ML021080211

March 6, 2002 - RIC 2002 Presentation - W1 William R. Mccollum - Circumferential Cracking of Reactor Pressure Vessel Head Penetration Nozzles

ML021080211
Person / Time
Site:	Oconee
Issue date:	03/06/2002
From:	Mccollum W Duke Energy Corp
To:	Office of Nuclear Reactor Regulation
References
Download: ML021080211 (11)

Text

RIC 2002 Session W1 Circumferential Cracking of Reactor Pressure Vessel Head Penetration Nozzles Industry Experience: Management of RV Head Penetration PWSCC at Oconee Nuclear Station William R McCollum, Jr.

Vice President, Oconee Nuclear Station Duke Energy March 6, 2002 1

Achieving Operating Nuclear Excellence

Location of Inspection Ports 2

Achieving Operating Nuclear Excellence

Impact to Oconee Nuclear Station

• Loss of Unit Reliability

- Leakage events must be repaired

- 75 days of lost generation in repairs alone

• Radiation Exposure

- ~ 413 rem of unplanned personnel radiation exposure

- Workforce and staffing challenges

• RPV Head Replacement

- Spring 2003 Oconee Unit 3

- Fall 2003 Oconee Unit 1

- Spring 2004 Oconee Unit 2 3

Achieving Operating Nuclear Excellence

Evolution of Top of the RPV Head Bare Metal Visual Inspections

• Amount of boric acid crystals around penetrations can be very small and in some cases < 1/2 cubic inch

- Leakage may appear as popcorn pushed up around the nozzle, or as a string coming from the annulus, or as flow

• All boric acid deposits should be cleaned from head each outage

• Perform additional NDE inspections of nozzles that may be masked by boron or other deposits 4

Achieving Operating Nuclear Excellence

After Cleaning 11*

5 Achieving Operating Nuclear Excellence

Inspection Techniques

• Techniques for detection and sizing of ID flaws is now well developed

• Developed blade probe capability to search for OD circumferential indications

• Improved analysis techniques and delivery systems to increase detectability of OD nozzle cracks 6

Achieving Operating Nuclear Excellence

Evolution of Repair Techniques

• Repairs during ONS-1 RFO and ONS-3 Maintenance Outage accomplished by manual excavation and welding

• The ID Temper Bead repair technique

- First demonstrated for ONS-2 repairs 7

Achieving Operating Nuclear Excellence

Evolution of Repair Techniques

• The ID Ambient Temper Bead was developed in time for the ONS-3 Fall 2001 refueling outage

• ASME Relief Requests were needed for all repair methods 8

Achieving Operating Nuclear Excellence

Lessons Learned

• PWSCC in CRDMs is a real problem

• Significant progress has been made in a short period of time

• Alloy 600 material is very flaw tolerant and even when cracks develop the material maintains significant structural capacity 9

Achieving Operating Nuclear Excellence

Lessons Learned

• Management of PWSCC in the RPV closure head penetrations is a long term undertaking

• Less dose intensive methods for performing the inspections must be developed and the capabilities demonstrated 10 Achieving Operating Nuclear Excellence

Lessons Learned

• Clear and frequent communication with NRC Staff is imperative

• Better automated repair methods must be developed and demonstrated

• Develop management plans for other Alloy 600 locations in contact with primary water 11 Achieving Operating Nuclear Excellence