05000423/LER-2022-002, Two Main Steam Safety Valves Installed in Wring Location Resulting in Failure to Lift within the Technical Specification Acceptance Criteria
| ML22151A121 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/31/2022 |
| From: | O'Connor M Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 22-157 LER 2022-002-00 | |
| Download: ML22151A121 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4232022002R00 - NRC Website | |
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Dominion Energy Nuclear Connecticut, Inc.
Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 Dominion Energy.com U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Submitted electronically by NRC Electronic Information Exchange (EIE)
DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2022-002-00 Dominion Energy MAY 3 1 2022 Serial No.
MPS Lie/DCB Docket No.
License No.22-157 RO 50-423 NPF-49 TWO MAIN STEAM SAFETY VALVES INSTALLED IN WRONG LOCATION RESULTING IN FAILURE TO LIFT WITHIN THE TECHNICAL SPECIFICATION ACCEPTANCE CRITERIA This letter forwards Licensee Event Report (LER) 2022-002-00, which documents a condition discovered at Millstone Power Station Unit 3, on April 5th and April 6th of 2022. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's Technical Specifications.
If you have any questions or require additional information, please contact Mr. Dean E. Rowe at (860) 444-5292.
Sincerely, Michael J. O'Connor Site Vice President-Millstone Attachments: 1 Commitments made in this letter: None
Electronically via EIE:
U.S. Nuclear Regulatory Commission Region I 475 Allendale Road Suite 102 King of Prussia, PA 19406-1415 Electronically via eMail:
R.V. Guzman Serial No.22-157 Docket No. 50-423 Licensee Event Report 2022-002-00 Page 2 of 2 NRC Senior Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C-2 Rockville, MD 20852-2738 cc:
NRC Senior Resident Inspector Millstone Power Station
ATTACHMENT Serial No.22-157 Docket No. 50-423 Licensee Event Report 2022-002-00 LICENSEE EVENT REPORT 2022-002-00 TWO MAIN STEAM SAFETY VALVES INSTALLED IN WRONG LOCATION RESULTING IN FAILURE TO LIFT WITHIN THE TECHNICAL SPECIFICATION ACCEPTANCE CRITERIA MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Abstract
On April 5th and April 6th, 2022, with the plant in Mode 1 at 90% power, lift setting testing of all Millstone Power Station Unit 3 Main Steam Safety Valves (MSSVs) was conducted. Two MSSVs failed to lift within the +/- 3% acceptance criteria listed in Technical Specifications.
The two MSSVs were adjusted, retested, and declared operable before proceeding with remaining valve tests. Both valves were returned to operable status by two successive tests with results within +/- 1 % of the set pressure.
The direct cause of the two MSSVs to lift outside of the required lift setting pressure range was installing two properly set valves in the wrong locations during the previous refueling outage in October of 2020.
This condition is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's Technical Specifications.
1. EVENT DESCRIPTION
On April 5th and April 6th, 2022, with the plant in MODE 1 at 90% power, lift setting testing of the Millstone Power Station Unit 3 (MPS3) Main Steam Safety Valves (MSSVs) was conducted per plant procedure SP 3712G, Main Steam Code Safety Valve Surveillance Testing. Two of the twenty valves did not meet their as found acceptance criteria of+/- 3% of the required setpoint. The MSSV from the 'B' Steam Generator, 3MSS*RV22B, lifted above the maximum lift setting and the MSSV from the 'D' Steam Generator, 3MSS*RV26D, lifted below the minimum lift setting as specified in MPS3 Technical Specification (TS) Table 3.7-3, Steam Line Safety Valves Per Loop.
TS Table 3.7-3 allows a+/- 3% setpoint tolerance (allowable value) on the as-found lift setting, to account for drift over an operating cycle. During this testing, the MSSVs are OPERABLE provided that the actual as-found lift settings are within +/-
3% of the required lift setting. A footnote to TS Table 3.7-3 requires that the lift setting be within +/-1 % of the required lift setting following testing. The as-found lift pressures for the two valves exceeded the +/- 3% TS allowable values and were therefore inoperable. Each valve was adjusted, retested, and declared operable before the next safety valve was tested.
Both valves were returned to operable status by two successive tests with results within +/- 1 % of the set pressure within the four hours allowed by the action statement. Each valve was declared operable before the next MSSV was tested.
The TS lift setting of 3MSS*RV26D is 1225 psig, with a tolerance of+/- 3% (1188.3 to 1261.7 psig). On April 5th, 2022, the first lift of the valve resulted in a lift setting value within +/- 3% of the TS lift setting of 1225 psig; however, the second lift of the valve was 3.9% below the TS lift setting value of 1225 psig, or 10.8 psi below the acceptance range. An adjustment was made to raise the set pressure and the valve was returned to operable following two successive lifts, with the as-left set pressure within 1 % of the TS lift setting pressure, per the procedural and TS requirements.
