Environmental Engineering Reference
In-Depth Information
Reactor pressure
vessel
Steam dryer
Steam outlet nozzle
Steam separator
Feedwater inlet
nozzle
Reactor water cleanup/sh utdown
cooling section nozzle
Condensor return nozzle
Core grid
Fuel assembly
Control rod
guide tubes
Control rod
drives
Shield wall
Figure 6.3 Cutaway of a boiling water reactor.
propensity. Thus, the reduction of the liquid content of the coolant water automatically slows the
chain reaction.
In a BWR, the core is enclosed in the primary containment vessel made of steel and sur-
rounded by reinforced concrete. A secondary containment vessel made of reinforced concrete
(the dome-shaped building visible at nuclear power plants) contains the steam separator and the
spent fuel storage pool. The steam turbine, condenser, and electric generator are located outside of
the secondary containment vessel. Even though the coolant water is demineralized, some radioac-
tive material may leach from the core into the coolant water and subsequently be transferred by the
steam to the steam turbines. Furthermore, the coolant water may contain traces of mildly radioactive
isotopes of hydrogen (tritium [ 3 H]) and nitrogen ( 16 N and 17 N). The steam remaining in contact
with the turbine and other equipment loses its radioactivity quite fast, and with proper precaution no
significant exposure is presented to workers in the power plant or the population outside the plant.
6.4.2
Pressurized Water Reactor (PWR)
The majority of nuclear power plants in the United States and worldwide are of the PWR type. A
schematic of a PWR is depicted in Figure 6.4. In the primary loop surrounding the reactor core,
the coolant water is kept at a high pressure of about 15 MPa, so that the water does not boil into
 
 
 
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