ML24318C508

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Condition Prohibited by Technical Specifications
ML24318C508
Person / Time
Site: South Texas STP Nuclear Operating Company icon.png
Issue date: 11/13/2024
From: Tomlinson J
NRC Region 4
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
STI 35669765 LER 2024-005-00
Download: ML24318C508 (1)
v • d • e


Text

November 13, 2024 NOC-AE-24004079 10 CFR 50.73 STI: 35669765 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 2024-005-00 Condition Prohibited by Technical Specifications Pursuant to reporting requirements in 10 CFR 50.73(a)(2)(i)(B), STP Nuclear Operating Company (STPNOC) hereby submits the attached South Texas Project (STP) Unit 1 Licensee Event Report 2024-005-00.

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

There are no commitments in this letter.

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

Enclosure:

Unit 1 LER 2024-005-00, Condition Prohibited by Technical Specifications 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: 2024.11.13 15:11:20 -06'00'

NOC-AE-24004079 Enclosure Enclosure Unit 1 LER 24-005-00 Unit 1 LER 2024-005-00, Condition Prohibited by Technical Specifications

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 n

00498 5

Condition Prohibited by Technical Specifications 09 16 2024 2024 005 00 11 13 2024 1

100%

4 Zachary Dibbern, Licensing Engineer 361-972-4336 A

AB TE R135 Yes 4

It was discovered on September 16, 2024, that a temperature channel for the Reactor Trip System instrumentation was not reading the expected value. The temperature channel was then declared inoperable and was recalibrated with corrected data. The channel was declared Operable on September 18, 2024. It was later discovered that the associated Reactor Coolant System Loop Temperature Channel had been incorrectly calibrated on September 9, 2024, and therefore the temperature channel was inoperable for greater than the Technical Specification Allowed Outage Time. The cause of the condition was the use of normalized data instead of raw data when calculating the new slope and offset. Corrective actions include:

(1) correction of the slope and offset for the temperature element and (2) revision of the slope and offset adjustment guidance.

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 10 CFR 50.73(a)(2)(i)(B) as a condition that was prohibited by the Plants Technical Specifications (TS). The following Technical Specification Limiting Conditions for Operation (LCOs) were not met, and the required TS Actions were not met:

TS 3.3.1, Reactor Trip System Instrumentation, As a minimum, the Reactor Trip System instrumentation channels and interlocks of Table 3.3-1 shall be OPERABLE with RESPONSE TIMES as shown in Chapter 16 in the Updated Final Safety Analysis Report (UFSAR).

TS 3.3.2, Engineered Safety Features Actuation System Instrumentation, The Engineered Safety Features Actuation System (ESFAS) instruments channels and interlocks shown in Table 3.3-3 shall be OPERABLE with their Trip Setpoints set consistent with the values shown in the Trip Setpoint column of table 3.3.-4 and with RESPONSE TIMES as shown in Chapter 16 in the UFSAR.

The Reactor Coolant System (RCS) temperature element B1RCTE0430Z channels for Delta Temperature and Average Temperature were inoperable longer than the allowed outage time without taking the required actions. Consequently, Unit 1 was in a condition prohibited by Technical Specifications.

B. Plant Operating Conditions Prior to Event Prior to the event on September 16, 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 are Central Daylight Time) 09/09/24 (1311) - Commenced the Delta T and T Average Analog Channel Operation Test (ACOT) per WAN 701459 Calibrate B1RCTE0430Z with New Slope and Offset for Loop 3. Declared Loop 3 Delta T and T Average Channel inoperable for testing. Entered TS 3.3.1 Items 8 Over Temperature Delta Temperature (OTDT) and 9 Overpower Delta Temperature (OPDT) and Action 6, and TS 3.3.2 Item 5.f. and Action 20. Actions dictate that with the number of OPERABLE channels one less than the Total Number of Channels, STARTUP and/or POWER OPERATION may proceed provide the following conditions are satisfied: For Functional Units with installed bypass test capability, the inoperable channel may be placed in bypass, and must be placed in the tripped condition within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Note: A channel may be bypassed for up to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> for surveillance testing per specification 4.3.1.1/4.3.2.1, provided no more than one channel is in bypass at any time.

