ML022750053

Brian Sheron Presentation to INPO on August 29, 2002 Re Davis-Besse RPV Head Corrosion Activities: Status & Future Plans on Vhp Nozzle & RPV Head Inspections

ML022750053
Person / Time
Site:	Davis Besse
Issue date:	08/29/2002
From:	Sheron B Office of Nuclear Reactor Regulation
To:
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Download: ML022750053 (11)

Text

DAVIS-BESSE RPV HEAD CORROSION ACTIVITIES:

STATUS AND FUTURE PLANS ON VHP NOZZLE AND RPV HEAD INSPECTIONS Brian Sheron US Nuclear Regulatory Commission Office of Nuclear Reactor Regulation NRC/INPO Conference August 29, 2002

BACKGROUND ON VHP NOZZLE CRACKING

& RPV HEAD DEGRADATION HISTORY

 First cracking of CRDM nozzles identified in France in 1991 - axial cracking

 Industry analyses - axial cracking not a safety concern; circ. cracking unlikely

 NRC issued Generic Letter 97-01

 Spring 2001 Outages -- Circumferential flaws detected (boric acid deposits)

< Oconee Units 2 & 3 - 2 nozzles 165E through-wall cracks

< Chronology of circumferential cracks Axial cracks in J-groove welds or HAZ allow leakage into annular region Leakage to vessel head OD may be restricted by interference fit of nozzles Circumferential cracks initiate on OD and grow in aggressive environment

 NRC issued Bulletin 2001-01 (August 2001) - inspections for circumferential cracks

 Spring 2002 Outages - vessel head degradation identified at Davis-Besse

 NRC issued Bulletin 2002-01 (March 2002) - no head degradation at other plants

 NRC issued Bulletin 2002-02 (August 9, 2002) - inspections to prevent leakage Typical Reactor Vessel Head - Oconee Unit 1 (Babcock & Wilcox)

Schematic View of B&W Design CRDM Nozzle Area FUTURE INSPECTIONS

 Management by leakage detection not considered sufficient

< Visual examination inspectability

< Insufficient Davis-Besse root cause report

< Technical specification limit of no pressure boundary leakage

 Need further information to support visual examinations alone

< On-going MRP activities

< Support not sufficiently mature at this time

< Lack of understanding about wastage (corrosion) rates

< Lack of predictive models for crack growth in welds

< Cracking is becoming more prevalent as plants age BULLETIN 2002-02 EXAMPLE INSPECTIONS

 High Susceptibility Plants ( > 12 EDY) - ~ 33 plants

< UT of nozzle base metal every RFO

< Surface examination (eddy current or PT) every RFO

< Bare metal visual every RFO

 Moderate Susceptibility Plants ( > 8 EDY & <12 EDY) - ~ 15 plants

< UT of nozzle base metal at RFO after next RFO and then every other RFO

< Surface examination (eddy current or PT) at RFO after next RFO and then every other RFO

< Bare metal visual at next RFO and then every other RFO

 Low Susceptibility Plants ( < 8 EDY) - ~ 21 plants

< UT of nozzle base metal within 5 years and then at least once every 5 years

< Surface examination (eddy current or PT) within 5 years and then at least once every 5 years

< Bare metal visual within 3 years and then at least once every 5 years PLANNED SUPPLEMENT TO BULLETIN 2002-01

 Bulletin 2002-01 issued March 18, 2002

< Within 60-days: Describe boric acid corrosion prevention program for ensuring integrity of reactor coolant pressure boundary

 Licensee responses inadequate due to:

< Lack of specificity regarding BAC prevention programs Inspection techniques Scope and frequency of inspections Degree of insulation removal Evaluation criteria Corrective actions

< Staff could not make a reasonable assurance finding that the boric programs have been implemented effectively.

OUTLOOK FOR ADDRESSING VHP NOZZLE AND RPV HEAD INSPECTIONS

 Review Bulletin 2002-02 responses - status of inspection plans

< Pursue regulatory actions for plants with inadequate inspections

 Develop technical basis to support inspection programs

 Pursue changes to ASME Section XI

< Section XI Task Group on Alloy 600/182/82 Issues

< Request for formation of task group on changes to inspection requirements Insulation removal Inaccessible components Local corrosion areas

 Revise 10 CFR 50.55a as appropriate INDUSTRY NEEDS TO TAKE MORE PROACTIVE ACTIONS TO ADDRESS ISSUES

 Industry needs to provide adequate technical justification to reduce necessary reliance on supplemental non-visual examinations

 New heads with Inconel 690 tubes will have to follow the same inspection criteria as head with Inconel 600 until industry provides technical basis for changes NRC WEB-SITE INFORMATION Alloy 600 Cracking (including Circumferential Cracking of CRDM Nozzles) http://www.nrc.gov/reactors/operating/ops-experience/alloy600.html RPV Head Degradation http://www.nrc.gov/reactors/operating/ops-experience/vessel-head-degradation.html