Page 193 - Dynamics and Control of Nuclear Reactors

CHAPTER

Pressurized heavy water

reactors 14

14.1 Introduction
This chapter contains a brief description of the characteristics of pressurized heavy
water reactors (PHWRs), and their dynamics and control [1, 2]. But the PHWR itself
is very different than the PWR described previously.
The discussion of PHWRs deserves inclusion here because a number of units
operate in Canada and in other countries. The dynamic characteristics and control
system designs of PHWRs differ significantly from those of the more common light
water reactors.
The PHWR was developed in Canada where the design was called the CANDU
reactor (for CANada Deuterium Uranium). Canada’s nuclear power program and its
development provide an interesting and informative story. Upon deciding to “go
nuclear”, Canada could have easily decided to depend on the U.S. to sell them reac-
tors as was done in many other countries. But Canada decided to develop its own
reactors. Canada innovatively developed a design that could be realized with their
own resources and manufacturing infrastructure. Canada might not fully succeed
in the world-wide competition for reactor sales, but its accomplishments deserve
admiration. CANDU reactors were built in Canada and were exported to several
other countries. References [3, 4] provide additional details related to reactor physics
and CANDU-6 design features.

14.2 PHWR characteristics

Fig. 14.1 shows a typical PHWR nuclear steam supply system [1].
The reactor is contained in a large cylindrical vessel, called the calandria that is
positioned horizontally. The calandria vessel has a diameter of 7.6m (25ft) and the
wall is made of stainless steel (3cm thick). The D 2 O moderator in this vessel is main-
tained at low pressure and temperature. The calandria contains an array of about 380
horizontal tubes (Zircaloy) that contain bundles of UO 2 fuel rods surrounded by
heavy water coolant. The pressure tubes are the boundary between high temperature,
high pressure heavy water inside the tubes and low temperature, low pressure heavy
water outside the tubes. Thus, a PHWR reactor has separate moderator and coolant
and both produce reactivity feedbacks.
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