05000446/LER-2024-002, Turbine Driven Auxiliary Feedwater Pump Unavailable Following Transition from Mode 4 to Mode 3
| ML25016A035 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 01/16/2025 |
| From: | Sewell S Vistra Operations Company |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| CP-202400458, TXX-24081 LER 2024-002-00 | |
| Download: ML25016A035 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4462024002R00 - NRC Website | |
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COMANCHE PEAK NUCLEAR POWER PLANT CP-202400458 TXX-24081 January 16, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Comanche Peak Nuclear Power Plant (CPNPP)
Docket No. 50-446 Steven K. Sewell Vice President Nuclear Site Vistra Operations Company LLC P.O. Box 1002 6322 North FM 56 Glen Rose, TX 76043 Office: 254.897.6113 Ref 1 0CFR50. 73 Turbine Driven Auxiliary Feedwater Pump Unavailable Following Transition from Mode 4 to Mode 3 Licensee Event Report 2-24-002-00
Dear Sir or Madam:
Attached is Licensee Event Report (LER) 2-24-002-00, "Turbine Driven Auxiliary Feedwater Pump Unavailable Following Transition from Mode 4 to Mode 3" for Comanche Peak Nuclear Power Plant (CPNPP) Unit 2.
This communication contains no new commitments regarding CPNPP Units 1 or 2.
Should you have any questions, please contact Kassie Mandrell at (254) 897-6987 or Kassie.Mandrell@vistracorp.com.
Sincerely, Steven Sewell (Jan 15, 2025 11:18 CST)
Steven K. Sewell
Attachment:
Abstract
On November 18, 2024, at 0830, the 2-01 turbine driven auxiliary feedwater (TDAFW) pump was found in an inoperable condition following a change from Mode 4 to Mode 3 that occured on 11/17/2024 at 1633. Operations personnel identified that the TDAFW remained uncoupled following maintenance during a Unit 2 refueling outage.
Auxiliary feedwater (AFW) is required by Technical Specification (TS) Limiting Condition for Operability (LCO) 3. 7.5 to be operable in Modes 1, 2 and 3 with no exception allowed by TS LCO 3.0.4 for mode changes when applicable conditions are not met. The TDAFW was returned to service on November 18, 2024 at 2051.
The cause analysis of this event is ongoing. Preliminary causes involve inaccurate communication of system status and unclear work instruction. Results of the completed analysis and associated corrective actions will be provided in a supplemental report.
I. DESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
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446
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002 This event is reportable under 10CFR50.73(a)(2)(i)(B). CPNPP did not meet LCO 3.0.4 during a mode change from Mode 4 to Mode 3 as it applies to LCO 3.7.5, for AFW operability.
B. PLANT CONDITION PRIOR TO EVENT Comanche Peak Nuclear Power Plant (CPNPP) Unit 2 was in MODE 4 during end of outage safety system restoration.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND CONTRIBUTED TO THE EVENT There were no structures, systems, or components that were inoperable prior to the event which contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES During a Unit 2 refueling outage in October 2024, Comanche Peak (CPNPP) performed scheduled maintenance of the turbine driven auxiliary feedwater (TDAFW) pump [EIIS:(BA)(P)]. Following the planned maintenance, the work group left the TDAFW pump in an uncoupled condition. The clearance task was inadvertently marked as "work complete" under the assumption that an uncoupled run would be performed, and workers signed off the the associated work orders. The work orders were then transferred from a Mode 3 restricted condition in the work control database to a Mode 2 restricted condition for post work testing (PWT).
On 11/17/2024, at 1633, CPNPP Unit 2 entered Mode 3. The following day at 0830, the uncoupled condition was identified by an Equipment Operator and was immediately reported to the Outage Control Center. Operations initiated a clearance to re-couple the pump and a 72-hour Limiting Condition of Operability (LCO) was entered for LCO 3.7.5 condition B for one auxiliary feedwater (AFW) [EIIS:(BA)] train inoperable. The pump was then re-coupled and the associated clearance was released. The required post work testing was completed and the AFW system returned to operable status on 11/18/2024 at 2051.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL PERSONNEL ERROR A Plant Equipment Operator discovered the uncoupled pump during walkdowns and notified the Operations Duty Manager in the Outage Control Center.
