05000247/LER-2012-003
| Indian Point 2 | |
| Event date: | 03-12-2012 |
|---|---|
| Report date: | 0-9-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2472012003R00 - NRC Website | |
Note: The Energy Industry Identification System Codes are identified within the brackets {}.
DESCRIPTION OF EVENT
On March 12, 2012, during a scheduled refueling outage (RO) boric acid program walk down inspection, two locations on Reactor Coolant System (RCS) {AB} pressure boundary (RCPB) branch piping {PSP} had boron deposits that appeared not to be due to packing or mechanical joint leakage. The areas were cleaned and non-destructive surface examinations confirmed that the boric acid deposits were due to through wall defects.
The two defects were (1) Pressure Control Valve PCV-455A Spray Inlet Stop valve 4152 contained a defect on the top of the 1/2 inch diameter horizontal leak-off pipe in the base metal approximately one inch from where the pipe connects to the valve bonnet, and (2) the socket weld of a 3/8 inch diameter tubing "tee" fitting {TBG} down stream of valve 4138 contained a defect. Valve 4138 is the isolation valve for RCS pressure transmitters PT-402 and PT-413. The condition was recorded in the Indian Point Energy Center (IPEC) Corrective Action Program (CAP) as Condition Report CR-IP2-2012-01733.
Inspections are performed during ROs on systems, components and piping inside containment that contain borated water and fall within the requirements of the Boric Acid Program. During the Unit 2 2012 spring RO, inspections identified locations where dry boron had accumulated. Each location was evaluated to determine if additional actions are required. As a result of these inspections two locations with boron deposits identified through wall defects in RCPB branch lines. The remaining locations with boron deposits were attributed to packing or mechanical joint leakage. Technical Specification (TS) 3.4.13 (RCS Operational Leakage) Limiting Condition of Operation (LCO) 3.4.13.a allows no RCPB leakage.
Defect #1 was a small through wall 1/8 inch indication on the top of the horizontal leak-off pipe for valve 4152 in the base metal approximately 1 inch from where the pipe connects to the valve bonnet. Valve 4152 is a manual 3 inch 1500 lb gate valve built in accordance with ASME Section III, Class 1. The leak-off pipe is a 1/2 inch schedule 80 pipe, material specification ASTM A312 Type 304 Stainless Steel (SS) with a socket welded cap. Design documentation shows that the leak-off pipe aligns with a lantern ring located between two sets of packing rings. The intent is that the lower set of packing provides the pressure boundary seal around the valve stem and any leakage past this packing would go through the lantern ring and out the leak-off pipe to a leak-off collection point. The upper packing set prevents leakage to the containment atmosphere. The current configuration has the lower set of packing replaced by a carbon spacer that performs no sealing function. Under the current installed packing arrangement and installed leak-off pipe cap, the leak-off pipe is pressurized to RCS pressure.
Defect #2 was a pin hole in the socket weld of a 3/8 inch diameter tubing "tee" fitting down stream of valve 4138. Valve 4138 is downstream of valve 954A located in the RCS sample line for hot leg loop 1. Valve 4138 is the isolation valve for pressure transmitters PT-402 and PT-413. The tubing tee was installed by a modification (MMC 77-2-02) in 1977 when PT-413, PT-433 and PT-443 were added to the system. The tubing is designed to class 2505 (Type 304 or 316 SS tubing, Type 316 SS Cajon Tee). The weld lacked sufficient reinforcement at the defect location.
An extent of condition review determined the following: For defect #1 there are additional valves at unit 2 (valves 535, 536, 4153, 4154, and 4155) and at unit 3 (valves 345, PCV-455a, RC-591, RC-593, RC-594, and RC-595) that have capped leak-off pipes with a similar arrangement as found on valve 4152.
Corrective Actions
The following corrective actions have been or will be performed under the Corrective Action Program (CAP) to address the cause of this event.
- The bonnet of valve 4152 containing the leak-off pipe was replaced.
- The socket welded tubing "tee" down stream of valve 4138 was replaced with a Swagelok "tee" eliminating the two field welds that were lacking reinforcement.
- An engineering change (EC) and associated work orders (WO) will be prepared to eliminate the capped leak-off pipes on RCS valves at unit 2 and 3.
- A visual inspection on 10% (random sampling) of applicable field welds will be performed.
Event Analysis
The event is reportable under 10CFR50.73(a) (2)(i) (B). The licensee shall report any operation or condition which was prohibited by the plant's Technical Specification (TS). This event meets the reporting criteria because the Limiting Condition for Operation (LCO) for TS 3.4.13 allows no RCPB leakage and based on surface examinations and boron deposits, it was concluded the condition existed during past plant operation.
Past Similar Events
A review was performed of the past three years of Licensee Event Reports (LERs) for events reporting a TS violation due to a through wall defect in the RCPB. LER-2010-004 reported a leak in the RCPB on a 3/4 inch pipe (#76) upstream of check valve 256B on the 22 Reactor Coolant Pump seal bypass line. The leak was discovered during a RO inspection under the Boric Acid Program. The defect was a through wall indication as a result of a minor weld defect from the time of construction. This event is different as it was a result of missing weld due to poor workmanship. Inspections in 2010 did identify boron on this leak-off pipe but a surface exam at that time did not show any indication of a defect.
Safety Significance
This event had no significant effect on the health and safety of the public. There were no actual safety consequences for the event because there were no significant failures in the RCPB. Periodic inspections identify leaks when they are small so that repairs can be performed to prevent RCPB degradation. TS 3.4.13 has Surveillance Requirement 3.4.13.1 to verify RCS leakage is within limits by performance of RCS inventory balance every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This surveillance ensures the integrity of the RCPB is maintained and provides a trend of leakage early before significant degradation. An early warning of RCPB leakage or unidentified leakage is provided by the systems that monitor containment atmosphere radioactivity and operation of the containment sump. Failure of a RCPB would be a Loss of Coolant Accident (LOCA). A LOCA is analyzed in UFSAR Section 14.3. A minor pipe break (small break) is defined as a rupture of the RCPB with a total cross-sectional area less than 1.0 square foot in which the normally operating charging system flow is not sufficient to sustain pressurizer level and pressure. The results of analysis in UFSAR Section 14.3.3.4 concluded the limiting break was a 3 inch cold leg break. The results of the analysis demonstrated that for a small break LOCA, the Emergency Core Cooling System will meet the acceptance criteria contained in 10CFR50.46. The LOCA analysis of Section 14.3 are bounding for the components reported in this LER.