Oconee Nuclear Station ALLOY 600 REPAIRS 1EOC23

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

Alloy 600 Locations in B&W Plants

Butt Weld Locations B&W Design Plants 5 6 9 3 4 10 2 8 13 1 7 11 12

Butt Weld Locations B&W Design Plants Application Pressurizer - Surge Line Nozzle - Spray Nozzle - PORV Nozzle - Safety Relief Nozzles Identification Number 1 2 3 4 Typical Temperature ( F) 650 Typical ID (inches) 10 4 2.5 2.5-3 Typical Number Reactor Vessel 2 - Core Flood Nozzle 5 577 14 2 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 6 7 8 9 10 11 601-605 10 12 557 28 28 2.5 1.5-2.5 12 13 RT 14 2 2 2 1. 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). 1 1 1 2 1 1 4 4 4 4

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

Scope of Work 6 Overlays

3 Relief Valve Nozzles

Spray Line Nozzle

Surge Line to Hot Leg

Surge Line to PZR

9 Replacements

6 Level Tap Nozzles

1 Vent Nozzle

ThermoWell

1 Sample Nozzle

Assumptions

Lower PZR insulation and support structure would remain in place Assumptions

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

Preparation ALARA planner attended process validation and vendor crew training

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

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

Target Dose *40 +12 Spray line will be shielded with 6 of 1.5 Radishield TM

Target Dose *60 +10 *120 +25 Shielded with 1.5 X 12 Radishield TM Spray Line Above 2 nd Grating

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

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

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

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.

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.

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

Detailed estimates created for each area/task

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

ALARA Challenges 4500 lb. LOCA restraint impacting work area

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.

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.

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.

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 35-50 mr/hr to 400-600 mr/hr Sample line increased from 10-20 mr/hr to 300 mr/hr

ALARA Challenges Shifting scope & changing conditions challenged estimate process

ALARA Successes Rapid development & deployment of remote tooling by WSI

Lower Layout Marking Tool Weld Overlay Lower Weld

Upper Layout Marking Tool

Base Metal Surface Prep

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

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.

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

ALARA Successes Use of Gamma imagery for crew briefing

1st UT - Standard PJB - 2.5 hrs 122 mr 2 nd UT - Enhanced PJB - 2.9 hrs 68 mr due to different body position

AREA INSP-RP THER SRV SAMPLE VENT SPRAY WATER SPACE STEAM SPACE HL SRG Pzr SRG TOTAL DOSE 764 659 933 895 511 1177 2618 2159 3069 6822 19,607 EXPOSURE 7114 RWP Hours

Pzr Surge Nozzle Inspect/ RP Grinding (Hand) Support Activities NDE 218 1265 2373 640 Surface Prep (Machine) Tool Setup 506 694 Welding 1126

Highest 10 Individual Exposures Exposure Distribution 411 407 407 349 343 338 328 326 319 311 # of Workers by Exposure 158 59 28 13 8 3 0-50 50-100 100-200 200-300 300-400 400+ mr

Still ahead

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