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The Improvement of ALARA for the Steam Generator Maintenance

The Improvement of ALARA for the Steam Generator Maintenance. Radiation Safety Department The 3 rd Plant, Ulchin Nuclear Power Site. CONTENTS. ■ Background ■ Summary ■ Review of ALARA ■ The main improvements and effects ■ Conclusions. BACKGROUND.

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The Improvement of ALARA for the Steam Generator Maintenance

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  1. The Improvement of ALARA for the Steam Generator Maintenance Radiation Safety Department The 3rd Plant, Ulchin Nuclear Power Site

  2. CONTENTS ■ Background ■ Summary ■ Review of ALARA ■ The main improvements and effects ■ Conclusions

  3. BACKGROUND ■ALARA performed focusing on the SG maintenance during the 2nd overhaul of Ulchin Unit 5 in 2006. ●the highest occupational exposure ●the greatest spread of contamination ● in particular with poor radiation work environment

  4. SUMMARY ■Flow chart of SG Maintenance

  5. SUMMARY ■Radiation work dose ●work duration : 9/11/2006~10/4/2006 (24 days) ●workers : 92 persons (932 man-days) ●radiation dose - Individual dose [mSv/person] * regulatory limits

  6. SUMMARY - Collective dose (man-mSv) * ECT maintenance dose was 16.6% of the total dose for overhaul (298.7 man-mSv/34days)

  7. REVIEW OF ALARA ■SG cooling method before the year 2006 ●Tube and chamber cooled and dried by air blower after reactor coolant water made them cooled - Took a long time to reach the proper temperature (about 30℃) - The maintenance should be performed in the work environment with high temperature and humidity to meet the overhaul schedule. ● The temporary manway cover did not completely seal the hole of SG manway due to a decrease the function of the air blower to dry and purify the contamination and humidified air inside SG tube.

  8. REVIEW OF ALARA • ■Radiation protection • ●Work planning • ● Source of radiation • ● Protection of radiation worker • ●Area contamination control • ● Environmental condition of work place

  9. THE MAIN IMPROVEMENTS & EFFECTS ■Efficient maintenance minimized the radiation dose by modifying the cooling method of SG ●Cooling to utilize the heat exchanger of the SG blow down system - cooling time : about 46 hours - outlet temp of cooling water : 15℃ ●Installing the manway temporary cover-only to seal the hole of SG manway (hot leg and cold leg) - dimension : (dia.) 700 × (T) 3 mm - air exhaust hole : (dia.) 50 × (H) 80 mm - spray nozzle hole : (dia.) 50 × (T) 2 mm - material : SS304

  10. THE MAIN IMPROVEMENTS & EFFECTS ■Cooling Flow

  11. THE MAIN IMPROVEMENTS & EFFECTS ■The manway temporary cover-only BEFORE AFTER

  12. THE MAIN IMPROVEMENTS & EFFECTS ■Results ●Optimization of working environment - working hours were shorter and the troubles of ECT equipment were less than those of the previous SG maintenance ● Comparison to 2005

  13. THE MAIN IMPROVEMENTS & EFFECTS ■Reduction of radiation dose and prevention of contamination ●Dose rate reduction of work area ◆shielded the hot spot (manway retainer plate) with lead blanket - before shielding : 4.0 mSv/hr - after shielding : 0.9 mSv/hr ◆put the high radiation waste probe into the lead shield cask promptly and dispatched the cask to the temporary stored area. ◆ decontaminated quickly when the surface over the work area was contaminated from the high contaminations such as the sludge of the waste ECT equipment probe.

  14. THE MAIN IMPROVEMENTS & EFFECTS ■Prevention of internal and external contamination ●worn respirator - air supplied respirator for jumper - full-face mask for ECT and manway working ●should not touch own face and head ■Preventing the spread of contamination ●wore the safety shoes for work place-only ●kept the step barrier when going in and out ●monitored the trend of surface contamination level and air borne activity ●used the tools and equipment with proper packing, and installed the cable for ECT to the upper side ●periodically checked contamination of safety shoes and exchanged as necessary ■Decontaminated and cleaned overall area such as floor, pipes, grating etc in the end of overhaul

  15. CONCLUSIONS ■ Our plant could successfully achieve the reduction in radiation dose as well as raising the quality of maintenance by optimizing the work environment such as improvement of the SG cooling method, and decreasing the dose rate of work area. ■ Preventing the spread of contamination through absolute analysis for ALARA from the preparation to the beginning of SG maintenance.

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