05000454/LER-2003-002
| Byron, On, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| 4542003002R01 - NRC Website | |
LEMON
ivy A. Plant OperatinE Conditions Before The Event:
Unit: 1 � Event Date: 2/16t2003 � Event Time: 1303 MODE: 1 � Reactor Power: 94 percent Reactor Coolant System (RCS) [AB] Normal Operating Temperature and Pressure.
No structures, systems, or components were inoperable at the start of the event that contributed to the event.
B. Description of Event:
Byron Station, Unit I is configured with four steam generators. Each steam generator has five Main Steam Safety Valves (MSSV) (SBi, which provide overpressure protection. On February 16, 2003, Unit I MSSV mid-cycle setpoint testing was being performed on six MSSV's in order to gain performance information for the X-750 Inconel discs installed in these valves. This testing is a corrective action from previous concerns with the X-750 Inconel disc material being susceptible to disc bonding. Five of the valves (i.e., 1MS013A, 1MS014C, 1MS014D, 1MS015B, and 1MS016C) selected were refurbished with X-750 Inconel material during the last refueling outage (B1R11) in March 2002. The remaining valve selected (i.e., 1MS015C), was refurbished with X-750 Inconel material during the outage previous to B1R11 (i.e., BlRl 0) in October 2000. This valve was selected to be in the test population because it lifted out of tolerance on the high side during B1R11.
There are three additional MSSV's on Unit 1 with X-750 Inconel disc material installed during B1R10, however, those three valves were satisfactorily tested in B1R11 after a long continuous run of over 500 days. Therefore, they were not selected for mid-cycle testing because they are not considered to be susceptible to disc bonding.
The Technical Specification 3.7.1, "Main Steam Safety Valves," allows a plus or minus 3% tolerance on the as found lift nominal setting and requires all tested valves to be set to a plus or minus 1% as left tolerance. The setpoint test determines each valve's actual lift setting using normal system pressure with assistance from a hydraulic testing device. The MSSV testing was performed in accordance with procedure BMP 3114-15, "Main Steam Safety Valve Verification of Lift Point Using Furmanite's Trevitest Equipment." The procedure's as left acceptance criteria require two consecutive lift tests within plus 0% or minus 1% of the valve's required lift nominal setpoint with no adjustments performed between these tests.
The six MSSV tests were initiated and completed on February 16, 2003. The MSSV tests, and any required valve adjustments, were performed on only one valve at a time. Valves not meeting acceptance criteria were adjusted and satisfactorily tested before proceeding to the next valve.
The initial lift tests performed on two of the six MSSV valves (i.e., 1MS015B and 1MS013A) exceeded the plus or minus 3% Technical Specification as found limit (on the low - 3% side). These NRC ORM 166A (1-200I) U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1) DOCICE7 (2) LER NUMBER 6) PAGE (3) Byron, Unit 1 STN 05000454
MAWR
NumBEA valves required setpoint adjustment to leave them within the plus 0% or minus 1% as left criteria.
The failed valves and their applicable Technical Specifications Action Condition entry and exit times were as follows:
Valve Action Condition Entry Action Condition Exit 1MS015B 02/16/03 at 09:48 02/16/03 at 10:00 1MS013A 02/16/03 at 13:03 02/16/03 at 13:26 The specified lift, initial, and as-left settings for each of the failed valves, the plus or minus 1% and plus or minus 3% Technical Specification limits, and the initial low lift tolerance percentage were as follows:
Valve Tech Spec Setpt (psi) +1-3% Tech Spec As- Found Limits (psi) Initial Lift (psi) Initial lift % Diff.
As-Left Lift (psi) - +1-1% Tech Spec As-Left Limits (psi) 1MS015B 1205 , 1169 —1241 , 1167 , -3.2% 1195 1193 —1217 1MS013A 1235 1198 —1272 1190 -3.6% 1227 1223— 1247_ This condition is reportable to the NRC in accordance with 10CFR 50.73 (a)(2XiXb), as a condition prohibited by Technical Specifications.
C. Cause of Event:
The cause of the two MSSV failures is unknown. Various factors were reviewed for potential to cause low lifts. These factors include individual valve performance history, calibration of test equipment, setpoint testing methodology, MSSV body temperature, and past unit operations during the cycle. No definitive link could be determined that would explain the low lifts experienced.
A comparison of the testing methodologies between the on-site Furmanite testing and the off-site test vendor was conducted. The conclusion is that the two testing methodologies achieve essentially the same test results. Consequently, differences in the test methodologies did not account for the two MSSVs lifting low.
D. Safety Consequences:
The primary purpose of the MSSVs is to provide overpressure protection for the secondary system.
These valves also provide protection against over-pressurizing the Reactor Coolant pressure boundary by providing a heat sink for the removal of energy from the Reactor Coolant if the NRC � M 366.4.
(I-2001) U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1) DOCKET (2) ' LER N'UMBER 5) PAGE (3) „---- � STN 05000454 _ � REVISION preferred heat sink provided by the condenser [SD] is not available. The MSSVs also serve as containment isolation valves.
An engineering evaluation was conducted to determine the effect of the two MSSV out of tolerance condition on the Chapter 15, "Accident Analyses," in the Updated Final Safety Analysis Report.
This analysis concluded that considering the as-found MSSV setpoints, the conclusions of Chapter 15 analyses still remain valid. Therefore, the overall impact on plant safety due to the identified condition was minimal. In addition, a risk management review indicates that there was no impact on the Unit I online risk profile for the site due to the as found setpoints of the two MS SV's that were found at 3.2% and 3.6% below the nominal +1-3% setpoint of the valves. This condition is not a safety system functional failure.
E . � Corrective Actions:
Maintenance immediately notified Operations after each of the initial MSSV lifts that exceeded the +/-3% Technical Specification limit and the appropriate LCO was entered. Following additional lifts on the 1MS015B and IMS013A valves, the valves were adjusted and re-tested satisfactorily.
F . � Previous Occurrences:
During the previous 4 years there have been several LERs at Byron involving multiple MSSV lifting outside their acceptance criteria, however these events involve the MSSV lifting high and attributed to the disc bonding phenomena. No previous occurrences were found involving multiple valves lifting low.
G. � Component Failure Data:
Manufacturer � Nomenclature � Model � Mfg. Part Number Dresser � Main Steam Safety Valve (MSSV) � 3707R � N/A