ML101370125

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Recent SCC Incidents and Commendable Practices in the U.S
ML101370125
Person / Time
Site: Davis Besse 
Issue date: 05/25/2010
From: Csontos A, Darrell Dunn, David Rudland, Robert Tregoning
NRC/RES/DE, NRC/RES/DE/CIB, NRC/RES/DE/CMB
To:
Dunn, Darrell - RES/DE/CMB 301-251-7621
References
Download: ML101370125 (20)
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Text

Recent SCC Incidents and Commendable Practices in the U.S.

Mr. Darrell S. Dunn Dr. Aladar A. Csontos, Dr. David Rudland, and Dr. Rob Tregoning U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research

Presentation Outline

Primary water stress corrosion cracking (PWSCC)

Weld residual stress program

  • Commendable practices in the U.S.
  • Future efforts May 25, 2010 2

OECD/NEA Workshop

Davis-Besse -

2002 SCC Observations

  • 2003 - Reactor pressure vessel head (RPVH) was replaced Unused, similar design from the canceled Midland plant Alloy 600 with Alloy 182/82 welds Temporary replacement until new RPV head manufactured May 25, 2010 OECD/NEA Workshop 3

Davis-Besse -

2010 SCC Observations

  • March 2004 - Davis-Besse restarted Inspected nozzles prior to service No boric acid leakage identified in bare metal visual inspections o 2005 mid-cycle o 2006 refueling outage o 2008 refueling outage March 2010 - PWSCC identified during NRC-required inspections Licensee has confirmed one nozzle with active leakage Licensee is repairing twenty-four penetration nozzles o Twelve nozzles had rejectable UT indications o Four welds/nozzles had rejectable PT indications o Eight welds had rejectable ET indications No significant boric acid corrosion damage 5.5 EFPY with replacement RPVH Half nozzle repair will be conducted Planned RPVH replacement in 2014 Alloy 690 nozzles with Alloy 152/52 welds May 25, 2010 OECD/NEA Workshop 4

NRC Research-IASCC Areas of Study

  • Causes, mechanisms and effects of SCC on BWR internals
  • Effect of welding, thermal processes, and cold work on crack growth rates 10-9 10-8 10-7 al CGR (m/s) 6 x NUREG-0313 Curve Irradiated Stainless Steels 289C Open Symbols: NWC BWR Env.

Closed Symbols: HWC BWR Env.

on crack growth rates

  • Crack growth rate models for BWRs and PWRs
  • IASCC mitigation methods Hydrogen water chemistry Grain boundary engineering
  • Radiation embrittlement
  • Void swelling
  • Stress relaxation May 25, 2010 OECD/NEA Workshop 5

10-12 10-11 10-10 5

10 15 20 25 30 35 40 304L 3.0 dpa 316L 3.0 dpa 316 3.0 dpa 347 2.5-3.0 dpa 304 4.0 dpa Experimenta Stress Intensity K (MPa m1/2)

Material & Dose NUREG-0313 Curve

NRC Research - PWSCC International collaboration

Industry representatives

Licensees

Operators

Regulators Specific working groups

Crack initiation, 1.E-08 1.E-07 1.E-06 mm/s)

MRP115 Alloy 182 A182/10 A182/100 A182/1000 PNNL A152 PNNL A52 GE A152 Crack initiation,

Crack growth rate testing

Data application Areas of Study

Cracking mechanisms

Evaluate microstructure, composition, materials processing, and fabrication effects May 25, 2010 OECD/NEA Workshop 6

1.E-11 1.E-10 1.E-09 10 20 30 40 50 60 70 CGR (m K (MPa-m0.5)

GE A52 KAPL A52M

NRC Research -

Weld Residual Stress Program

  • Joint NRC/EPRI program Residual stress measurements o Plates and cylinders o Pressurizer surge line o Pressurizer safety and relief nozzles removed from service and mockups o Cold leg nozzles removed from service and mockups

May 25, 2010 OECD/NEA Workshop 7

SCC Mitigation -

Commendable Practices BWR

  • Environmental Modification Water chemistry Noble metal addition
  • Material Replacement S

i li d h t t t

t PWR

  • Environmental Modification Hydrogen water chemistry
  • Material Replacement Alloy 690/152/52 replacement f All 600/182/82 Specialized heat treatments Optimized compositions Cladding/inlays FSWOL
  • Stress Improvement MSIP Induction heating SI (IHSI)

Heat sink welding (HSW) of Alloy 600/182/82

  • Stress Improvement FSWOL OWOL MSIP May 25, 2010 OECD/NEA Workshop 8

PWR RCS Common Dissimilar Metal Weld Locations

  • Hot leg nozzles
  • Cold leg nozzles
  • Pressurizer surge nozzle nozzle
  • Pressuriser spray and safety relief nozzles (not shown)

