SAFETY OF HEAVY-WATER REACTORS.

The safety characteristics of Canada Deuterium Uranium-Pressurized Heavy Water (CANDU-PHW) reactors are reviewed. The include: control systems with limited reactivity range, because of on-power fuelling; a lattice already near its most reactive array; delay and rate requirements determined by the maximum loss-of-coolant through the void coefficient, modified by a long neutron lifetime; shutdown and control devices located outside the heat transport system pressure boundary and unaffected by the loss-of-coolant; safety systems testable on power to 99. 9% availability; and a cool moderator available as a backup heat sink. The effectiveness of the safety systems is discussed.