Decay heat removal systems: design criteria and options. [PWR; BWR]

Design criteria and alternate decay heat removal system concepts which have evolved in several different countries throughout the world were compared. The conclusion was reached that the best way to improve the reliability of pressurized water reactor (PWR) decay heat removal is first to focus on improving the reliability of the auxiliary feedwater and high pressure injection systems to cope with certain loss of feedwater transients and small loss of coolant accidents and then to assess how well these systems can handle special emergencies (e.g., sabotage, earthquake, airplane crash). For boiling water reactors (BWRs), it was concluded that emphasis should be placed first on improving the reliability of the residual heat removal and high pressure service water systems to cope with a loss of suppression pool cooling following a loss of feedwater transient and then to assess how well these systems can handle special emergencies. It was found that, for both PWRs and BWRs, a design objective for alternate decay heat removal systems should be at least an order of magnitude reduction in core meltdown probability