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South Texas Unit 1 00498 2024 005 00 n

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 09/09/24 (1630) - Completed Satisfactory the Delta T and T Average ACOT per WAN 701459. Declared Loop 3 the Delta T and T Average OPERABLE following testing and satisfactory channel check. Exited TS 3.3.1 and 3.3.2. [This was after calibrating with the incorrect new slope and offset and would have still been inoperable]

09/16/24 (0800) - Declared Loop C Delta T and T Average inoperable due to RCS Loop 3 Delta T found out of Tolerance. Entered LCO 3.3.1 Items 8 OTDT and 9 OPDT and Action 6, and TS 3.3.2 Item 5.f. and Action 20.

09/18/24 (0202) - Completed Delta T and T Average ACOT per WAN 701459 to Calibrate B1RCTE0430Z with New Slope and Offset with corrected values for Loop 3. Loop 3 Delta T and T Average channel remains inoperable pending further testing.

09/18/24 (1200) - Completed review of WAN 701459 satisfactory. All surveillance testing has been completed satisfactory. Declared Loop C / Loop 3 Delta T and T Average Operable. Exited associated LCO 3.3.2 and 3.3.1 Actions.

E. Method of Discovery The discovery of the inoperable channel of temperature element B1RCTE0430Z was self-revealing when it was found that RCS Delta-T Loop 3 power indication point was reading lower than normal and out of band during a weekly channels check on September 16, 2024.

II. Component Failures A. Failure Mode, Mechanism, and Effect of Failed Components Prior to September 9, 2024, at 1311, the Loop 3 Delta T and T Average channel for temperature element B1RCTE0430Z was OPERABLE. Loop 3 Delta T and T Average channel for B1RCTE0430Z was declared inoperable at that time to calibrate with new slope and offset values. The new slope and offset values were incorrectly calculated; and as a result, the power indication point read around 97.2% when expected to read around 100% on September 16, 2024. Therefore, the channel was outside the tolerance and inoperable since September 9, 2024. The mechanism of failure was due to using Mode 3 temperature-corrected cross-calibration data of resistance values to calculate the new slope and offset values, which is acceptable for cross-calibration activities but is not suitable for design purposes. The temperature-corrected data is normalized in a spreadsheet to correct differences between resistance values, and in this case because the adjustment was greater than three degrees Fahrenheit (F) the calculated slope and offset values were amplified and resulted in exceeding administrative and technical specification limits in TS Table 2.2-1. The effect of the failed temperature element is that the number of OPERABLE channels was one less than the total number of four channels, and would have required compensatory Actions per TS Tables 3.3-1 and 3.3-1. However, the TS Minimum Channels Operable requirement of three channels OPERABLE would have still been met.

B. Cause of Component Failure There was no material condition associated with temperature element B1RCTE0430Z; the calibration of the temperature element B1RCTE0430Z was completed with miscalculated new slope and offset values. The miscalculation was the result of using temperature-corrected data that was normalized in a spreadsheet instead of using the raw data of actual resistance values.

3 5

South Texas Unit 1 00498 2024 005 00 n

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 C. Systems or Secondary Functions That Were Affected by the Failure of Components with Multiple Functions The inoperability of the Delta T and T Average channels reduced the total number of OPERABLE channels from four to three. There were no other systems or secondary functions affected.

D. Failed Component Information There was no component failure.

System: Reactor Coolant System (AB)

Component: Element, Temperature (TE)

Manufacturer: RDF Corp (R135)

Model: 21232-1 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 The temperature element B1RCTE0430Z was determined to be inoperable from 1311, September 9, 2024, to 1200, September 18, 2024, when the temperature element was declared OPERABLE following updating of slope and offset values. This was a total time of 8 days, 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br />, and 49 minutes.

C. Safety Consequences and Implications A risk evaluation was performed to estimate the Incremental Core Damage Probability (ICDP) associated with this event.

The calculated ICDP from the inoperability of RCS Loop 3 Delta T and T Average was determined to be a very small change in risk and is of very low safety significance. 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 The cause of the event was the calibration of the temperature element B1RCTE0430Z with new slope and offset values that were miscalculated using temperature-corrected data that was normalized in a spreadsheet instead of using the raw data for actual resistance values.

V. Corrective Actions On September 18, 2024, the corrected slope and offset values for temperature element B1RCTE0430Z were used to re-calibrate the temperature element and then declare the Delta T and T Average Channel OPERABLE following testing.

The slope and offset adjustment guidance will be reviewed and updated to ensure raw data is used for design adjustments, with clear guidance on the appropriate use of the cross-calibration data.

4 5

South Texas Unit 1 00498 2024 005 00 n

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 VI. Previous Similar Events There were no previous recent similar events identified.

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South Texas Unit 1 00498 2024 005 00 n

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