05000336/LER-2023-001, For Millstone, Unit 2, Structural Integrity of a Train Service Water Header Piping Could Not Be Demonstrated Causing the Unit to Operate in a Condition Prohibited by Technical Specifications
| ML23188A132 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/07/2023 |
| From: | O'Connor M Dominion Energy Nuclear Connecticut |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 23-162 LER 2023-001-00 | |
| Download: ML23188A132 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3362023001R00 - NRC Website | |
text
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 JUL O 7 2023 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION Unit 2 LICENSEE EVENT REPORT 2023-001-00
~
Dominion
=--' Energy Serial No.:
23-162 MPS Lie/JP RO Docket No.: 50-336 License No.: DPR-65 STRUCTURAL INTEGRITY OF "A" TRAIN SERVICE WATER HEADER PIPING COULD NOT BE DEMONSTRATED CAUSING THE UNIT TO OPERATE IN A CONDITION PROHIBITED BY TECHNICAL SPECIFICATIONS.
This letter forwards Licensee Event Report (LER) 2023-001-00, documenting a condition that was discovered at Millstone Power Station Unit 2 (MPS2) on May 9, 2023. MPS2 could not demonstrate the structural integrity of the "A" Train Service Water header piping and determined that this condition existed longer than its Technical Specification Allowed Outage Time. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
There are no regulatory commitments contained in this letter or its enclosure.
Should you have any questions, please contact Mr. Dean E. Rowe at (860) 444-5292.
Sincerely,
~\\~~
Michael J. O'Connor Site Vice President - Millstone Enclosure: LER 336/2023-001-00
cc:
U.S. Nuclear Regulatory Commission Region I 4 75 Allendale Road, Suite 102, King of Prussia, PA 19406-1415.
R. V. Guzman NRC Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.23-162 Docket No. 50-336 Licensee Event Report 2023-001-00 Page 2 of 2
ATTACHMENT Serial No.23-162 Docket No. 50-336 Licensee Event Report 2023-001-00 LICENSEE EVENT REPORT 2023-001-00 STRUCTURAL INTEGRITY OF "A" TRAIN SERVICE WATER HEADER PIPING COULD NOT BE DEMONSTRATED CAUSING THE UNIT TO OPERATE IN A CONDITION PROHIBITED BY TECHNICAL SPECIFICATIONS.
MILLSTONE POWER STATION UNIT 2 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Abstract
On May 09, 2023, while Millstone Power Station Unit 2 (MPS2) was in Mode 6 for a refueling outage, external inspections of the Unit 2 "A" Train Service Water header piping identified a through-wall piping flaw. Previous internal inspections conducted on this piping did not identify this potential through-wall flaw. The cause of degradation was internal liner failure which allowed the seawater to come in contact with ductile cast iron piping and led to corrosion. The degraded portion of the piping was replaced. Engineering evaluated the degraded condition and could not demonstrate the structural integrity of "A" Train Service Water header piping. The magnitude of flaw provides reasonable evidence that the through-wall flaw and loss of structural integrity existed during the past operating cycle for a period longer than permitted by the plant's Technical Specifications. Therefore, this report is being submitted pursuant to 10 CFR 50.73 (a)(2)(i)(B), an operation or condition that was prohibited by the plant's Technical Specifications.
- 2. DOCKET NUMBER
- 3. LER NUMBER I
3~
i=7 NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 001 1-0 On May 09, 2023, while Millstone Power Station Unit 2 (MPS2) was in Mode 6 for a refueling outage, external inspections of the Unit 2 "A" Train Service Water header piping identified a through-wall piping flaw with an approximate 6 dpm leak in the 24"-KE-1 ductile cast-iron piping, adjacent to a gland ring at a bell and spigot joint. The degraded area of through-wall flaw was significant, although gross leakage at this location was not identified due to an internal liner which prevented external system leakage.
Although Service Water is not required to be operable in Mode 6, a historical review was performed to determine if this flaw had existed during the operating cycle. Technical Specification 3.7.4.1 requires two service water loops to be OPERABLE for Modes 1, 2, 3, and 4. With one service water loop inoperable, the requirement is to restore the inoperable loop to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in COLD SHUTDOWN within the next 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Technical Requirement Manual (TRM) 3.4.10 for structural integrity requires that, if structural integrity cannot be established and the affected component cannot be isolated from service, that the component be declared nonfunctional.
Engineering evaluated the degraded condition and could not demonstrate the structural integrity of "A" Train Service Water header piping. The cause of the through-wall flaw was determined to be corrosion which had developed over a period of time. The magnitude of the flaw provides reasonable evidence that the flaw and loss of structural integrity existed during the past operating cycle for a period longer than the Technical Specification action statement allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Therefore, this report is being submitted pursuant to 10 CFR 50.73 (a)(2)(i)(B), an operation or condition that was prohibited by the plant's Technical Specifications.
CAUSE
The cause of degradation was internal liner failure which allowed seawater to come in contact with ductile cast iron piping and led to corrosion. Additionally, previous internal inspections on this piping did not identify this potential failure mode.
ASSESSMENT OF SAFETY CONSEQUENCES
The condition identified above did not have any actual safety consequence as no significant leakage from the 'A' Train Service Water header piping occurred due to the presence of this through-wall flaw. The potential safety significance of this condition is determined to be low based upon the availability of the 'B' Service Water Train to continue to deliver required flow to the safety related heat exchangers with the flow diversion out of the through-wall flaw on the 'A' Service Water header piping and the relative timing associated with flooding impacts on the equipment located on the 14'-6" elevation of the Turbine Building.
Flooding associated with this bounding flow rate would take greater than one hour to fill the Service Water tunnel before beginning to flood the 14'-6" elevation of the Turbine Building. At this point, service water will flow to the condenser pit, raising the water level in the pit to the point where switches will trip the circulating water pumps, which will indirectly cause a reactor trip. If the flooding is not identified prior to the reactor trip, operators will have approximately 90 minutes following the reactor trip to identify the cause of the circulating water pump trip and stop the "A" Service Water pump prior to water levels in the Turbine Building challenging the motor driven AFW pumps. In addition, the unimpacted 'B' Service Water Train remained capable of performing its safety related function during the operating cycle, except for short periods of time as part of a planned evolution for maintenance and surveillance testing in accordance with approved plant procedures and Technical Specifications. In this bounding scenario, RCS decay heat removal and all other post-trip safety functions would be satisfied.
CORRECTIVE ACTIONS
- 2. DOCKET NUMBER
- 3. LER NUMBER I
336 r:::7 NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 001 1-0 The degraded portion of the piping was replaced. Additional corrective actions will be taken in accordance with the Station Corrective Action Program including an evaluation of identification and remediation methods for this class of lined piping.
PREVIOUS OCCURRENCES
There have been no similar events related to Unit 2 Service Water header piping degradation leading to a Service Water Train inoperable for a period longer than the Technical Specification action statement allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> at Millstone Power Station over the last 3 years.
ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES PSP - Pipe Bl - Essential Service water system Page 3
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