The Effect of Dissolved Oxygen on Stress Corrosion Cracking of 310S in SCW

CNNC NPIC The Effect of Dissolved Oxygen on Stress Corrosion Cracking of 310S in SCW Liu Jinhua Bin Gong

Outline 1 Introduction 2 Experimental 3 Results and Discussion 4 Conclusions 5 Future Work 2016/10/28

Outline 1 Introduction 2 Experimental 3 Results and Discussion 4 Conclusions 5 Future Work 2016/10/28

1. Introduction 25 22.1 15 10 7 PV SCWR PWR CANDU PHWR BWR Critical Point PT SCWR Liquid Solid Vapour Temperature ( o C) SCWR(supercritical wate reactor), Generation IV Great thermal efficiency, Smaller and simpler system, significant economy The promising research program has already been made by Japan, Canada, EU and Russia respectively.

1. Introduction Materials for CSR1000 Fuel assembly Reactor internals Reactor vessel 310S HR3C 508-III Basic coolant chemistry Condition (25 ) ph Conductivity Cl - O 2 7 <0.1μS/cm < 0.002 ppm < 0.01 ppm CSR1000

1. Introduction Reliability Material integrity Life Irradiation dosage Coolant chemistry Waste treatment Operation supercritical water is highly corrosive to metallic materials. The coolant chemistry effect on SCWR.

1. Introduction Theory Model Kinetics Radicals effect (G-value, Rate constant) Radiolysis (O, H, OH..) SCC Corrosion For Water Chemistry Specification Corrosion products Chemical properties (Composition, solubility..) General corrosion Irradiation Corrosion effect fatigue Control methods (Purification) Monitor (ph, ECP..) Dynamical behaviors (Transfer, deposition..)

1. Introduction Current design for the SCWR * : direct cycle system 25MPa Temperature: 280 ~ 620 Selecting appropriate candidate materials for fuel cladding is the most important issue for SCWR design SCC is one of the major concerns in selection of materials and is still an important technical issue * A. Sáez-Maderuelo, D. Gómez-Briceño. Stress corrosion cracking behavior of annealed and cold worked 316Lstainless steel in supercritical water [J]. Nuclear Engineering and Design, 2016, 307: 30-38.

1. Introduction more research is urgently needed: 1. As a result of radiolysis effect, there exists an elevated dissolved oxygen 2. SCC of austenitic stainless steels is influenced by water chemistry: O 2 3. Lack of data on SCC susceptibility of 310S

Outline 1 Introduction 2 Experimental 3 Results and Discussion 4 Conclusions 5 Future Work 2016/10/28

2. Experimental Test facilities SCW-SCC Test Loop Max. Temp: 650 at 30MPa Vessel Capacity: 2.5L Flow rate: 3L/h (15~30MPa)~15L/h (8~15MPa) Inlet and outlet chemistry parameters monitor and control: O 2, H 2, ph, Cond, ORP The refresh time of autoclave can reach up to 6 times/h

2. Experimental The supercritical environment corrosion testing machine system was constructed in the end of 2012. Loop system for chemistry control SCC loading system

Material 2. Experimental 310S Solution at 1250 ºC 15min and quenched in water Chemical Composition (wt%) C Mn Si P S Cr Ni Fe Nb N Al Ti 0.064 1.48 1.62 0.021 0.003 24.51 19.55 Bal. - - - - Mechanical Properties ( room temperature) Yieth Strength (MPa) Tensile Strength (MPa) Elongation (%) 255/260 570/565 51/50.5 ASTM standard E8

2. Experimental Slow Strain Rate Tensile (SSRT) Test Temperature: 620 Pressure: 25MPa Strain rate: 7.5 10-7 s -1 DO concentration: 0 ~ 8000 ppb Specimens Characterization Strain-Stress Curve Optical Microscopy: GX71, OLYMPUS, Japan Scanning Electron Microscope: FE-SEM JSM-7500, Japan Energy Dispersive Spectroscopy: EDS-GENESIS-2000XMS Electron probe micro-analyzer: EPMA-1720, Japan

Outline 1 Introduction 2 Experimental 3 Results and Discussion 4 Conclusions 5 Future Work 2016/10/28

3. Results and Discussion stress strain curves The elongation exhibited a strong dependence on DO decreased dramatically with the increasing of DO ranged between 36 45%

3. Results and Discussion Summary of the Test Parameters and Key Results DO UTS YS Elongation Fracture time Fracture mode (ppb) (Mpa) (Mpa) (%) (hh:mm) 0 229 186 45.6 169:08 Brittle, IG 500 225 170 44.7 165:48 Brittle, IG 1000 234 184 39.8 147:30 Brittle, IG 2000 229 174 38.9 144:17 Brittle, IG 8000 233 190 36.7 133:38 Brittle, IG DO had negligible effect on both UTS and YS. Fracture mode was brittle, showing IG. Elongation and fracture time had the same tendency.

3. Results and Discussion 8000 ppb 2000 ppb 1000 ppb 500 ppb 0 ppb Before Test The length and color had obvious change. The specimens were longer, and the color was blue and black.

