Civil Engineering Reference
In-Depth Information
Table 3.1
(continued)
Kraftwerk Union
(KWU-PWR)
AREVA
(EPR)
PWR-1,300
EPR-1,600
Fuel cycle
Average fuel burn up
MWd/ton
55,000
70,000
Refueling sequence
1/3 to 1/4 per year
1/5 per year
Average fissile fraction in
spent fuel
U-235
wt%
0.8
0.8
Plutonium
wt%
0.7
0.7
3.2.2 Reactor Pressure Vessel
The fuel elements, control elements and core monitoring instruments are contained
in a large reactor pressure vessel (RPV) designed to withstand the operating
pressures at operating temperatures (Fig.
3.5
). The vessel has an inner diameter
of about 5 m, a thickness of the cylindrical wall of about 200-250 mm, and a height
of up to approx. 13 m. The cover head of the vessel, which holds all the control rods
and control rod drive mechanisms (CRDM), can be removed for refueling. The
water flowing at a rate of 18.8 t/s (KWU-PWR) and 21.4 t/s (EPR), respectively,
enters the reactor vessel through two (AP1000) or four (KWU-PWR, US-APWR,
EPR) inlet nozzles close to the top and flows downward through the annulus
between the vessel and the thermal shield and neutron reflector to the core inlet
near the bottom. It then returns upward through the core being heated up there and
leaving the two or four outlet nozzles of the pressure vessel. The reactor vessel is
made of, e.g. 22NiMoCr37 steel, in case of Kraftwerk Union PWRs and of
16 MND5 for EPR. Its inner surface is plated with austenitic steel.
3.2.3 Coolant System
The water leaving the outlet nozzles of the pressure vessel transports the heat
generated in the reactor core through two (AP1000) or four (KWU-PWR,
US-APWR, EPR) identical primary coolant circuits to two or four steam generators
and is then recirculated to the pressure vessel. The inner diameter of the primary
system pipes is, e.g. 750 mm for the KWU-PWR or 780 mm for EPR. Each primary
coolant pump has a pressure head, e.g. of 0.8 (KWU-PWR) or 1.0 MPa (EPR) and
consumes 5.4 or 9 MW(e) of electrical power, respectively. The whole primary
system is also plated with austenitic steel. The pressure of 15.5 MPa (KWU-PWR)
or 15.8 MPa (EPR) in the primary coolant system is maintained by a pressurizer
filled partly with water and partly with steam. It has heaters for boiling the water
