1. Measures for containing an increase in pipes’ dose-equivalent rate in the hydrogen-injected environment at the Shimane Nuclear Power Station Unit 1 １ Tomohiro Minami The Chugoku Electric Power Co., Inc. Shimane Nuclear Power Station

2. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Table of Content ○ Outline of Shimane Nuclear Power Station ○ Hydrogen injections performance at Shimane Nuclear Power Station ○ Transition of PLR piping dose-equivalent rate ○ Management of gradual hydrogen injection termination ○ Current piping dose-equivalent rate ○ Future tasks ２

3. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Niigata Tokyo Fukuoka Hiroshima Osaka Sendai Kyoto CHUGOKU REGION Sapporo SHIMANE NUCLEAR POWER STATION Shimane Prefecture Yamaguchi Prefecture Hiroshima Prefecture Okayama Prefecture Tottori Prefecture Hiroshima Matsue Yamaguchi Yonago Okayama ★ Outline of Shimane NPS(1/2) ３

4. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Outline of Shimane NPS(2/2) Unit No.Capacity (MW) Reactor Type Commerci al Operation 1460BWRMar.1974 2820BWRFeb.1989 Unit 2Unit 1 ４

5. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Hydrogen injections performance at Shimane Nuclear Power Station ５ YearOutage/Cycle Feed-water hydrogen concentration (ppm) Description January 199820th outage －・ Installed a hydrogen injection facility (Trailer system) February 199821st cycle 0 ～ 0.7 0.50 ・ Gradual injection test (increment of 0.1ppm) ・ Started continuous injection March 199922nd cycle0.45 ・ Conducted gradual injection and regular termination ・ Changed hydrogen concentration due to influence on the MS monitor May 1999 - May 2000 22nd outage －・ Conducted shroud replacement (Chemical decontamination inside the reactor in the HOP method) April 200023rd cycle0.40 ・ Changed hydrogen concentration due to influence on the MS monitor December 200124th cycle0.40 ・ Conducted gradual injection and regular termination February 200525th outage － ・ PLR piping repair work (Chemical decontamination of PLR pump inlet and outlet piping in the HOP method) August 200526th cycle －・ Preliminary oxidative operation ・ Conducted gradual injection and regular termination

6. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of PLR piping dose-equivalent rate (Pump A (21th outage)) PLR(A) inlet vertical piping PLR(A) outlet vertical piping ６

7. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of PLR piping dose-equivalent rate (Pump B (21th outage)) PLR(B) inlet vertical piping PLR(B) outlet vertical piping ７

8. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Dose-equivalent rate distribution in the axis / circumferential directions at the PLR pump outlet piping 21st outage Dose-equivalent rate of the A-PLR pump outlet piping flow ８ The fluctuation of dose- equivalent rate in the axis and circumferential directions was evaluated as attributable to cladding buildup and the increase of dose-equivalent rate.

9. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Base material In the HWC environment (low hydrogen peroxide), reactor water is in reductive atmosphere, oxidizing chromium acid forms clad deposits on piping internal surfaces. In the NWC environment, chromium oxide clad on piping's internal surfaces ionizes and elutes into the reactor water. Chromium forms under the HWC / NWC environment ９ HWC environment NWC environment Cr 2 O 3 (Insoluble) CrO 4 2- (Soluble)

10. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Hydrogen injection termination/start pattern (21st cycle) Hydrogen injection termination/start pattern in the 21st cycle 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Feed-water hydrogen concentration （ ppm ） Continuous injection started at the feed-water hydrogen concentration of 0.5ppm Termination of hydrogen injection associated with CR pattern adjustment Feed-water hydrogen concentration 0.5ppm→0.1ppm(maintained for 24 hours )→Termination 21st cycle21st outage February 1998 Start of injection 0.5ppm 0.1ppm Continuous operation for around 300 days １０ （ day ）

11. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of reactor-water conductivity and chromium acid concentration (21st cycle) １１ （ Time ）

12. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. External layer (Ferrite) Internal layer(Chromite) Clad deposit (Fe, Cr) Base material Radioactive ion Shimane Unit 1 21st outage Continuous 300-day HWC operation increased the amount of chromium deposit from reactor water. The change of environment (HWC -> NWC) eluted chromium, causing uneven piping's internal surfaces, thereby increasing the amount of cladding. Mechanism of how the dose-equivalent rate of PLR outlet piping increased (21st outage) １２

13. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Mechanism of how hot spots developed at the PLR pump outlet PLR pump outlet piping Swirls at the PLR pump and elbow outlets disturbed the flow significantly. Environmental change and flow disturbance at the pump outlet increased partial dissolution of Chromium oxides on piping's internal surfaces and aggravated surface unevenness. The amount of clad deposits at the PLR pump outlet piping showed a localized increase. Increase of dose-equivalent rate at the PLR pump outlet piping １３ After extended stable operation with hydrogen injection (around 300 days), terminated hydrogen injection and resumed the injection upon changing the pattern (12/1998). Reactor water environment Reductive → Oxidative Reactor water’s radioactive concentration increased upon termination of hydrogen injection.

14. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Management of gradual hydrogen injection termination (reflection to the 22nd cycle) Pattern of hydrogen injection termination / start Termination pattern Feed-water hydrogen concentration 0.45ppm → 0.2ppm (maintained for 24 hours) → Termination (3 days) → 0.2ppm (maintained for 24 hours) → 0.45ppm Maintained for 24 hours 0.45ppm 0.2ppm 0ppm 0.45ppm 0.2ppm Hydrogen injection termination once every three months １４ Operation for around 3 months 3 day stoppage

15. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of reactor-water conductivity and chromium acid concentration (21st and 22nd cycles) １５ （ Time ）

16. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of PLR piping dose-equivalent rate (Pump A (22nd outage)) PLR(A) inlet vertical piping PLR(A) outlet vertical piping １６

17. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of PLR piping dose-equivalent rate (Pump B (22nd outage)) PLR(B) inlet vertical piping PLR(B) outlet vertical piping １７

18. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of PLR piping dose-equivalent rate (Pump A (23rd outage)) PLR(A) inlet vertical piping PLR(A) outlet vertical piping Shroud replacement work (Chemical decontamination inside the reactor) ↓ Shroud replacement work (Chemical decontamination inside the reactor) ↓ １８

19. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Transition of PLR piping dose-equivalent rate (Pump B (23rd outage)) PLR(B) inlet vertical piping PLR(B) outlet vertical piping １９ Shroud replacement work (Chemical decontamination inside the reactor) ↓ Shroud replacement work (Chemical decontamination inside the reactor) ↓

20. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Base material Mechanism of how radioactive deposits built up in the HWC environment (23rd outage onward) ２０ HWC Environment NWC Environment Radioactive ion Clad deposits(Fe 、 Cr) External layer (Ferrite) Internal layer (Chromite) The HWC environment (low hydrogen peroxide) encourages a buildup of the external layer (ferrite) with low protective property, and an internal layer (chromite) that readily captures Co, thereby increasing the amount of Co-60 deposit. Operation under the NWC environment forms a dense external layer. This reduces elution of metal ions from the base, and contains the growth of the external layer (ferrite) and internal layer (chromite), thereby decreasing Co-60 deposits.

21. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Current PLR piping dose-equivalent rate (Pump A (25th outage)) PLR(A) inlet vertical piping PLR(A) outlet vertical piping Shroud replacement work (Chemical decontamination inside the reactor) Shroud replacement work (Chemical decontamination inside the reactor) PLR piping repair work (Chemical decontamination) PLR piping repair work (Chemical decontamination) ２１

22. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Current PLR piping dose-equivalent rate (Pump B (25th outage)) PLR(B) inlet vertical piping PLR(B) outlet vertical piping Shroud replacement work (Chemical decontamination inside the reactor) Shroud replacement work (Chemical decontamination inside the reactor) ２２ PLR piping repair work (Chemical decontamination) PLR piping repair work (Chemical decontamination)

23. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. PLR piping dose-equivalent rate after chemical decontamination (comparison with other plants) ２３

24. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Future tasks Dose-equivalent rate assessment after preliminary oxidization operation Application to Shimane Unit 2 Introduction of a startup hydrogen injection facility at Shimane Unit 1 ２４

25. All Right Reserved. Copyright © 2006,THE CHUGOKU ELECTRIC POWER CO., INC. Thank you. Measures for containing an increase in pipes’ dose-equivalent rate in the hydrogen-injected environment at the Shimane Nuclear Power Station Unit 1 ２５