EPRI-NRC Cooperative Research Project: PWSCC Crack Initiation Characterization of Alloys 600/182 and Alloys 690/52/152 - Status Update

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1 EPRI-NRC Cooperative Research Project: PWSCC Crack Initiation Characterization of Alloys 600/182 and Alloys 690/52/152 - Status Update Paul Crooker (EPRI), Eric Focht (NRC), and Mychailo Toloczko (PNNL) EPRI LWR Materials Reliability Conference Chicago, IL August 1-4, 2016 The views expressed in this presentation are those of the authors, not necessarily those of the U.S. NRC

2 Outline Objectives Technical Approach Status and Preliminary Data Summary 2

3 Objectives Obtain primary water stress corrosion cracking (PWSCC) initiation data for Alloy 182 to support the xlpr Code development project Understand uncertainties and accuracy of PWSCC initiation models Obtain PWSCC initiation data for Alloy 690/152/52 to develop inspection requirements for components made from these alloys Support reviews of potential submittals requesting credit for the use of more resistant materials 3

4 Approach Overview The NRC and EPRI have entered into a memorandum of understanding (MOU) to conduct cooperative research on PWSCC initiation testing at PNNL The program is planned to test Alloy 600/182 and Alloy 690/152/52 for a total estimated project duration of about five years: Support xlpr validation Provide data to support inspection requirements for Alloy 690/152/52 Perform initiation testing on multiple heats/welds of: Alloy 600 to serve as a benchmark for Alloy 182 results and for a factor of improvement (FOI) for Alloy 690 results Alloy 182 as a function of stress, temperature, cold work, and possibly other factors for xlpr and for FOI benchmark for Alloy 690/152/52 Alloy 690/152/52 to obtain FOI. 4

5 Time (hours) CGR (mm/s) 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 Technical Approach Selection of Cold Work Level The French have shown that most initiation events in reactor structures occurred in a cold worked, highly stressed surface layer. PNNL+KAPL data on Alloy 600 and French data on Alloy 182 indicate a substantial decrease in SCC initiation time for a yield stress 450 MPa or plastic strain 10%. PNNL has selected 15% cold work (CW) for relevance to service components and to serve as a test accelerant. PNNL SCC crack growth rate (CGR) testing is revealing a strong difference in CGR between non-cold worked and cold worked alloy Alloy 182 Initiation Response C Primary Water cracked capsules uncracked capsules cracked tensiles uncracked tensiles CW causes 1000x-10000x higher CGR Alloy 600 CGR vs K NX6106XK-11 19%CR* MRP-55 75% 360 C M7929 MA M3935 MA service CRDM* From: Amzallag, et al., Proc. 10th Env. Deg., NACE, 2002 NX6106XK-11 15%CF* NX6106XK-11 AR(MA)* * indicates that a material has also been initiation tested 5 Toloczko, 17 th Env Deg Alloy True Stress (MPa) 360 C tests or corrected to 360 C Some tests are ongoing PNNL 03/ K (MPa m)

6 CGR (mm/s) 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 Technical Approach Selection of Cold Work Level PNNL SCC crack growth rate testing is revealing a strong difference in CGR betwen non-cold worked and cold worked Alloy % cold rolled (CR) Alloy 600 has x higher SCC CGR than non-cold worked. CW causes 1000x-10000x higher CGR Alloy 600 CGR vs K NX6106XK-11 19%CR* MRP-55 75% 360 C Response for 15% cold forged (CF) material also be evaluated to compare to non-cold worked. Strong difference in SCC CGR is consistent with strong reduction in SCC initiation time for CW Alloy 600. NX6106XK-11 15%CF* M7929 MA M3935 MA service CRDM* NX6106XK-11 AR(MA)* * indicates that a material has also been initiation tested 360 C tests or corrected to 360 C Some tests are ongoing PNNL 03/ K (MPa m) 6

7 Technical Approach Material Characterizations Yield strength measurement, hardness, general microstructure, and SEM-EDS for compositional variations are underway. Materials have been or will be SCC crack growth rate tested. Use this information to: Characterize range of SCC crack growth susceptibility of the selected materials. Allow comparisons between SCC initiation time and SCC CGR response. Alloy 182 Welds 7

8 CGR (mm/s) 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 Technical Approach Material Characterizations Crack growth rate characterization of all four Alloy 182 weldments has been completed for as-welded material. Response measured to stress intensity of as low as 10 MPa m. Studsvik and KAPL welds exhibited highest SCC susceptibility. Flawtech was midrange. Phase 2B lowest. High SCC CGRs in Studsvik and KAPL suggest possibility of very low SCC initiation times. As-welded Alloy 182 Studsvik Phase 2B K (MPa m) MRP-115 A182 75% 360 C MRP-55 75% 360 C KAPL Flawtech 360 C tests Uncorrected data. Some tests are ongoing. PNNL 03/2016 Alloy 182 Welds 8

9 Technical Approach Test Systems PNNL Facility Two 36-specimen testing systems Based on similar test system developed for DOE-NE Light Water Reactor Sustainability program All specimens at the same load; stress controlled by adjusting gauge diameter Load train will carry the load of a failed specimen Crack initiation detected using direct current potential drop (DCPD) System 1: Alloy 690/52/152 Operational since December 2015 System 2: Alloy 600/182 Operational since April 2016 PNNL 36 Specimen Load Train 9

