ML18153D143
| ML18153D143 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/05/1992 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 92-595, NUDOCS 9210090375 | |
| Download: ML18153D143 (4) | |
Text
VIRGINIA ELECTRIC AND PowER CoMPA~Y RICHMOND, VIRGINIA 23261 October 5, 1992 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Serial No.92-595 SPS/RCB/GDM R7 Docket Nos.
50-280 50-281° License Nos.
DPR-32 Gentlemen:
. VIRGINIA ELECTRIC AND POWER COMPANY
- SURRY POWER STATION UNITS 1 AND 2 GAS VOIDS IN LOW HEAD SAFETY INJECTION PIPING DPff-37 In N RC Inspection Report Nos. 50-280/92-17 and 50-281 /92-17 dated September 4, 1992, you identified an Inspector Follow-up Item to evaluate our long term plans to prevent gas vo.ids in the Low Head Safety Injection (LHSI) System.
Also, you requested a written response describing our proposed long-term corrective actions within thirty <;Jays of the date of the report. This response is provided in the attachment.
The information discussed herein is consistent with our presentation and your comments provided at the counterparts meeting held at our corporate office on
- septe~mber 24, 1992.
Please contact us if you have any questions or require additional information.
Very truly yours,
/;'0 r, /
l Y* f: 0/V-0-i*L/?.v~
~v* W. L. Stewart Senior Vice President - Nuclear Attachment cc:
U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N.W.
Atlanta, Georgia 30323 Mr. Morris Branch NRC Senior Resident Inspector Surry_ Power Station l.C,,r..
9210090375 921005.
PDR ADOCK 05000280 G
ATTACHMENT CORRECTIVE ACTIONS FOR GAS VOIDS iN LOW HEAD SAFETY INJECTION PIPING
Corrective Actions
Background
As described in the Inspection Report 92-17, gas voids were detected in the Low Head Safety Injection (LHSI) piping for both units at Surry. Initially, several areas requiring evaluation were identified:
Potential for the Charging/High Head Safety Injection (HHSI) Pumps to become inoperable following transfer to the recirculation mode of safety injection (SI) due to gas binding Potential for exceeding the LHSI piping system design pressure during LHSI pump startup transients, and Potential for a LHSI relief valve lifting during a pressure spike and failing to reseat following a LHSI pump sta.rt transient.
Since the possibility of gas binding of the HHSI pumps placed the *plant in an unanalyze6 condition, c;i four-hour non-emergency report was made to the NRG in accordance with 1 O CFR 50.72 on July 11, 1992. After further analysis determined that the existence of the void in the piping would not have significantly degraded pump.
performance, this report was withdrawn on July 27, 1992.
Utilizing a fluid transient computer model of the LHSI system, estimates have been made of the probable pressure effects of gas voids at various locations in the system.
The results showed that the magnitude of the pressure transients experienced is consistent with pressure transients which normally occur during startup, shutdown or realignment of systems. Although these transients involve short duration pressure spikes above the cor.itinuous design pressure for certain components in the system, they are accommodated by the overall conservatism of the code and no damage to the piping o( components is expected to occur. Additionally, the potential for a LHSI system relief valve to lift and fail to reseat is considered small as recent periodic testing and operational history indicate that the relief valves, /which may momentarily lift during such a pump startup transient, have reseated properly and tested satisfactorily.
Based on the above, a Justification for Continued Operation (JCO) was prepared and presented to the Station Nuclear Safety and Operating Committee (SNSOC). SNSOC approved the JCO on July 17, 1992, with the following compensatory actions specified:
The affected piping must be periodically vented to minimize gas in the system.
The bulk Refueling Water Storage Tank (RWST) level must be monitored for increases to trend check valve back-leakage, as this is believed to be a significant contributor to the gas accumulation in Unit 2.
I Current Status In compliance with the bases for the JCO, Operations personn,el are venting the SI system at designated locations and frequencies:
The quantity of gas vented is recorded and trended, and the venting frequency is adjust~d as necessary_based on these results.
Since its initiation, the venting frequency and the quantity of gas discovered has decreased.
During future periodic testing of the LHSI system,
- additional instrumentation will be installed to determine the effectiveness of gas venting to prevent or reduce pressure spikes in.the system. Also, RWST levels have continued to be monitored as the means to detect any i,:icrease in check valve back-leakage.
Proposed Long Term Corrective Actions Our corrective actions are focused on the elimination or reduction of gas voids to the extent that any remaining voids can be categorically assessed as of no significance.
T_o that end the following actions will be taken to reduce voiding:
Continuation of Ongoing Corrective Actions: Periodic venting of the SI systems, monitoring of RWST levels, and investigation of LHSI pump pressure spiking during normal pump surveillance testing will continue as long as gas voids are present.
Procedure Changes to Minimize Gas Voids: Operating, testing, maintenance, and post-maintenance testing procedures will be reviewed and enhanced as necessary ~o minimize gas voids in the SI systems.
Evaluation of the SI systems: The SI systems will be reviewed to determine whether additional system vents should be installed, or if other actions or modifications would be beneficial.