Sometimes a Demo Job isn’t a Demo Job

Issue 7 and Volume 120.

By Brendan O’Brien, P.E., and Jeff Pope, P.E., Burns & McDonnell

Brendon O’Brien
Jeff Pope

Demolition lets you start over at your site, but frequently circumstances limit a utility owner’s ability to demolish their aging generation asset. This can be due to lack of required funding, environmental and remediation concerns, proximity to currently operating units, regulatory issues, or even contractor availability.

In instances where a full demolition of a power generation asset cannot be completed, going “cold and dark” in a single unit should be considered. This refers to disconnecting all utilities to the asset, removing all hazardous chemicals and environmental concerns, and leaving the asset in place. This may be an ideal solution for a utility owner with limited resources, but is not as easy as it seems – it frequently requires a decommissioning expert to consult and guide the asset decommissioning process. The following are common problems that must be addressed while decommissioning one asset in a group of multiple generating units.

  • A plant with shared utilities requires a more complex decommissioning. In new power generation construction, utilities such as electricity, air, water, steam, controls, and sewage are frequently shared among units. Little thought is given to retiring the assets when built, therefore a spider web of piping, electrical, and communication lines is inadvertently created. This creates a complex arrangement that requires extensive planning to decommission as removing the utilities from one unit may compromise others. Caution must be undertaken in separating the utilities.
  • Decommissioning units requires new utilities for the remaining units. When units share utilities as mentioned above, decommissioning of a single unit can be detrimental to the operation of remaining units. New utilities must be engineered, sized, and incorporated in plant control systems prior to the decommissioning process in order to supply the remaining units. The installation of these utilities should be timed appropriately with plant outages to minimize unit downtime.
  • Chemical, environmental, and health concerns should be evaluated. All plant chemicals must be catalogued and removed prior to decommissioning. All fuels, fuel tanks, piping, and lubricating oils should be drained and flushed. Soil and concrete samples should be taken around polychlorinated biphenyls (PCB-) containing devices or oil stained areas to rule out environmental contamination. Finally, the safety of decommissioning workers and plant personnel must always be at the forefront. A full evaluation for asbestos and lead-based paint must be completed in order to either remove as part of decommissioning or manage going forward.
  • Capping the stacks prevents water damage to the newly nonfunctioning units. Operating stacks function at a high temperature, causing evaporation of ambient water and preventing water damage to the structural elements of the stack. Non-operational units have no heat protection against rainwater. During decommissioning, a stack capping and inspection plan should be developed. The caps should be designed from corrosion-resistant materials. The relevant Federal Aviation Administration (FAA) regulations should be identified and any aircraft warning light compliance measures should be maintained. For safety purposes, you may also consider full demolition of the stacks.
  • Structural integrity inspections should be conducted regularly for the remaining plant. As the asset will sit idle and age, portions of the unit may in time deteriorate. Furthermore, the rate of decomposition may be higher in nonfunctional units than in those still in operation as an operating plant is designed for a hot, dry environment; in the dormant state, the “cold and dark” asset will suffer from weather deterioration. Regular structural inspections must be performed in order to identify unsafe conditions or impending structural compromise that could lead to a catastrophic outcome, hurting plant personnel or harming neighboring plant assets. A decommissioning plan will incorporate structural inspections at regular intervals after decommissioning.

Full or partial decommissioning can be complicated. Decommissioning should involve an extensive and detailed plan prior to decommissioning, multiple quality checks during the process, and a structural integrity plan after the project is completed. A decommissioning specialist can help identify and solve these issues before they become a problem.