05000306/LER-2018-001-01, Automatic Actuation of Emergency Diesel Generator D5

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Automatic Actuation of Emergency Diesel Generator D5
ML18260A371
Person / Time
Site: Prairie Island Xcel Energy icon.png
Issue date: 09/17/2018
From: Sharp S
Northern States Power Company, Minnesota, Xcel Energy
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
L-Pl-18-053 LER 2018-001-01
Download: ML18260A371 (8)
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LER-2018-001, Automatic Actuation of Emergency Diesel Generator D5
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
10 CFR 50.73(a)(2)(viii)(A)
10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
10 CFR 50.73(a)(2)(viii)(B)
10 CFR 50.73(a)(2)(iii)
10 CFR 50.73(a)(2)(ix)(A)
10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)(x)
10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
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)(i)(B), Prohibited by Technical Specifications
10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
10 CFR 50.73(a)(2)(i)
3062018001R01 - NRC Website
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text

1717 Wakonade Drive Welch, MN 55089 800.895.4999 xcelenergy.com U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant, Unit 2 Docket No. 50-306 Renewed Facility Operating License No. DPR-60 SEP 1 7 2018 Xcel Energy RES PO N S I B LE B V NAT U RE L-Pl-18-053 10 CFR 50.73 Licensee Event Report 50-306/2018-001-01, Automatic Actuation of Emergency Diesel Generator D5 References: 1) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "LER 50-306/2018-001-00, Automatic Actuation of Emergency Diesel Generator D5". (ADAMS Accession ML18197A413)

Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), encloses a revised Licensee Event Report (LER) 50-306/2018-001-01, Automatic Actuation of Emergency Diesel Generator D5. This LER is a revision to Reference 1, which was submitted on July 16, 2018. This revision incorporates changes based on the revised Root Cause Evaluation.

If there are any questions or if any additional information is needed, please contact Frank Sienczak, at 612-342-8987.

Summary of Commitments Z'J~mmitments and no revisions to existing commitments.

Scott Sharp Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota

Document Control Desk Page 2 Enclosure cc:

Regional Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC State of Minnesota

Document Control Desk Page 3 ENCLOSURE Licensee Event Report 50-306/2018-001-01 5 Pages Follow

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017) htti;1://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3D the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.

13. PAGE Prairie Island Nuclear Generating Plant Unit 2 05000-306 1 OF5
4. TITLE Automatic Actuation of Emeraencv Diesel Generator D5
5. EVENT DATE
6. LER NUMBER
7. REPORT DATE
8. OTHER FACILITIES INVOLVED SEQUENTIAL FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR REV MONTH DAY YEAR NUMBER NO.

05000 FACILITY NAME DOCKET NUMBER 5

17 2018 2018

- 001
- 01 9

17 2018 05000

9. OPERATING MODE
11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

Unit 2 Mode 1

  • 20.2201(b)

D 20.2203(a)(3)(i)

  • 50.73(a)(2)(ii)(A)

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

  • 20.2201 (d)

D 20.2203(a)(3)(ii)

  • 50.73(a)(2)(ii)(B)

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

D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.73(a)(2)(iii)

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

D 20.2203(a)(2)(i)

  • 50.36(c)(1)(i)(A)

~ 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

10. POWER LEVEL D 20.2203(a)(2)(ii)
  • 50.36(c)(1)(ii)(A)

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

D 73.71(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)

Unit2 100%

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

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

D 73.77(a)(1)

D 20.2203(a)(2)(v)

  • 50.73(a)(2)(i)(A)

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

D 73.77(a)(2)(i)

D 20.2203(a)(2)(vi)

  • 50.73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 73.77(a)(2)(ii)

  • 50.73(a)(2)(i)(C)
12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT rELEPHONE NUMBER (Include Area Code)

!Frank Sienczak

~12-342-8987 CAUSE SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE FACTURER TOEPIX FACTURER TOEPIX

