Passive Emergency Heat Rejection Concepts for CANDU Reactors

Abstract

A study is in progress at AECL to assess the safety and capital cost implications of a more extensive use of passive design features in CANDU reactors. The study is focussed on emergency heat rejection and applies passive design principles to enhance the independence of core cooling via the moderator as distinct from core cooling via the emergency coolant injection system. Emergency heat rejection from the moderator and from containment is integrated via a water jacket formed in part by the cylindrical wall of a steel containment vessel. The water jacket acts as an interim heat sink and ultimately transfers its heat to the outside air. The concepts have been applied to a 2 loop CANDU 6 plant and a preliminary assessment has been completed. Core melt frequency appears to be improvedby at least an order of magnitude and capital cost seems to be competitive with conventional plant. Simplified methods were used and further calculations are in progress using more sophisticated techniques. Design enhancements are described: improvements in the fuel channel design eliminate the need for subcooling of the moderator and in turn eliminate the need for pumps even during normal operation.