05000498/LER-2023-004-01, Condition Prohibited by Technical Specifications Due to Inoperable Train of Essential Chilled Water
| ML24116A317 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/25/2024 |
| From: | Tomlinson J South Texas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NOC-AE-24004030, 35580872 LER 2023-004-01 | |
| Download: ML24116A317 (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 |
| 4982023004R01 - NRC Website | |
text
NOC-AE-24004030 Attachment
Attachment
LER 2023 -004-01
Supplement to Condition Prohibited by Technical Specifications Due to Inoperable Train of Essential Chilled Water
Abstract
On 11/20/23 at 1530 Essential Chiller 12C was declared OPERABLE following maintenance. The following day at 1245, Train 'C' Essential Chilled Water System (EChWS) was declared inoperable due to excessive chilled water leakage. A subsequent Engineering evaluation determined that due to the leakage, Train 'C' EChWS should be considered inoperable from the date and time the 12C Essential Chiller was restored from maintenance and declared OPERABLE. With only two EChWS loops OPERABLE, Technical Specification (TS) 3.7.14 Action a requires restoration of the inoperable loop within 7 days or application of the Configuration Risk Management Program (CRMP), or to be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The Engineering evaluation determined that Train 'C' EChWS was inoperable without any of the required TS actions taken from 1530 on 11/20/23 to 1245 on 11/28/23 when the CRMP was entered. This is a total of 189 hours0.00219 days <br />0.0525 hours <br />3.125e-4 weeks <br />7.19145e-5 months <br /> and 15 minutes which exceeds the 174 hours0.00201 days <br />0.0483 hours <br />2.876984e-4 weeks <br />6.6207e-5 months <br /> (7 days plus 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />) allowed by the TS. Therefore, this event is reportable under 10 CFR 50.73(a)(2)(i)(B) as a condition which is prohibited by the plant's TS.
I. Description of Event
A.Reportable Event Classification On 11/11/23 a condition report identified Train C Essential Chilled Water Expansion Tank level lowering over the past three months to the low-level alarm setpoint. Subsequent maintenance was performed from 11/14/23 to 11/20/23. On 11/20/23 at 1530 Essential Chiller 12C was declared OPERABLE following maintenance. The following day, 11/21/23 at 1245, Train 'C' Essential Chilled Water was declared inoperable due to excessive chilled water leakage. An Engineering evaluation was requested and it was completed on 12/7/2023. The evaluation determined that due to the excessive chilled water leakage, Train 'C' Essential Chilled Water should be considered to have been inoperable from the date and time (11/20/23 at 1530) the 12C Essential Chiller was restored from maintenance and declared OPERABLE until 12/3/23 at 2254. Technical Specification 3.7.14 Action a requires implementation of the following actions with only two Essential Chilled Water System loops OPERABLE: within 7 days restore at least three loops to OPERABLE status or apply the requirements of the Configuration Risk Management Program (CRMP), or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. It was determined that Train 'C' Essential Chilled Water was inoperable without any of the required Technical Specification actions taken from 1530 on 11/20/23 to 1245 on 11/28/23 when the CRMP was entered. This is a total time of 189 hours0.00219 days <br />0.0525 hours <br />3.125e-4 weeks <br />7.19145e-5 months <br /> and 15 minutes which exceeds the 174 hours0.00201 days <br />0.0483 hours <br />2.876984e-4 weeks <br />6.6207e-5 months <br /> (7 days plus 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />) allowed by Technical Specification. Therefore, this event was determined to be reportable under 10 CFR 50.73(a)(2)(i)(B) as a condition which is prohibited by the plants Technical Specifications. The event date for this LER is considered to be 11/27/23, which is the date that the Technical Specification Action statement allowed time (174 hours0.00201 days <br />0.0483 hours <br />2.876984e-4 weeks <br />6.6207e-5 months <br />) for the Essential Chilled Water System was exceeded. However, the event was not discovered until completion of the Engineering evaluation on 12/7/23. Therefore, the report date for this event i s 2/5/24 (60 days from the date of discovery).
B.Plant Operating Conditions Prior To Event Prior to the event on November 27, 2023, Unit 1 was in MODE 1 at 100% power.
C. Status Of Structures, Systems, and Components That Were Inoperable At the Start of the Event and That Contributed To the Event There were no inoperable Structures, Systems, or Components at the start of the event that contributed to the event.
