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Pre-Filming Method of Reducing Metal Release from Alloy 690 for SG in Primary Water of PWR

Pre-Filming Method of Reducing Metal Release from Alloy 690 for SG in Primary Water of PWR. 2009 ISOE Asian ALARA Symposium Aomori September 9, 2009 Sumitomo Metal Industries, Ltd. Akihiro Uehira Manabu Kanzaki Kazuyuki Kitamura Hiroyuki Anada. 1. September 2009. Contents.

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Pre-Filming Method of Reducing Metal Release from Alloy 690 for SG in Primary Water of PWR

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  1. Pre-Filming Method of Reducing Metal Releasefrom Alloy 690 for SG in Primary Water of PWR 2009 ISOE Asian ALARA Symposium Aomori September 9, 2009 Sumitomo Metal Industries, Ltd. Akihiro Uehira Manabu Kanzaki Kazuyuki Kitamura Hiroyuki Anada 1 September 2009

  2. Contents • Background • 2) Selective oxidation of Cr oxide for pre-filming and characterization • Ni release of pre-filmed alloy 690 • 4) Conclusion 2 September 2009

  3. Background • Radioactive resources are mainly released metal, Co and Ni • etc. from primary water structures in PWR. • Especially, area ofSG (Steam Generator) tubescontacting • with the primary water is the largest among those • of primary water structures. • Therefore, reduction of metal release from SG tubes is • the most effective in order to reduce exposure. 3 September 2009

  4. Ni Release from SG Tubes • Radioactive nuclide that governs radiation effect is mainly 58Co which comes from • Ni base alloy used as SG tube. • It is important to study the method of reducingmetal release from SG tube from the viewpoint of reducing exposure. Steam Generator (SG) Ni releases from SG tube to primary water. Primary water SG tube 58Ni 58Ni (Alloy 690： 60Ni-30Cr-9Fe) Release Move to reactor core. Reactor Core Nuclear fuel Primary water 58Ni n(Neutron) Ni is transformed to radioactive Co. 58Co Figure 1 Adhere to primary circuit structures. 4 September 2009

  5. Ni Release from SG Tubes during Operation Cycle Main Ni release from SG tubes occurs in the early operation period. In order to reduce total Ni release, reduction of Ni release in the early operation period is the most effective. Ni release is decreasing during the early operation period because the barrier generates on the surface of SG tubes. Ni Release from SG Tubes Operation Cycle Main Ni Release Figure 2 Image of Ni Release from SG Tubes during Operation Cycle 5 September 2009

  6. Reduction of Ni Release by Pre-Filming on SG Tubes Surface Pre-filming on the SG tube surface is expected to reduce Ni release in the early operation period. Pre-filmed barrier Primary water SG tube Ni Release 58Ni Prevent Ni migration. Ni release reduction by pre-filming Operation Cycle Figure 3 Image of Ni Release Reduction 6 September 2009

  7. Commercial Application of Pre-Filming Method Co release in Higashidori Nuclear Power Station, BWR, decreased by pre-filming on the surface of feed water heater tube, about 1/2 compared with other plant without pre-filming method. (*)Sato, Tohoku Electric Power Company, The thermal and nuclear power generation convention 2008 Sendai Co Ion Concentration [ppb] Higashidori applying pre-filming method Co concentration decreased. 　EFPH (Equivalent Full Power Hours) Figure 4 Process of Co Ion Concentration in Nuclear Reactor Water 7 September 2009

  8. R&D of Pre-Filming Method to Alloy 690 As different pre-filming method from below methods, we researched oxidation at high temperature. Released metal weight (mg/dm2) Figure 5 Quantity of Released Metal during the Corrosion Test ( L. Guinard, EDF, Water Chemistry of Nuclear Reactor Systems 8, BNES, 2000) 8 September 2009

  9. Possibility of Cr Oxide as Pre-Film Candidate Cr oxide is stable in primary water of PWR. We considered that Cr oxide film is suitable as a barrier against Ni release from SG tubes to primary water during operation. Stable region of Cr2O3 Potential (Volts vs SHE) Primary water in PWR pH Figure 6 Potential-pH Diagram of Cr in 300℃ Water 9 September 2009

  10. Cr Oxide on alloy 690 Alloy 690 contains 30% Cr. We considered that Cr oxide can be formed on the surface of alloy 690 by control of oxygen potential and temperature. 2Ni+O2=2NiO 2Fe+O2=2FeO 4/3Cr+O2=2/3Cr2O3 Partial Pressure of Oxygen Cr is oxidized selectively in this region. Temperature Figure 7 Relationship between Type of Oxide and Oxidation Condition 10 September 2009

  11. Objective 1) Clarify the possibility of selective oxidation of Cr in alloy 690 by controlling oxygen partial pressure and temperature. 2) Clarify the effectiveness of pre-filming on Ni release reduction from alloy 690. 11 September 2009

  12. Preparation of Test Specimen Specimen : Alloy 690 sheet (60Ni-30Cr-10Fe) Heat treatment →Cold rolling →Sampling test specimen →Surface polishing →Pre-filming 12 September 2009

  13. Pre-Filming Method • Oxide film formation by oxygen at high temperature. • 2) H2O in H2 gas as oxygen source. Electric furnace Test specimen H2O in H2 Gas Quartz vessel Figure 8 Pre-Filming Equipment 13 September 2009

  14. Appearance of Oxide Film Bare specimen (Before pre-filming) After pre-filming Photo 1 Appearance of Specimen 14 September 2009

  15. Cross Section of Oxide Film Homogenous oxide film was formed on the surface of the specimen. Oxide film Specimen (Alloy 690) 1 μm Photo 2 Crosse Section of Oxide Film (SEM) 15 September 2009

  16. Composition of Oxide Film Oxide film is mainly composed of Cr2O3. MnCr2O4 Cr2O3 Specimen 100 120000 100000 80 Ni O Cr 80000 60 Proportion (%) of Constituent Metal Element Relative Oxygen Intensity Thickness of oxide film 60000 40 40000 Fe 20 Mn 20000 0 0 0 500 1000 1500 2000 2500 Depth from Surface (nm) Figure 9 Analysis of oxide film by SIMS 16 September 2009

  17. Ni Release Test on Various Thickness Oxide Film 17 September 2009

  18. Ni Release Test Method Platinum container After immersion in deionized water at 320 ℃ for 1000 hrs, Ni content in deionized water was measured by ICP. Electric furnace Deionized water Test specimen Figure 10 Ni Release Test Equipment 18 September 2009

  19. Ni Release Test Result of Pre-Filmed Specimen Ni release decreased from 0.9 ppm to 0.01 ppm by pre-filming, regardless of oxide film thickness. Ni release decreased Drastically by pre-filming. Figure 11 Effect of Oxide Film on Reduction of Ni Release 19 September 2009

  20. Conclusion Following results were obtained. • 1) Cr oxide film can be formed on the surface of alloy 690 • by using H2O in H2 gas at high temperature. • 2) The oxide film is mainly composed of Cr2O3. • Pre-filming of Cr2O3 decreased Ni release from alloy 690 • by a factor of 0.1. • 4) Ni release from SG tubes in PWR can be expected to reduce • by this pre-filming. 20 September 2009

  21. Thank you for your attention. 21 September 2009

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