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. maintenance during the 2nd overhaul of Ulchin Unit 5 in 2006.
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]
limit
average
maximum
remarks
work dose
accumulated dose
16 (20*)
0.55
3.61
15.31
worker of ECT
* regulatory limits

6. SUMMARY - Collective dose (man-mSv) SG maintenance planned real
remarks
manway (open/close) 9
6.58
- 2.42
nozzle dam (install/remove)
8.86
- 0.14
ECT
38.5
28.02
lancing & FOSAR 12
6.25
- 5.75
total
69.5
49.71
* 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
items
2005 (the 1st OH)
2006 (the 2nd OH)
remarks
work duration
18 days
14 days
- 4 days
temperature 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

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 in radiation dose as well as raising the quality of
■ 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.