ISOE ･ ATC 2006 ALARA Symposium 1 Approach of Hitachi for Dose Rate Reduction October 12, 2006 Hitachi, Ltd.

ISOE ･ ATC 2006 ALARA Symposium 2 Trend of Occupational Exposure ☆ Dose rate reduction Apply water chemistry control, low Co content material, decontamination and shielding In recent year, occupational exposure in Japan is in the highest level in the world. ☆ Suppressing of Number of worker and working time Apply remote or automatic machine Review frequency and item of inspection Apply on line maintenance etc. Man-Sv ＝ Σ ｗ (Dose rate ×Number of workers ×Working time) ｗ

ISOE ･ ATC 2006 ALARA Symposium 3 Dose Rate Reduction dΓ/dt = δ× Ｃ－ λΓ Deposition ∝ Deposition × 60 Co Conc. （Ｃ） Amount （ Γ ） Rate Coeff. （ δ ） How should we reduce the deposition Γ ？ 1) To reduce the concentration of radio activities in reactor water as low as possible 2)To adopt the methods to suppress the incorporation of radio-activities in the surface film of pipings. 3)Best combination of the methods should be selected. It may be different plant by plant depending on the specific plant condition.

ISOE ･ ATC 2006 ALARA Symposium 4 Dose Rate Reduction Methods dΓ/dt = δ× Ｃ－ λΓ Deposition ∝ Deposition × 60 Co Conc. （Ｃ） Amount （ Γ ） Rate Coeff. （ δ ） Decontamination （ Chemical Decon. etc. ） HOP(*1) method Decontamination （ Chemical Decon. etc. ） HOP(*1) method -Zn Injection -Low Fe/High Ni Control -Reduction of Surface Roughness (Electric Polishing or Mechanical Polishing) -Alkaline Prefilming -HiF-Coat (Hitachi Ferrite Coating) -Air Oxidation Treatment -H 2 O 2 Preconditioning -RHR Low Temp.Operation -Zn Injection -Low Fe/High Ni Control -Reduction of Surface Roughness (Electric Polishing or Mechanical Polishing) -Alkaline Prefilming -HiF-Coat (Hitachi Ferrite Coating) -Air Oxidation Treatment -H 2 O 2 Preconditioning -RHR Low Temp.Operation Hitachi Tech. １） Reduction of Parent Nuclei of RI -Low Cobalt Mater. -Wear Resistive Mater. （ Hitachi Hyper Valve ） ２） Stabilization of RI on Fuel Surface -Improved Fe/Ni Ratio Control -Zn Injection ３） Increase of RWCU Capacity １） Reduction of Parent Nuclei of RI -Low Cobalt Mater. -Wear Resistive Mater. （ Hitachi Hyper Valve ） ２） Stabilization of RI on Fuel Surface -Improved Fe/Ni Ratio Control -Zn Injection ３） Increase of RWCU Capacity *1)Hydrazine Oxalic Acid, Potassium Permanganate

ISOE ･ ATC 2006 ALARA Symposium 5 Dose Rate Reduction Methods Hitachi Recommends Construction Phase Operating Phase /Adopt low cobalt mater. /Adopt wear resistive mater. (Hitachi Hyper Valve) /Apply Alkaline Prefilming (RWCU) /Replace to wear resistive mater. /Apply Fe/Ni ratio control /Apply H 2 O 2 precond. after decon. of PLR /Apply Zn injection /Apply chemical decontamination (HOP) /Apply RHR low temperature operation NWC* HWC** /Apply surface polishing (for S/S pipings) Reduction of conc. Reduction of δ /Apply HiF-Coat. after decon. of PLR * NWC:Normal Water Chemistry **HWC:Hydrogen Water Chemistry

ISOE ･ ATC 2006 ALARA Symposium 6 Formation & Deposition Processes of RI Inflow of 58 Co ， 58 Ni, and Fe from FW ① Dissolution of 59 Co ， 58 Ni （ spacer spring etc. ） Depo. on fuel surface （ by boiling condensation and dry-out ） Activation by neutron （ ５９ Co （ｎ、 γ ） ６０ Co 、 ５８ Ni （ｎ、 ｐ） ５８ Co ） Redissolution of radioactivity ② RW radioactivity conc. ③ Deposition on piping surface ④ Removal at RWCW Different in process between Fe-control and low Fe control Fuel area Fe control : By controlling inflow amount of Fe ①, suppress the radioactivity concentration ③. Low Fe control: By suppressing inflow of Fe ①, increase Ni conc. to reduce incorporation of radioact. ④

ISOE ･ ATC 2006 ALARA Symposium 7 Deposition of Radioactivity in Oxide Film of C/S under NWC (2)Ni(Co) x Fe 3-x O 4 Base metal (1)α-Fe 2 O 3 （ Crud ） Co 2+ Dissol. Recrystl. Crud RW Ｆｅ，Ｎｉ ions ＦｅＦｅ Co 2+ Co 2+ ・ Oxide film is mainly composed of Fe based oxides. Cr contained film is not formed in this case. ・ In this case, as supply of Fe component is abundant compared with S/S, even high Ni concentration cannot prevent 60 Co deposition in oxide film. Crystal structures in oxide films

ISOE ･ ATC 2006 ALARA Symposium 8 Concept of Prefilming 酸化皮膜厚さ プレフィル ミング ( 放射能 ) 放射能付着開始 酸化皮膜厚さ 放射能付着量 実運転 時間 放射能付着量 酸化皮膜厚さ放射能付着量 図 3 プレフィルミングの概念 従来 プレフィルミング Oxide Film Thickness and/or Radio Activity Deposition Amount Oxide Film Thickness Radio Activity Deposition Amount Time Pre-film Oxide Film Thickness Radio Activity Deposition Amount Time Start of Plant Operation Ordinary OperationEffect of Prefilming

ISOE ･ ATC 2006 ALARA Symposium 9 60 Co Deposition Rate Coefficient of RWCU System Piping dt δ= 60 Co deposition rate coeff.(cm/h) EFPH N.Suzuki ‘An ABWR Water Chemistry Control Design Concept for Low Radiation Exposure and the Operating Experience at the Fist ABWR’9 ｔｈ International Conference on Water Chemistry in Nuclear Reactor Systems (Avignon,Apr.22-26,2002) The deposition rate of RWCU carbon steel piping with alkaline prefilming is smaller than that without alkaline prefilming.

