05000249/LER-2002-004, Regarding Main Steam Safety Valves Failed TS as Found Lift Setpoint
| ML023570312 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/13/2002 |
| From: | Hovey R Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RHLTR #02-0096 LER 02-004-00 | |
| Download: ML023570312 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2492002004R00 - NRC Website | |
text
ExeI en SM Exelon Generation wwwexeloncorp com NEuxe deanr Dresden Generating Station 6500 North Dresden Road Morris, IL 60450-9765 Tel 815-942-2920 10 CFR 50.73 December 13, 2002 RHLTR: #02-0096 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 3 Facility Operating License No. DPR-25 NRC Docket No. 50-249
Subject:
Licensee Event Report 2002-004-00, "Main Steam Safety Valves Failed the Technical Specification As-Found Lift setpoint" Enclosed is Licensee Event Report 2002-004-00, "Main Steam Safety Valves Failed the Technical Specification As-Found Lift Setpoint," for the Dresden Nuclear Power Station Unit 3.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any event or condition which was prohibited by the plant's Technical Specifications."
If you have any questions, please contact Jeff Hansen, Regulatory Assurance Manager at (815) 416-2800.
Respectfully,
.JHovey Site Vice President Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region IlIl NRC Senior Resident Inspector - Dresden Nuclear Power Station
B f
Abstract
On October 14, 2002, during Dresden Station Nuclear Power Station's Unit 3 refueling outage (D3R17), two Main Steam Safety Valves (MSSV) failed the Technical Specification lift setpoint Surveillance Requirement (SR) 3.4.3.1. The SR requires the valves to test within plus/minus one percent of the lift setpoint. The valves both lifted at minus 2.6 percent.
Following testing, the valves were disassembled and inspected by NWS Technologies. Following disassembly, no discrepancies were found that would account for the low setpoint lifts. A review of industry events and discussions with the manufacturer found this to be attributed to routine drift. Setpoint drift of as much as three percent without any mechanical failures is normal throughout the industry.
The root cause of this event has been determined to be setpoint drift. The setpoint drift can be attributed to the inherent characteristics of the valve hardware in conjunction with heating/cooling cycles and the vibration on the valves during service. Corrective action to prevent recurrence is to expand the Technical Specification setpoint tolerance for Main Steam Safety Valves.
The event did not affect the safe operation of the plant or the health and safety of the public. The two MSSVs addressed in this report both lifted below the setpoint specified in the Technical Specifications. The MSSVs provide overpressure protection during the most severe pressurization transient. The safety significance of this event is minimal, since the MSSVs lifting below the setpoint would not have prevented the valves from performing their overpressure protection function should they have been required to perform this safety function.U.S. NUCLEAR REGULATORY APPROVED BY OMB NO.3150-0104 COMMISSION EXPIRES 07131/2004 (7-2001)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1)
DOCKET NUMBER (2)
ER NUMBER (6 PAGE (3)
YEAR SEQUENTIAL REVISION Dresden Nuclear Power Station Unit 3 05000249 NUMBER NUMBER 2002 004 00 2 of 3 (If more space is required, use additional copies of NRC Form 366A)(17)
A.
Plant Conditions Prior to Event:
Unit: 03 Event Date: 10-14-2002 Event Time: 1421 CDT Reactor Mode: 5 Mode Name: Refuel Power Level: 000 percent Reactor Coolant System Pressure: 000 psig B.
Description of Event
This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), 'Any operation or condition which was prohibited by the plant's Technical Specifications."
During D3R17, four Main Steam Safety Valves [SB] (MSSV) valves were removed and shipped to NWS Technologies in South Carolina for testing. On October 14, 2002, the four valves were tested, and two (BK6265 and BK6270) of the four valves were outside of the required Technical Specifications (TS) lift setpoint of plus/minus one percent of the setpoint. The as-found lift for valve BK6265 (setpoint of 1260 psig) was minus 2.6 percent (1227 psig). A second informational lift was performed and the result was minus 2.2 percent. During testing of valve BK6270 (setpoint of 1240 psig) the as-found lift was minus 2.6 percent (1208 psig). A second informational lift was performed and the result was minus 2.5 percent. Based on the Inservice Testing Program and American Society of Mechanical Engineers requirements, all four valves were within plus/minus three percent of the setpoint, eliminating the need for expanded testing of the other four Unit 3 valves.
