ARTICLE:

• EFFECTIVENESS OF THE MODERATOR AS A HEAT SINK DURING A LOSS-OF-COOLANT ACCIDENT IN A CANDU-PHW REACTOR  download article

D. B. Sanderson
AECL, Whiteshell Laboratories Pinawa, Manitoba ROE 1LO

R. G. Moyer
AECL, Whiteshell Laboratories Pinawa, Manitoba ROE 1LO

R. Dutton
AECL, Whiteshell Laboratories Pinawa, Manitoba ROE 1LO

ABSTRACT

In a CANDU^® Pressurized Heavy Water (PHW) reactor, the fuel and coolant are separated from the heavy-water neutron moderator by horizontal fuel channels. The fuel channel consists of a Zr-2.S Nb pressure tube and a Zircaloy-2 calandria tube, separated by a gas-filled annulus. The separation between the primary heat transport fluid and the moderator is a distinctive feature of CANDU reactors. In particular, the moderator provides a backup heat sink for the reactor core, should both the normal and emergency cooling systems fail. This heat sink (about 10 mm away from the hot pressure tube( provides an inherently passive heat removal mechanism in postulated loss-of-coolant accident (LOCA) scenarios.
Demonstration of the effectiveness of the moderator as a heat sink during a LOCA has been the focus of an extensive and ongoing research program at Atomic Energy of Canada Limited (AECL). Small-scale separate-effects experiments have been performed to develop and then validate mathematical models which describe the phenomena. These validated models have been incorporated into computer codes linking the various phenomena to predict the integrated fuel channel response to a LOCA. Large-scale integrated experiments were then performed to validate the codes.
This paper describes the moderator as a heat sink in a CANDU reactor and experiments that verify its operation. Recent efforts aimed at improving the effectiveness of the moderator as a heat sink for future CANDU designs through improved fuel channel concepts are also presented.

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