ML12103A352

Special Inspection Charter to Evaluate Catawba Loss of Offsite Power

ML12103A352
Person / Time
Site:	Catawba
Issue date:	04/10/2012
From:	McCree V M Region 2 Administrator
To:	Rapp C W NRC/RGN-II/DRP/RPB1
References
Download: ML12103A352 (4)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II 245 PEACHTREE CENTER AVENUE NE, SUITE 1200 ATLANTA, GEORGIA 30303-1257 April 10, 2012 MEMORANDUM TO: Curtis W. Rapp Senior Project Engineer FROM: Victor M. McCree /RA By Leonard D. Wert, Jr. For/ Regional Administrator

SUBJECT:

SPECIAL INSPECTION CHARTER TO EVALUATE CATAWBA LOSS OF OFFSITE POWER

You have been selected to lead a Special Inspection (SI) to assess the circumstances concerning a loss of offsite power which occurred on April 4, 2012, at Catawba Nuclear Station Units 1 and 2. Catawba declared a Notice of Unusual Event (NOUE) due to loss of all offsite power to essential busses. Your onsite inspection should begin on April 10, 2012. Pauline Braxton and Jonathan Montgomery will be supporting you in this inspection.

A. Basis On Wednesday, April 4, 2012, at 8:12 p.m., Catawba declared a NOUE due to a loss of all offsite power to essential busses. Prior to the loss of power, Unit 1 was operating at 100 percent power and Unit 2 was in Mode 5 with essential busses powered from Unit 1. Initial investigation by the licensee determined that the 1D reactor coolant pump tripped which led to a reactor trip due to low flow conditions. By design, the turbine tripped and the main generator circuit breakers opened. However, although the main generator was disconnected from the switchyard, a decrease in the main generator frequency caused an under-frequency relay to open the switchyard power circuit breakers (PCBs) isolating offsite power from both units' essential busses. All four emergency diesel generators started and supplied power to their essential busses. The Standby Shutdown Facility (SSF) diesel generator also started, but failed to reach rated voltage. This condition did not appear to affect any plant safety system response or the recovery of offsite power. The NOUE was exited on Thursday April 5, 2012, at 1:37 a.m., following restoration of offsite power to one essential bus on each unit.

The specific issues of concern are:

• The loss of offsite power to both units that resulted from a single unit trip

• The failure of the SSF diesel generator, which is utilized by both units for certain events and conditions, to produce rated voltage.

CONTACT: Jonathan H. Bartley, RII/DRP (404) 997-4607

C. Rapp 2 In accordance with MD 8.3, "NRC Incident Investigation Program," deterministic and conditional risk criteria were used to evaluate the level of NRC response for this operational event. The event involved the deterministic criterion of significant unexpected system interactions. The updated Conditional Core Damage Probability (CCDP) for the event was in the overlap region of a Special Inspection and an Augmented Inspection Team. A Special Inspection was deemed appropriate in this case. Accordingly, the inspection objectives are to determine the facts surrounding the loss of offsite power at Catawba, evaluate the licensee's response to the event, determine the impact of the Zone G digital relay modification, and assess any site specific and/or generic implications.

B. Scope To accomplish these objectives, the following will be performed:

1. Develop timelines associated with the installation of the digital relay modification (Zone G) and the event, including the design and implementation of the relay modification and the response of Catawba Units 1 and 2 to the loss of offsite power initiator.

2. Asses the apparent causes and licensee follow-up actions for:

2.1 The 1D reactor coolant pump trip.

2.2 Factors which allowed the reactor coolant pump failure to propagate to the main switchyard breakers and opening the PCBs.

2.3 The licensee's design and implementation of the Zone G relay modification, including the design, implementation, and testing phases of the modification.

2.4 Whether the Zone G modification errors have potential generic risk implications.

2.5 The common SSF diesel generator (DG) not achieving its 600V design rating.

3. Assess the licensee's activities related to the problem investigation performed to date (e.g., root cause analysis, extent of condition, additional equipment failure mechanisms, adequacy of operator actions etc.).

4. Determine the impact of the SSF DG low voltage and any significance affecting plant recovery from the LOSP.

5. Document the inspection findings and conclusions in an inspection report within 45 days of the inspection which should address all applicable areas specified in section 3.02 of IP 93812.

6. Conduct an entrance and exit meeting.

C. Rapp 3 C. Guidance Inspection Procedure (IP) 93812, "Special Inspection," provides additional guidance to be used during the conduct of the inspection. Your duties will be as described in IP 93812 and should emphasize fact-finding in its review of the circumstances surrounding the degraded condition. Safety or security concerns identified that are not directly related to the event should be reported to the Region II office for appropriate action.

You will report to the site, conduct an entrance, and begin inspection no later than April 10, 2012. It is anticipated that the on-site portion of the inspection will be completed during the same week. An initial briefing of Region II management will be provided the second day on-site at approximately 4:00 p.m. In accordance with IP 93812, you should promptly recommend a change in inspection scope or escalation if information indicates that the assumptions used in the MD 8.3 risk analysis were not accurate. At the completion of the inspection you should provide recommendations for improving the Reactor Oversight Process baseline inspection procedures and the Special Inspection process based on any lessons learned.

This charter may be modified should you develop significant new information that warrants review. Should you have any questions concerning this charter, contact Jonathan H. Bartley at (404) 997-4607.

Docket Nos.: 50-413, 50-414 License Nos.: NPF-35, NPF-52

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G SUNSI REVIEW COMPLETE OFFICE RII:DRP RII:DRP RII:DRP RII:ORA RII:ORA SIGNATURE ?RA By E-Mail/ /RA By E-mail/ /RA/ /RA/ /RA By LWert For/ NAME CRapp JBartley RCroteau LWert VMcCree DATE 04/ 10 /2012 04/ 10 /2012 04/10 /2012 04/10 /2012 04/10 /2012 E-MAIL COPY? YES NO YES NO YES NO YES NO