05000298/LER-2021-003, Re Failure of High Pressure Coolant Injection Flow Indicating Switch Results in Condition Prohibited by Technical Specifications
| ML21361A084 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 12/27/2021 |
| From: | Dent J Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2021068 LER 2021-003-00 | |
| Download: ML21361A084 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982021003R00 - NRC Website | |
text
H Nebraska Public Power District NLS2021068 December 27, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 "Always there when you need us" Subject: Licensee Event Report No. 2021-003-00 10 CFR 50.73 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2021-003-00.
There are no regulatory commitments contained in this letter.
Sincerely, J(ttnl,I 0,'t-- fvvp:,"v--B-NJ ~****
John Dent, Jr.
Vice President and Chief Nuclear Officer
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Attachment:
Licensee Event Report 2021-003-00 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 October 28, 2021, the High Pressure Coolant Injection (HPCI) Flow Indicating Switch (FIS) (HPCI-FIS-78) failed to trip prior to exceeding the Technical Specification Limiting Condition for Operation 3.3.5.1 (Emergency Core Cooling System (ECCS) Instrumentation) Function 3.f (HPCI Pump Discharge Flow-Low (Bypass)) during the performance of the surveillance procedure.
The cause of the failure was determined to be a shift in setpoint due to the initial over-range conditions experienced on September 14, 2021, by a new FIS that had been installed on July 27, 2021. The initial shift in setpoint due to over-range operation is a previously unpublished characteristic of Barton 289A switches, not identified in any Vendor literature or Industry Operating Experience.
The As Found trip value would not have prevented the HPCI pump from performing its required functions. There was not an impact on nuclear safety, plant reliability, radiological safety, or industrial safety. Corrective actions completed were HPCI-FIS-78 was calibrated within As Left Tolerance (ALT), followed by the application of an over-range pressure equivalent to HPCI full flow for 45 minutes, and then tested once again and found to be within ALT. The remaining corrective actions are to revise the associated Vendor Manual and Maintenance procedure with respect to initial set-up for switches used in over-range applications.
PLANT STATUS Cooper Nuclear Station (CNS) was in Mode 1, Power Operation, at 100 percent power, when the event was discovered; i.e., October 28, 2021. No other equipment was inoperable or non-functional that contributed to this event.
BACKGROUND Technical Specifications Bases for Limiting Condition for Operation (LCO) 3.3.5.1 (Emergency Core Cooling System (ECCS) Instrumentation), Function 3.f (High Pressure Coolant Injection (HPCI) Pump Discharge Flow-Low (Bypass)) states that the HPCI [EIIS: BJ] minimum flow instrument [EIIS: PDS] is provided to protect the HPCI pump [EIIS: P] from overheating when the pump is operated at reduced flow. The HPCI minimum flow line valve [EIIS: V] is opened when low flow is sensed and either 1) the pump is on, or 2) the system has initiated; and the valve is automatically closed when the flow rate is adequate to protect the pump.
One Flow Switch (i.e., HPCI-FIS-78) [EIIS: BJ, PDS] is used to detect the HPCI Pump flow rate. HPCI-FIS-78 contains two internal switches that provide open and close permissive signals to the HPCI minimum flow (bypass) valve. On low system flow, HPCI-FIS-78 Switch #1 provides the low flow permissive signal to open the HPCI minimum flow (bypass) valve to protect the HPCI pump from overheating (Function 3.f: Allowable Value (AV) >/= 490 gpm). The AV is established high enough to ensure that the HPCI pump flow rate is sufficient to protect the pump.
Once system flow is adequate to protect the pump, HPCI-FIS-78 Switch #2 provides a permissive signal to close the HPCI minimum flow (bypass) valve. The HPCI minimum flow (bypass) valve is required to close to achieve the Technical Specification required ECCS injection flow for HPCI (>/= 4250 gpm), but is not required to close to achieve the ECCS flow assumed [EIIS: BJ] in the analyzed transients that require HPCI injection
(>/= 3825 gpm). Therefore, this instrument does not have a Technical Specifications AV associated with the HPCI minimum flow (bypass) valve closure.
EVENT DESCRIPTION
HPCI-FIS-78 was replaced on July 27, 2021, with a new Barton 289A Flow Indicating Switch (FIS) and was satisfactorily calibrated using station procedures. Then, on September 14, 2021, a surveillance procedure was performed to test the HPCI pump to ensure that it can produce its Technical Specifications required flow of>/= 4250 gpm. However, the surveillance procedure did not functionally test HPCI-FIS-78.
