The Assessment of Advanced HWR with Dual Moderator Concept

The advantages of existing Candu-PHWR reactor over other types are, better safety performance because of the low excess reactivity by the use of natural U oxide, the separation of D2O as a moderator and as a coolant, and better neutron economy. The result in the long period power excursion behavior, cool moderator that can act as long term heat sink, and the flexibility in fuel option. The problem of positive feedback in the Candu design is to be overcome by the use of the so called dual moderator concept, in which two moderator systems are used, i.e. a main moderator system outside calandria tube and an annular moderator system inside annular space. The result of this calculation showed that, this concept can achieve not only a negative local power feedback but also promises a greater simplicity in the power regulating system by the possibility of elimination of adjuster rod and incorporation of more than one passive shutdown systems. The boiling of annular moderator can also be used as a power regulating system as well as a core excess reactivity compensation system