ALARA Activities at Ohi NPP Ohi Nuclear Power

ALARA Activities at Ohi NPP Ohi Nuclear Power Plant Kansai Electric Power Co. , Inc.

Outline of Ohi NPP １ Unit 1　　1, 175 MW Started March 1979 Unit 2　　1, 175 MW Started December 1979 Unit 3　　1, 180 MW Started December 1991 Unit 4　　1, 180 MW Started February 1993 Japan ○Fukui Wakasa Osaka Kansai

Vision for 2010 ２ Vision for 2010 Vision of Ohi NPP for the 21 century “The best nuclear power plant in the world” Actions to achieve the vision Established goals and strategies to achieve the vision Three strategies for the vision ・World’s best reliability ・World-class economic efficiency ・World-class nuclear power plant In view of major changes in the management environment and present status of the company, the vision for 2010 was introduced to survive the 21 century. ○World’s best reliability ・Capacity factor: Over 92% (three-year-average) ・Unplanned capacity factor loss: 0. 2% and below (three-year-average) ・Dose: 1. 4 man･Sv (three-year-average) ・Automatic Shutdown: 0. 1 time (three-year-average) ・Solid nuclear waste production: 1, 000 drams and less (three-year-average) ・Days without labor accidents: Continuing more than 1000 days

Main Measures Taken at Ohi NPP to Reduce Dose ３ 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Use of automatic positioner of R/V stud bolt tensioner Introduction of automatic equipment Use of cavity decontamination equipment Use of tube-sheet inspection robot during S/G tube ECT Use of lead shielding of R/V head Improved oxidization during reactor shutdown Reduction of dose equivalent in working environment Decontamination of RCP internals Chemical cleaning of inside of primary coolant thermometer bypass piping/removal of piping Decontamination of primary coolant piping internal surface Decontamination of S/G channel head Permanent installation of S/G tube ECT cable Use of S/G tube ECT probe Streamlining work activities Use of S/G manway head handling tool Use of dose equivalent rate indicator Promotion of irradiation prediction training Other measures Implementation of joint patrol for radiation control Use of labels to draw attention to radiation and designation of waiting position Schedule adjustment Start of Ohi-1 operation S/G replacement

４ Applied Primary Water Chemistry Programs Suppression of CP Generation 1970 ･ Low Cobalt Material ・ TT 690 SG Tubing ・ Improved Startup Chemistry during HFT Suppression of CP Transfer Removal of CP ・ Improved p. H Control ・ Ammonia Addition ・ Removal of CP during Shutdown (Improved Shutdown Chemistry) ・ Increase of Purification Flow Rate during Shutdown ・ Fine Mesh Filter (CVCS etc. ) 1980 1990

５ Changes of dose per unit Increase in dose due to repair work on Unit-3 reactor vessel head

６ Dose reduction activities at Ohi NPP Comparison of dose with major nations 1. Significant reduction in Belgium (reduced to about 1/3 in 10 years) 2. Ohi’s dose is nearly the same as Japan’s average, 　　　but has leveled off recently. Vision for 2010 Goal: Achieve the dose of 1. 4 man-Sv/year/4 units (on a par with the achievement of Doel NPP, which is one of the best performers according to the WANO dose index) Current status: approx. 3. 4 man-Sv/year (total dose from scheduled outage)

７ Dose from the 8 th scheduled outage at Ohi Approx. 40% of inspection-related dose is from RCP inspection Approx. 90% of RCP-related dose is from assembling of backup internals, disassembling/inspection of internals and decontamination.

８ Comparison with other units in Japan The average dose related to RCP disassembling/inspection activities is 110 man･m. Sv/RCP. The doses from the same activities at Ohi 3 and 4 are approximately twice as much. Committed to ｄｏｓｅ reduction in RCP inspection activities. Goal: Reduction to 100 man･m. Sv (lower than the average)

９ Establishment of system to review dose reduction measures ALARA working group consisting of all organizations related to RCP inspection ALARA working group Radiation Control Department of Kansai Maintenance Department of Kansai Plant management Manufacturers Opinions from various aspects Site-focused review Inspection Contractors

10 Elicit exposure factors (by questionnaire survey) Questionnaires were sent to about 50 persons involved in inspection activities to identify factors from multiple aspects.

