ML24130A271

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Re Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function
ML24130A271
Person / Time
Site: South Texas 
Issue date: 05/09/2024
From: Tomlinson J
South Texas
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
NOC-AE-24004040 ler 2024-002-00
Download: ML24130A271 (1)
v • d • e


Text

May 9, 2024 NOC-AE-24004040 10 CFR 50.73 STI: 35595184 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 2024-002-00 Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function Pursuant to reporting requirements in 10 CFR 50.73(a)(2)(v)(D), STP Nuclear Operating Company (STPNOC) hereby submits the attached South Texas Project (STP) Unit 1 Licensee Event Report 2024-002-00. A causal investigation is ongoing. Once completed, a supplement to this LER will be provided.

The event did not have an adverse effect on the health and safety of the public.

There are no commitments in this submittal.

If there are any questions regarding this submittal, please contact Zachary Dibbern at 361-972-4336 or me at 361-972-8945.

Jason R. Tomlinson Site Vice President

Attachment:

Unit 1 LER 2024-002-00, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function cc:

Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511 Jason R Tomlinson Digitally signed by Jason R Tomlinson Date: 2024.05.09 17:00:02 -05'00'

NOC-AE-24004040 Attachment Attachment Unit 1 LER 24-002-00 Unit 1 LER 2024-002-00, Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function

NRC FORM 366 (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

(See Page 2 for required number of digits/characters for each block)

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

1. Facility Name 052 050
2. Docket Number
3. Page 1 OF
4. Title
5. Event Date Month Day Year
6. LER Number Year Sequential Number Revision No.
7. Report Date Month Day Year
8. Other Facilities Involved Facility Name Facility Name Docket Number Docket Number
9. Operating Mode
10. Power Level 050 052
11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 10 CFR Part 20 20.2201(b) 20.2201(d) 20.2203(a)(1) 20.2203(a)(2)(i) 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(2)(v) 20.2203(a)(2)(vi) 20.2203(a)(3)(i) 20.2203(a)(3)(ii) 20.2203(a)(4) 10 CFR Part 21 21.2(c) 10 CFR Part 50 50.36(c)(1)(i)(A) 50.36(c)(1)(ii)(A) 50.36(c)(2) 50.46(a)(3)(ii) 50.69(g) 50.73(a)(2)(i)(A) 50.73(a)(2)(i)(B) 50.73(a)(2)(i)(C) 50.73(a)(2)(ii)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(iii) 50.73(a)(2)(iv)(A) 50.73(a)(2)(v)(A) 50.73(a)(2)(v)(B) 50.73(a)(2)(v)(C) 50.73(a)(2)(v)(D) 50.73(a)(2)(vii) 50.73(a)(2)(viii)(A) 50.73(a)(2)(viii)(B) 50.73(a)(2)(ix)(A) 50.73(a)(2)(x) 10 CFR Part 73 73.77(a)(1) 73.77(a)(2)(i) 73.77(a)(2)(ii) 73.1200(a) 73.1200(b) 73.1200(c) 73.1200(d) 73.1200(e) 73.1200(f) 73.1200(g) 73.1200(h)

OTHER (Specify here, in abstract, or NRC 366A).

12. Licensee Contact for this LER Licensee Contact Phone Number (Include area code)
13. Complete One Line for each Component Failure Described in this Report Cause System Component Manufacturer Reportable to IRIS Cause System Component Manufacturer Reportable to IRIS
14. Supplemental Report Expected Yes (If yes, complete 15. Expected Submission Date)

No

15. Expected Submission Date Month Day Year
16. Abstract (Limit to 1326 spaces, i.e., approximately 13 single-spaced typewritten lines)

South Texas Unit 1 I

00498 5

Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function 03 10 2024 2024 002 00 05 09 2024 1

