05000281/LER-2002-001
| Event date: | 04-13-2002 |
|---|---|
| Report date: | 06-12-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2812002001R00 - NRC Website | |
FACILITY NAME (1)
SURRY POWER STATION
1.0 DESCRIPTION OF THE EVENT On April 13, 2002 at 03:16 hours, during plant heatup with Unit 2 at cold shutdown and RCS pressure approximately 300 psig, evidence of leakage discovered by Operations personnel during a plant startup walkdown was reported on the "B" residual heat removal (RHR) pump %-inch balance line [EIIS-BP, PSP]. At 05:05 hours, an engineering inspection determined that the 3/4-inch balance line had a through-wall leak approximately 1/2" from a sockolet which was attached to the suction piping of the "B" RHR pump.
This through-wall leak was not isolable from the suction of "A" or "B" RHR pumps because it was upstream of "B" RHR pump suction isolation. Thus, both trains of RHR were declared inoperable. However, both trains of RHR continued to operate.
Additionally, both trains of RHR remained capable of performing their intended function because the structural integrity of the pipe was maintained. RHR was declared inoperable due to the ASME Code noncompliance, and not due to loss of safety function.
Technical Specification 3.1.A.1.d.1 requires a minimum of two non-isolated loops, consisting of any combination of RCS loops or RHR loops, to be operable. Because both trains of RHR were inoperable and no reactor coolant system (RCS) loops were operable at that time due to plant conditions, the Technical Specification 3.1.A.1.d.1 requirements were not met. This condition is therefore reportable pursuant to 10CFR50.73(a)(2)(i)(B).
The piping leak was not isolable from the RHR suction header, therefore the two independent trains of the RHR System were declared inoperable. This condition is therefore also reportable pursuant to 10CFR50.73(a)(2)(vii).
On April 13, 2002, ultrasonic thickness (UT) measurements were performed for a length of approximately 16-inches on the "B" RHR pump 34-inch balance line with the lowest reading measuring 0.109-inches, which is above the manufacturer's tolerance of 0.099- inches minimum. UT measurements were also taken on the "A" RHR pump 3/4-inch balance line and were satisfactory. Based on these UT measurements it was determined that the leak was localized, and there were no indications that the piping was degrading at other locations. Periodic monitoring of the leakage was initiated.
Plant heatup proceeded, keeping the RHR System in service, until the second RCS loop was put into operation at 23:56 hours on April 13, 2002, which restored compliance with the Technical Specifications.
On April 14, 2002, Engineering performed a visual inspection of the leak. Two circumferential, linear indications were found in the 3/4-inch diameter, schedule 40 pipe downstream from the sockolet that is welded to the 14-inch line. Some surface pitting was apparent around the leak location. The leak was very slow (approximately 2-3 drops per minute) and continued to be visually monitored
- eriodicall to yen the min was not FACILITY NAME (1)
SURRY POWER STATION
DOCKET
05000 - 281 LER NUMBER (6) PAGE (3) � 00 degrading.
On April 15, 2002, Engineering performed another visual inspection of the leak. The indications were re-measured and no changes were found in the linear lengths. Boric acid was found solidifying at the leak location. With the system in service, the linear indications were not expected to propagate. The 3/4-inch balance line on the "A" RHR pump was visually inspected with no indications of any through-wall leaks.
On April 16, 2002, with RCS loops in operation and the RCS temperature above 200 degrees F, the RHR System was taken out of service and the 3/4-inch diameter line was replaced. Post maintenance testing was completed, and the RHR System was declared operable at 16:29 hours on April 16, 2002.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS Even with this through-wall leak in the balance line associated with the "B" pump, both RHR pumps were still able to perform their intended function because the structural integrity of the pipe was maintained. RHR was declared inoperable due to ASME Code,Section XI, Class II noncompliance, and not due to loss of safety function.
3.0 CAUSE Following removal of the leaking line, the failed segment was sectioned to allow detailed examination with the scanning electron microscope. The 3/4-inch section of RHR pipe failed as a result of transgranular stress corrosion cracking (TGSCC) initiated from the outside surface from an external foreign contaminant which caused surface pitting. It was from these pits that the two cracks appear to have initiated. One of these cracks propagated through the pipe until a through-wall leak developed. Based on the width of the crack and the amount of oxide on the fracture, the crack growth rate appears to have been very slow. The pitting that was present on the outer surface of the pipe adjacent to the cracks was suggestive of chloride-induced corrosion pitting. The source of the chloride contamination is unknown.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Plant heatup proceeded, keeping the RHR System in service, until the second RCS loop was put into operation at 23:56 hours on April 13, 2002, which restored Technical Specification compliance. On April 16, 2002, with RCS loops in operation and the RCS temperature above 200 degrees F, the RHR System was taken out of service and the 3/4- inch diameter line was replaced.
FACILITY NAME (1)
SURRY POWER STATION
DOCKET LER NUMBER 16) 5.0 ADDITIONAL CORRECTIVE ACTIONS Post maintenance testing was completed, and the RHR System was declared operable at 16:29 hours on April 16, 2002.
6.0 ACTIONS TO PREVENT RECURRENCE A VT-2 inspection will be completed on the Unit 1 RHR 34-inch balance lines during the next cold shutdown of Unit 1 to detect flaws such as TGSCC, or pitting which could lead to TGSCC.
7.0 SIMILAR EVENTS None.
8.0 MANUFACTURER/MODEL NUMBER The 34-inch line was schedule 40, 304 stainless steel.
9.0 ADDITIONAL INFORMATION None.