05000298/LER-2024-007, Inoperable Pressure Switch During Mode Change Results in Operation or Condition Prohibited by Technical Specifications
| ML24366A126 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 12/31/2024 |
| From: | Dia K Nebraska Public Power District (NPPD) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NLS2024075 LER 2024-007-00 | |
| Download: ML24366A126 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982024007R00 - NRC Website | |
text
H Nebraska Public Power District "Always there when you need us" 10 CFR 50.73 NLS2024075 December 31, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Subject: Licensee Event Report No. 2024-007-00 Cooper Nuclear Station, Docket No. 50-298, Renewed License No. DPR-46 The purpose of this correspondence is to forward Licensee Event Report 2024-007-00.
This letter does not contain regulatory commitments.
Sincerely, Khalil Dia Site Vice President
/jo
Attachment:
Licensee Event Report 2024-007-00 cc:
Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment USNRC - NRR Plant Licensing Branch IV Senior Resident Inspector w/attachment USNRC-CNS SRAB Administrator w/attachment NPG Distribution w/attachment INPO Records Center w/attachment via IRIS entry SORC Chairman w/attachment CNS Records w/attachment COOPER NUCLEAR STATION 72676 648A Ave/ P.O. Box 98 / Brownville, NE 68321 http://www.nppd.com
Abstract
On November 3, 2024, with the Cooper Nuclear Station (CNS) reactor in Mode 1, Power Operation, scheduled surveillance testing of the eight Safety Relief Valves (SRV) was being performed. During this testing, pressure switch (MS-PS-3008) did not actuate when SRV71 B was taken to the OPEN position. As such, Operations personnel declared MS-PS-3008 inoperable.
Review of a picture taken in the area of SRV71 B on October 16, 2024, while the reactor was in Mode 5, Refueling, revealed that the flex hose that extends from the SRV tailpipe to the pressure switch may be damaged. This was later confirmed when maintenance personnel found the flex hose on top of the SRV tailpipe and the connection port for MS-PS-3008 damaged. Repairs were made and subsequent testing performed satisfactorily, and Operations personnel declared MS-PS-3008 operable.
CNS made the change from Mode 4 to Mode 2 while this condition existed, violating Technical Speciation (TS)
Limiting Condition for Operation 3.0.4, and is reporting this event as an operation or condition prohibited by plant TS.
PLANT STATUS
- 2. DOCKET NUMBER
- 3.
LER NUMBER 05000-298 YEAR 2024 SEQUENTIAL NUMBER 007 REV NO.
00 Cooper Nuclear Station (CNS) was in Mode 1, Power Operation, at 18 percent power at the time of the event on November 3, 2024.
BACKGROUND The pressure relief system includes three American Society of Mechanical Engineers (ASME) code safety valves (SV) [EIIS: SB] and eight safety relief valves (SRV) [EIIS: RV], all of which are located on the main steam lines [EIIS: SB] within the drywell [EIIS: NH], between the reactor vessel [EIIS: RPV] and the first main steam isolation valve [EIIS: ISV]. The SVs provide protection against over pressurization of the nuclear system and discharge directly into the interior space of the drywell. The SRVs discharge to the suppression pool and provide three main functions: overpressure relief operation to limit the pressure rise and prevent safety valve opening, overpressure safety operation to prevent nuclear system over pressurization, and depressurization operation (opened automatically or manually) as part of the emergency core cooling system [EIIS: BJ, BM, BO].
Each SRV is equipped with a pressure switch mounted in its discharge tailpipe. When a SRVs associated discharge pressure switch senses tailpipe pressure of at least 30 psig, the SRV can be determined to be in the OPEN position. When the pressure switch is actuated at 30 psig, an amber indicating light will illuminate in the Control Room and the annunciator for the relief valve will alarm, indicating the SRV is open.
EVENT DESCRIPTION
On November 3, 2024, while performing scheduled surveillance testing of the eight Safety Relief Valves (SRV) during plant start-up activities from Refueling Outage (RE33), pressure switch (MS-PS-300B) did not actuate when SRV71 B was taken to the OPEN position. SRV71 B tailpipe temperature did immediately rise, however, the temperature was approximately 100 degrees Fahrenheit lower than expected for a fully open SRV and the temperature profile exhibited erratic behavior. The main turbine bypass valve position responded as expected, confirming SRV71 B did fully open. As such, MS-PS-300A was declared inoperable on November 3, 2024.
As a result of the low temperatures on the SRV71 B tailpipe, questions arose regarding the possibility of a disconnected flex hose that extends from the SRV71 B tailpipe to MS-PS-300B. SRV71 B was not cycled open prior to RE33 and was not subjected to abnormal operating conditions that would have induced a vibration or fatigue failure of the flex hose. A picture taken near the area of SRV71 B on October 16, 2024, was reviewed and it was discovered that the flex hose may have been inadvertently disconnected.
Maintenance personnel were dispatched to SRV71 B and confirmed that the flex hose was disconnected and was laying on top of the SRV71 B tailpipe. The threaded connections of the flex hose and the connection port on the SRV71 B tailpipe were found damaged. Page 2 of 3 (04-02-2024)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nureqs/staff/sr1022/r3/}
- 3.
LER NUMBER Cooper Nuclear Station YEAR SEQUENTIAL NUMBER 05000-298 2024 007 MS-PS-3008 was repaired, surveillance testing was performed satisfactorily, and MS-PS-3008 declared operational on November 4, 2024.
BASIS FOR REPORT REV NO.
00 The damaged flex hose existed prior to the change from Mode 4, Cold Shutdown, to Mode 2, Startup, as evidenced by the picture taken on October 16, 2024. As such, CNS is reporting this event as an operation or condition which was prohibited by plant TS per 10 CFR 50. 73(a)(2)(i)(B). CNS made the change from Mode 4 to Mode 2 while this condition existed, violating Technical Speciation (TS) Limiting Condition for Operation 3.0.4, and is reporting this event as an operation or condition prohibited by plant TS.
SAFETY SIGNIFICANCE
Each SRV is equipped with a pressure switch mounted on its discharge tailpipe. Each SRV can be determined to be open (in part) when its associated discharge pressure switch senses tailpipe pressure of at least 30 psig.
Following pressure switch actuation (30 psig), an amber indicating light will illuminate and an annunciator will alarm, indicating the SRV has opened. Although this condition prevented the Control Room to receive the OPEN indication, it would not have prevented the ability to open SRV71 B to perform its safety function to prevent reactor vessel over pressurization. This is considered an isolated incident; the station risk of recurrence of the equipment failure is minimal.
CAUSES
The direct cause of the failed SRV surveillance test was caused by a damaged and separated flex hose extending from the SRV71 B tailpipe to MS-PS-3008.
The cause, date, and time of the flex hose becoming damaged and separated from SRV71 B is unknown, as there is no documentation of potential damage to the equipment in the area. Historical data revealed that surveillance testing performed in November 2022 following RE32 demonstrated that MS-PS-3008 was not damaged during RE32 and was operable during Operating Cycle 33. Additionally, SRV71 B was not cycled OPEN during Operating Cycle 33, eliminating the possibility that the flex hose damaged occurred prior to RE33.
CORRECTIVE ACTIONS
The flex hose and SRV71 B tailpipe connection port were repaired, and subsequent surveillance testing performed satisfactorily. An extent of condition review was performed with no additional common mode failure implications identified.
PREVIOUS EVENTS A review of CNS licensee event reports for the last three years was performed. There were no previous occurrences involvin a similar failure to that discussed in this report. Page 3 of 3