Columbia Energy was selected to design, fabricate, engineer, mockup and prototype test, and deliver to Washington River Protection Solutions a Large Riser for installation in the 241-C Tank Farm to support the deployment of the mobile arm retrieval system (MARS) in single shell tank 241-C-107.

The new 47-inch diameter riser was successfully installed in the center of the 241-C-107 tank dome. This required the previous center riser hole to be increased by cutting into the dome.

The Large Riser design considerations included: structural limits on the tank dome, radiological worker dose during construction, time required to abrasive jet cut through the concrete dome and structural steel, lift plans, and mapping the reinforcing steel within the concrete shell.

Columbia Energy also fabricated the containment box that is positioned atop the large riser at the tank opening and is designed as a mountable base for waste retrieval equipment, such as the MARS, to be anchored and lowered into the tank.


  • 100,000-lb. compressive strength
  • 47” diameter


  • Project Management Institute – CBC Project of the Year


  •  U.S. Department of Energy (DOE)
  • Washington River Protection Solutions (WRPS)
  • Office of River Protection (ORP)


  • Mechanical Engineering
  • Design
  • Fabrication
  • NQA-1 Oversight
  • Construction
  • Testing and Mock-up
  • Operator Training

Design Features

  •  Structural stabilization for mounting mobile arm to radioactive waste tank
  • Radiation Hardened
  • CGD components