Project Description

Elimination of Drywell-to-Wetwell Differential Pressure

Client Challenge

Client’s Plant Operates with a Differential Pressure (∆P) Between Drywell and Wetwell

Plant Required to Maintain ∆P Since Mid-70’s to Mitigate Loads on Torus Resulting from a Loss of Coolant Accident


  • Perform State-of-the-Art Analyses to Allow Our Client to Operate Their Plant in a Zero ∆P Condition
  • Analyses Performed on the Torus Structure and Many Associated Piping Systems
  • Analyses Goals are Qualification of Structures and Components While Minimizing or Eliminating Difficult, Costly Modifications
  • Analyses are Required By Law to Show that the New Design Basis Accident Condition of Zero ∆P Maintains or Increases Health and Safety of the Public


  • Large Quantities of Nitrogen are Required to Maintain ∆P. Nitrogen Usage is Reduced
  • Plant Operators’ Burden to Maintain ∆P is Eliminated. Operator Focus Can Be Placed Elsewhere
  • Associated 2” Increase in Downcomer Submergence Provides Additional Operator Flexibility
  • Quarterly Surveillances Require De-Inert and Inert Which are Costly, Operator Intensive Activities. These Surveillances are Eliminated

Cost Savings

  • Imperia Analyses: $350K
  • Annual Estimated Cost Savings to Client: $500K
  • Client Savings Over Remaining Life of Plant: $10M