The Improvement of ALARA for the Steam Generator Maintenance

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 9/11/200610/4/2006 (24 days)
• ? workers 92 persons (932 man-days)
• ? radiation dose

- Individual dose mSv/person
limit average maximum maximum remarks
limit average work dose accumulated dose remarks
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) 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)
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 - 22.36
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.