05000251/LER-2010-006, Regarding Automatic Reactor Trip Due to Spurious High Pressurizer Pressure Trip Signal

Regarding Automatic Reactor Trip Due to Spurious High Pressurizer Pressure Trip Signal

ML103330189
Person / Time
Site:	Turkey Point
Issue date:	11/19/2010
From:	Kiley M Florida Power & Light Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-2010-266 LER 10-006-00
Download: ML103330189 (5)

LER-2010-006, Regarding Automatic Reactor Trip Due to Spurious High Pressurizer Pressure Trip Signal

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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)(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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(iv)(B), System Actuation
2512010006R00 - NRC Website

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0 IPL.

POWERING TODAY.

EMPOWERING TOMORROW.

NOV 19 2010 10 CFR § 50.73 L-2010-266 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555-0001 Re:

Turkey Point Unit 4 Docket No. 50-251 Reportable Event: 2010-006-00 Date of Event: September 21, 2010 Automatic Reactor Trip Due to Spurious High Pressurizer Pressure Trip Signal The attached Licensee Event Report 05000251/2010-006-00 is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) due to a valid actuation of the Reactor Protection System.

If there are any questions, please call Mr. Robert Tomonto, Licensing Manager at 305-246-7327.

Sincerely, Michael Kiley Vice President Turkey Point Nuclear Plant Attachment SM cc: Regional Administrator, USNRC, Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant an FPL Group company

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/201

ý10-2010)

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 Section (T-5 F53), U.S. Nuclear LICENSEE EVENT REPORT (LER)

Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects.resourse@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.

3. PAGE Turkey Point Unit 4 05000251 1 of 4

4. TITLE Automatic Reactor Trip Due to Spurious High Pressurizer Pressure Trip Signal

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

[

8. OTHER FACILITIES INVOLVED T

FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.

09 21 2010 2010 -

006

- 00 11 19 2010

9. OPERATING MODE

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

El 20.2201(b)

El 20.2203(a)(3)(i)

[E 50.73(a)(2)(i)(C)

El 50.73(a)(2)(vii)

El 20.2201(d)

El 20.2203(a)(3)(ii)

El 50.73(a)(2)(ii)(A)

[I 50.73(a)(2)(viii)(A)

El 20.2203(a)(1)

El 20.2203(a)(4)

[I 50.73(a)(2)(ii)(B)

El 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A)

E-50.73(a)(2)(iii)

[I 50.73(a)(2)(ix)(A)

10. POWER LEVEL 12 20.2203(a)(2)(ii)

El 50.36(c)(1)(ii)(A)

[E 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

E-20.2203(a)(2)(iii)

El 50.36(c)(2)

El 50.73(a)(2)(v)(A)

El 73.71(a)(4)

El 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii)

Dl 50.73(a)(2)(v)(B)

El 73.71(a)(5) 100%

El 20.2203(a)(2)(v)

[I 50.73(a)(2)(i)(A)

El 50.73(a)(2)(v)(C)

[E OTHER El 20.2203(a)(2)(vi)

[E 50.73(a)(2)(i)(B)

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

Specify in Abstract below or in As part of the event investigation, the surveillance procedure 4-SMI-041.10 was re-performed again on Channel II (Pressurizer Pressure Loop P-4-456). During the performance of this procedure, Channel I alarm came in and reset repeatedly. Based on this information, it was concluded that the Unit 4 reactor trip event was attributed to a spurious trip of Channel I concurrent with Channel II already being tripped due to the surveillance procedure.

Several potential causes were evaluated as part of the root cause investigation. Review of operating experience at Turkey Point identified that activities associated with the NUS Instruments Module replacement project have resulted in connector pin separation that have challenged component operation. As part of the investigation, the team inspected Channel I NUS Instrument Module Comparator PC-4-455A and found pins with excessive separation in the ELCO connectors that caused the Channel I spurious trip signal.

