Page 195 - Dynamics and Control of Nuclear Reactors

14.2 PHWR characteristics 193

2
The heavy water coolant is pressurized (around 10MPa or 1450lb./in at the bun-
dle exit) to permit high temperature without boiling. Coolant inlet temperature is
typically around 266°C and the outlet temperature is around 312°C. Coolant flow
in half of the channels flows from left-to-right and the other half flows from
right-to-left.
The PHWR fuel is natural Uranium. A typical 600-MWe CANDU reactor con-
sists of about 4500 fuel bundles, weighing about 90 Te (90,000 Kg). Refueling of
CANDU reactors occurs daily while the reactor operates at power. The refueling
is an online loading system, controlled remotely. The fuel is Uranium oxide pellets
enclosed in Zircaloy cladding and arranged in bundles as shown in Fig. 14.2.
A typical bundle has 37 fuel pins.
Fuel bundles are short (around 49.5cm or 19.5in.). A channel contains a string of
these bundles arranged end-to-end. Refueling involves use of a special refueling
machine that opens a channel, removes an old fuel bundle and inserts a new fuel bun-
dle. This is an automated on-line refueling machine. Approximately 15 fuel bundles
are replaced every day. Refueling occurs while the plant operates at power. Fuel
residence time in the reactor is typically one year.

Pressure Tube
Inter Element Spacers

Zircaloy End Cap

Zircaloy Fuel Sheath

Canlub Graphite Interlayer
Uranium Dioxide Pellets

Zircaloy End Support Plate Zircaloy Bearing Pads

FIG. 14.2
A PHWR fuel bundle showing the fuel elements. The fuel bundle is in a pressure tube and is
surrounded by the calandria tube. The calandria vessel contains the D 2 O moderator.
Courtesy of UNENE, Ontario, Canada (W.J. Garland (Editor-in-Chief), The Essential CANDU: A textbook on the
CANDU Nuclear Power Plant Technology, University Network of Excellence in Nuclear Engineering (UNENE),
McMaster University, Hamilton, Canada, 2019, Retrieved from https://www.unene.ca/education/candu-
textbook, Chapter 8).