Peng DeQuan*, Wang Hui, Hu Yong, Zhang BaoLiang The effect of oxygen and hydrogen on stress corrosion cracking of 304NG stainless steel in high temperature water with trace chloride ion for PWR primary loop Peng DeQuan*, Wang Hui, Hu Yong, Zhang BaoLiang (China Institute of atomic energy, P.O. Box 275-53, Beijing 102413, China) pengdequan@tsinghua.org.cn Phone:+86-10-69359296, Fax:+86-10-69358012.

Outline Background Experimental Results and discusion Conclusion

Background Stress corrosion cracking (SCC) susceptibility of stainless steel Chinese 304NG in deoxygenized, air-saturated, oxygenated and reductive hydrogen atmosphere with trace chloride ion was studied using slow strain rate testing (SSRT), the basic water chemistry is simulated the primary loop of pressurized water reactor (PWR) where high temperature and high pressure water contains boric and lithium ions.

Chemical composition of materials 304NG Element C Si S Mn P Ni Cr N Cu Co Fe concentration（wt%） 0.024 0.44 0.0016 1.48 0.021 9.68 19.43 0.11 0.081 0.054 Bal. Fig 1 Sketch of 304NG specimen for slow strain rate testing

Experimtal conditions Specimen T/℃ O2(mg/L) Cl-(mg/L) H2(MPa) Solution BLi 300 0.02 - 1000mg/L B+2.2mg/L Li Cl1 1 Cl2 2 O2BaoBLi 8 O2baoCl1 O2baoCl2 O2BLi ＞40 O2Cl1 -- O2Cl2 H2BLi 0.16 H2Cl1 H2Cl2 H2Cl5 5

Fig 2. Stress-strain curves of 304NG at different conditions in high pressure and high temperature water containing boric acid and lithium ions.

Table 3. Slow strain rate testing results of 304NG at 300℃ with different conditions Specimen Broken stress (f(kg/mm2) Elongation E(%) Broken time Tf(hour) Yield stress (s(kg/mm2) Max broken power (kg/mm) Fracture type IsccX BLi 48.08 55.17 36.78 16.512 396.26 MF - Cl1 47.925 54.84 36.56 15.172 401.75 0.6 Cl2 49.061 55.6 37.067 16.93 419.95 -0.78 O2BaoBLi 47.433 50.405 33.603 18.539 375.64 O2baoCl1 47.052 55.825 37.217 12.386 399.39 -10.8 O2baoCl2 49.594 54.925 36.617 15.92 418.41 -9.0 O2BLi 50.756 57.305 38.203 16.038 442.53 O2Cl1 49.725 52.575 35.05 16.323 389.84 8.3 O2Cl2 47.812 46.7 31.14 17.163 340.49 MF+TG 18.5 H2BLi 47.347 55.035 36.69 13.802 393.35 H2Cl1 44.528 51.99 34.66 12.15 338.07 5.5 H2Cl2 46.089 55.135 36.757 13.737 380.38 -0.18 H2Cl5 46.114 52.185 34.79 14.748 357.17 5.2 IsccX=(Tfi-Tfx)/Tfi*100%, Tfi-broken time of as-received samples, Tfx-broken time of samples at different chloride concentration. MF-Mechanical Fracture, TG-Transgranular Fracture.

Fig 3，Morphology of fractured specimens of 304NG after SSRT at oxygen or hydrogen chloride solution

Fig 4. Fractography and EDX spectrum of fractured O2BaoBLi specimen Table 4. The chemical composition of air-saturated oxygen sample at edge zone and center area (atomic percentage, at%) Position At%O At%Si At%Cr At%Mn At%Fe At%Ni B 5.75 1.19 20.06 1.75 63.02 8.22 D 11.73 1.0 20.37 1.82 58.35 6.72

Fig 5. Fractography and EDX spectrum of fractured O2BLi specimen Position O(at%) C 3.22 E 4.05

Position O Si Cr Mn Fe Ni C 3.22 0.82 21.33 2.01 63.94 8.68 E 4.05 Table 5. The chemical composition of oxygenated sample at edge zone and center area as for (atomic percentage, at%) Position O Si Cr Mn Fe Ni C 3.22 0.82 21.33 2.01 63.94 8.68 E 4.05 0.71 20.72 62.99 9.51

Conclusion Results showed the SCC susceptibility of 304NG increased with the order of air-saturated, deoxygenized, hydrogen charging and oxygenated. The tensile property of specimen with oxygenated was much better than that of air-saturated without chloride ion. The chemical analysis on fractography of tested samples showed that the oxygen content of oxygenated specimen was much lower than that of air-saturated specimen. The compact oxide film was formed on the surface of oxygenated sample, which prevent the dissolution of substrate metal. The compact oxide film could not form on the surface of air-saturated sample. If the trace chloride ion was doped in solution, the compact oxide film was destroyed, the synergy effect of chloride and oxygen was much more evident than the protective effect of oxide film, the SCC susceptibility of oxygenated sample was much higher than that of air-saturated sample.

Acknowledgement Chinese national major projects funded project 2011ZX06004-009, 2011ZX06004-017 and nuclear energy development projects funded HK • DG1001-20102301.

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