D. Narrative Summary of the Event
Timeline (Note: All times are Central Standard Time)
11/10/23 (1413) - Essential Chilled Water 'C' train declared inoperable due to exceeding the maximum compressor discharge pressure.
11/17/23 (0642) - Entered CRMP.
11/20/23 (1530) - Essential Chilled Water C train declared OPERABLE following completion of maintenance and successful post-maintenance testing. Technical Specification 3.7.14 and CRMP exited.
11/21/23 (1245) - Essential Chilled Water C train declared inoperable due to excessive chilled water leakage.
11/28/23 (1245) - Entered CRMP.
12/03/23 (2254) - Essential Chilled Water C train declared OPERABLE, Technical Specification 3.7.14 and CRMP exited.
12/07/23 (1639) - Shift Manager concurrence that the event was reportable was obtained following completion of an Engineering evaluation which determined the excessive Essential Chilled Water 'C' train leakage would render the system incapable of meeting its safety-related function for a prolonged duration beginning with the time of completion of maintenance on 11/20/23 (1530).
E. Method of Discovery
The excessive chilled water leakage that led to the inoperability of Essential Chilled Water 'C' train was self-revealing.
Following Engineering evaluation, it was discovered that the Technical Specification Action statements for Essential Chilled Water were not met.
II. Component Failures
A.Failure Mode, Mechanism, and Effects of Failed Component Chilled water system leakage was found to have been at the chiller evaporator end bells. The condition report associated with this event discusses an unexpected trend of the Train C Essential Chilled Water Expansion Tank level lowering and more frequently refilling the tank to restore level for three months prior to this event. The Engineering evaluation for this event concluded that the leak rate occurring in the three months leading up to this event was within acceptable limits.
However, the leak rate increased significantly from 11/20/24 to 11/21/24. The Engineering evaluation of this increased leakage concluded that the leakage rendered the system incapable of meeting its safety-related function for a prolonged duration, beginning with the time after the maintenance ending on 11/20/23 at 1530 and recommended that the system be considered to have been inoperable from 11/20/23 at 1530 until 12/3/23 at 2254.
B.Cause of Component or System Failure The cause of the component failure was corrosion of the sealing surfaces of the tube sheet combined with the incorrect orientation of the end bell gasket (installed backwards).
C.Systems or Secondary Functions That Were Affected by the Failure of Components with Multiple Functions Inoperability of Essential Chilled Water 'C' train rendered the 'C' train of the following systems inoperable: High Head Safety Injection, Low Head Safety Injection, Containment Spray, Control Room Envelope HVAC.
D.Failed Component Information System: Chilled Water System {KM}
Component: Chiller Unit {CHU}
Manufacturer: York {Y018}
Model: OTK5C1-IMCS-R11
Ill. Analysis of Event
A. Safety System Responses that Occurred No safety system responses occurred because of this event.
B. Duration of Safety System lnoperability Essential Chilled Water Train 'C' was inoperable from 1530 on November 20, 2023, to 2254 on December 3, 2023. This was a total of 319 hours0.00369 days <br />0.0886 hours <br />5.274471e-4 weeks <br />1.213795e-4 months <br /> and 24 minutes.
C. Safety Consequences and Implications
A risk evaluatio n was performed to estimate the Incremental Core Damage Probability (ICDP) associated with this event.
The calculated ICDP is above the Non-Risk Significant threshold but below the Potentially Risk Significant threshold.
The event did not result in any offsite release of radioactivity or increase of offsite dose rates and there were no personnel injuries or damage to any other safety-related equipment associated with this event.
Therefore, there was no adverse effect on the health and safety of the public.
IV. Cause of Event
Station troubleshooting processes were not used to evaluate the inventory loss associated with Essential Chiller 12C.
V. Corrective Actions
- 1. Complete an evaluation on processes used by Operations, Engineering, and Maintenance to ensure the troubleshooting process is entered appropriately.
VI. Previous Similar Events
STP Nuclear Operating Company submitted two Licensee Event Reports in January 2024 associated with the Essential Chilled Water System. Unit 1 LER 2023-003-00 was submitted on 01/09/24 and Unit 2 LER 2023-001-00 was submitted on 01/15/24. Each event was reported under 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented fulfillment of a safety function which is a different reporting criteria than this event (10 CFR 50.73(a)(2)(i)(B)). STPNOC has performed additional evaluations to determine if any common causes exist between this event and the other two Essential Chilled Water System events.