100



Zachary Dibbern / Licensing Engineer 361-972-4336 BI PSP S280 Y

X KM CHU Y018 Y



06 27 2024 On 03/09/24 at 2126 CST train 'C' Essential Cooling Water and cascading equipment were declared inoperable due to a through-wall leak on Essential Cooling Water Pump 1C discharge vent line. On 03/10/24 at 0353 CDT, train 'B' Essential Chilled Water and cascading equipment were declared inoperable due to chilled water outlet temperature exceeding limits. This condition resulted in an inoperable condition on two out of the three safety trains for the accident mitigation function. This condition was determined reportable per 10 CFR 50.73(a)(2)(v)(D). Essential Cooling Water 'C' train inoperability was due to vent line wall thinning causing a through-wall leak. Causal evaluation is ongoing and when it is complete this LER will be supplemented. The Essential Chilled Water 'B' train inoperability cause was indeterminate. Corrective and preventative actions include (1) Essential Cooling Water 'C' was repaired and further corrective actions will be determined once the causal evaluation is complete, and (2) installation of temporary additional monitoring capabilities for Essential Chiller 12B in case the event repeats itself.

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

NARRATIVE NRC FORM 366A (04-02-2024)

Page of

1. FACILITY NAME
2. DOCKET NUMBER
3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 I. Description of Event A. Reportable Event Classification This event is reportable per 50.73(a)(2)(v)(D) as a condition that could have prevented fulfillment of a safety function of structures or systems that are needed to: mitigate the consequences of a accident.

B. Plant Operating Conditions Prior to Event Prior to the event on March 10, 2024, 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 have been converted to Central Standard Time) 03/09/24 (2126) - Train 'C' Essential Cooling Water and supported equipment was declared inoperable due to discovery of through-wall leakage on Essential Cooling Water Pump 1C discharge vent line.

03/09/24 (2151) - Trains 'A' and 'B' Essential Cooling Water Screen Wash Booster Pumps and Essential Cooling Water Pump 1A and 1B Traveling Screens were secured due to cross train operability.

03/09/24 (2253) - Started 'A' train CRE HVAC and Secured 'C' train CRE HVAC for chiller swaps.

03/10/24 (0221) - Started Essential Chill Water Pump 11B for equipment rotation.

03/10/24 (0223) - Started Essential Chiller 12B for equipment rotation.

03/10/24 (0253) - Train 'B' Essential Chiller and cascading equipment was declared inoperable due to outlet temperature exceeding limits.

03/10/24 (0340) - Train 'B' Essential Chiller and cascading equipment was declared operable following temperature adjustment performed per reference CR 24-2328.

03/10/24 (1005) - This event resulted in an inoperable condition on two out of the three safety trains for the accident mitigating function which could have prevented the fulfillment of a safety function, and was reported to NRC Headquarters Operations Officer. (Event Notification 57019) 2 5

South Texas Unit 1 00498 2024 002 00 I

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

NARRATIVE NRC FORM 366A (04-02-2024)

Page of

1. FACILITY NAME
2. DOCKET NUMBER
3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 E. Method of Discovery The discovery of the pinhole through-wall leak was self-revealing and was discovered during plant walkdown. The Chill Water temperature limit exceedance in Essential Chilled Water train 'B' was self-revealing.

II. Component Failures A. Failure Mode, Mechanism, and Effects of Failed Component On 03/09/24 at 2126, Essential Cooling Water Pump 1C was discovered to have a pinhole through-wall leak on the discharge vent line. 'C' train Essential Cooling Water and supported equipment was subsequently declared inoperable.

The mechanism of failure will be provided in an LER Supplement. The through-wall leak did not cause any immediate failures or trips, as the leak rate was small and the spray was not directed onto any safety-related equipment.

On 03/10/24 at 0253, the Essential Chiller 12B temperature control loop failed to operate properly, which resulted in the inability to maintain the leaving water temperature below the required maximum temperature. 'B' train Essential Chilled Water and supported equipment was subsequently declared inoperable.

B. Cause of Component or System Failure Essential Cooling Water Train 'C' Causal evaluation is ongoing and when it is complete this LER will be supplemented.

