Abstract
The problem of positive power feedback in the recent PHWR-CANDU design will be
overcome by the use of "dual moderator concept ", in which two moderator systems are used,
i.e. a main moderator outside the calandria tube and an annular moderator inside the annular
space. The numerical calculations have been performed for two core design namely HWR-DMST
and HWR-DM-X1 which can reach burn up of 16000 and 17500 MWd / ton U respectively.
The results for the two designs is that the values of k at fully anular moderator filling condition
are 1.0054 (HWR-DM-ST) and 1.0019 (HWR-DM-X1), while at completelly empty annular
moderator condition are 0.9634 (HWR-DM-ST) and 0.9143 (HWR-DM-X1). The decreasing of
coolant flow rate from 3043 kg/s to 853 kg/s gives a decreasing of k values of O.0109 (HWRDM-
ST) and 0.0232 (HWR-DM-X1). The increasing of inlet coolant enthalpifrom 2950 kJ/kg to
3175 kJ/kg gives a decreasing ofk values of 0.0074 (HWR-DM-ST) and 0.0239 (HWR-DM-X1).
Thus it can be summarized that these HWR-DM designs have negative power reactivity
feedback. These designs can achieve a thermal efficiencies of 38,5 % with the fuel utilizations of
120,75 and 110,52 kg of natural uranium / kWe-year for HWR-DM-ST and HWR-DM-X1
respectively.
Keywords: PHWR-CANDU, dual moderator concep