On October 28, 2021, at 12:08 Central Time, with the plant operating at 100% Power in Mode 1, the HPCI-FIS-78 Switch #1 failed to trip prior to exceeding the Technical Specifications LCO 3.3.5.1 Function 3.f, AV of>/= 490 gpm during the performance of the calibration procedure for HPCI-FIS-78.
HPCI-FIS-78 Switch #1 tripped at 473.5 gpm decreasing. Page 2 of 4 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER YEAR Cooper Nuclear Station 05000- 298 SEQUENTIAL NUMBER REV NO.
2021 003 On October 29, 2021, the vendor for the Barton 289A FIS (Cameron) was contacted to discuss the excessive shift in setpoint. The Cameron Engineering Manager determined that since this FIS is installed in an application where it would be over-ranged in one direction during normal operation, the FIS would experience a shift in the setpoint the first time the FIS was over-ranged due to the bellows in the Differential Pressure Unit (DPU) taking an inelastic set. The vendor went on to state that once the DPU bellows were set, the setpoint performance would be expected to be stable.
On October 29, 2021, HPCI-FIS-78 was calibrated satisfactorily, and then on October 31, 2021, HPCI-FIS-78 additional testing was performed to verify setpoint stability. This testing verified that Switch
- 1 of HPCI-FIS-78 was initially within As Found Tolerance (AFT), and then the FIS was subjected to an over-range pressure equivalent to rated HPCI pump flow (4250 gpm) for a minimum of 45 minutes to simulate normal operating conditions. After the simulation of normal over-range conditions, the calibration of the FIS was then tested again. HPCI-FIS-78 Switches #1 and #2 were both found to be within As Left Tolerance (ALT) limits, and HPCI-FIS-78 was declared Operable.
BASIS FOR REPORT 00 CNS is reporting this event as an operation or condition prohibited by plant TS per 10 CFR 50. 73(a)(2)(i)(B),
and also as a condition that could have prevented fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident as defined under 10 CFR 50. 73(a)(2)(v)(D).
An engineering review was performed for Loss of Safety Function and it documented that the HPCI-FIS-78 Switch #1 As Found trip value of 473.5 gpm would not have prevented fulfillment of the safety function of the HPCI system. The evaluation determined that this As Found trip value would not be expected to cause any change in HPCI system performance or cause damage to the HPCI pump.
Based on the engineering review, this event will not be counted as a Safety System Functional Failure for the Nuclear Regulatory Commission performance indicator since no actual loss of safety function occurred.
SAFETY SIGNIFICANCE
The condition was non-consequential. The As Found trip value of 4 73.5 gpm would not have prevented the HPCI pump from performing its required functions. There was not an impact on nuclear safety, plant reliability, radiological safety, or industrial safety.
CAUSE
The cause of the failure was determined to be a shift in setpoint due to the initial over-range experienced by the newly installed FIS during HPCI pump testing on September 14, 2021. HPCI-FIS-78 is a Barton 289A FIS with a calibrated range of O - 1000 gpm and a maximum allowable working pressure of 3000 psi. The HPCI system is designed to have a flow of>/= 4250 gpm, which results in the FIS being over-ranged every time the HPCI pump is operated, but maintaining the pressure well below the maximum allowable working pressure of 3000 psi. Page 3 of 4 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/readinq-rm/doc-collections/nureqs/staff /sr1 022/r3/)
- 3. LER NUMBER YEAR Cooper Nuclear Station 05000- 298 2021 SEQUENTIAL NUMBER
- - 003 REV NO.
00 The initial shift in setpoint due to over-range operation is a previously unpublished characteristic of Barton switches that has not been identified in any Vendor literature or Industry Operating Experience.
CORRECTIVE ACTIONS
HPCI-FIS-78 was calibrated within ALT, followed by the application of an over-range pressure equivalent to HPCI full flow for 45 minutes, and then tested once again and was found to be within ALT. This testing confirmed that both switches tripped within ALT limits and the switches had not been affected by the over-range conditions, confirming that the subsequent over-range did not affect setpoint performance.
The remaining corrective actions have been entered into CNS's corrective action program:
- 1. Revise Instrument and Control procedure for calibrating Barton Differential Pressure Indicating Switches to add steps to over-range new instruments during setup if the instrument is normally over-ranged during service.
- 2. Update Barton 289A vendor manual (VM 1733) with information received from Cameron describing the initial over-range effect on the setpoint.
PREVIOUS EVENTS None. Page 4 of 4