3. Results and Discussion Microstructure Obtained by OM (Optical Microscopy) 400 Before Test 500 ppb O 2, 620 ºC and 25 MPa 2000 ppb O 2, 620 ºC and 25 MPa

3. Results and Discussion 0 ppb O 2 500 ppb O 2 1000 ppb O 2 2000 ppb O 2 8000 ppb O 2 Morphology of gage surface 310S, 620 ºC/25 Mpa Gauge Surface Observation by SLM (Stereo Light Microscope) 25 Widely distributed over the whole gauge section. Mostly formed perpendicularly to the tensile direction.

3. Results and Discussion SEM Image of guage surface 0 ppb, 620 ºC 5000 ppb O 2, 620 ºC and 25 MPa 310S SEM Image of Gauge Surface ( 100) Density of cracks 1000ppb O 2, 620 ºC and 25 MPa 20000 ppb O 2, 620 ºC and 25 MPa 80000 ppb O 2, 620 ºC and 25 MPa

3. Results and Discussion SEM images, 620, DO 500ppb DO(ppb ) Cr Fe O 0 7.55 62.22 30.22 500 12.82 56.84 30.34 1000 16.60 52.83 30.36 2000 40.28 28.77 30.95 8000 63.91 4.61 31.48 At the corner of the cracks, the oxide film was detected by EDS.

3. Results and Discussion 0 ppb 500 ppb O 2 310S, 620 ºC/25 MPa SEM Image of Fractures Surface Covered by thick oxide 1000 ppb O 2 2000 ppb O 2 8000 ppb O 2

3. Results and Discussion 0 ppb 500 ppb O 2 310S, 620 ºC/25 MPa SEM Image of Fractures Surface Oxide was removed Failure mode Showed brittle rupture 1000 ppb O 2 2000 ppb O 2 8000 ppb O 2

3. Results and Discussion 0 ppb, 620 ºC 500 ppb O 2, 620 ºC and 25 MPa 310S, 620 ºC/25 MPa SEM Image of Fracture Surface ( 1000) 1000 ppb O 2, 620 ºC and 25 MPa 2000 ppb O 2, 620 ºC and 25 MPa 8000 ppb O 2, 620 ºC and 25 MPa We can more clearly identify the brittle rupture.

3. Results and Discussion C 0.36 Fracture Surfaces 620, DO 0ppb Cr 22.23 Cr 2 O 3 Fe 38.09 Fe 2 O 3 O 29.35 Ni 9.98 C 0.19 Cr 5.57 Cr 2 O 3 Fe 64.12 Fe 2 O 3 SEM image, exhibited similar character. EDS, element distribution was different. Cr: Center <edge O 30.12

3. Results and Discussion 0 ppb 5000 ppb 310S, 620 ºC/25 MPa Cross Section ( 25) Cracks penetrate the oxide 10000 ppb 20000 ppb 80000 ppb

3. Results and Discussion The highest crack depth increases with the increasing DO concentration Corrosion rate and the thickness of oxide film increase with increasing DO, and oxides grew inside the crack can exert higher stress at crack tips * This phenomenon is correspondent with the reduction of ductility. * Pantip Ampornrat, Gaurav Gupta, Gary S. Was. Tensile and stress corrosion cracking behavior of ferritic martensitic steels in supercritical water [J]. Journal of Nuclear Materials, 2009, 395(?): 30-36.

3. Results and Discussion Energy Dispersive Spectrometer(EDS) of eletronic probe O O 2 8000 ppb Cross Section 15.0kV( 1000) Fe Composed of three phases: Matrix Cr-riched Fe-riched Cr

3. Results and Discussion Wavelength Dispersive (WDS) of eletronic probe 620 ºC/25MPa/8000 ppb Cross Section COMPO 15.0kV 160 120μm 150.00 ms/point two-layer structures deplete Cr at crack tip Ni enriched

3. Results and Discussion SCC mechanism Synergistic effect Fe 2 O 3 Fe 3 Ospinel 4 Precipitation of Cr 23 C 6 Depletion of Cr near the grain boundary Stress concentration in the Cr 23 C 6 precipitation region Crack source such as void Cr depleted region is oxidized Fe 2 O 3 (outer) \Fe 3 O 4 (middle)\(fe,cr) 3 O 4 (inner) Grain boundary strength decreases Weak passivation at the tip of crack Base metal exposure to SCW IGSCC

Outline 1 Introduction 2 Experimental 3 Results and Discussion 4 Conclusions 5 Future Work 2016/10/28

4. Conclusions The elongation reduced dramatically with the increasing of oxygen concentration. A brittle fracture mode was observed on the fracture surface, and only IG cracks were found on the gauge surface. Cracks on 310 S were widely distributed over the whole gauge section. Crack density was high at different oxygen concentration. The highest crack depth increased with the oxygen concentration, implying that increased dissolved oxygen promotes IG cracking susceptibility. Oxides in the cracks with two-layer structures were observed, an outer Ferich oxide layer and an inner Cr-rich oxide layer.

Outline 1 Introduction 2 Experimental 3 Results and Discussion 4 Conclusions 5 Future Work 2016/10/28

5. Future Work Research on supercritical water chemistry of SCWR Schedule: Start 2017.01 End 2019.12 Material: 310S Pressure:25MPa Temperature:550 ºC 620 ºC water chemistry: hydrogen water chemistry oxygenated water chemistry alkaline water chemistry Objective: The supercritical water chemistry is considered one of the main obstacles in the development of the SCWR. The goal of this work is to evaluate these water chemistries by the corrosion experiments on 310S, and try to obtain the key water chemistry parameters.

CNNC NPIC