05000498/LER-2019-002, Condition Prohibited by Technical Specifications and Loss of Safety Function Due to Inoperable Reactor Head Vent Throttle Valves

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Condition Prohibited by Technical Specifications and Loss of Safety Function Due to Inoperable Reactor Head Vent Throttle Valves
ML19273C695
Person / Time
Site: South Texas 
Issue date: 09/30/2019
From: Schaefer M
South Texas
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-19003687, STI: 34918172 LER 2019-002-00
Download: ML19273C695 (7)
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LER-2019-002, Condition Prohibited by Technical Specifications and Loss of Safety Function Due to Inoperable Reactor Head Vent Throttle Valves
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)(A), Loss of Safety Function - Shutdown the Reactor
10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
10 CFR 50.73(a)(2)(iii)
10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)(viii)(A)
10 CFR 50.73(a)(2)(viii)(B)
10 CFR 50.73(a)(2)(ix)(A)
10 CFR 50.73(a)(2)(x)
10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
10 CFR 50.73(a)(2)(v), Loss of Safety Function
10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
10 CFR 50.73(a)(2)(i)
4982019002R00 - NRC Website
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text

Nuclear Operating Company South Texas Project Electric Generating Station P.O. Box 289 Wadsworth, Texas,7483 September 30, 2019 NOC-AE-19003687 10CFR 50.73 Attention: 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 2019-002-00 Unit 1 Condition Prohibited by Technical Specifications and Loss of Safety Function due to Inoperable Reactor Head Vent Throttle Valves Pursuant to reporting requirements 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(v)(A), STP Nuclear Operating Company hereby submits the attached South Texas Project Unit 1 Licensee Event Report 2019-002-00 for a condition prohibited by the plant Technical Specifications that could have prevented fulfillment of a safety function.

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, please contact Nic Boehmisch at 361-972-8172 or me at 361-972-7888.

Michael A. Schaefer Site Vice President Attachment: Unit 1 LER 2019-002-00, Condition Prohibited by Technical Specifications and Loss of Safety Function due to Inoperable Reactor Head Vent Throttle Valves.

STI: 34918172

NOC-AE-19003687 Attachment Attachment Unit 1 LER 2019-002-00 Condition Prohibited by Technical Specifications and Loss of Safety Function due to Inoperable Reactor Head Vent Throttle Valves

NRC FORM 366 (04-2018)

^'"^

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

(See Page 2 for required number ofdigits/charactere for each block)

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www,nrc,gov/readina-mVdoc-(>>llections/^

APPROVED BY 0MB: N0.3150-0104 EXPIRES: 03/31/2020 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 teamed are Incoiporated Into the licensing process and fed back to Industry. Send comments regarding burden est'mate to the Infomiaton Services Branch (T-2 F43), U.S. Nuclear Regulatoiy Commission, Washington, DC 20555-0001, or by e-mail to lnfocollects.Resource@nro.gov, and to the Desk OfBcer, Oflce of Information and Regulatoiy Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid 0MB conb-ol number, the NRC may not conduct or sponsor, and a person is not required to respond to, the informaUon collection.

1. Facility Name South Texas Unit 1
2. Docket Number 05000498
3. Page 1 OF 5
4. Title Condition Prohibited by Technical Specifications and Loss of Safety Function due to Inoperable Reactor Head Vent Throttle Valves.
5. Event Date
6. LER Number
7. Report Date
8. Other Facilities Involved Month Day Year Year Sequential Number Rev No.

Month Day Year Facility Name N/A Packet Number 05000 07 30 2019 2019 - 002 - 00 09 30 2019 Facility Name N/A Pocket Number 05000

9. Operating Mode
11. This Report is Submitted Pursuant to the Requirements of 10 CFR§: (Check all that apply)

D 20.2201 (b)

D 20.2201 (d)

D 20.2203(a)(1)

D 20.2203(a)(2)(i)

D 20.2203(a)(3)(i)

D 20.2203(a)(3)(ii)

D 20.2203(a)(4)

D50.36(c)(1)(i)(A)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(ii)(B) a 50.73(a)(2)(iii)

D 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(viii)(A)

D 50.73(a)(2)(viii)(B)

D 50.73(a)(2)(ix)(A)

D 50.73(a)(2)(x)

10. Power Level D 20.2203(a)(2)(ii)

D50.36(c)(1)(ii)(A)

S 50.73(a)(2)(v)(A)

D73.71(a)(4)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

D 50.73(a)(2)(v)(B)

D 73.71 (a)(5)

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

D 50.73(a)(2)(v)(C) a 73.77(a)(1) 100 D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

D 50.73(a)(2)(v)(D)

D 73.77(a)(2)(ii)

D 20.2203(a)(2)(vi)

El 50.73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 73.77(a)(2)(iii)

D 50.73(a)(2)(i)(C)

D Other (Specify in Abstract below or in summary of the event On December 31, 2018, at 20:39 reactor head vent throttle valve (RHVTV) 'A' unexpectedly auto transferred to the Auxiliary Shutdown Panel (ASP). Local investigation of the ASP showed indication for RHVTV 'A' in the Main Control Room position. Train 'A' reactor head vent path was subsequently declared INOPERABLE.