14. SUPPLEMENTAL REPORT EXPECTED
15. EXPECTED MONTH DAY YEAR 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

~ NO SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On May 17, 2018, at 11 :15 Central Daylight Time (CDT), with Unit 2 in Mode 1 at 100% power, the station experienced an auto-start of Emergency Diesel Generator (EDG), D5. The Bus 25 Potential Transformer fuse drawer was opened by a supplemental worker, causing Breaker 25-16 to open and de-energize Bus 25. Operators were able to manually close the EDG D5 output breaker to re-energize Bus 25. All equipment functioned as designed. EDG D5 was restored to a normal condition on May 17, 2018, at 16:44. This event was reported in accordance with 1 O CFR 50. 72(b )(3)(iv)(A) as an event that results in a valid actuation of the EDG.

The Direct Cause of this event was that the Worker opened FU/B25 25-16 POT "BUS 25 POT TO 25 LOAD SEQ PH AB and CB FUSES" (Human Performance).The Root Cause was that the risk of performing the Prairie Island Open Phase Project online with Bus 25 energized was not recognized and understood by the organization.

Immediate Action taken in the field placed the equipment in a safe condition and investigation efforts were completed to identify the direct cause of the condition and restoring power to Bus 25.

Corrective Actions include, develop and execute a targeted observation initiative to drive improvement in walk down rigor for Design Engineering, Maintenance Planning and Operations Planning. Tagging procedure was revised to specify the requirements of the meeting required for clearances associated with modifications. POT drawers were labeled with equipment ID. Open action to install locking device and caution to instruct operator approval prior to opening drawer and contain a physical barrier such as a lock, zip tie or screws to discourage opening.

NRC FORM 366 (04-2017)

DESCRIPTION OF EVENT

YEAR 2018 SEQUENTIAL NUMBER

- 001 REV NO.
- 01 On May 17, 2018 at 11: 15 Central Daylight Time (CDT), with Unit 2 in Mode 1 at 100% power, the station experienced an auto-start of Emergency Diesel Generator1 (EOG), D5. During the 4kV2 Bus Modification for the Open Phase project, installation activities were being performed by supplemental workers in the Bus 25 room. During the performance of work activities, the Bus 25 Potential Transformer (PT) fuse drawer was opened. The circuits associated with this PT drawer provide the voltage signal to the Bus 25 Load Sequencer undervoltage relays. With the PT drawer open, degraded, under voltage and loss of voltage signals were detected. An actual abnormal voltage condition did not exist prior to opening the PT drawer. This caused Breaker 25-16 to open and de-energized Bus 25.

This event was initiated by human error, whereby a supplemental worker took action to open the PT drawer in an effort to complete work activities. The worker believed the component was isolated as part of the work-clearance but did not perform adequate verification to ensure that Fuse/Bus 25 Potential Transformer (FU/B25 25-16POT) was included on the tag-out list prior to taking action. The crew had reviewed the copy of a tag affixed to fuses removed from Fuse/ 2RY Potential Transformer (FU/2RY 25-16POT) (included in the tag-out list and located in cubicle 25-14), noted the "25-16" in the Equipment ID and were in a mindset that the fuses they observed were from the equipment they were about to manipulate. The equipment ID for the PT drawer in cubicle 25-16 was not labeled and the worker believed the fuses were for the PT drawer. However, this PT drawer was actually FU/B25 25-16POT which senses power to Bus 25.

As a result, when the PT drawer above Breaker 25-16 was opened, degraded voltage, undervoltage, and loss of voltage signals were detected and the Load Sequencer proceeded with the voltage restoration program. This program gives a trip signal to all source breakers. Upon receipt of the trip signal, breaker 25 "CT12 Source to Bus 25" opened as designed and the Load Sequencer performed as expected to re-energize the bus via the D5 EOG output breaker (25-2) approximately 8 seconds later. However, because the PT Drawer remained open after the completion of sequencing, voltage restoration to Bus 25 was not indicated to the Load Sequencer. The Load Sequencer then opened EOG D5 output breaker BKR 25-2 as designed. With no power to Bus 25, Bus 25 was inoperable. Operators were able to manually close the D5 EOG output breaker 25-2 to re-energize Bus 25. All equipment functioned as designed.