Elicit exposure factors Major factors were identified using the cause and effect diagram. Workers: Skilled workers are required. Inspection method: The impeller still keeps high radiation dose even after decontamination; removing the impeller is time consuming; workers operate close to high dose parts. Tools: Handling of internals takes time. Environment: Shielding is inadequate. 11

Preparation and evaluation of reduction measures Important factors Detailed factors Proposed measures Specific measures Evaluation of specific measures Including dose reduction and cost efficiency 12

Measure 1: Introduction of ultrasonic cleaning unit to decontamination tank 13 Decontamin ation tank Improved by 3. 2 times Spray pipe Effluent discharge line Reduced by 32 m. Sv Ultrasonic cleaning unit ＜Currently＞ Chemical cleaning (high-pressure cleaning) alone is inadequate to clean the inside of internals. ＜Improvement＞ The effectiveness of the ultrasound unit has already been proved with the cask with decontamination function. The cleaning unit is expected to enhance decontamination at the inner surface of the bottom of internals. Expected reduction of 32 man･m. Sv

14 Measure 2: Enhancement of shielding in greenhouse RCP inspection room (greenhouse) <Currently> The walls of the inspection room consist of frames, lead sheets with 6 -9 mm thickness and 1. 6 mm steel sheets. <Improvement> 　　　　　The walls (shaded) are to be enhanced with the combination of lead and steel sheets. The enhanced shielding is comparable to the shielding effect of 20 mm lead sheet. The height is 2 m above the floor. Expected reduction of 17 man･m. Sv

15 Measure 3: Impeller shielding box <Currently> Lead shielding mats are used. They are removed when maintenance, measurement or PT inspection are conducted. <Improvement> The impeller shielding box, which enables maintenance, measurement and PT without removal, will be introduced. <Features of shielding box> 1. 60 mm steel sheets are used for shielding. 2. The shield part divided into two segments is equipped with a rotary shaft. The impeller can be revolved circumferentially. Also, it can be revolved axially with a gear box. 3. The shield has an inspection window, which allows maintenance, measurement or PT inspection without removing the impeller. <Expected reduction> Dose equivalent rate can be reduced to one seventh. 　　　 Expected reduction of 15 man･m. Sv

Measure 4: Improvement of internals hoisting device Turn buckle 16 Internals hoisting device Bracket Worker A Worker B Fixed with screw nuts Worker D Worker C High radiation <Currently> ・When handling internals with a crane, fine focusing is difficult. It takes time to fix the main flange and side bars. ・When installing and removing the hoisting device, workers close to the radiation source receive higher dose. <Improvement> ・All the activities can be performed on the main flange, which is expected to result in the reduction of dose. ・Fewer workers ・Shorter working hours Expected reduction of 9 man･m. Sv

Measure 5: Time reduction in removing the impeller When removing the impeller from the rotor, a special tool is used to fix the impeller onto bolts. Adoption of electric tool instead of manual operation can save substantial time. Expected reduction of 3 man･m. Sv Measure 6: Enhancement of training Training for less experienced workers has been enhanced by using audio and visual materials. Expected reduction of 4 man･m. Sv 17

18 Expected reduction ＜Measures＞ ＜Expected reduction　man･m. Sv＞ Introduction of ultrasonic cleaning unit to decontamination tank ３２ Enhancement of shielding in inspection room １７ Installation of impeller shielding box １５ Improvement of Internals hoisting device ９ Time saving in removing the impeller ３ Enhancement of training ４ 250 Dose（man･m. Sv） 210. 7 200 129 150 100 50 0 The 8 th scheduled outage at Ohi 4 After improvement (outage scheduled for 2008) ８２ man･m. Sv

19 First step Second step Third step Dose reduction activities related RCP disassembling 　 ＰＤＣＡ 　Verification 　　 　Reduction activities related to SG and R/V inspection Reduction efforts for regular inspection activities not covered by the measures

20 Conclusion ・Multi aspects of dose reduction possibilities were discussed through the participation of all the people involved in inspection activities including Kansai’s radiation control department, maintenance department, manufacturers and workers. Through discussions all the participants shared a common objective---the reduction of dose. The management and workers worked together to develop measures through trial and error processes. The efforts resulted in effective measures that met the needs of workers on site. ・The validation of the measures will start in 2008. After the validation continuous improvement will be made through PDCA cycle. ・The current program focuses on the inspection of RCP. We are continuously committed to dose reduction. Reduction efforts will be expanded to other inspection activities.