Essential Chilled Water Train 'B' As a result of the required Operator action to adjust the Essential Chiller 12B temperature controller, per plant procedure, the Chilled Water temperature returned to within limits and further causal analysis was deemed unwarranted. As a result, the cause of the higher than expected outlet temperature was indeterminate. Multiple possible scenarios for degradation or failure of components that could affect the Essential Chiller temperature control loop, previous operating experience (OE), and past events related to Chiller issues documented in the corrective actions were considered.

As part of the corrective actions after this event, STP installed digital chart recorders at all the Essential Chillers. The trend data collected on one occasion found that temperature sensor was performing erratically, and this in turn caused relay chattering at one of the relays inside the TCM to the point of permanent damage.

C. Systems or Secondary Functions That Were Affected by the Failure of Components with Multiple Functions Inoperability of Essential Cooling Water 1C due to through-wall leakage rendered C trains of the following systems inoperable: Engineered Safety Feature (ESF) Diesel Generator, Residual Heat Removal (RHR), Component Cooling Water (CCW), Containment Spray (CS), Reactor Containment Fan Coolers (RCFCs) Control Room Envelope(CRE)

HVAC, and Emergency Core Cooling System (ECCS). Inoperability of Essential Chiller 12B rendered B train of the following system inoperable: ECCS, CRE HVAC, CS, and Electrical Penetrations HVAC.

3 5

South Texas Unit 1 00498 2024 002 00 I

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

NARRATIVE NRC FORM 366A (04-02-2024)

Page of

1. FACILITY NAME
2. DOCKET NUMBER
3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 D. Failed Component Information System: Essential Cooling Water {BI}

Component: Pipe (Spool) {PSP}

Manufacturer: Southwest Fabricating and Welding Company {S280}

Model: 3-inch Schedule 40 Al-Brz Pipe System: Essential Chilled Water {KM}

Component: Chiller Unit {CHU}

Manufacturer: York Division of Borg - Warner {Y018}

Model:OTK5C1-IMCS-R11 III. Analysis of Event A. Safety System Responses that Occurred No safety systems responses occurred because of this event.

B. Duration of Safety System Inoperability Essential Chilled Water trains 'B' and 'C' were INOPERABLE from 0253, 03/10/2024, to 0340, 03/10/2024, when Essential Chilled Water train 'B' was declared OPERABLE. This was a total of 47 minutes.

C. Safety Consequences and Implications The accumulated incremental risk during this time period with two trains inoperable for Incremental Core Damage Probability (ICDP) and Incremental Large Early Release Probability (ILERP) are very low.

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 Essential Cooling Water 1C Causal evaluation is ongoing and when it is complete this LER will be supplemented.

Essential Chilled Water Train 'B' The cause of the Essential Chilled Water 'B' train inoperability was indeterminate.

4 5

South Texas Unit 1 00498 2024 002 00 I

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid OMB control number.

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

NARRATIVE NRC FORM 366A (04-02-2024)

Page of

1. FACILITY NAME
2. DOCKET NUMBER
3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050 V. Corrective Actions Essential Cooling Water 1C On 03/11/24, the Essential Cooling Water Pump 1C Discharge Vent Line was repaired. Further corrective actions to be determined once causal evaluation is complete.

Essential Chilled Water Train 'B' On 03/15/24, a temporary modification was developed and installed on Essential Chiller 12B to provide additional monitoring to aid in determining cause of failure in case the high outlet temperature event repeats.

VI. Previous Similar Events LER 2023-001-00, "Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function; dated January 15, 2024.

LER 2023-003-00, "Two Essential Chilled Water Trains Inoperable Resulting in a Condition That Could Have Prevented Fulfillment of a Safety Function;" dated January 9, 2024.

LER 2023-004-00, "Condition Prohibited by Technical Specifications Due to Inoperable Train of Essential Chilled Water;"

dated February 5, 2024.

5 5

South Texas Unit 1 00498 2024 002 00 I

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