05000315/LER-2021-001, Main Steam Safety Valve Setpoints Found Outside Technical Specifications Limits
| ML21161A329 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 06/10/2021 |
| From: | Lies Q Indiana Michigan Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| AEP-NRC-2021-37 LER 2021-001-00 | |
| Download: ML21161A329 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3152021001R00 - NRC Website | |
text
An AEP Company BOUNDLESS ENERG Y-June 10, 2021 Docket No.: 50-316 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike Rockville, MD 20852 Donald C. Cook Nuclear Plant Unit 2 LICENSEE EVENT REPORT 316/2021-001-00 Indiana Michigan Power Cook Nuclear Plant One Cook Place Bridgman, Ml 49106 indianamichiganpower.com AEP-NRC-2021-37 10 CFR 50.73 Main Steam Safety Valve Setpoints Found Outside Technical Specifications Limits In accordance with 10 CFR 50. 73, Licensee Event Report (LER) System, Indiana Michigan Power Company, the licensee for Donald C. Cook Nuclear Plant Unit 2, is submitting as an enclosure to this letter the following report:
LER 316/2021-001-00: Main Steam Safety Valve Setpoints Found Outside Technical Specifications Limits There are no commitments contained in this submittal.
Should you have any questions, please contact Mr. Michael K. Scarpello, Regulatory Affairs Director, at (269) 466-2649.
Sincerely, alU::::-). ~
Site Vice President SJM/mll
Enclosure:
Licensee Event Report 316/2021-001-00: Main Steam Safety Valve Setpoints Found Outside Technical Specifications Limits
U.S. Nuclear Regulatory Commission Page 2 c:
R. J. Ancona - MPSC EGLE - RMD/RPS J.B. Giessner-NRC Region Ill NRC Resident Inspector R. M. Sistevaris - AEP Ft. Wayne J. E. Walcutt - AEP Ft. Wayne S. P. Wall - NRC, Washington D.C.
A. J. Williamson - AEP Ft. Wayne AEP-NRC-2021-37
Enclosure to AEP-NRC-2021-37 Licensee Event Report 316/2021-001-00 Main Steam Safety Valve Setpoints Found Outside Technical Specifications Limits
Abstract
On April 15, 2021, Donald C. Cook Unit 2 was in Mode 1 and holding at approximately 49% reactor power while performing Technical Specification (TS) surveillance testing on the Main Steam Safety Valves (MSSVs) prior to the Unit 2 Cycle 26 (U2C26) Refueling Outage.
The Unit 2 Steam Generator (SG) #3 MSSV 2-SV-1A-3 and 2-SV-2B-3 as-found lift setpoint test pressures were above the TS allowable setpoint pressure band of +/- 3 percent. SG #2 MSSV 2-SV-2B-2 as-found lift setpoint was below the allowable setpoint pressure. Setpoint drift was determined as the similar cause for the affected MSSVs. Following adjustments, the MSSVs met the as-left testing criteria of +/- 1 percent lift setpoint pressure The identified discrepancies would normally be considered to occur at the time of test. However, based on the guidance in NUREG-1022, Revision 3, for "Multiple Test Failures", the condition may have arisen over a period of time during the operating cycle. In accordance with NUREG-1022 guidance, MSSVs are considered to have been inoperable during plant operation, for a period longer than allowed by TS. Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B),
Operation or Condition Prohibited by Technical Specifications.
EVENT DESCRIPTION
SEQUENTIAL NUMBER 001 REV NO.
00 On April 15, 2021, Donald C. Cook Unit 2 was in Mode 1 and holding at approximately 49% reactor power while performing Technical Specification (TS) surveillance testing on the Main Steam Safety Valves (MSSVs) [SB] [RV],
prior to the Unit 2 Cycle 26 (U2C26) Refueling Outage.
The as found lift setpoint pressure of the Unit 2 Steam Generator (SG) [SG] #3 MSSV 2-SV-1A-3 was 1099.1 pounds per square inch gauge (psig), which was above the TS allowable lift setpoint pressure band of +/- 3% of 1065 psig. The valve met the seat-leakage requirement. After adjustment, the valve met the as left testing criteria of+/- 1 % of the lift setpoint of 1065 psig.
The as found lift setpoint pressure of the Unit 2 SG #3 MSSV 2-SV-2B-3 was 1126.8 psig, which was above the TS allowable setpoint pressure band of +/- 3% of 1075 psig. The valve met the seat-leakage requirement. After adjustment, the valve met the as left testing criteria of+/- 1 % of the lift setpoint of 1075 psig.
