Most U.S. power reactors were built with one concept in mind: to produce electricity as efficiently, economically, and safely as possible. Plants were not designed to facilitate simple and efficient deconstruction. Since decommissioning was not planned by the original construction team, dismantling is a completely new process that must be learned for each unique facility. Fortunately, the process is becoming more predictable and manageable because of experience gained to date. Dismantling is probably the phase of decommissioning with the strongest visual impact. A major portion of the project involves dismantling, removal, and size reduction of concrete structures and metal components, such as vessels, pipes, conduit, and structural steel. Generally, the metal and concrete components have radioactive, organic, chemical, or heavy metal contamination, thereby presenting potential exposure hazards. The site and facility characterization data will show which and how much of those materials must be dismantled and removed.
Dismantling involves decontamination, removal of components and structures, packaging of wastes, transport of packages, and disposal in a controlled burial facility. But the planning should be performed in reverse order. Once characterization has identified the waste streams, the next step is to contact the waste disposal facility to learn and understand its waste acceptance criteria, including permissible package/container radioactive inventory (curies and dose), package size and weight requirements, and documentation. If the facility will not accept the waste form or content, alternative measures must be taken. When the package sizes, weights, and radioactivity limits are selected, the mode of transport and number of shipments may be determined — truck, rail, or barge. The planner may then select the most cost-effective technology to segment piping, equipment, and structures to fit into the selected packages. The segmentation/removal production rates (tons/day) for each potential technique evaluated will determine the number of shipments per day or week and thereby set the overall schedule. Adjustments might be made as experience demonstrates improved productivity with other technologies.
This chapter will help the decommissioning planner choose appropriate technology for specific applications. Current dismantling, removal, and size reduction technologies include mechanical saws, circular cutters, abrasive cutters, diamond wire, explosive cutting, plasma arc torch, oxyacetylene torch, arc saw, abrasive water jet, and hydraulic shears. Backhoe hydraulic rams, conventional wrecking techniques, and explosives are used to dismantle large, thick concrete structures. The use of explosives requires a certified blasting expert for safety.