ML030910632

Slides: Reactor Pressure Vessel Head Material Degradation by B. Sheron at Penn State University

ML030910632
Person / Time
Site:	Davis Besse
Issue date:	09/30/2002
From:	Sheron B NRC/NRR/ADPT
To:
References
FOIA/PA-2003-0018
Download: ML030910632 (28)

Text

Reactor Pressure Vessel Head Material Degradation Dr. Brian W. Sheron Associate Director for Project Ucensing and Technical Analysis Office of Nuclear Reactor Regulation h

U.S. Nuclear Regulatory Commission Penn State University September, 2002 k,

I

Overview of Presentation

• Description of Degradation

• Safety Implications

• NRC's Actions

• Licensee's Actions September 2002

Typical Pressurized Water Reactor September 2002

a Typical Reactor Vessel Head September 2002

Davis-Besse Reactor Vessel September 2002

• Control Rod Drive Mechanisms lI I

Nozzle =3 Fae Contl September 2002

Typical CRDM Nozzle A

SA-182 F304 SB-167 UNS N06600 (Alloy 600) v OobFR awr F I

P ERNiCr4 (Alloy 82)

Outer Surtaoe of RPV Head

. A RPV Head (SA-533 Gr. B Cl. 1)

- Iner Surtace of RPV Head

\\

(Stainless Steel Cladding)

J-Groove Weld EnICrF4 (Alloy 182)

September 2002 J-Groove Weld EnlCrFe-3 (Alloy 182)

Davis-Besse RPV Head Inspection

• Davis-Besse Visual Inspection of RPV Head per NRC Bulletin 2001 -01 o February - March 2002

• UT Inspection of All 69 CRDM Nozzles o5 Nozzles with Indications, 3 with Throughwall Cracks 0 Cavity Found Adjacent to Nozzle #3

• Degraded Area Near Nozzle #2

• Significant Boron and Corrosion Deposits on the RPV Head l742te>,]

September 2002

CRDM Nozzle Map Axial Cracks m

September 2002 J-Groove Weld EriCrFe-3 (Alloy 182)

RPV Head Degradation September 2002

Contributors to Degradation

• Primary Water Stress Corrosion Cracking o Susceptible Materials o Alloy 600 Nozzles o Alloy 82/182 Welds o Highly Susceptible Heat of Material o 4 Out of the 5 Nozzles with M3935 Were Cracked o High Tensile Stress Because of Weld Residual Stresses (J-Groove Weld) oAggressive Environment, High Head Operating Temperature o Leakage Through Cracks in the Nozzles September 2002

Davis-Besse.RPV Head September 2002

Opportunities to Identify Degradation

• Boric Acid Buildup on RPV Head

• Corrosion on Vessel Flanges

• Containment Radiation Monitor Filter Clogging

• Containment Air Cooler Clogging a

Septenber 2002

Safety Implications

• Structural Margins Were Significantly Degraded

• Potential for Loss-of-Coolant Accident

• Plants Are Designed to Handle Loss-of-Coolant Accidents

• Prompt Action Warranted to Verify Condition of Other Plants September 2002

NRC Actions - Davis-Besse

• Special Inspections to Assess Compliance with Regulations

• Special Inspections for Modifications, Repair, or Replacement of RPV Head

• Confirmatory Action Letter o Determine Root Cause o Evaluate Rest of Reactor Coolant System for Corrosion o Obtain NRC Approval for Any Repair or Modifications o Obtain NRC Approval for Restart Septefter 2=

A NRC Actions - Generic

• Ongoing Evaluation of Other Plants o Most Licensees Repair Leaks and Remove Any Deposits o Some Licensees Leave Minor Debris and Isolated Boron Deposits on RPV Head

• Reevaluating the Basis for Licensee's RPV Head Inspection Programs o Bulletin 2002-02 Issued in August 2002 o Programs that Rely on Visual Examinations May Need to Be Supplemented with Non-Visual NDE September 2002

NRC Actions - Internal

• Identifying Improvements to Regulatory Processes

• Identifying Improvements to Inspection Programs

• Identifying Improvements to Regulations

• Initiated Confirmatory Research Studies September 2002

2 Davis-Besse Actions

• Plant in Safe, Shutdown Condition

• Investigating Extent and Cause of Degradation

• Conducting Root Cause Analysis oTechnical o Management and Human Performance

• Replacing RPV Head with One from a Canceled Nuclear Power Plant slot REC@7¢ 1.-

September 2002

Licensee's Investigation September 2002

Licensee's Investigation V4 _

I I

September 2002

Licensee's Investigation hi l WI/-PLs September 2002

Licensee's Investigation Crack In Cladding

_ "Bulged" Area September 2002

Licensee's Investigation Crack In Cladding

[

I 7

September 2002

Licensee's Investigation,

Carbon Steel RPV Head V S Stainless Steel Cladding September 2002

Davis-Besse Actions - Root Cause

• Pressurized Water Stress Corrosion Cracking of Control Rod Drive Mechanism Nozzle o Leakage Onto Head

• Licensee's Inspection Program Inadequate and Not implemented Properly

• Changes in Plant Conditions Inadequately Investigated oArmount and Color of Deposits on RPV Head 0 Clogging of Air Coolers o Fouling of Radiation Monitor Filters I

September 2002

Davis-Besse Actions - Repairs &

Corrective Actions

• RPV Head Being Replaced

• Management Team Has Been Replaced

• Procedures for Detecting and Correcting Problems Is Being Enhanced

• Safety Focus of Plant Personnel and Managers Is Being Addressed

• Plant Safety Systems Being Inspected and Repaired, If Needed September 2002

Davis-Besse Actions Licensee has to demonstrate its readiness to operate the plant safely.

September 2002

Addational Information A

I http://www.nrc.gov/reactors/operating/ops-experience/vessel-head-degradation.html

.O l

a September 2002