ISOE ･ ATC 2006 ALARA Symposium 10 HOP method has been applied 20 times for total 13 plants. ▼ Application HWC Application Experiences of HOP Method

ISOE ･ ATC 2006 ALARA Symposium 11 ・ After chemical decontamination, dose rate increased under HWC ・ Dose rate was decreased by Zn injection R.L.Cowan ‘Modern BWR Chemistry Operating Strategies’10 ｔｈ International Conference on Water Chemistry in Nuclear Reactor Systems (San Francisco,Oct.11-14,2004) 2500 BRAC Dose Rate(mR/hr) Mar-83 Mar-85 Mar-87 Mar-89 Mar-91 Mar-93 Mar-95 Mar-97 Mar-99 Mar-01 Mar-03 DZO Pleated Condensate Filters HWC Recirc System Decons scfm 20 scfm 35 scfm 39.6scfm Dose Rate Behavior of a US BWR

ISOE ･ ATC 2006 ALARA Symposium 12 Year after Chemical Decom Rebound Rate Dose Rate before Decon. 0 ＝ US HWC Plants Japanese NWC Plants ・ Rebound rate of Japanese NWC plants ： 20 ～ 100 ％ ・ Rebound rate of US HWC plants ： 200 ％ and over Chemical Decon. Dose rate behavior of NWC is different from that of HWC Dose Rate Behavior after Chemical Decontamination is applied Rebound Rate (-) Dose Rate after Decon.

ISOE ･ ATC 2006 ALARA Symposium 13 Oxide film is formed Oxide film is removed Chemical Decon. Oxide film is restored Outer Layer Inner Layer Base metal Crud Deposition Radioactibity ion HWC 、 NWC NWC ： normal water chemistry HWC:hydrogen water chemistry Deposition Behavior on SUS after Chemical Decontamination Base metal After the chemical decontamination, the surface of the pipings is restored to the original condition as time elapses. Under these circumstances, dose rate behaviors of the pipings are expected to be strongly affected by the water chemistry.

ISOE ･ ATC 2006 ALARA Symposium 14 Index H 2 O 2 /ppb Prefi lmin g NO ○ △ □ ◆ Yes ○□ △ Exposure time （ｈ） Amount of 60 Co deposition(Bq/cm 2 ) HWC ( 0.5ppm H2 injection into feed water) HWC (1.0ppm H2 injection into feed water) NWC NWC Prefilming * Time Dependency of Co-60 Deposition on Specimens N. Usui, M. Fuse, H. Hosokawa, S. Uchida., “Effects of Hydrogen Peroxide on Radioactive Cobalt Deposition on Stainless Steel Surface in High Temperature Water”, Nucl. Sci. Technol.,. 42, 75 (2005) *:200 hours pre exposure in NWC before HWC) The 60 Co deposition on stainless steel under HWC condition is more than that under NWC condtion

ISOE ･ ATC 2006 ALARA Symposium 15 Fine magnetite film is formed by Hi-F Coat. RI deposition on stainless steel is mitigated by this film. Hi-F Coat ： Hitachi Ferrite Coating Hi-F CoatActual Plant Oxide Film OuterFe 3 O 4 Fe 3 O 4 、 Fe 2 O 3 、 Ni （ Co)Fe 2 O 4 Inner － CoCr 2 O 4 、 Cr 2 O 3 Particle Size ＜ 0.2μ ｍ 1 ～ 10μ ｍ Thickness ＜ 0.5μ ｍ 3 ～ 10μ ｍ Film Formation Temperature 90 ℃ 280 ℃ Countermeasure to reduce the Dose Rate ー Hi-F Coat ー

ISOE ･ ATC 2006 ALARA Symposium 16 Fine film (Magnetite) is formed by Hi-F Coat Deposited Carbon Base Metal （ SUS304 ） After exposed under NWC condition for 200 h (DO: 300 ppb) After Hi-F Coat Outer Layer(Magnetite) Inner Layer(Chromate ） Coating Layer(Magnetite ） Countermeasure to reduce the Dose Rate ー Hi-F Coat ー （ SEM photographs) Base Metal （ SUS304 ） Deposited Carbon

ISOE ･ ATC 2006 ALARA Symposium 17 Co-60 deposition in HWC could be suppressed by Hi-F Coat Hi-F Coat NWC Prefilming* Reference(No prefilming) About 1/5 Exposure time(h) Countermeasure to reduce the Dose Rate ー Hi-F Coat ー （ Effect on RI Deposition) Amount of 60 Co deposition(Bq/cm 2 ) *:200 hours pre exposure in NWC before HWC

ISOE ･ ATC 2006 ALARA Symposium 18 Summary Dose rate reduction methods are reviewed stressing the role of oxide films formed on the surface of the structural components. The control of the oxide film is considered to be an essential factor for a reduction of dose rate of piping. From this point of view, we should further understand the nature of oxide films for developing an effective method of dose rate reduction. It was found that alkaline prefilming for carbon steel and ferrite coating(Hi-F coat) for recirculation piping were promising methods for dose rate reduction.