05000298/LER-2022-002, Manual Core Spray Injection to Restore Skimmer Surge Tank Level
| ML22353A123 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 12/19/2022 |
| From: | Dia K Nebraska Public Power District (NPPD) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NLS2022051 LER 2022-002-00 | |
| Download: ML22353A123 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982022002R00 - NRC Website | |
text
Nebraska Public Power District "Always there when you need 11s" 10 CFR 50.73 NLS2022051 December 19, 2022 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Subject: Licensee Event Report No. 2022-002-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2022-002-00.
There are no regulatory commitments contained in this letter.
Sincerely, W?
Site Vice President
/bk
Attachment:
Licensee Event Report 2022-002-00 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.0. Box 98 I Brownville, NE 68321 http://www.nppd.com
Abstract
On October 22, 2022, during Refueling Outage 32, Operations personnel performed a pre-coat of the Fuel Pool Cooling (FPC) system B filter demineralizer. Following pre-coat, the FPC skimmer surge tank level began to rapidly decrease. This was due to valve FPC-AOV-A018B failing to fully close, thus providing a drain path to the Radwaste Waste Precoat tank. An attempt was made to isolate the drain path by closing another FPC valve, which was unsuccessful. Operations personnel then initiated Core Spray (CS) subsystem A injection to restore FPC skimmer surge tank level. Concurrently, valve team personnel manually closed FPC-AOV-A018B which isolated the drain path. CS-A flow was established, thus restoring the FPC skimmer surge tank to normal level.
After the event, the valve positioner for FPC-AOV-A018B, was replaced.
There was no impact on nuclear safety, plant reliability, radiological safety, or industrial safety.
This event was reported under Event Notification 5617 4 on October 22, 2022.
PLANT STATUS Cooper Nuclear Station was in Mode 5, Refueling, at O percent power at the time of the event on October 22, 2022. Residual Heat Removal (RHR) Shutdown Cooling (SOC) was not in service at the time of the event. Decay heat removal was provided by Fuel Pool Cooling (FPC) and Alternate Decay Heat Removal (ADHR) subsystem.
BACKGROUND 00 The FPC and Demineralizer system [EIIS: DA] removes decay heat released from the spent fuel assemblies and maintains a specified Spent Fuel Pool (SFP) water temperature, purity, water clarity, and water level.
The system consists of the original FPC and Demineralizer system and additional cooling capability from the ADHR subsystem.
The original FPC system consists of two parallel trains each consisting of a circulating pump [EIIS: P], heat exchanger [EIIS: HX], filter-demineralizer, and the required piping, valves [EIIS: V], and instrumentation.
The pumps circulate the pool water, taking suction from the skimmer surge tanks [EIIS: TK]. The ADHR subsystem includes a third FPC heat exchanger and two additional FPC pumps in parallel with the two existing parallel FPC trains. During refueling operations, the FPC system suction and discharge paths can be aligned to the reactor cavity.
In the event of low FPC skimmer surge tank level, the FPC pumps automatically trip which would result in a loss of decay heat removal from the SFP and Reactor Pressure Vessel cavity [EIIS: RPV].
Emergency Core Cooling System (ECCS) [EIIS: BJ, BM, BO] instrumentation initiates appropriate responses from the systems to ensure that the fuel is adequately cooled in the event of a design basis accident or transient. The ECCS is designed, in conjunction with Primary Containment [EIIS: NH] and Secondary Containment, to limit the release of radioactive materials to the environment following a Loss of Coolant Accident. On receipt of an initiation signal, ECCS pumps automatically start. Simultaneously, the system aligns, and the pumps inject water taken either from the Emergency Condensate [EIIS: SD] Storage Tanks or suppression pool into the Reactor Coolant System (RCS), and RCS pressure is overcome by the discharge pressure of the ECCS pumps.
The ECCS instrumentation actuates Core Spray (CS) [EIIS: BM]. The CS system may be initiated by either automatic or manual means and is composed of two independent subsystems. Each subsystem consists of motor-driven pumps, a spray sparger above the core, and piping and valves to transfer water from the suppression pool to the sparger. The CS system is designed to provide cooling to the reactor core when reactor pressure is low. Page 2 of 4 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 08/31/2023 EXPIRES:
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https:/lwww.nrc.gov/readinq-rmfdoc-collections/nureqs/staff/sr1022/r3/)
- 3. LER NUMBER YEAR Cooper Nuclear Station 05000-298 2022
EVENT DESCRIPTION
SEQUENTIAL NUMBER
- - 002 REV NO.