The MSSV BK6265 was disassembled. A gall was found between the compression screw and the top washer.
No other deficiencies were noted. The galled area showed no signs of surface irregularities that had flattened out to allow the spring to relax. There was no seat damage evident. The galled area was removed and the valve was assembled. The final lifts of the valve were obtained within the as-left acceptance limits of plus/minus one percent. The MSSV BK6270 was disassembled. During the inspection, only minor deficiencies were found. A rub area was noted between the disc holder and guide, but this would normally be suspect in the event of a high as-found lift. The rub was buffed out and determine to have no effect on valve performance. In addition, a gap between the bottom turns of the spring was noticeably closer than the other coil spacing. However, when disassembled the spring had the same configuration as when compressed and determined to have no effect on spring force and therefore was determined not to be a contributor to the early lift. Following reassembly, the final lifts of the valve were obtained within the as-left acceptance limits of plus/minus one percent.
C.
Cause of Event
The root cause of the two MSSVs lifting low is setpoint drift beyond the TS limit of plus/minus one percent. The setpoint drift can be attributed to the inherent characteristics of the valve hardware in conjunction with heating/cooling cycles and the vibration on the valves during service. (NRC Cause Code X)
D.
Safety Analysis
The consequences of this event had minimal impact on the health and safety of the public and reactor safety. The two MSSVs both lifted below the setpoint specified in TS. Safety valves lifting at these lower limits will not prevent the valves from performing their overpressure protection function. The overpressure protection system must accommodate the most severe pressurization transient. Evaluations have determined that the most severe transient is the closure of all main steam isolation valves (MSIVs),
followed by reactor scram on high neutron flux (i.e., failure of the direct scram associated with MSIV
- - U.S. NUCLEAR REGULATORY APPROVED BY OMB NO.3150-0104 COMMISSION EXPIRES 07/3112004 (7-2001)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL REVISION Dresden Nuclear Power Station Unit 3 05000249 1
NUMBER NUMBER 2002 004 00 3 of 3 (If more space Is required, use additional copies of NRC Form 366A)(17) position). For the purpose of the analysis, eight safety valves are assumed to operate in the safety mode.
The analysis results demonstrate that the design safety valve capacity is capable of maintaining reactor pressure below the ASME Code limit of 110% of vessel design pressure.
E.
Corrective Actions
Inspected, refurbished, and tested both valves BK 6265 and 6267.
Engineering to perform the required analyses in accordance with Updated Final Safety Analysis Report Section 15,
'Accident and Transients Analysis," to justify a revision to the Technical Specifications in order to increase the Main Steam Safety Valve setpoint tolerance.
Engineering to perform all required containment and plant equipment analysis to support increased Main Steam Safety Valve tolerance established from the Updated Final Safety Analysis Report Section 15 analysis.
Regulatory Assurance to submit a Technical Specification Amendment Request to the Nuclear Regulatory Commission to increase the Main Steam Safety Valve setpoint tolerance as reflected in the analyses performed.
F.
Previous Occurrences
LER 98-007-00, 03/27/98 - "Main Steam Safety Valves 2-02034A and 2-0203-4B As-Found Lift Setpoint Outside Tech Spec Limit Due to Setpoint Drift." MSSVs 2-0203-4A and 2-0203-4B lifted outside the Technical Specification limit of plus/minus one percent. The as-found setpoints were minus 2.3 percent and plus 1.03 percent respectively. Both of these failures were attributed to setpoint drift. Corrective actions included inspection, refurbishment, and testing of the failed safety valve.
G.
Component Failure Data
Manufacturer Nomenclature Model Number Consolidated Valve Corp/Dresser Main Steam Safety Valve 3777Q