Civil Engineering Reference
In-Depth Information
3.2 Pressurized Water Reactors
In the 1950s PWRs were developed in the USA particularly as power plants for
nuclear submarines (“N.S. Nautilus” 1954). The successful application of the PWR
concept then resulted in the construction of the first non-military experimental
nuclear power plants in the USA and Russia.
Present PWRs have been or are built basically according to the same technical
principles by a number of manufacturers in various countries (USA, Russia, France,
Germany, Japan, South-Korea, China). In this chapter, the modern PWRs of
manufacturers in the USA, Japan and Europe are presented. These are the standard
PWR of 1,300 MW(e), which will be described as built in the 1990s by Kraftwerk
Union in Germany (KWU-PWR) [
1
]. In addition, the Advanced Pressurized Water
Reactors AP1000 and the US-APWR, developed by Westinghouse (USA) and
Mitsubishi (Japan), are presented [
2
,
3
]. Finally the 1,600 MW(e) European Pres-
surized Water Reactor (EPR) will be described as built by AREVA (France)
[
4
]. PWR designs by other manufacturers have small technical differences relative
to the above design concepts but these are not relevant for a general understanding
of the basic principles of safety design.
Figure
3.1
shows the main design principles of a PWR. The heat generated by
nuclear fission in the reactor core is transferred from the fuel elements to the coolant
in the primary system. The highly pressurized water (15.5 or 15.8 MPa for AP1000,
US-APWR, KWU-PWR and EPR) is circulated by coolant pumps and heated in the
reactor core from inlet temperatures of 281
C (AP1000), 288
C (US-APWR),
292
C (KWU-PWR) or 296
C (EPR) to outlet temperatures of 321
C (AP1000),
328
C (US-APWR), 326
C (KWU-PWR) or 328
C (EPR) (Tables
3.1
and
3.2
). It
flows to two or four steam generators, where it transfers its heat to the secondary
steam system. In the secondary system, steam of 5.5 (AP1000), 6.7 (US-APWR),
6.8 (KWU-PWR) or 7.8 MPa (EPR) and 273
C (AP1000), 284
C (US-APWR),
285
C (KWU-PWR) or 293
C (EPR) is generated. The steam drives the turbine
and the generator. The steam exhausted by the turbine is precipitated in the
condenser, and the condensate water is pumped back into the steam generators.
Waste heat delivered to the condenser is discharged into the environment either to
river, lake or sea water or through a cooling tower.
3.2.1 Core
The core initially contains fuel elements with three or four different levels of U-235
enrichment. In case of EPR, e.g. some fuel elements also contain gadolinium as
burnable poison. The higher enriched fuel elements are arranged at the core
periphery, the less enriched fuel elements are distributed throughout the interior
of the core (Fig.
3.2
). This provides for a relatively flat power distribution over the
core and adapts to later so-called equilibrium core loadings. In later core reloadings,
