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Advancements in Hi-F Coat Application for Reducing Recontamination at Shimane Unit 1 Nuclear Plant

The application of Hi-F Coat at Shimane Unit 1 demonstrates a significant reduction in recontamination post-operation. By forming a fine magnetite film on surfaces, the technique effectively mitigates the formation of inner oxide films responsible for high dose rates. Results show a remarkable decrease in 60Co deposition, with a stable reduction in dose rates following multiple thermal cycles. This method not only enhances decontamination but also facilitates easy removal of the coating. The study suggests further benefits through the use of zinc injection to optimize the recontamination reduction process.

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Advancements in Hi-F Coat Application for Reducing Recontamination at Shimane Unit 1 Nuclear Plant

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  1. Application of Hi-F Coatfor Recontamination Reduction at Shimane Unit 1 Hitachi-ＧＥ Nuclear Energy, Ltd. M. Nagase, N. Usui, S. Oouchi Energy & Environmental Research Laboratory, Hitachi, Ltd. H. Hosokawa Chugoku Electric Power Company, Ltd. H. Kajitani, A. Yamashita, T. Minami

  2. Background • Dose rate reduction effects don’t last long after operation. • Recontamination reduction is needed to keep low dose rate.

  3. What is Hi-F Coat Principal of recontamination reduction Formation of fine outer magnetite film before power operation 　⇒Reduction of inner oxide film formation to pick upＣｏ Hi-F Coat : Hitachi Ferrite Coating

  4. Section photograph of film Formation of fine magnetite film（thickness：～0.3μm） Outer (magnetite particle） Coating layer (magnetite） Inner (chromite） Vapor deposited carbon Vapor deposited carbon Base metal（type 304 SS） Base metal（type 304 SS） Film of Hi-F Caot Film formed under NWC 200ｈ (DO: 300 ppb)

  5. Reduction effect of activity deposition（laboratory data) ・Remarkable reduction of 60Ｃｏ deposition under HWC ・Continuous effect after ６ times of heat and cool（Stable) DO:<10ppb, DH:50ppb, DH2O2:5ppb Polished (no film) Amount of 60Co deposition (Bq/cm2) ～1/5 NWC treatment Hi-F Coat treatment Time (h)

  6. Outline of treatment procedure Heat-up Fe2O3，MFe2O4 (M : Fe, Ni, Co) KMnO4 Base metal Cr2O3 Oxidation C2H2O4 N2H4 ＨＯＰ method Dissolution of chromium oxides Reduction, clean-up Repeat Base metal Decomposition, clean-up Dissolution of iron oxides Base metal Fe（HCOO）2 H2O2 N2H4 Hi-F Coat treatment Base metal Hi-F Coat method Decomposition Formation of fine ferrite (Fe3O4) film Base metal Final clean-up

  7. Surge tank （with heater） Catalyst column Additional chemical injection system Pump Cooler Ion exchange column Target （PLR piping etc.） Filter Pump Outline of Hi-F Coat treatment equipments Only a little equipments are needed to decontamination equipments.

  8. Outline of Hi-F Coat treatment chemicals Only iron formate is added to HOP method chemicals. *：LOMI is one of chemical decontamination method.

  9. Target of HOP decontamination & Hi-F Coat PLR piping・PLR pump inlet & outlet・Ring header ・Riser piping (A & B loops)

  10. Hi-F Coat treatment conditions

  11. Hi-F Coat treatment results Test piece unit Surge tank P Temporary piping P

  12. Hi-F Coat treatment results More than target value of 0.1μm（60μg/cm2) was achieved.

  13. Surface observation (SEM)

  14. Dose rate of PLR piping (1/2)

  15. Dose rate of PLR piping (2/2)

  16. Effect of dose rate reduction (1/4) Point 1: inlet piping

  17. Effect of dose rate reduction (2/4) Point 2: inlet piping

  18. Effect of dose rate reduction (3/4) Point 3: outlet piping

  19. Effect of dose rate reduction (4/4) Point 4: outlet piping

  20. Effect on chemical decontamination Hi-F Coat film was easy to be removed by chemical decontamination.

  21. 100 Polished 80 Hi-F Coat 60 60Co deposition amount (Bq/cm2) 40 20 0 0 2 4 6 Zn conc. (ppb) Effect of Zn injection on Hi-F Coat Farther Co deposition reduction can be expected with Zn injection. Time：500h Temp.：280℃ ECP：-0.5V Hitachi laboratory data

  22. Summary • Hi-F Coat was first applied to Shimane Unit 1 after chemical decontamination. • Hi-F Coat treatment was successfully applied to the decontaminated surface. Deposited amount of film was about 270 μg/cm2 which was more than target value of 60 μg/cm2. • Recontamination was suppressed about 1/2 to 1/3 after one operation cycle. • Coated film was easy to be removed by chemical decontamination. • Farther dose rate reduction can be expected with Zn injection.

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