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Measures for Reduction of Radiation Exposure at Higashidori Nuclear Power Station

Measures for Reduction of Radiation Exposure at Higashidori Nuclear Power Station. Nuclear Power Dept. Tohoku Electric Power Co. Higashidori NPS. Onagawa NPS. Tokyo. Tohoku Electric Power Company Nuclear Power Plants. Electricity Supply area. Onagawa MWe Type Commercial

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Measures for Reduction of Radiation Exposure at Higashidori Nuclear Power Station

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  1. Measures for Reduction of Radiation Exposure at Higashidori Nuclear Power Station Nuclear Power Dept. Tohoku Electric Power Co.

  2. Higashidori NPS Onagawa NPS Tokyo Tohoku Electric Power CompanyNuclear Power Plants Electricity Supply area Onagawa MWe Type Commercial Operation Unit-1(O-1) 524 BWR4 1984 Unit-2(O-2) 825 BWR5 1995 Unit-3(O-3) 825 BWR5 2002 Higashidori MWe Type Commercial Operation Unit-1(A-1) 1100 BWR5 2005

  3. Exposure reduction measures at Higashidori Nuclear Power Station Remote handling and automation Reliability improvement Improvement of equipment 保守・点検作業の省力化 Labor-saving in maintenance and checking 作業性の改善 Operational improvement ◎ Adoption of hollow fiber membrane filters for condensate cleanup system Adoption of weather resistant steel and low-alloy steel for turbine system Crud reduction Enhanced measures of storage during construction and commissioning Oxygen injection into feed water system Adoption of low-cobalt stainless steel Cobalt reduction Alternative to stellite Adoption of low-cobalt Inconel ◎ Electropolishing Material surface treatment Pre-filming of feedwater heater tubes ◎ Water chemistry control Operation at extremely low iron concentration Reduction of CUW pump temperature Anti-adhesion Radiation shielding Installation of permanent shielding

  4. Radiation sources that control plant doses Replacement-type sources Radioactive ions in reactor water are incorporated in the oxidized film (oxidized scale) generated on hot portions of the reactor piping system. ・PLR/ CUW piping and components Oxidized film Base metal Reactor water Ion Crud Replacement-type sources Reactor water Crud Base metal Radioactive crud in reactor water is deposited at horizontal portions and other portions where water flow is stagnant or slow. ・CRD flanges ・Filters ・Low-temperature pipe sections, such as 　　those in the RHR system ・Horizontal portions of PLR/CUW 　piping ・Nozzle sleeves Deposition-type sources

  5. Measures to reduce crud(Clean plant action No. 1) ① Improvement of work environment ② Protection ③ Maintenance of inner surface cleanliness Thorough storage management and maintenance of cleanliness on inner/outer surfaces of system piping and equipment Prevention of carried-in dust by installing air guns and jet sprays at doorways

  6. Measures to reduce crud(Clean plant action No. 2) ★ Thorough storage management During system test 系統試験時 Purity control of test water Primary system cleanup operation During start-up test ★ Condensate/feedwater purification operation ★ Condensate/feedwater swing operation Reduction of carried-in crud ★ Cleanup of hot well Cleanup of residual heat removal system Control of water treatment system Suppression of reactor water activity concentration First cycle

  7. Measures to reduce crud(Amount of crud generated in start-up test) Higashidori unit 1 Performance of existing plants for reference Other BWR units Observed Target value Onagawa units 2 and 3 Amount of crud generated in condensedwater (in kg as Fe) 340 340 255 255 220 220 270 270 230 230 320 320 ～ ～ ～ ～ Amount of carried-in crud In feedwater (in kg as Fe) 2.7 2.7 2.7 2.7 2.3 2.3 2 2 . . 5 5 2.6 2.6 3.3 3.3 ～ ～ ～ ～

  8. Water chemistry control (operation with extremely-low iron and high nickel concentrations) ニッケル鉄比制御 極低鉄運転 Fe Fe 燃料表面 ①ﾌｪﾗｲﾄ化 ①ﾓﾉｵｷｻｲﾄﾞ化 Ni,Co Ni,Co ②放射化 , 蓄積 ②放射化 での挙動 ③ Co-60 溶出 ③ Co-60 蓄積 せず、即溶出 配管 配管 配管への Co-60 Co-60 密な NiFe O 2 4 放射能付着 疎な NiFe O 2 4 取り込まれる 取り込まれない Control of nickel/iron ratio Operation with extremely low iron concentration Behavior on fuel surface (1) Ferritizing (1) Mono-oxidization (2)Activation and accumulation (2) Activation (3) Immediate elution of Co-60 without accumulation (3) Elution of Co-60 Piping Piping Adhesion of radioactive material to piping Dense NiFe2O4 Sparse NiFe2O4 ｸﾛﾑﾘｯﾁ Cr-rich Incorporated Non incorporated

  9. Water chemistry control(Progress of feed water iron concentration and reactor water nickel concentration)

  10. Material surface treatment Pre-filming of feedwater heater tubes 復水 復水 脱塩 ろ過 装置 装置 Specifications of second high-pressure feedwater heater SUS304TB-S equivalent Material Second high-pressure feedwater heater Reactor vessel 15.88 15.88 1.0mm 1.0mm × × Outer diameter x thickness Turbine Average effective length 15214mm 15214mm Total number of heat transfer tubes 2780 2780 Condenser First high-pressure feedwater heater 2 Heat transfer area 2110m　/ unit Low-pressure feedwater heater 【Steam oxidation treatment】 (first to fourth) Reactor recirculation pump Thermal treatment of heat transfer tubes is performed in a “hydrogen + steam” atmosphere. (conventionally, performed in a hydrogen atmosphere) 復水 Condensate demineralizer Condensate filtration unit 脱塩 【 【Purpose】 装置 Filtration demineralizer of reactor water cleanup system Suppression of ion elution

  11. Material surface treatment (Progress of Cr ion concentration in feedwater) Effective full power hours (until the end of the first cycle)

  12. Material surface treatment(Progress of Co-60 activity concentration in reactor water) Effective full power hours (until the end of the first cycle)

  13. Material surface treatment(Progress of Co ion concentration in reactor water) Effective full power hours

  14. Effect of radiation exposure reduction measures (No. 1) Dose rate on PLR piping Chemical decontamination performed Domestic BWRs Number of periodic inspections

  15. Effect of radiation exposure reduction measures (No. 2)(Air dose rate in reactor containment vessel) Geometrically averaged dose rate: 0.03 mSv/h n=48 Area dose rate: 0.04 mSv Area dose rate: 0.01 mSv Geometrically averaged dose rate: 0.01 mSv/h n=48 O-3 First measurement A-1 First measurement Four days after reactor shutdown On the floor of recirculation pump motor

  16. Summary Surface oxidation of feedwater heater tubes was effective in suppressing carried-in Cr ions. Suppression of carried-in Cr ions was effective in suppressing the increase of Co-60 activity concentration in the reactor water. Dose rate on PLR piping was suppressed successfully. Air dose rate in the dry well was suppressed successfully. Total radiation exposure during periodic inspection was reduced successfully.

  17. Collective Dose in BWR（2005-2007 Average）

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