the improvement of alara for the steam generator maintenance radiation safety department the 3 rd...
DESCRIPTION
BACKGROUND ■ ALARA performed focusing on the SG maintenance during the 2 nd overhaul of Ulchin Unit 5 in ● the highest occupational exposure ● the greatest spread of contamination ● in particular with poor radiation work environmentTRANSCRIPT
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The Improvement of ALARA The Improvement of ALARA for for
the Steam Generator the Steam Generator MaintenanceMaintenance
Radiation Safety Department The 3rd Plant, Ulchin Nuclear
Power Site
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CONTENTS
■ Background ■ Summary■ Review of ALARA ■ The main improvements and
effects ■ Conclusions
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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
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SUMMARY ■ Flow chart of SG Maintenance
RCS COOLING & DRAIN
SG MANWAYOPEN
SG MANWAYTEMPORARY
COVER INSTALL
AIR BLOWERINSTALL
SG TUBECOOLING & DRAIN
NOZZLE DAMINSTALL
ECTLANSINGFOSAR
NOZZLE DAMREMOVE
SG MANWAYCLOSE
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SUMMARY■ Radiation work dose
● work duration : 9/11/2006~10/4/2006 (24 days) ● workers : 92 persons (932 man-days) ● radiation dose
limit average maximum
remarks work dose accumulate
d dose 16
(20*) 0.55 3.61 15.31 worker of ECT
* regulatory limits
- Individual dose [mSv/person]
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SUMMARY - Collective dose (man-mSv)
SG maintenance planned real remarks
manway (open/close) 9 6.58 - 2.42nozzle dam (install/remove) 9 8.86 - 0.14
ECT 38.5 28.02 - 10.48
lancing & FOSAR 12 6.25 - 5.75
total 69.5 49.71 - 19.79
* ECT maintenance dose was 16.6% of the total dose for overhaul (298.7 man-mSv/34days)
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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.
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REVIEW OF ALARA
■ Radiation protection● Work planning● Source of radiation● Protection of radiation worker● Area contamination control● Environmental condition of work place
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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
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■ Cooling Flow
THE MAIN IMPROVEMENTS & EFFECTS
SG
A
SG
B
wet lay-uprecirculation
pump A
wet lay-uprecirculation
pump B
non-regeneration heat exchanger A, B
mixed beddemineralizer A, B
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THE MAIN IMPROVEMENTS & EFFECTS■ The manway temporary cover-only
BEFORE AFTER
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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 1st OH)
2006 (the 2nd OH) remarks
work duration 18 days 14 days - 4 daystemperature in chamber about 80℃ less than 30 ℃ - 50 ℃
replacement of ECT probe 176 ea 117 ea - 59 ea
work dose [man-mSv] 72.07 49.71 - 22.36
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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.
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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
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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.