10 Technical Approach Test System Performance The average temperature and total load (the sum of the servo load and the tare load from the pull rod) were calculated from continuous measurements during 2.4 hour intervals thus giving a measure of the long term drift. Load stable to within 3 kg Temperature drift < 0.05 C non-referenced strain (%) N2-wskdn - 15% CF Alloy 600 MA C, 1000 ppm B, 2.0 ppm Li, 25 cc/kg H 2 N2 Shakedown Test in High Temperature Water Six Instrumented Specimens All Loaded to 470 MPa servo displacement Caused by experimental changes to the DCPD electronics settings total load outlet cond T ( mc) (kg*10) 0 O-cond (µs/cm), servo (µm), load (kg*10), T ( mc) time (hrs)

11 parameter change Technical Approach Test System Performance (Cont.) Instantaneous measurements of servo load, tare load, and autoclave temperature measured every ~48 seconds (interval is adjustable) Servo load is varying by no more than +/- 0.5 kg during these measurements and represents the noise resolution of the equipment Tare load calculated from the water pressure has an hour-by-hour stability of +/- 0.5 kg Instantaneous temperature variations of +/- 0.1 C are at the measurement resolution of the system These levels of variations represent <0.5% changes in these key environmental variables NRCI2 360 C Water Shakedown instantaneous measurements every ~48 sec time (hrs) delta-tare (kg) delta-servo (kg) delta-t ( C) 11

12 Technical Approach Test System Performance (Cont.) Load Balancing Equal loading between the strings accomplished using an articulating balance plate. Friction in loading strings might prevent complete load redistribution if elongation in one string is extensive relative to the others. Testing procedure was modified such that the load is reduced by ~15% during specimen failure process to allow balance plate to operate more effectively and properly redistribute the load. U-Joint Design 12

13 Technical Approach Test System Performance (Cont.) Reduced Impact Loading Following Specimen Failure: Impact loads following specimen failure due to stored elastic energy in the string with the failing specimen may exceed the applied load by ~5% in the load string with the failed specimen. Impact loading is low in the other strings Impact absorbers attached to loading linkage to reduce impact loading. Testing procedure was modified such that the load is temporarily reduced by ~15% during specimen failure process to reduce stored elastic energy upon failure and prevent load from exceeding original target test load. 13

14 non-referenced strain (%) outlet conductivity (µs/cm) or servo displacement (µm) non-referenced strain (%) outlet conductivity (µs/cm) or servo displacement (µm) Program Status Initiation Testing NRC-EPRI Alloy 600 SCC Initiation Test #1 360 C, 1000 ppm B, 2.0 ppm Li, 25 cc/kg H 2 IN158 - A600 15% CF B, 558 MPa IN159 - A600 15% CF B, 551 MPa IN160 - A600 15% CF NX6106XK-11, 544 MPa IN161 - A600 15% CF NX6106XK-11, 547 MPa Alloy 690/152/52 testing * hours accumulated Utilizing 36-specimen test system. 3 specimens each of four heats of Alloy specimens each of Alloy 152, Alloy 152M, Alloy 52, Alloy 52M specimens are at their yield strength 120 hr initiation Alloy 600 testing 975* hours accumulated Utilizing 36-specimen test system. 6 specimens each of two heats (NX6106XK-11, B). First initiations observed in B heat at 120 and 830 hours. Expect all specimens to initiate by 2000 hours. Alloy 182 testing 800* hours accumulated Utilizing two PNNL 3-specimen test systems. Testing 3 specimens each of two welds (KAPL, Studsvik). Indications of possible initiation in <100 hours for both welds. Tests were stopped and specimens are being examined by SEM for observable cracks. * NOTE: Total hours accumulated as of 07/12/ time (hrs) NRC-EPRI Alloy 600 SCC Initiation Test #1 - String #3 360 C, 1000 ppm B, 2.0 ppm Li, 25 cc/kg H 2 specimens are at their yield strength 1 st Alloy 600 initiation IN162-15% CF B, 547 MPa IN163-15% CF B, 558 MPa IN164-15% CF NX6106XK-11, 544 MPa IN165-15% CF NX6106XK-11, 547 MPa IN162 = 830 hr 2 nd Alloy 600 initiation time at target load (hrs) 30

15 Summary NRC and EPRI are conducting cooperative research under an MOU to develop PWSCC initiation data for Alloys 600/182 and Alloys 690/52/152 to support xlpr validation efforts and inform inspection requirements for Alloy 690/52/152. NRC and EPRI contracted in 2015 with PNNL to: Develop test plan Assemble two new testing systems Obtain, process and characterize test materials, and fabricate specimens Perform testing and post-testing evaluations PNNL test plan was reviewed by expert panel. Published as EPRI Product in November Product ID# , freely downloadable at Status: Materials acquired, and specimen fabrication complete. Some materials characterization still in-progress. Alloy 690 and 52/152 weld materials tests began in December 2015 Alloy 600 and 182 weld materials tests began in April 2016 Anticipated five-year project ending in ~

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