ML16209A265

LER 16-001-00 for Limerick, Unit 2 Regarding Manual Actuation of the Reactor Protection System When Critical Due to Wiring Design Error

ML16209A265
Person / Time
Site:	Limerick
Issue date:	07/27/2016
From:	Libra R W Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LG-16-083 LER 16-001-00
Download: ML16209A265 (4)

Text

Exelon Generation

.. LG-16-083 July 27, 2016 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 2 Renewed Facility Operating License No. NPF-85 NRC Docket No. 50-353 10CFR50.73

Subject:

LEA 2016-001-00, Manual Actuation of the Reactor Protection System This Licensee Event Report (LEA) addresses a manual actuation of the reactor protection system (RPS) following a trip of both reactor recirculation pumps. The pump trips occurred during testing of a modification to the Plant Process Computer (PPC). The manual scram was directed by the unexpected/unexplained change in core flow procedure (OT-112) due to the tripping of the reactor recirculation pumps at power. An error in the modification wiring design caused an actuation of the reactor recirculation pump trip relays. This LEA is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv)(A).

There are no commitments contained in this letter. If you have any questions, please contact Robert 8. Dickinson at (610) 718-3400.

Respectfully, '"

Richard W. Libra Site Vice President

-Limerick Generating Station Exelon Generation Company, LLC cc: Administrator Region I, USNRC USNRC Senior Resident Inspector, LGS NRC FORM 366 (01-2014) NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION(01-2014)

LICENSEE EVENT REPORT (LER) (See Page 2 for required number of digits/characters for each block)

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 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, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory 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 OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection. 1. FACILITY NAME Limerick Generating Station, Unit 2 2. DOCKET NUMBER 05000353 3. PAGE 1 OF 3 4. TITLE Manual Actuation of the Reactor Protection System When Critical Due to Wiring Design Error 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 DOCKET NUMBER 05000 06 01 2016 2016 - 001 - 00 07 27 2016 FACILITY NAME DOCKET NUMBER 05000 9. OPERATING MODE 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)

10. POWER LEVEL 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 100 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME Robert B. Dickinson, Manager - Regulatory Assurance TELEPHONE NUMBER (Include Area Code) 610-718-3400 13. COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT CAUSE SYSTEM COMPONENT MANU-FACTURER REPORTABLETO EPIX CAUSE SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX B AD P G080 Y 14. SUPPLEMENTAL REPORT EXPECTED YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

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

A manual actuation of the reactor protection system (RPS) when the reactor was critical was initiated during Plant Process Computer (PPC) modification testing at power. A modification wiring design error caused an actuation of both reactor recirculation pump (RRP) trip relays when a circuit isolation switch was closed. The direct cause of the event was a circuit wiring design error implemented in the field that caused energization of the RRP adjustable speed drive (ASD) trip coils. The root cause of the event was a failure of station personnel to appropriately apply Technical Human Performance (THU) error prevention techniques to identify the design error and prevent its installation and testing as part of the modification. The isolation switch for the mis-wired circuit was opened to enable reset of the ASD trip coils. The 2A and 2B ASDs were returned to service. The corrective actions are to change the circuit design to correct the design error. The human performance aspects of the event will be addressed through several management actions that include reinforcement of proper standards and behaviors related to THU error techniques with station personnel.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION(01-2014)

LICENSEE EVENT REPORT (LER) CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 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, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory 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 OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection. 1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGELimerick Generating Station, Unit 2 05000353 YEAR SEQUENTIAL NUMBER REV NO. 2 OF 3 2016 - 001 -00 NARRATIVE NRC FORM 366A (01-2014)

Unit Conditions Prior to the Event

Unit 2 was in Operational Condition (OPCON) 1 (Run) at approximately 100 percent power with PPC modification testing in progress. There were no structures, systems or components out of service that contributed to this event.

Description of the Event

On Wednesday, June 1, 2016, Limerick Unit 2 was operating at 100 percent power with PPC (EIIS:CPU) modification testing in progress. The modification testing directed closure of a circuit isolation switch which resulted in the trip of both RRPs (EIIS:P) due to an error in the modification wiring design. The control room supervisor (CRS) entered the procedure for an unexpected/unexplained change in core flow (OT-112) due to the trip of both RRPs. The procedure directed a manual actuation of RPS.

All control rods inserted and safety significant systems functioned as expected. Reactor level initially increased then decreased to approximately +0 inches which is less than the

+12.5 inch low level setpoint for RPS. Level then stabilized at normal level. Nuclear Steam Supply Shutoff System Groups IIA and IIB isolations actuated on low level at +12.5 inches. The digital feedwater level control system functioned as designed. Reactor pressure vessel pressure was controlled by the main steam bypass valves.

The investigation of the event identified that a wiring design error caused an unplanned actuation of both RRP trip relays when a circuit isolation switch was closed as directed by the modification acceptance test procedure.

A four-hour ENS notification (#51968) was completed on Wednesday, June 1, 2016, at 1041 hours0.012 days <br />0.289 hours <br />0.00172 weeks <br />3.961005e-4 months <br /> as required by 10CFR50.72(b)(2)(iv)(B) for an actuation of RPS when the reactor is critical. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv)(A) for a manual actuation of RPS.

Analysis of the Event

There was no actual safety consequence associated with this event. The potential safety consequences of this event were minimal. All control rods were verified to be fully inserted following the RPS actuation. The 2A RRP was restarted at 1548 hours0.0179 days <br />0.43 hours <br />0.00256 weeks <br />5.89014e-4 months <br /> on June 1, 2016 and the 2B RRP was restarted at 0326 hours0.00377 days <br />0.0906 hours <br />5.390212e-4 weeks <br />1.24043e-4 months <br /> on June 2, 2016.

The PPC replacement modification was in progress and computer input points were being transferred from the original computer to the new computer. When the second RRP related computer point was placed in service by closure of a circuit isolation switch both 2A and 2B RRP trip relays were energized due to an error in the wiring design.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION(01-2014)

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGELimerick Generating Station, Unit 2 05000353 YEAR SEQUENTIAL NUMBER REV NO. 3 OF 3 2016 - 001 - 00 NARRATIVE NRC FORM 366A (01-2014) LICENSEE EVENT REPORT (LER) CONTINUATION SHEET Cause of the Event

The direct cause of the event was a circuit wiring design error that was implemented in the field and caused energization of the RRP ASD trip coils.

The root cause of the event was a failure of station personnel to appropriately apply THU error prevention techniques to identify the design error and prevent its installation and testing as part of the modification.

Corrective Actions Completed The isolation switch for the mis-wired circuit was opened to enable reset of the ASD trip coils.

The 2A and 2B ASDs were returned to service.

Corrective Actions Planned

The wiring design error will be corrected and the Modification Acceptance Test will be revised to ensure the change is correctly tested per the requirements of the Acceptance Test Criteria.

The human performance aspects of the event will be addressed through several management actions that include reinforcement of proper standards and behaviors related to THU error techniques with station personnel.

Previous Similar Occurrences

There was no previous RPS actuation in the past five years due to modification testing.

Component data

System: AD Reactor Recirculation System Component: P Pump Component number: 2A-P201-DR Component name: Reactor Recirculation Pump Manufacturer: G080 General Electric Company Model number: 5K46385AA1