May 25, 2010 OECD/NEA Workshop 9

FSWOL Example PZR Safety Nozzle May 25, 2010 OECD/NEA Workshop 10

FSWOL Evaluation

  • FSWOL provides structural layer that is y

resistant to PWSCC

  • ASME design margins are retained assuming 100%

circumferential cracking of original weld

  • Residual stress profile affected by component dimensions and method of application May 25, 2010 OECD/NEA Workshop 11 SS Safe End A508 Class 2 SS Pipe SS Buffer Layer (15 Passes)

FSWOL Evaluation Axial Stress After 182/82 weld Hoop Stress After 182/82 weld May 25, 2010 OECD/NEA Workshop 12 After SS safe end weld After FSWOL After SS safe end weld After FSWOL

Inlay Evaluation -

Natural Growth Model Nozzle Ferritic Steel (A508)

SS Cl d IN 182 Weld SS Safe End (316 SS)

SS Pipe (316 SS)

SS Weld Butter 6

6 mm 3 mm i

Alloy 52 Inlay with 182/82 dissimilar metal weld Faster crack growth rate for Alloy 182/82 Analysis must consider crack growth rates in different materials and ductile tearing May 25, 2010 OECD/NEA Workshop 13 SS Clad (304 SS)

IN 52 Inlay 6 mm min 6 mm min min

Inlay Evaluation -

Natural Growth Model Initial Flaw 1.5 mm 5 mm 6.525 years May 25, 2010 OECD/NEA Workshop 14 7.775 years 2.31 inch 9.6 years

Inlay Evaluation -

Natural Growth Model Case #

WRS case Total time, years (Idealized Growth)

Total time, years (Natural Growth)

Inlay TWC Rupture Inlay TWC Rupture 1

50% pre-service repair 9.7 25.1 33.7 11.9 31.6 37.4 2

50% PWSCC repair 10.9 15.9 24.8 8.5 NA 19.3 4

75%(2-inch) PWSCC repair 7.5 12.1 23.3 6.5 11.1 13.2 Natural crack growth slightly faster than idealized growth Significant effects even with Alloy 52 PWSCC crack growth rate improvement factors of 30 - 100 vs. Alloy 182 Sensitivity study does not support proposed inspection interval for hot leg welds May 25, 2010 OECD/NEA Workshop 15 11 75%(2-inch) PWSCC repair (A52=1/30(A182))

3.4 8.4 16 1.6 5.2 6.8 16 75%(2-inch) PWSCC repair (Larger Bending Moment) 6.9 10.2 17.5 6.0 9.5 11.5

Future Efforts -

New Nickel-based Welding Alloys

  • Improvements to weld metal composition to reduce hot cracking and ductility dip cracking susceptibility
  • NRC has material and testing plans for:

g Alloy 152M Alloy 52MSS (Mo addition)

May 25, 2010 OECD/NEA Workshop 16

Future Efforts -

PWR Water Chemistry

  • Hydrogen concentration Industry and international evaluation of both increased and decreased hydrogen concentrations Increased hydrogen may decrease PWSCC ti t

propagation rate Decreased hydrogen may reduce PWSCC initiation (radiolysis concerns at low hydrogen concentrations)

Zinc additions Beneficial for reducing worker dose Perhaps beneficial for PWSCC initiation May 25, 2010 OECD/NEA Workshop 17

Future Efforts -

Surface Modification Surface treatments have been applied as a mitigation process at susceptible locations in BWR/PWRs in Japan EPRI developing technical bases for domestic application:

Fiber Laser Peening Water Jet Peening Low Plasticity Burnishing Cold Spray ReNew & ReNew + Water Jet Peening Combination Stabilized Chrome Process NRC will review and evaluate industrys technical bases as processes are provided for approval May 25, 2010 OECD/NEA Workshop 18

Future Efforts -

Excavation and Weld Repair (EWR)

  • Potential alternative when FSWOL/OWOL or MSIP cannot be used
  • Outer portion of the tibl DMW susceptible DMW, dilution zone, and HAZ removed by excavation
  • Excavated weld repaired with Alloy 52M
  • Temper bead welding technique (no PWHT)

May 25, 2010 OECD/NEA Workshop 19 Excavated weld material Weld Repair

Summary

  • Recent SCC incidents have been identified during mandated inspections
  • Commendable practices have been effective in reducing SCC frequency and consequences
  • No PWSCC has been observed in subsequent inspections of components after mitigation by FSWOL inspections of components after mitigation by FSWOL, MSIP, or material replacement with Alloy 690/152/52
  • The NRC is actively engaged with industry efforts in the development and evaluation of SCC mitigation methods
  • Inspection criteria, results of confirmatory research, and process modeling will be used to assess improvements to existing mitigation methods as well as methods currently under development May 25, 2010 OECD/NEA Workshop 20
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