The TS lift setting of 3MSS*RV22B is 1185 psig, with a tolerance of+/- 3% (1149.5 to 1220.5 psig). On April 6th, 2022, the as found test result for 3MSS*RV22B was 3.5% above the TS lift setting of 1185 psig, or 5.3 psi above the acceptance range. An adjustment was made to lower the set pressure and the valve was returned to operable following two successive lifts without prior adjustments, with the as-left set pressure within 1 % of the TS lift setting, per the procedural and TS requirements.
There was no lnservice Test (1ST) program test scope expansion required because testing was planned to be performed on all 20 MSSVs. The other 18 MSSVs were tested, and all as-found lift settings were found to be within +/- 3% of their set pressures. After testing was completed, all 20 MSSVs as-left set pressures were within +/- 1 % of their design set pressure per TS requirements.
There are five main steam safety relief valves for each of the four steam generators. The five valves are set to lift at different pressure settings of 1185, 1195, 1205, 1215 and 1225 psig.
Both 3MSS*RV26D and 3MSS*RV22B were replaced during the previous refueling outage in October of 2020, and this was the first time they were tested since installation. A review of the installation work orders revealed that a safety valve with the wrong lift setting had been used for each work order. The safety valves had been correctly set at the vendor at the lift setting listed on its nameplate. This resulted in a safety valve with a lift setting of 1225 psig, being installed in the 3MSS*RV22B location, and a safety valve with a lift setting of 1185 psig being installed in the 3MSS*RV26D location. The 3MSS*RV22B location was supposed to receive a safety valve with a lift setting of 1185 psig, and the 3MSS*RV26D location was supposed to receive a safety valve with a lift setting of 1225 psig.
- 1. EVENT DESCRIPTION (continued):
Therefore, the 'B' steam generator operated with two safety valves with a set pressure of 1225 psig, and the 'D' steam generator operated with two safety valves with a set pressure of 1185 psig. If the safety valves had been installed in their proper locations, both safety valves would have passed their as found test.
This condition is reportable under 10 CFR 50.73(a)(2)(i)(B), "any operation or condition prohibited by the plant's technical specifications".
2. CAUSE
The direct cause of the two safety valves lifting outside of their TS allowed lift settings was that they had been installed in the wrong locations.
3. ASSESSMENT OF SAFETY CONSEQUENCES
The as-found condition of the MSSVs is of low safety significance. As described in the Final Safety Analysis Report (FSAR), the MSSVs protect the steam generators and portions of the main steam and feedwater systems from overpressure conditions. The valves also serve as a heat sink for the reactor coolant system in the event that the main condenser is not available. The accidents presented in FSAR Section 15.2 assume all MSSVs open at 3% higher than their nominal set pressure.
In the testing prior to 3R21, only one of twenty valves opened at lift pressure that was slightly above the 3% tolerance (the valve in the 3MSS*RV22B position opening at 103.5%). Of the remaining valves, 9 opened below their nominal TS setpoint (with the valve in the 3MSS*RV26D position opening at 95% of its expected setpoint) and none of the remaining 10 valves opened at more than 101.5% of their nominal TS setpoint. The average of all 20 MSSVs was nearly exactly the nominal lift set pressure.
Additionally, while the 3MSS*RV22B valve opened at 103.5% of the intended lowest pressure setpoint (1185 psig), the nominally highest pressure valve on the 'B' steam generator, 3MSS*RV26B, opened at 98% of its nominal setpoint rather than the 103% assumed in the Chapter 15 safety analysis.
Therefore, if a FSAR Chapter 15 event had occurred, the MSSVs would have provided adequate pressure relief to ensure the safety analysis assumption would not be challenged and the accident analysis results would remain within the overpressure acceptance criteria.
4. CORRECTIVE ACTIONS
Adjustments were made to the lift settings of 3MSS*RV22B and 3MSS*RV26O and each valve was returned to operable following two successive lifts, with the as-left lift settings within +/- 1 % of the TS lift setting pressure.
Additional corrective action will be taken in accordance with the Corrective Action Program.
5. PREVIOUS OCCURENCES
There have been prior LER reports for failed MSSV Simmer testing, but they were due to safety valve performance issues.
There have been no prior issues with MSSVs installed in the wrong locations.
- 6. ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES SB Main Steam RV Relief Valve Page 4
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