-NETNUC- SCC Properties and Oxidation Behaviour of Candidate Materials at SCW conditions NETNUC/GEN4FIN meeting , VTT, Espoo Sami Penttilä

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 2 Content Weight gain tests SCC susceptibility Status of oxidation studies using bellows system Summary

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 3 Chemical compositions of the studied alloys (wt-%) Weight gain tests MaterialChemical analysis 1 P910.1Ni 8.3Cr 0.96Mo 0.11C 0.43Mn 0.23V 0.41Si 2 P920.02Ni 8.9Cr 0.49Mo 0.08C 0.42Mn 2.1W 0.22V 0.09Si 3 HCM120.28Ni 11.9Cr 0.34Mo 0.09C 0.62Mn 1.96W 0.25V 0.34Si 0.45Cu 4 Eurofer 978.9Cr 0.11C 0.47Mn 1.1W 0.2V 0.14Ta 5 Eurofer ODS (2)0.03Ni 9.2Cr 0.02Mo 0.035C 0.4Mn 1.3W 0.21V 0.03Si 6 Eurofer ODS (1)0.05Ni 9Cr 0.02Mo 0.021C 0.36Mn 1.3W 0.21V 0.12Si 7 PM2000, ODS0.03Ni 20.1Cr 0.09Mo 0.005C 0.08Mn 0.03V 0.02Si 0.43Ti 8 316NG (LN)11.3Ni 16.6Cr 2.11Mo 0.014C 0.8Mn 0.42Si 0.07Co 0.23Cu Ni 17-19Cr 2Mn 1Si 0.08C >5*%C Ti 10 TP347H10.7Ni 17.6Cr 0.048C 1.8Mn 0.29Si 0.56Nb 11 Sanicro Ni 26.7Cr 3.34Mo 0.015C 0.065N 1.7Mn 0.41Si 0.87Cu 12 BGA415.4Ni 22.9Cr 0.14Mo 0.11C 0.19N 6.1Mn 1.5W 0.31V 0.61Nb 0.49Si 2.7Cu 13 15Cr15NiTi (1.4970)15.3Ni 15Cr 1.18Mo 0.095C 1.68Mn <0.01W 0.53Si 0.45Ti 0.04Al 0.02Cu 14 Incoloy 800H30.8Ni 20.5Cr 0.13Mo 0.06C 0.67Mn 0.36Si 0.36Ti 0.26Al 15 Inconel Fe 22.4Cr 9.1Mo 0.02C 0.05Mn 0.12W 3.3Nb 0.07Si 0.25Ti 0.29Al 16 Inconel Cr 7-11Fe 0.05C 0.5Mn 0.5Si 0.5Cu Sixteen materials from the four different alloy groups for screening stage:

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 4 Weight gains at different temperatures for selected alloys after ~600 h exposure to SCW conditions (25 MPa)

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 5 Weight gain test Weight gains of 316L pipe with different surface treatments T = 650°C, t = 1000 h, p = 25 MPa and D0 2 = 125 ppb

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 6 316L pipe samples with different surface finishes after 1000 h exposure to SCW at 650°C machinedas receivedgrit #600grit #1200

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 7 Optical images of the 316L pipe samples after 1000 h exposure to SCW at 650°C grit #1200 surface finishmachined surface oxide thickness ~ 40 – 50 µmoxide thickness ~ 2 µm

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 8 Effect of CW An enhanced Cr diffusivity increased defect density Results to a more compact and continuous (uniform diffusivity) Cr-oxide layer Dense Cr-oxide layer decrease the outward/inward transport of Fe and O Babcock-Hitachi Europe Gmbh, Advanced materials for AD700 boilers, Milano, Italy, Chemical composition, Cr content > 18% 2.GB modification → thermomechanical processing 3.Application of surface treatment, e.g. CW Improving corrosion and oxidation behavior of materials at SCW conditions

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 9 SCC susceptibility - SSRT T = 500°C and 650°C, p = 25 MPa and DO 2 = 125 ppb Strain rate of 3x10 -7 s -1 Materials 316NG 347H BGA4 PM2000

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 10 Stress-strain curves for the studied alloys under SCW conditions at 500°C and 650°C 500°C650°C

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 11 SEM images of the fracture surface of alloy after SSRT at 500°C

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 12 SEM images of the fracture surface of alloy BGA4 after SSRT at 500°C

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 13 AlloyMaximum stress (MPa) Strain to failure (%)TGSCC (y/n)IGSCC (y/n) Side craks at the gauge surface (y/n) 500°C 46545No Yes, morphology not identified 650°C NA 500°C Interrupted at 330 Interrupted at 33NA Yes, IG and TG 650 °C 19538Yes No 500°C 67526No Yes, morphology not identified 650°C 36028Badly oxidized Yes, morphology not identified 500°C 42541Yes Yes, IG 650°C NA 500°C 325Interrupted at 50No PM °C 10040No Summary of SCC susceptibility after SSRT at 500°C and 650°C under SCW conditions

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 14 Oxidation kinetic studies (CER/CEI) using pneumatic servo-controlled bellows system

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 15 Status of DB-system Problems with pressure tube material (316L) Problems with welding New miniature DB-system has been designed by P. Moilanen Purpose is to perform mechanical loading (3-PB etc.) tests for selected materials at SCW conditions Oxidation kinetic studies using CER/CEI methods CEI and CER analysis have showed that most of the commercial materials behave like semiconductors under SCW conditions

VTT TECHNICAL RESEARCH CENTRE OF FINLAND 16 Summary The oxidation rate of F/M steels is too high for SCWR core components even at the temperatures below 500°C Austenitic stainless steels, which have a good enough oxidation resistance up to 500 – 550°C have been selected as a candidate materials for most HPLWR core components 20% Cr ODS steel was selected for the fuel rod cladding material because of its excellent oxidation resistance even up to 650°C, its SCC resistance and its good creep specifications However, the SSRT results in this work are not in line with the creep strength specifications More studies are needed in the behaviour of high Cr F/M ODS steels in supercritical water Other problems with the ODS materials are the difficulties in welding and high prices Therefore these materials are recommended to applications where high strength and oxidation resistance are needed, but only little additional joining is required A possible road for the fuel cladding development may be coating of austenitic stainless steels or F/M steels Processes that have been studied are diffusion coatings (i.e. slurry application, CVD) and overlay coatings (thermal spray, PVD, electroless coatings)