13.56. The pressure tubes are supported by tube sheets at the two ends of the cylindrical reactor vessel, called a calandria, with its axis horizontal. The calandria contains the heavy water at essentially atmospheric pressure. Some heat (about 5 percent of the reactor total) is generated in the mod­erator by the slowing down of fast neutrons. The moderator is consequently circulated through a heat exchanger and also through a purifier.

13.57. A fairly complex piping system serves to connect the inlet and outlet ends of each pressure tube to coolant manifolds (see Fig. 13.12). Pressurized heavy-water coolant flows between and around the fuel rods in each bundle; the flow is in opposite directions in adjacent channels. The heated coolant leaving the reactor is collected in a header (or manifold) from which it passes to a steam generator of the conventional type. The coolant is then pumped back to the reactor. A simplified representation of the CANDU cooling system is shown in Fig. 13.13. Two coolant exit headers are provided, one at each end of the calandria, and each header is attached to a steam-generator-pump loop. A single pressurizer, of the same type as is used in PWRs (§13.16), maintains the coolant system pressure.

Power Thermal Electrical (net) Specific power Power density

Length

Diameter

Rod, OD Clad thickness Spacing between rods Rods per bundle Bundle length Bundle diameter U02 per bundle Fuel loading, U02

Ave. burnup 650 GJ/kg

2064 MW 600 MW 24 kW(th)/kg U 7.46 MW(th)/m3

Core 5.94 m (19.5 ft) 7.7 m (25.2 ft)

Fuel

13.1 mm (0.515 in.)

0. 38 mm (0.015 in.)

1.02 mm (0.0047 in.)

37

0.495 m (19.5 in.)

0.102 m (4.0 in.)

21.3 kg (46.5 lb)

97 x 103 kg (214 x 103 lb)

(7,500 MW • d/t)