II. COMPONENT OR SYSTEM FAILURES A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE I
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- 3. LER NUMBER 10 SEQUENTIAL REV NUMBER NO.
446
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002 The 2-01 turbine driven auxiliary feedwater pump was left uncoupled following system maintenance. This condition rendered the TDAFW inoperable while operating in Mode 3. Preliminary causes involve inaccurate communication of system status and unclear work instruction. Results of the completed analysis and associated corrective actions will be provided in a supplemental report.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT Human performance errors and process weaknesses led to the inoperable status of the TDAFW pump.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS This event did not involve any additional systems or secondary functions which were affected by the TDAFW inoperability.
D. FAILED COMPONENT INFORMATION
The auxiliary feedwater system is comprised of two electric motor-driven auxiliary feedwater (MDAFW) pumps and associated valves, piping, and controls and a third turbine-driven auxiliary feedwater pump with associated valves, piping, and controls, which is independent of the electrical power supply to the motor-driven pumps. Three pumps are necessary to ensure an adequate supply of auxiliary feedwater following an accident, coincident with the single failure of a pump.
Each motor driven pump provides 100% of AFW flow capacity, and the turbine driven pump provides 200% of the required capacity to the steam generators, as assumed in the accident analysis. The turbine driven AFW pump supplies a common header capable of feeding all steam generators with normally open, DC powered, air operated control valves.
One pump at full flow is sufficient to remove decay heat and cool the unit to residual heat removal (RHR) entry conditions.
The AFW System actuates automatically on steam generator water level - low-low level. The system also actuates on loss of offsite power and on an Anticipated Transient without Scram (A TWS) Mitigation System Actuation Circuitry (AMSAC) signal; however, AMSAC start of the AFW pumps is not required for AFW system operability. The motor driven pumps also start on safety injection and trip of all MFW pumps. During low power plant operations, the AFW system, under manual control, is used to maintain SG water level.
Ill. ANALYSIS OF THE EVENT A. SAFETY SYSTEM RESPONSES THAT OCCURRED No safety system responses occurred due to this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY CPNPP entered Mode 3 on 11/17/2024 at 1633. The auxiliary feedwater system was later declared operable on 11/18/2024 at 2051. Total duration of inoperable condition, while in Mode 3, was approximately 29 hours3.356481e-4 days <br />0.00806 hours <br />4.794974e-5 weeks <br />1.10345e-5 months <br />. This is less than the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> completion time for LCO 3. 7.5 condition B.
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- 2. DOCKET NUMBER
- 3. LER NUMBER 10 SEQUENTIAL REV NUMBER NO.
446
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002 C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT The AFW System automatically supplies feedwater to the steam generators to remove decay heat from the Reactor Coolant System upon the loss of normal feedwater supply. The AFW system is composed of two motor driven and one steam driven pump configured into three trains. Each motor driven pump provides 100% of AFW flow capacity, and the turbine driven pump provides 200% of the required capacity to the steam generators, as assumed in the accident analysis.
Both MDAFW pumps were operable when mode 3 was entered and the TDAFW pump is the assumed single active failure in the accident analysis. Therefore, no safety system functional failure existed during the period of inoperability.
This event had no impact on nuclear safety, reactor safety, radiological safety, environmental safety or the safety of the public. These events have been evaluated as not meeting the definition of a safety system functional failure per 10 CFR 50.73(a)(2)(v). The TDAFW pump was returned to operable status in less time than the LCO 3.7.5 condition B, completion time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
IV. CAUSE OF THE EVENT
Preliminary causes involve inaccurate communication of system status and unclear work instruction. Results of the completed analysis and associated corrective actions will be provided in a supplemental report.
V. CORRECTIVE ACTIONS
Preliminary causes involve inaccurate communication of system status and unclear work instruction. Results of the completed analysis and associated corrective actions will be provided in a supplemental report.
VI. PREVIOUS SIMILAR EVENTS
There have been no recent similar events or conditions related to mode changes with inoperable equipment at CPNPP. Page 4
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