SCC Mapping of SUS316L in Hot Water Dissolved with Hydrogen and/or Oxygen

Transcription

1 1 st IAEA workshop on Challenges for coolants in fast spectrum system: Chemistry and materials Vienna, 5th-7th July, 2017 SCC Mapping of SUS316L in Hot Water Dissolved with Hydrogen and/or Oxygen Y.-J. Huang 1 and A. Kimura 2 1 Graduate School of Energy Science, Kyoto Unversity 2 Institute of Advanced Energy, Kyoto University 1 SUS316L(SA), SSRT, 288, 7.8MPa, Dissolved Hydrogen=0.4 ppm

2 Background-1 >>Fusion systems involve high content of tritium (hydrogen isotope). >>Water Cooled Solid Breeder (WCSB) blanket/iter-tbm In radioactive water environment > Corrosion, SCC - temperature, water chemistry, dpa,. > Radiation-enhanced radiolysis: - Dissociation of H 2 O by ionized radiation (neutrons, γ photons from plasma) - Various radiolytic species are produced inside spurs - Tritium could be involved, produce THO (isotope-exchanging phenomena) > Behaviors of these isotopes could be similar as H 2 γ photons H 2 O n e, H, H +, OH, H 2 O 2, HO 2, O 2 H 2, D 2, THO, etc Schematic of ITER ITER-TBM Cooling water SCC inducing factors. 2

3 Background-2 Stress Corrosion Cracking: - One of major degradation issues of LWRs - Three major factors: susceptible material, tensile stress, corrosive environment - Locations: core shrouds, RPV head penetrations, circulation pipes etc. - Roadmap of countermeasures: 70s 80s 90s 00s 10s 20s Materials SUS L 316L/316L(NG) Stress Environment NWC Sensitization,[O 2 ], [H 2 O 2 ] Welding heat input control Cold-Work (CW) control Metal Dissolution G.B. M n+ HWC CW@SA Manufacture QC NMCA/ONLC [H 2 ]@SA Hydrogen Embrittlement H H G.B. Crack Fission Fusion? SUS304.SEN DO 10ppm SUS316L.SA CW SCC at Shroud H6a Weld in Fukushima2 Unit3, TEPCO. JAERI (2002) SUS316L.SA DH0.4ppm 3

4 Objectives - H 2 solubility: ~ 20 ppm at 70ºC/15 MPa. i.e. radiolysis make the cooling water saturated with Hydrogen Isotope (HI) - SUS316LN piping may suffer SCC in the tritiated water at a condition of temperature and contents of dissolved HI. Objectives 1. Mapping of SCC appearance w/ different temperature and H content 2. Tailoring SCC mechanism 4

5 Experimental (1) Materials: wt% Fe Cr Ni C Mo Mn Si S P 304 bal L bal L bal metallographic of 316L Flowchart: 304,304L,316L SA:1050 o C,1h,W.Q. SEN:700 o C,100h,W.Q.@316L 650 o C,124h,W.Q.@304,304L polishing/grinding #1200-# μm -0.25μm SSRT in HT.HP water Testing condition: - Temp.: o C - Pressure:7.8,15.5,25MPa - Strain rate: /s - a.dissolved-oxygen (DO): ppm, b.dissolved-hydrogen (DH): ppm, c.deaerated (DO.DH<10ppb) Specimen: σ-ε curve, SEM, EBSD Heat treatment: SA: Solution-Annealing SEN: Sensitization 5

6 Experimental (2) Testing loops: Hot Water Loop: Parameter HW loop SCWR loop Temp. ( o C) Pressure (MPa) Flow Rate (L/h) Cond. (us/cm) <0.1 Strain rate (s-1) 5x10-7 Water condition (ppm) Dissolved-Oxygen (DO) - 10,8,4,1,0.2 Dissolved-Hydrogen (DH) 0.1,0.4, ,1.4 Deaerated DO,DH < 0.1 SCWR loop: 6

7 Results-Maps of all tests 1. SCC in DO cond. (SA/SEN) 3. Temp. Dependence in DH cond. 2. SCC in DH cond.(sa) unit: o C DO L 316L SA SEN Temp.: o C, Pressure:7.8-25MPa, ἐ:5x10-7 /s unit: ppm DH

8 1. SCC in DO cond. (SA/SEN) SCC in DO cond. (SA/SEN) unit: o C DO L 316L SA SEN Temp.: o C, Pressure:7.8-25MPa, ἐ:5x10-7 /s unit: ppm DH

9 SCC in DO cond. (SA/SEN) 1. SCC in DO (10ppm) cond. (SA/SEN) - Low carbon (304 -> 304L) - Add Mo (304L->316L) - SA heat treatment (SEN->SA) Can decrease SCC susceptibility SCC susceptibility decreases Material 304.SEN 304L.SA 304L.SEN 316L.SA 316L.SEN Side Fracture IG+TG[%]

