The Improvement of ALARA for the Steam Generator Maintenance Radiation Safety Department The 3 rd...

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

CONTENTS

■ Background ■ Summary■ Review of ALARA ■ The main improvements and

effects ■ Conclusions

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

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

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]

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)

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 : SS304

■ 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

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 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

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.

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.