Civil Engineering Reference
In-Depth Information
1
MAIN COOLANT PUMP
8
PREHEATER
2
PRESSURIZED WATER REACTOR
9
FEEDWATER PUMP
3
STEAM GENERATOR
10
COOLING WATER PURIFICATION
SYSTEM
4
WATER SEPARATOR
5
TURBINE
11
COOLING WATER PUMP
6
GENERATOR
12
OVERFLOW BASIN
7
CONDENSER
13
COOLING TOWER
Fig. 3.1
Functional design diagram of a pressurized water reactor power plant (Kraftwerk Union)
[
1
]. 1. Main coolant pump, 2. Pressurized water reactor, 3. Steam generator, 4. Water separator,
5. Turbine, 6. Generator, 7. Condensor, 8. Preheater, 9. Feedwater pump, 10. Cooling water
purification system, 11. Cooling water pump, 12. Overflow basin, 13. Cooling tower
fuel elements with different burnups and different enrichments are also arranged in
similar patterns. The specific power density in the core is about 95 (EPR) to
110 (AP1000) kW(th)/l. Around 2008 the average maximum burnup of the fuel
was about 55,000 MWd/ton over an irradiation period in the core of about 4 years.
Around 2010-2020, a maximum burnup to 70,000 MWd/ton is strived for. A 1 year
reloading cycle can be reached by unloading either one fourth or one fifth of the fuel
elements at maximum burn up.
Uranium dioxide (UO
2
) is used as a core fuel. The UO
2
powder is pressed and
sintered into pellets of about 10 mm height and diameter with an average density of
10.4 g/cm
3
. The pellets along with pressurized helium are placed into tubes
(cladding) made of Zircaloy with an active core length of 3.6-4.2 m. This cladding
material is chosen for its low neutron absorption as well as good mechanical and
corrosion properties. The tubes are welded and assembled into fuel elements
(Fig.
3.3
).
A fuel element of a 1,300 MW(e) or 1,600 MW(e) reactor contains 236 or
265 fuel rods, respectively. The core has 157-257 fuel elements (Tables
3.1
and
3.2
), with a total uranium mass of 84 tons (AP1000), 125 tons (KWU-PWR),
153 tons (EPR) and 138.5 tons (US-APWR). Some of the fuel elements contain
control elements with 20-69 axially moveable absorber rods (Fig.
3.4
)[
6
,
7
]. These
absorber rods are filled with boron carbide or silver-indium-cadmium as neutron
absorbing materials.
