The Improvement of ALARA for the Steam Generator

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

SUMMARY ■ Flow chart of SG Maintenance

SUMMARY ■ Radiation work dose ● work duration : 9/11/2006~10/4/2006 (24 days) ● workers : 92 persons (932 man-days) ● radiation dose - Individual dose [m. Sv/person] maximum limit 16 (20*) average 0. 55 * regulatory limits work dose accumulated dose 3. 61 15. 31 remarks worker of ECT

SUMMARY - Collective dose (man-m. Sv) SG maintenance planned real remarks manway (open/close) 9 6. 58 - 2. 42 nozzle dam (install/remove) 9 8. 86 - 0. 14 38. 5 28. 02 - 10. 48 12 6. 25 - 5. 75 69. 5 49. 71 - 19. 79 ECT lancing & FOSAR total * ECT maintenance dose was 16. 6% of the total dose for overhaul (298. 7 man-m. Sv/34 days)

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.

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

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 : SS 304 ●

THE MAIN IMPROVEMENTS & EFFECTS ■ Cooling Flow

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

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 items 2005 (the 1 st OH) 2006 (the 2 nd OH) remarks 18 days 14 days - 4 days about 80℃ less than 30 ℃ - 50 ℃ replacement of ECT probe 176 ea 117 ea - 59 ea work dose [man-m. Sv] 72. 07 49. 71 - 22. 36 work duration temperature in chamber

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 m. Sv/hr - after shielding : 0. 9 m. Sv/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.

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

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.