00 On October 22, 2022, during Refueling Outage 32, Operations personnel performed a pre-coat of the FPC system B filter demineralizer [EIIS: FDM] for restoration from Diesel Generator 2 (DG) [EIIS: EK] sequential load testing. Restoration of the FPC B filter demineralizer would allow placing a third FPC pump in service to provide additional margin for SFP decay heat removal, and to keep temperatures as low as possible for personnel working on the refuel floor. Station procedure requires that a FPC demineralizer be in service when three FPC pumps are in service.
At approximately 12:49, following B filter demineralizer pre-coat activities, the FPC skimmer surge tank level began to rapidly decrease. This was due to valve FPC-AOV-AO18B, filter demineralizer waste precoat return valve, failing to fully close, as required, thus providing a drain path from the FPC skimmer surge tank to the Radwaste Waste Precoat tank. An attempt was made to isolate the drain path by closing another FPC valve, which was unsuccessful.
At 12:56, Operations personnel manually initiated CS subsystem A injection into the RPV to prevent tripping of the FPC pumps on low surge tank level. CS flow was established at approximately 3700 gallons per minute to restore FPC skimmer surge tank level and was secured at 12:59. Skimmer surge tank level had decreased to approximately 14.6% of tank inventory before normal level was restored. Concurrently, valve team personnel manually closed FPC-AOV-AO18B, which successfully isolated the drain path.
At the time of this event, decay heat removal was provided by FPC because RHR SOC was not in service due to performance of DG-2 sequential load testing. Operations made the determination to not return SOC to service after completion of the DG sequential load test as restoration would have taken several hours followed immediately by its removal from service again for a surveillance scheduled the following shift.
After the event, the valve positioner for FPC-AOV-AO18B was replaced. There was no evidence found that the positioner had been replaced prior to this failure.
BASIS FOR REPORT This event is reportable under 10 CFR 50. 73(a)(2)(iv)(A) - Any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50. 73(a)(2)(iv)(B); specifically, (a)(2)(iv)(B)(4)- ECCS for boiling water reactors including high-pressure and low-pressure core spray systems, high-pressure coolant injection system, and low-pressure injection function of the residual heat removal system.
This event was also reported under Event Notification 56174 on October 22, 2022. Page 3 of 4 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 08/31/2023 EXPIRES:
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https:/lwww.nrc.govlreading-rm/doc-collections/nuregs/stafflsr1022/t3/)
- 3. LER NUMBER YEAR Cooper Nuclear Station 05000- 298 2022
SAFETY SIGNIFICANCE
SEQUENTIAL NUMBER
- - 002 REV NO.
00 This event was non-consequential. With the RPV water level flooded to the refuel floor, and fuel pool gates removed, water level would not have lowered below the FPC surge tank skimmers. Decay heat from the SFP and RPV was maintained throughout the skimmer surge tank level transient, and the A and D FPC pumps remained in service. Following the CS-A injection, FPC and Reactor Water Clean Up [EIIS: CE] filter demineralizers restored reactor vessel water clarity.
There was no impact on nuclear safety, plant reliability, radiological safety, or industrial safety.
CAUSE
The direct cause of this event was the failure of FPC-AOV-AO18B to close following pre-coat operations of the FPC system B filter demineralizer.
The causal factor was an ineffective maintenance strategy for FPC system components whose failure could impact decay heat removal.
CORRECTIVE ACTIONS
The valve positioner was replaced, and the top of the reactor core was inspected to verify no material from CS injection was present.
Maintenance Plans for replacement of valve positioners FPC-CVP-AO18A and FPC-CVP-AO188 will be created.
Risk elimination actions for single component failures introduced during different plant configurations, with respect to the FPC system, will be re-evaluated. Results of this re-evaluation will be presented to the station's Plant Health Committee.
PREVIOUS EVENTS There have been no Licensee Event Reports submitted within the past 10 years regarding a valid actuation of ECCS systems. Page 4 of 4