IR 05000346/2002003

IR 05000346/2002-003, Davis-Besse Nuclear Power Station. Inspection Conducted on 03/12-04/05/2002, Augumented Inspection Team

ML021260141
Person / Time
Site:	Davis Besse
Issue date:	05/03/2002
From:	Dyer J NRC/RGN-III/DNMS/FCB
To:	Bergendahl H FirstEnergy Nuclear Operating Co
References
IR-02-003
Download: ML021260141 (41)

Text

SUBJECT:

DAVIS-BESSE NUCLEAR POWER STATION NRC AUGMENTED INSPECTION TEAM - DEGRADATION OF THE REACTOR PRESSURE VESSEL HEAD - REPORT NO. 50-346/02-03(DRS)

Dear Mr. Bergendahl:

Your staff provided information to the NRC between March 6 and 10, 2002, concerning the identification of a large cavity in the reactor vessel head adjacent to a control rod drive nozzle.

On March 13, 2002, the NRC issued a Confirmatory Action Letter outlining specific actions your staff are expected to take in response to this event. One of those actions is obtaining NRC approval prior to restart of the Davis-Besse plant.

On March 12, 2002, the NRC dispatched an Augmented Inspection Team (AIT) to the Davis-Besse site in accordance with NRC Management Directive 8.3, NRC Incident Investigation Program. The AIT was chartered to determine the facts and circumstances related to the significant degradation of the reactor vessel head pressure boundary material. The AIT developed a sequence of events, interviewed plant personnel, collected and analyzed factual information relevant to the degraded condition and conducted visual inspections of the reactor vessel head. The enclosed report provides the AIT findings which were summarized for you and your staff during a public exit meeting on April 5, 2002.

The cavity in the reactor vessel head was discovered during maintenance activities for problems found during inspections conducted pursuant to NRC Bulletin 2001-01, Circumferential Cracking of Reactor Pressure Vessel Head Penetration Nozzles. The degraded area covers approximately 30 square inches where the thick low-alloy structural steel was corroded away, leaving only the thin stainless steel cladding layer as a pressure boundary for the reactor coolant system. This represents a loss of the reactor vessels pressure retaining design function, since the cladding was not considered as pressure boundary material in the structural design of the reactor pressure vessel. While the cladding did provide a pressure retaining capability during reactor operations, the identified degradation represents an unacceptable reduction in the margin of safety of one of the three principal fission product barriers at the Davis-Besse Nuclear Power Station.

The AIT concluded that the cavity was caused by boric acid corrosion from leaks through the control rod drive nozzles in the reactor vessel. These leaks were caused by primary water stress corrosion cracking of the nozzle material leading to a through-wall crack and corrosion of low alloy steel that went undetected for an extended period of time. The boric acid corrosion control program at the site included both cleaning and inspection requirements, but was not effectively implemented to detect the leakage and prevent the significant corrosion of the reactor vessel head over a period of years. Similarly on several occasions, maintenance and corrective action activities failed to detect and address the indications in the containment that the significant corrosion of the reactor vessel head was occurring. The NRC views these as missed opportunities to identify and correct this significant degradation to the reactor pressure vessel head.

The AIT did not address the verification of compliance with NRC rules and regulations, provide recommendations for enforcement actions, or assess the risk significance of this issue. A followup special inspection effort will be scheduled in the near future to pursue these aspects of the regulatory process.

In accordance with 10 CFR 2.790 of the NRCs "Rules of Practice," a copy of this letter and its enclosures will be available electronically for public inspection in the NRC Public Document Room or from the Publicly Available Records (PARS) component of NRCs document system (ADAMS). ADAMS is accessible from the NRC Web site at http://www.nrc.gov/NRC/ADAMS/index.html (the Public Electronic Reading Room).

Sincerely,

/RA by J. L. Caldwell for/

J. E. Dyer Regional Administrator Enclosure: NRC Augmented Inspection Report No. 50-346/02-03(DRS)

cc w/encl: B. Saunders, President - FENOC Plant Manager Manager - Regulatory Affairs M. OReilly, FirstEnergy Ohio State Liaison Officer R. Owen, Ohio Department of Health Public Utilities Commission of Ohio