Description of a Pressurized Water Reactor
History and Overview
The first PWR was the 60 MWe plant in Shippingport, PA., which began producing electricity commercially in 1957. PWR's are constructed by three companies in the Unites States: the Westinghouse Electric Co., Combustion Engineering, Inc., and Babcock and Wilcox Co., as well as by several organizations in other countries. PWR's are built with either two, three, or four independent cooling and steam generation systems. The steam generators may be either once-through or multiple-pass design.
How it Works
A diagram of a PWR with a two-loop steam cycle is shown here:
from Encyclopaedia Americana
The primary loop contains water under a pressure of about 2250 pounds per square inch (psi) or 15.5 megapascals (MPa). The water flows through the reactor core at a rate on the order of 44,000 pounds (20,000 kg) per second. As it flows through the core, the water is heated to a temperature of 625 F (330 C) by fission. When it reaches the steam generator, the primary fluid transfers thermal energy to the secondary fluid (also water) -- losing about 55 F (30 C) in the process. The cooler water in the secondary cooling loop increases in temperature by about 140 to 160 F (60 to 70 C) at a pressure of about 1000 to 1100 psi (6.9 to 7.6 MPa) as it passes through the steam generator. Under these temperature and pressure conditions, this water is converted to stream, which then drives the turbine used to generate electricity. Finally, the spent steam is cooled back to liquid form by the condenser loop before it is again pumped through the steam generator. A nearby lake, river, of ocean provides the cooling water for the condenser loop. Cooling water may also be passed through a water tower to dispel heat.
Existance of PWR's Today
By 1985 more than 55 PWR's, with a total capacity of 47,000 MWe, were in operation in the United States. Worldwide, over 175 PWR's, with a capacity of nearly 136,000 MWe, were in operation in 21 countries.