Bus 25 was re-energized from EOG D5. Technical Specification (TS) 3.8.9. Condition A, Distribution Systems-Operating was exited on May 17, 2018 at 12:07 (52 minutes). Bus 25 was restored to offsite source on May 17, 2018 at 15:30. Operations shutdown and secured EOG D5 on May 17, 2018 at 16:44.

This event was reported on May 17, 2018 at 18:33 CDT, (Event Notification53408), in accordance with 1 O CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the EOG.

EVENT ANALYSIS

EOG, is a backup to the normal standby AC power supply, it is capable of sequentially starting and supplying the power requirements to one of the redundant sets of engineered safety features for the associated reactor Unit. In addition, in the event of a station blackout (SBO) condition, each EDG is capable of sequentially starting and supplying the power requirements of the hot shutdown (Mode 3, Hot Standby in TS) loads for its unit, as well as the essential loads of the blacked out unit, through the use of manual bus tie breakers interconnecting the 4kV Buses.

1 EIIS System Code - EK 2 EIIS System Code - EA NRG FORM 3668 (04-2017)

Page 2 of 5 U.S. NUCLEAR REGULATORY COMMISSION (04-2017)

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{~AJi:'j LICENSEE EVENT REPORT (LER)

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CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nu regs/staff/sr1 022/r3D APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER YEAR Prairie Island Nuclear Generating Plant 05000-306 Unit 2 2018 SEQUENTIAL NUMBER
- 001 REV NO.
- 01 Plant management incorrectly determined that the work could be performed online (as written and planned) and removed the modification for the Open Phase project from the 2R30 outage scope. The risk assessment, job planning and preparation of the work order operation allowed the workers to enter the field with an approved work order and clearance that was inadequate for the required work. Reviews, consultations and walkdowns failed to recognize that the work order activities placed the workers in the immediate vicinity of energized 4kV equipment that interfered with the proposed cable routing per the design drawing. Adequate cable routing detail was not included in the work order because the cubicle internals were not considered in the planning walkdown. The work order was planned at risk and completed prior to the approval of PT design. This lack of detail contributed to a less than adequate understanding of the scope of work by the Operations Planner when completing the clearance tag-out and plant impact statement. The Operations Planner did not identify the clearance as "exceptional" or perform a walkdown to identify all hazards associated with the work.

A walkdown should have been performed and the isolation should have been made both complex and exceptional in accordance with the fleet tagging procedure. A clearance is considered exceptional when the normal requirements of the tagging process cannot be fully implemented. Permission to work must be approved by Operations Management and documented in the clearance order. An explanation for the reason the clearance is exceptional and the compensatory actions stated that a face to face brief with Operations is required prior to signing the clearance. If energy is discovered during the zero energy test, stop work and contact Operations.

Operators responded to the alarm response procedures addressing the Bus 25 undervoltage condition and transitioned to re-energizing the 4kV, Bus 25 per the Abnormal Operating Procedure (AOP) using D5 EOG. The PT fuse drawer was verified to be re-installed and applicable relays reset on the Bus 25 Load Sequencer. The Bus 25 Load Sequencer was returned to service per the associated AOP. Operators shut down EOG D5 per Operating Procedures. This event is being reported under 1 O CFR 50.73(a)(2)(iv)(A) as an event that resulted in valid/automatic actuation of an EOG.

Bus 25 is required to be operable in modes 1 through 4 by TS 3.8.9, Distribution Systems - Operating, and in modes 5 and 6 when required by TS 3.8.10, Distribution Systems - Shutdown. The Bus 25 Voltage Instrumentation is required to be operable by TS 3.3.4, 4kV Safeguards Bus Voltage Instrumentation, in modes 1 through 4 or when the associated EOG is required to be operable by LCO 3.8.2, AC Sources - Shutdown.

