ML113250495

Special Inspection Charter to Evaluate Brunswick Reactor Vessel Head Tensioning Issue

ML113250495
Person / Time
Site:	Brunswick
Issue date:	11/21/2011
From:	Mccree V Region 2 Administrator
To:	Renee Taylor Reactor Projects Branch 7
References
Download: ML113250495 (4)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II 245 PEACHTREE CENTER AVENUE NE, SUITE 1200 ATLANTA, GEORGIA 30303-1257 November 21, 2011 MEMORANDUM TO: Ryan Taylor, Senior Project Inspector Reactor Projects, Branch 7 Division of Reactor Projects FROM: Victor M. McCree /RA/

Regional Administrator

SUBJECT:

SPECIAL INSPECTION CHARTER TO EVALUATE BRUNSWICK REACTOR VESSEL HEAD TENSIONING ISSUE You have been selected to lead a Special Inspection (SI) to assess the circumstances concerning the integrity of the Brunswick Unit 2 nuclear plant reactor coolant system pressure boundary during start-up on November 16, 2011. During start-up from a scheduled outage on November 16, 2011, Brunswick declared a Notification of Unusual Event (NOUE) due to elevated drywell unidentified leakage. The licensee has initiated its own investigation including quarantining the equipment used for bolt tensioning. Your onsite inspection should begin on November 21, 2011. Eric Stamm and Phil OBryan will be assisting you in this inspection.

A. Basis On November 16, 2011, at 2:08 a.m., Brunswick Nuclear Plant Unit 2 calculated a drywall floor drain leak rate of 5.88 gpm following several hours of gradually rising floor drain leakage during a plant startup. Technical Specification 3.4.4 A was entered requiring floor drain leakage to be restored below 5 gpm within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. At 2:53 a.m.,

the calculated leak rate was 10.11 gpm. At 3:01 a.m., a NOUE was declared for unidentified leakage exceeding 10 gpm. At 3:09 a.m., the licensee initiated a manual reactor scram from approximately 7% power. Following the scram, reactor pressure was decreased and the unidentified leak rate dropped below 10 gpm within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and less than 5 gpm within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The leak rate at 6:14 a.m. was 3.82 gpm with reactor pressure at 228 psig.

The NOUE was exited at 8:15 a.m. on November 16, 2011, when leakage could be maintained below 10 gpm due to decreasing pressure. The unit was cooled down and reached cold shutdown at 2:38 p.m. on November 16, 2011.

On November 17, 2011, the licensee determined that the reactor head flange was leaking due to inadequate reactor vessel head stud tensioning. The licensee had access to 15 of 64 head studs. Twelve of the 15 stud nuts could be rotated by hand.

CONTACT: Randy Musser RII/DRP (404) 997-4603

R. Taylor 2 The specific issues of concern are:

• Was the reactor vessel head, stud, and flange damaged as a result of the head lifting after the vessel was pressurized?

• Was operator response during the event adequate?

• Was the stud tensioning process implemented properly?

• Were ASME vessel pressure testing requirements met?

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. One deterministic criteria was met. The issue involved a significant loss of integrity of the fuel, primary coolant pressure boundary, or primary containment boundary of a nuclear reactor. The updated Conditional Core Damage Probability (CCDP) for the event was in the overlap region of a Special Inspection and an Augmented Inspection Team. Following discussion with NRR, a special Inspection was deemed appropriate based on the limited technical and operational complexity of this event (flange leak).

Accordingly, the objectives of the inspection are to: (1) determine the facts surrounding the degraded condition of the Brunswick reactor vessel head; (2) evaluate the licensees response to this condition; and, (3) evaluate corrective actions.

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

• Develop a timeline associated with this event.

• Assess the ability of the reactor vessel to meet its design basis functions with the as-found condition.

• Assess the tensioning method for the head studs, the training provided to maintenance, and quality control inspectors for this evolution.

• Assess the data and procedures from the last Unit 1 refueling outage to determine if the head tensioning process was completed correctly.

• Assess the completed outage procedures for head tensioning to determine if all of the verifications and quality control hold points were completed prior to mode changes.

• Assess the condition of the reactor vessel head bolts, the reactor vessel head flange and the o-rings and seating surfaces to determine if damage occurred due to the leakage.

• Assess the test program for verifying reactor coolant system integrity after head installation to determine if the licensee was in compliance with ASME testing requirements.

R. Taylor 3

• Assess operator performance during the event to determine if there were earlier indications of RCS leakage prior to reaching mode 2 and seven percent.

• Assess the licensees activities related to the problem investigation performed to date (e.g., root cause analysis, extent of condition, additional equipment failure mechanisms, etc.), including any safety culture aspects.

• Assess the licensees actions for previous significant outage events to determine if lessons learned could have prevented the issue.

• Assess the significance of additional issues and provide recommendations to Region II if escalation to an augmented inspection is warranted.

• Document the inspection findings and conclusions in an inspection report within 45 days of the inspection.

• Conduct an exit meeting.

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 November 21, 2011. It is anticipated that the on-site portion of the inspection will be completed during the following days November 21-23, and November 28 - December 2.

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 utilized in the MD 8.3 risk analysis were not accurate. A report documenting the results of the inspection should be issued within 45 days of the completion of the inspection.

The report should address all applicable areas specified in section 3.02 of IP 93812. 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 Randy Musser at (404) 997-4603.

Docket Nos.: 50-324, License Nos.: DPR-62

ML113250495_____ G SUNSI REVIEW COMPLETE OFFICE RII:DRP RII:DRP RII:ORA RII:ORA SIGNATURE RAM RXC2 VMM for VMM NAME RMusser RCroteau LWert VMcCree DATE 11/21/2011 11/21/2011 11/21/2011 11/21/2011 E-MAIL COPY? YES NO YES NO YES NO YES NO YES NO YES NO YES NO