Oconee Nuclear Station ALLOY 600 REPAIRS 1EOC23

Transcription

1 Oconee Nuclear Station ALLOY 600 REPAIRS 1EOC23

2 We re requiring more inspections due to susceptibility of material to cracking Some utilities have implemented mitigative actions Stress improvement Weld overlays Some utilities have found indications requiring repairs Replacement Overlays Stress improvement Many utilities planning near-term mitigative actions Focusing on pressurizer welds first, mostly because of configuration

3 Alloy 600 Locations in B&W Plants

4 Butt Weld Locations B&W Design Plants

5 Butt Weld Locations B&W Design Plants Application Pressurizer - Surge Line Nozzle - Spray Nozzle - PORV Nozzle - Safety Relief Nozzles Identification Number Typical Temperature ( F) 650 Typical ID (inches) Typical Number Reactor Vessel 2 - Core Flood Nozzle RCS Hot Leg Pipe - Surge Line Nozzle - Decay Heat Nozzle RCS Cold Leg Pipe - RCP Inlet Nozzles - RCP Outlet Nozzles - High Pressure Injection Nozzles - Letdown/Drain Nozzles Core Flood Tanks - Outlet Nozzle - Pressure Relief RT Figures only show locations in pipes greater than 1" NPS and operating at temperatures greater than about 550 F. 2. As of July 2004, there are two remaining B&W plants that have reactor vessel closure heads with Alloy 600 CRDM nozzles and Alloy 82 nozzle-to-flange butt welds (69 4" welds at temperature < 605 F)

6 SRV s Vent Line Spray Line Steam Space nozzles(3) Alloy 600 Project H/L Surge Thermo Well Water Space nozzles(3) Overview Sample Line PZR Surge

7 Scope of Work 6 Overlays

8 3 Relief Valve Nozzles

9 Spray Line Nozzle

10 Surge Line to Hot Leg

11 Surge Line to PZR

12 9 Replacements

13 6 Level Tap Nozzles

14 1 Vent Nozzle

15 ThermoWell

16 1 Sample Nozzle

17 Assumptions

18 Lower PZR insulation and support structure would remain in place Assumptions

19 Assumptions Unit 1 should be similar to Units 2 & 3 Unit 3 PZR Surge nozzle

20 Preparation ALARA planner attended process validation and vendor crew training

21 Preparation A comprehensive shielding plan was compiled using planning photos from June forced outage

22 OCONEE Unit 1 Alloy 600 Shielding Plan ONS Radiation Protection/ALARA

23 Target Dose * Spray line will be shielded with 6 of 1.5 Radishield TM

24 Target Dose * * Shielded with 1.5 X 12 Radishield TM Spray Line Above 2 nd Grating

25 Custom Shielding Material Temperature Resistant / non-hazardous material was ordered Radishield 40lb/ft Pipe Wrap for Small-bore piping

26 ALARA Initiatives Area walkdowns to identify low dose areas, camera angles, and shielding opportunities Extensive digital photography to assist planners, brief crews, and reduce # of entries

27 Early removal & decon of significant dose contributors scheduled Bar Code scans created to track dose by task & area

28 Weld head attendants staged on the 4th Floor or in a shielded booth on the 2nd Grating level to allow rapid access to work areas. Equipment operators situated in the Basement and on the 4th Floor; Extensive use of remote tooling for welding and abrasive operations to minimize personnel exposure.

29 Use of 3-D drawings to provide orientation Camera coverage of work areas to reduce entries for oversight or informational purposes while allowing more flexible and efficient use of RP resources.

30 Shielded hut was constructed adjacent to work areas Enclosures were constructed to contain grinding dust

31 Detailed estimates created for each area/task

32 Detailed estimates created for each area/task

33 ALARA Challenges Unanticipated dose rates on PZR Surge nozzle Insulation restricted access to top of nozzle

34 ALARA Challenges 4500 lb. LOCA restraint impacting work area

35 ALARA Challenges Initial plan did not call for automation of pre weld surface prep process. Remote tooling was not vigorously pursued during planning and validation phases. Higher than anticipated dose rates required implementation of remote process.

36 ALARA Challenges First time deployment of tooling increased reliance on vendor provided occupancy times. This resulted in inflated dose estimates as tasks were completed in a fraction of time projected. ALARA bonus may lead vendors to inflate estimates.

37 ALARA Challenges Work on PZR Surge nozzle was initially planned for inside the Wagon Wheel opening, forcing workers into close proximity to source. We eventually removed insulation panels which changed the access and allowed work from an increased distance.

38 ALARA Challenges PZR Spray block valve remained open during induced crudburst, allowing higher activity RCS to enter the PZR and increase dose rates on lower components Instrument valves went from mr/hr to mr/hr Sample line increased from mr/hr to 300 mr/hr

39 ALARA Challenges Shifting scope & changing conditions challenged estimate process

40 ALARA Successes Rapid development & deployment of remote tooling by WSI

41 Lower Layout Marking Tool Weld Overlay Lower Weld

42 Upper Layout Marking Tool

43 Base Metal Surface Prep

44 Contour Measuring Weld System Weld Head Tractor Scanning Laser Video Front-End Laser Path

45 ALARA Successes Newly developed phased array ultrasonic techniques reduced exposure to NDE technicians. The beam direction is electronically swept through multiple angles, eliminating the need for a variety of probes.

46 ALARA Successes Modification of access to PZR Surge nozzle saved substantial dose Lower PZR insulation panels were removed to allow better access

47 ALARA Successes Use of Gamma imagery for crew briefing

48 1st UT - Standard PJB hrs 122 mr 2 nd UT - Enhanced PJB hrs 68 mr due to different body position

49 AREA INSP-RP THER SRV SAMPLE VENT SPRAY WATER SPACE STEAM SPACE HL SRG Pzr SRG TOTAL DOSE ,607 EXPOSURE 7114 RWP Hours

50 Pzr Surge Nozzle Inspect/ RP Grinding (Hand) Support Activities NDE Surface Prep (Machine) Tool Setup Welding 1126

51 Highest 10 Individual Exposures Exposure Distribution # of Workers by Exposure mr

52 Still ahead

53 Core Flood Nozzles Hot Leg Nozzles 4-48 RCP Nozzles LetDown Line Nozzle Decay Heat Nozzle