The as found lift setpoint pressure of the Unit 2 SG #2 MSSV 2-SV-2B-2 was 1040.0 psig, which was below the TS allowable setpoint pressure band of +/- 3% of 1075 psig. The valve met the seat-leakage requirement. After adjustment, the valve met the as left testing criteria of+/- 1 % of the lift setpoint of 1075 psig.
Due to the as found lift setpoint pressure of 2-SV-1A-3, 2-SV-2B-3, and 2-SV-2B-2 being outside of acceptance limits, the ASME OM Code requires all 20 SG MSSVs to be tested. All of the remaining valves tested from SG
- 1, SG #2, SG #3, and SG #4 were within the as found acceptance criteria of +/- 3% of the lift setpoint pressure.
TS Limiting Condition For Operation 3.7.1 requires a minimum of 20 MSSVs (5 per SG) to be operable in Modes 1, 2, and 3. Based on the guidance in NUREG-1022, Revision 3, 2-SV-1A-3, 2-SV-2B-3, and 2-SV-2B-2 were considered to be inoperable longer than allowed by TS, since this condition may have arisen over a period of time and thus, the MSSVs may not have been operable during plant operation. Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), Operation or Condition Prohibited by Technical Specifications.
COMPONENT The MSSVs are Consolidated-Dresser model 3707RA Valves.
CAUSE OF THE EVENT
A failure mode effects and analysis evaluation was performed for the three valves 2-SV-1A-3, 2-SV-2B-3, and 2-SV-28-2. This evaluation determined that setpoint drift is responsible for not meeting the surveillance test acceptance criteria. No further corrective action is necessary due to the low frequency of failure of these valves and the historical randomness of setpoint drift.
CORRECTIVE ACTIONS
SEQUENTIAL NUMBER 001 REV NO.
00 Safety valves 2-SV-1A-3, 2-SV-2B-3, and 2-SV-2B-2 were successfully adjusted and subsequently met the as left testing criteria of +/- 1 % of the setpoint.
All of the additional expanded scope valves tested from SG#1, #2, SG #3, and SG #4 were within the as found acceptance criteria of +/- 3% of the lift setpoint pressure.
ASSESSMENT OF SAFETY CONSEQUENCES
NUCLEAR SAFETY There was no actual or potential nuclear safety hazard resulting from the Main Steam Safety Valve Setpoints being found outside Technical Specification limits.
INDUSTRIAL SAFETY There was no actual or potential industrial safety hazard resulting from the Main Steam Safety Valve Setpoints being found outside Technical Specification limits.
RADIOLOGICAL SAFETY There was no actual or potential radiological safety hazard resulting from the Main Steam Safety Valve Setpoints being found outside Technical Specification Limits.
PROBABILISTIC RISK ASSESSMENT (PRA) 2-SV-28-3 lifted high at 1126.8 psig, which is above its setpoint of 1075 psig. A similar valve on the same steam generator, 2-SV-1A-3 also lifted high at 1099.1 psig, which is above its setpoint of 1065 psig. The MSSVs are responsible for protecting Unit 2 SG #3 from damage due to an overpressure event. Each SG has five of these MSSVs and one Power-Operated Relief Valve (PORV). Because these valves serve to mitigate an overpressure event following an increase in SG pressure to the MSSV setpoint, their failure to lift does not contribute to the frequency of occurrence of these overpressure events. Due to the presence of multiple redundant pieces of equipment, such as the SG PORVs and remaining SG SVs, it is unlikely that an overpressure event would occur concurrent with sufficient additional equipment failures that its mitigation would be impacted. The function of these valves in the PRA model is to remain closed following a postulated SG tube rupture (SGTR) event. The as found lift pressure of 2-SV-1A-3 and 2-SV-2B-3 does not impact the ability to meet the PRA-modeled function.
2-SV-28-2 lifted low at 1040 psig compared to the setpoint of 1075 psig. This lower lift pressure may result in a SG safety valve lifting during attempts to isolate an SG following a SGTR. However, as the Reactor Coolant System is cooled down, in response to a SGTR, the SG pressure will be rapidly lowered below 1040 psig, negating any adverse impact on accident mitigation. Thus, 2-SV-28-2 lifting low would not have complicated a SGTR event or increased the likelihood of another event occurring.
Therefore, it can be concluded that this event was of very low safety significance.
PREVIOUS SIMILAR EVENTS
SEQUENTIAL NUMBER 001 REV NO.
00 Licensee Event Report 315\\2019-001-00, Two Main Steam Safety Valve Setpoints Found Outside Technical Specification Limits, on Unit 1, was submitted April 30, 2019. The cause was due to setpoint drift and the affected valves were successfully adjusted back within specified setpoints. Page 4 of 4