10 SCC in DH cond. (SA) 2. SCC in DH cond. (SA) unit: o C DO L 316L SA SEN Temp.: o C, Pressure:7.8-25MPa, ἐ:5x10-7 /s unit: ppm DH

11 SCC in DH cond. (SA) 2. SCC in DH cond. (SA) Initiation: IG, Propagation: TG i.e. DH shifts SCC mechanism SUS316L-SA SUS304L.SA DH0.1 Material 304.SA 304L.SA 316L.SA Side Fracture IG+TG[%]

12 SCC in DH cond. (SA) 2. SCC in DH cond. (SA) Fracture mode analysis at 316L, DH:0.1ppm shows that surface IGSCC forms at deformed area High strain Low strain what will DH affects Solution-annealed 316LN SS, the major structure material of fusion reactor? 12

13 Temp. Dependence in DH cond. 3. Temp. Dependence in DH cond. unit: o C DO L 316L SA SEN Temp.: o C, Pressure:7.8-25MPa, ἐ:5x10-7 /s unit: ppm DH

14 Temp. Dependence in DH cond. 3. Temp. Dependence in DH cond. ( o C) 316L.SA, T test : o C Temp_DH 288_De. 288_DH _DH1.4 Side Fracture IG+TG[%] Temp_DH 150_DH _DH _DH1.4 25_DH1.4 Side Fracture IG+TG[%]

15 SCC Fracture Mode in DH cond. 3. Temp. Dependence in DH cond. ( o C) 288 o C,DH 0.4ppm, IG+TG. 316L.SA, T test : o C 288 o C,DH 1.4ppm, shows IG+TG crack, 220 o C shows TG 220 o C 288 o C 15

16 Temp. Dependence in DH cond. 3. Temp. Dependence in DH cond. ( o C) 316L.SA, T test : o C Temp_DH 500.De. 500.DH DH1.4 Side Fracture IG+TG[%] Temp_DH 288.De 340.De 288.DH DH1.4 Side Fracture IG+TG[%] o C is too high to form H 2 atmosphere at dislocation or crack tip -The intermediate temp. favors SCC -The H 2 effect is dependent on both [H 2 ] and Temp. 16

17 Temp. Dependence in DH condition 3. Temp. Dependence in DH cond. At PWR cond. (15.5MPa, DH 1.4ppm), fracture mode changes with temp. => IG area ratio drastically increase 316L.SA, T test :288/340 o C 316L.SA.DH 1.4ppm.288 o C 316L.SA.DH 1.4ppm.340 o C 17

18 Temp. Dependence in DH condition - SSRT of 316L, 25~288 o C(BWR) - SSRT of 316L, 288~500 o C (PWR/SCWR) The presence of H 2 shortened total elongation, make material brittle (HE) 18

19 Summary of Results unit: o C DO D 316L.SA D D D ST D D D D T IT T T IT T D D IT IT IT T ST D unit: ppm DH Initiation: TG, Propagation: TG Initiation: IG, Propagation: TG D:Ductile T:TGSCC / I:IGSCC IT:IG and TG ST: only surface TG - The presence of H 2 shift SCC mechanism from MD to HE - H 2 effect peaks around 340 o C, DH 1.4 ppm - Need to tailor SCC mechanism to fit IG-TG SCC phenomena 19

20 D H C H T / α Discussion-Temp. Dependence Dissolved Hydrogen (ppm) - Critical amount of H 2 at dislocation is necessary H 2 Diffusivity H 2 trapping amount HE index curve Parameters (γ-iron) Diffusivity Activation Energy Binding Energy (w/ disl.) Assumed. C L = 1.6 DH α SCC map and TGSCC boundary (soluted H 2 amount) *H 2 concentration at lattice is proportional to dissolved-hydrogen SCC No SCC DH=0.0ppm DH=0.1ppm DH=0.4ppm DH=1.4ppm SCC occur SCC No SCC SCC (only suface) Temperature ( C) ( o C) Temperature ( C) ( o C) SCC TGSCC IGSCC - TGSCC 20

21 Discussion-Fracture Mechanism H IGSCC Oxide layer H :disl. H H H H IGSCC TGSCC H Oxide layer H H IGSCC Dislocation generation Hydrogen pick up TGSCC Trapping at dislocations Hydrogen Embrittlement TGSCC 21

22 Conclusion In the fusion systems, THO in coolant may cause Hydrogen-induced SCC. Hence we made a map of SCC occurrence under BWR/PWR/SCWR environments with various water chemistry, so as to include all possible scenarios. Our conclusions are: 1. Temp. Dependence: Temp. SCC susceptibility 2. DH content dependence: DH Content,SCC susceptibility 22

23 Thanks for your attention. 23