The original Pressurizer Pressure Protection instrument Loop Hagan Modules were replaced by NUS Instruments Modules in 2008. The original ELCO connectors in the instrument loop rack wiring were not replaced. The two halves of the ELCO connector are provided with keyed alignment guides such that the two halves of the connectors can only be mated in the designed configuration. The ELCO connector electrical pins are very small and the design distance between these bifurcated pins is approximately 10 mils. Inspection of these pins in the instrument loop racks could be challenging due to the location of the connectors in the rack, the area lighting, and the quality of vision of the individual performing the inspection. This is especially true for the pins of cable end connector [CBL,con] that are recessed in the connector housing. These electrical pins provide an audible snap when properly installed in the connector. They are held in tight alignment for connection with the mating half. The guide pins help to ensure that the electrical pins are aligned before engagement. The connector jackscrew ensures the connector halves are tight.

ELCO connector electrical pins can be damaged during mating of the connector halves if care is not taken to ensure that the pins and connectors are aligned properly. Connector pins can also be damaged by the jackscrew during installation, if it is not properly installed and aligned.

The original NUS module replacement modification did not include any special instruction for installation or inspection for electrical pins of the connectors. When the excessive pin separation concerns were identified in 2008, an inspection sheet with visual inspection criteria was developed and included in all NUS module work order instructions for installation/replacement of an NUS instrument module to address the knowledge gap that existed for not recognizing that excessive pin separation could cause operational failures.

The inspection criterion was inadequate for field rack conditions because it was based on a qualitative visual inspection and judgment for validating such a critical pin dimension. The acceptance criteria and method of verification were not adequately addressed. Additionally, the instruction sheet for excessive pin separation inspection was briefed only to a limited number of Maintenance personnel. There was no formal training developed and presented for identifying pin separation. The actions taken have not been effective in preventing the cause of excessive pin separation in ELCO connectors or identifying the damaged pins once separation has occurred.

Cause of the Event

The root cause of the event is excessive pin separation in ELCO connectors which is causing component failures due to inadequate installation instructions and inspection criteria. A contributing cause is that the modification implementation instruction contains no special installation instruction with respect to pin separation in ELCO connectors.

Reportability

The event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) due to any event or condition that resulted in an automatic actuation of the Reactor Protection System when an unplanned reactor trip occurred during the performance of the Pressurizer Pressure Protection Loop surveillance. This event is also reportable in accordance with 10 CFR 50.73(a)(2)(iv)(B) due to automatic actuation of the Auxiliary Feedwater System.

Analysis of Safety Significance This event resulted in an automatic reactor trip due to an erroneous High Pressurizer Pressure signal and was followed by an automatic turbine trip on reactor trip. The plant responded as expected to the automatic trip. The Auxiliary Feedwater system actuated on the low steam generator level as designed and the plant was stabilized in Mode 3. No significant equipment or human performance issues were identified. There were no adverse effects on plant parameters and the health and safety of the public was not compromised nor adversely affected.

Corrective Actions

1. Immediate corrective actions included the replacement of NUS Instruments Comparator Module PC-4-455A.

2. ELCO connector inspection requirements will be added to a plant procedure.

3. Formal training will be conducted for Maintenance personnel to properly inspect NUS module ELCO connector pins and to properly mate the ELCO connectors.

4. NUS modules with ELCO connectors will be inspected during the next scheduled preventive maintenance activity.

Corrective actions to address the event's root cause and contributing factors have been entered in the Turkey Point Corrective Action Program in AR 00581322.

Additional Information

MIS Codes are shown in the format [IEEE system identifier, component function identifier, second component function identifier (if appropriate)]

Condition Report AR 00581322 was initiated to evaluate this event.

Similar Events

None Failed Components: Reactor Protection System Component Identification: Pressurizer Pressure Protection Loop-Comparator NUS Instruments Module (PC-4-445A)-ELCO Connector pins.