A 10 CFR 21 Report Notification of a Defect with Target Rock Modulating Valve Positioner; Model810000-X was received by STPNOC on March 7, 2019. Engineering performed a Plant Impact Evaluation of the report and concluded that the positioners for the RHVTV in Unit 1 were degraded and needed to be replaced at the next available opportunity.

On July 30, 2019, an Instrumentation and Control (I&C) Training instructor was demonstrating the plant data available on QDPS to a class. The instructor found the RHVTV 'B' position computer point reading bad data.

Based on the instructor's knowledge of the system this indication was interpreted as a symptom of a blown fuse in the RHVW 'B' control unit. The instructor immediately notified the control room. The control room declared the TRAIN 'B' reactor head vent path INOPERABLE. Operations failed to request a reportability review as required by procedure when two or more trains of a component or system are INOPERABLE.

Further evaluation by Engineering on July 31, 2019, discovered objective evidence that the fuses associated with RHVTV 'B' failed on or about June 24, 2019. Therefore, the condition existed longer than the associated 30-day Technical Specification action statement. The required shutdown Technical Specification ACTION requirements were not met.

RHVTV -B' was declared OPERABLE on August 01, 2019. RHVTV 'A' was declared OPERABLE on August 15, 2019.

Timeline (Note: All times are Central Standard Time):

December 31, 2018 [2039]: RHVTV 'A' unexpectedly auto transfers to the Aux Shutdown Panel. The control room declares the valve INOPERABLE.

March 7, 2019 [1117]: 10 CFR PART 21 Report Notification of a Defect with Target Rock Modulating Valve Positioner Model 810000-X is received.

March 11, 2019: System engineering performs a Plant Impact Evaluation of 10 CFR PART 21 report and concludes the positioners for the RHVTVs in Unit 1 are degraded.

July 30, 2019 [1521]: I&C Training instructor discovers RHVW'B'control unit has a blown fuse. The control room declares the valve INOPERABLE.

July 31, 2019 [1459]: Engineering determined that RHVTV'B'failed on or about June 24, 2019, exceeding the associated 30-day Technical Specification action statement allowed outage time.

August 01, 2019: RHVTV 'B' was declared OPERABLE.

August 15, 2019: RHVTV 'A' was declared OPERABLE.

F. Method of discovery

This event was discovered by an I&C Training instructor during a classroom demonstration.

II. Component failures

A. Failure Mode, mechanism, and effects of failed component Fuse failures in the control units resulted in the RHVTVs losing power and becoming INOPERABLE.

B. Cause of component failure

Based on vendor discussions it is suspected that high voltage transients are causing the power fuses to fail.

The controllers have high voltage transient protection circuitry which fails the fuse if the circuitry trips. The protection circuitry may have inadvertently made the controller more sensitive to voltage transients than previous designs. Additional discussions with the vendor are ongoing to fully determine the cause.

C. Systems or secondary functions that were affected by failure of components with multiple functions No additional systems were affected by the RVHVS failure.

D. Failed component information

Reactor Core System {AC }

Valve, Solenoid, Flow {FSV }

Manufacturer: Target Rock {T020 }

Model: {79AB-003}

III. Analysis of the event

A. Safety system responses that occurred No safety systems were required to respond as a result of this event.

B. Duration of safety system inoperability

The RVHVS was INOPERABLE for a period of 38 days from the QDPS indication on 06/24/2019 until RHVTV

C. Safety consequences and implications

Multiple trains of safety systems provide the primary means of accomplishing the functions supported by the RVHVS. Failure of the RVHVS does not cause an initiating event or fail other risk significant systems. In addition to this, the RVHVS would not be used for several hours following an event, providing ample time for recovery of other mitigation systems. The failure of the RVHVS for 38 days has a negligible impact on plant Core Damage Frequency (CDF) and Large Early Release Frequency (LERF).

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 the event

The Apparent Cause of the condition prohibited by technical specifications was determined to be:

1. Operations did not recognize that Unit 1 had lost a safety function with both valves INOPERABLE.

The cause of the loss of safety function was determined to be:

1. A fuse in the control unit of the required valve failed resulting in a loss of safety function.

V. Corrective actions

Completed:

1. Failed fuses were replaced in both trains of RHVTV, restoring each to OPERABLE status and restoring the safety function.

Planned:

2. Update the "Safety Function Checklist" for RHVTV to include in the notes to check QDPS to ensure the valve position indication is valid and if both valves are simultaneously INOPERABLE then this a loss of a safety function and is reportable per 10CFR50.72(3)(v).
3. Create a computer alarm for RHVTV position indications that will notify when position indication is invalid, indicative of blown fuses.
4. Determine required modifications to control unit (remove protection circuitry, install filter, monitor incoming voltage, or change fuse sizing.)

VI. Previous similar events

The review of external OE did not identify any opportunities to identify this event prior to its occurrence.

The review of internal OE identified the following similar condition:

1. LER 2018-001-01 : Condition Prohibited by Technical Specifications That Could Have Prevented the Fulfillment of a Safety Function Due to Two Inoperable Extended Range Monitors. (Condition Report 18-3967)Page ^^ ^ 5

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