SAFETY SIGNIFICANCE

There were no radiological, environmental, or industrial impacts associated with the auto-start of EOG D5, and the health and safety of the public were not affected. The plant was placed in an unplanned TS under 3.8.1 Condition D, for having both EOG D5 and 2RY (Offsite AC source) inoperable. Bus 25 was de-energized requiring entry into TS 3.8.9 Condition A, Distribution Systems-Operating on May 17, 2018 at 11: 15. Operators were able to manually close the EOG D5 output breaker to re-energize Bus 25. Bus 25 was re-energized from EOG D5. TS 3.8.9. Condition A, was exited on May 17, 2018 at 12:07 (52 minutes). Bus 25 was restored to offsite source on May 17, 2018 at 15:30. Operations shut down and secured EOG D5 on May 17, 2018 at 16:44.

There was a momentary loss of component cooling on the loss of 21 Component Cooling (CC) pump due to low pressure in the CC system. The 22 CC pump auto started as designed and restored system pressure with a minimum impact on the CC system.

This event was reportable per 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the EOG.

The auto-start of the EOG D5 did not challenge nuclear safety as all plant systems responded as designed. This event did not affect Bus 26 and there was no auto start of EOG D6. Both Bus 26 and EOG D6 were operable during this event.

As a result, there was no loss of safety function. Page 3 of 5 (04-2017)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www. nrc. gov/reading-rm/doc-collections/nuregs/staff/sr1 022/r3D

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER YEAR Prairie Island Nuclear Generating Plant 05000-306 SEQUENTIAL NUMBER REV NO, 1---u_n_i_t 2 ___________

__c_ ______________

L--2_0_1_s~ __ -_0_0_1_~_-0_1----1 I

CAUSE(s)

Direct Cause:

Worker opened FU/B25 25-16 POT "BUS 25 POT TO 25 LOAD SEQ PH AB and CB FUSES" (Human Performance).

Root Cause:

The risk of performing the Prairie Island Open Phase Project online with Bus 25 energized was not recognized and understood by the organization.

Contributing Cause

The Bus 25 POT drawer is not labeled with an Equipment ID and appropriate barriers to prevent the drawer from unintended manipulation.

CORRECTIVE ACTION(s)

Immediate action:

1. Actions that were taken in the field placed the equipment in a safe condition and investigation efforts were completed to identify the direct cause of the condition and restoring power to Bus 25.
2. A formal stop work order was established for the Open Phase project until further analysis reveals underlying causes.
3. This work was transitioned to the on line schedule after originally scheduled to be performed in refueling outage 2R30, actions were taken to review other similar work originally scheduled for offline performance to ensure the adequacy of the work plan for safe and event free performance.

Actions to correct this event include:

1. Develop and execute a targeted observation initiative to drive improvement in walk down rigor for Design Engineering, Maintenance Planning and Operations Planning.
2. Provide a walk down case study with Maintenance and Operations Planners to reinforce standards and improve walk down rigor.
3. Tagging procedure was revised to specify the requirements of the meeting required for clearances associated with modifications.
4. Revise supplemental oversight procedures to implement a review committee for the Supplemental oversight.plans.
5. Implement a program to change nuclear business unit work force behaviors for awareness, identification and mitigation of risk, including revision to relevant governance and the nuclear management model, to more proactively identify and mitigate risk in plant activities.
6. POT drawers were labeled with equipment ID. Open action to install locking device and caution to instruct operator Page 4 of 5 (04-2017)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3D

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER Prairie Island Nuclear Generating Plant Unit 2 05000-306 YEAR 2018 SEQUENTIAL NUMBER
- 001 approval prior to opening drawer and contain a physical barrier such as a lock, zip tie or screws to discourage opening.

PREVIOUS SIMILAR EVENTS

A review of the Prairie Island LERs for the past five years found no other similar events.

REV NO.

- 01 Page 5 of 5

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