4. Moderator system

4.1 General configuration

The moderator is an independent heavy-water system operating essentially at atmospheric pressure. The circulation system of type 304 stainless steel piping is illustrated schematically in figure  10 . The take-offs from the bottom of the reactor vessel (calandria) are pumped through two loops to Alloy 800-tubed heat exchangers that are cooled with the plant recirculating cooling water (RCW) before the D ₂ O is returned to the calandria via inlets at the circumferential shell. In a CANDU-6 about 5.4 % of the fission power is dispelled to the moderator and the temperature must be kept below the regulatory limit...