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Davis Besse Alloy 600 Mitigation Shielded Work Platform
Davis Besse Alloy 600 Mitigation Shielded Work Platform
Project Scope:
- Design and build two shielded work platforms to protect workers during an optimized weld overlay repair to be performed on two core flood nozzles simultaneously.
- Access to the nozzles required a 3’ x 3’ cut-out to be made in the five foot thick bioshield adjacent to the core flood pipe.
- Platforms were designed to be installed through this cut-out and cantilevered into the 28” inch wide annulus space between the reactor and the bioshield.
Description:
- Numerous interferences, including nuclear instrumentation tubing, check valves, and primary piping supports had to be accommodated in the design. The cut-out size limitation, as well as a tortuous access path to the cut-outs, required that the shield package be hand carried and manually installed. These 4 ton structures were installed in eight hours, and removed in less than six hours. The shielded platforms provide a tenth value reduction in radiation levels.
- Structural design, including seismic, performed using FEA analysis.
- Generated 3D virtual models of plant systems and structures to prove concept.
- Collaborated with welding contractor to ensure clearance for welding tracks and machine, and to design extremity shields and FME barriers.
- Provide 4” lead shield on platform deck, and 1” on walls in three layers of wall sections.
- Components sized for man-handling and movement through plant to installation location.
- Built full scale mockup to perfect installation methods and sequence. Mock up later used for extensive installation and removal crew training.
- The project was performed in parallel with the outage critical path without impact.