05000387/LER-2012-008, Regarding Loss of One of Two Offsite Power Sources

Regarding Loss of One of Two Offsite Power Sources

ML12241A131
Person / Time
Site:	Susquehanna
Issue date:	08/24/2012
From:	Helsel J Susquehanna
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PLA-6907 LER 12-008-00
Download: ML12241A131 (5)

LER-2012-008, Regarding Loss of One of Two Offsite Power Sources

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
3872012008R00 - NRC Website

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Jeffrey M. Helsel Nuclear Plant Manager

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PPL Susquehanna, LLC 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3510 Fax 570.542.1504 jmhelsel@pplweb.com

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U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop OP1-17 Washington, DC 20555-0001 SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387/2012-008-00 LICENSE NO. NPF-14 PLA-6907 Docket No 50-387 Attached is Licensee Event Report (LER) 50-387/2012-008-00. The event involved loss of one of two offsite power sources, resulted in automatic actuation of containment isolation valves in more than one system, and is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A).

There were no actual consequences to the health and safety of the public as a result of this event.

No regulatory commitments are associated with this LER.

J. M. Helsel

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Attachment: LER 50-387/2012-008-00 Copy: NRC Region I Mr. P. W. Finney, NRC Sr. Resident Inspector Ms. C. J. Sanders, NRC Project Manager Mr. L. J. Winker, DEP/BRP TM

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES:10/31/2013 (10-2010)

, the NRC digits/characters for each block) may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME

~- DOCKET NUMBER

3. PAGE Susquehanna Steam Electric Station Unit 1 05000387 1 OF4

4. TITLE LOSS OF ONE OF TWO OFFSITE POWER SOURCES

5. EVENT DATE

6. LEA NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.

MONTH DAY YEAR Susquehanna Steam Electric Station Unit 2 05000388 FACILITY NAME DOCKET NUMBER 06 28 2012 2012

- 008

- 00 08 2012 psooo

~- OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 4 D 20.2201 (b)

D 20.2203(a)(3)(i)

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

D 50.73(a)(2)(vii)

D 20.2201 (d)

D 20.2203(a)(3)(ii)

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

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

D 20.2203(a)(1)

D 20.2203(a)(4)

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

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

10. POWER LEVEL D 20.2203(a)(2)(i)

D 50.36(c)(1)(i)(A)

D 50.73(a)(2)(iii)

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

OOOo/o D 20.2203(a)(2)(ii)

D 50.36(c)(1 )(ii)(A)

[83 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

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

D 73.71 (a)(4)

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

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

D 73.71 (a)(5)

D 20.2203(a)(2)(v)

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

D 50.73(a)(2)(v)(C) 0 OTHER D 20.2203(a)(2)(vi)

D 50.73(a)(2)(i)(B)

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

Specify in Abstract below or in

CAUSE OF THE EVENT

3. PAGE 30F4 The direct cause of the event was an open ammeter switch contact causing a phase current imbalance that was detected by the protective relaying and initiated transformer lockout.

The root causes of the event were as follows:

Foreign material from the manufacturing process that prevented the ammeter switch contact from closing Design of protective relay scheme included shared metering function

ANALYSIS/SAFETY SIGNIFICANCE

Actual Consequences:

The immediate consequence from the switch failure was loss of one of the two offsite power sources for both Units.

At the time of the event, Unit 1 was in Mode 4, Cold Shutdown and Unit 2 was operating in Mode 1 at approximately 100% power. A review of the plant response to the event concluded that all automatic load shedding, bus transfers, and equipment response occurred as expected.

A consequence of the event was the loss of normal RHR shutdown cooling on Unit 1. Unit 1 was operating in Mode 4 at the time of the event with shutdown cooling provided by the 1 B RHR pump and 1 B RHR loop heat exchanger.

Loss ofT -20 resulted in undervoltage load shedding on 4kv ESS bus 1 B that included trip of the operating 1 B RHR pump. Review of data showed shutdown cooling was restored using the 1 D RHR pump on June 28, 2012 at 14:26.

As a result of the 32 minute loss of decay heat removal, 1 B heat exchanger inlet temperature increased from 105.7 degrees F to 111.2 degrees F, a change of 5.5 degrees F. The shutdown risk assessment report for June 28, 2012 identified the Unit 1 time to 200 degrees F was 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. The increase in coolant temperature did not challenge fuel cladding integrity as the resulting temperatures were within normal operating range for Mode 4.

As a result of the loss of T -20, the Security electrical system experienced an electrical transient. At the time of the event, battery charger 00584 was out of service for maintenance and inverter 00585 was on bypass and was not a buffer to the electrical transient caused by the loss ofT -20. As a result, a number of security components such as card readers were affected by the transient.

Potential Consequences:

T -20 is one of two sources of offsite power supply to Susquehanna Units 1 and 2. Loss of T -20 increases the frequency for a loss of offsite power initiating event. The PRA model baseline risk analysis identifies that a Loss of Offsite Power is the dominant initiating event for the station. For a unit operating in Modes 1, 2, or 3, the potential consequence of T -20 unavailability is an increase in core damage frequency and large early release frequency in the event of a Loss of Offsite power.

The increase in risk with T -20 unavailable was evaluated using the EOOS risk monitor software (no random maintenance model) and conservatively assumed the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO 3.8.1 completion time. The increase in risk to Unit 2, which was operating in Mode 1, was determined to be less than the NRC IMC 609 Appendix K Green/White Threshold of less than 1 E-06 ICDP and less than 1 E-07 ILERP.

Unit 1 was operating in Mode 4, Cold Shutdown, at the time of the event. Evaluation of the five key shutdown safety functions by the OCC risk analyst using the EOOS risk monitor identified a change in risk level from Green to Yellow in the overall plant risk and in the Electrical Systems key safety function. The change in risk level reflected the reduction in defense in depth of available AC power supply sources for mitigating equipment.

CORRECTIVE ACTIONS

Key corrective actions include:

U.S. NUCLEAR REGULATORY COMMISSION

6. LER NUMBER I

SEQUENTIAL NUMBER

- 008 I

REVISION NUMBER

- 00

3. PAGE 40F4

1.

As an interim compensatory measure, controls will be put in place to ensure that switches identified as being within the extent of condition are not operated.

2.

An engineering evaluation will be completed to select the best approach to correcting the condition. The evaluation will determine if testing and/or a preventive maintenance activity could resolve the problem, if a replacement switch is available that is not prone to the same failure, and select a design change to ensure that an ammeter switch failure does not actuate the protective relay function.

3.

The approach selected based on the engineering evaluation will be implemented.

PREVIOUS SIMILAR EVENTS

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