderate safety significance.
CORRECTIVE ACTIONS
Periodic venting from the division 1 FWLCS and RHR A crossover vents was performed as an immediate corrective action, to ensure the continued operability of FWLCS, LPCS and RHR A. Further venting is being performed to determine the rate at which air is accumulating and venting frequency will be adjusted accordingly. Procedures were modified to include additional vent points. Design modifications are being initiated to reduce the accumulation of air in the FWLCS.
PREVIOUS SIMILAR EVENTS
No previous water-leg pump air binding event was identified to have occurred during the review of records for the previous 7 years at the PNPP.
Energy Industry Identification System (EIIS) codes are identified in the text in the format [xx].