PWR Cycle

PWR Cycle

The Pressurized Water Reactor designs are similar for the units provided by the various manufacturers. Differences are illustrated by the table below:

Manufacturer	MWt	MWe	Loops	Pressurizer	Reactor Coolant Pumps per Loop	Steam Generators per Loop
Westinghouse	450-3000	167-1000	1-4	1	1	1
Framatome	2700-3600	900-1300	3-4	1	1	1
Babcock & Wilcox	2400-3000	800-1000	2	1	2	1
Combustion Engineering	2400-3600	800-1300	2	1	2	1
ABB	3000	1000	4	1	1	1
Mitsubishi	3000	1000	4	1	1	1

A number of simplified diagrams (courtesy Westinghouse) illustrate the design of the pressurized water reactor facilities.

The following are colored perspective and arrangement drawings of

The flow paths are illustrated by a colored graphic flow diagram and a black and white line drawing. The following describes the flow path and the linked drawings illustrate, in detail, the composition and major parts of the components.

Reactor - this diagram shows how the reactor is constructed with its major components. Water at 530F enters the reactor from the nozzles at about mid-height. The water flows downward on the outside of the core barrel to the bottom of the reactor. Then the flow turns upward past the fuel assemblies, removing heat from the assemblies and increasing in temperature to 590-600F. After leaving the core area, the water mixes in the upper plenum and leaves the reactor through nozzles. Flow then goes to the ...

Steam Generator where the radioactive Reactor Cooling System water enters at the bottom, flows through small (1/2-inch) inverted U-tubes. That water loses its heat as it passes through the tube being cooled by the non-radioactive water outside the tube. Non-radioactive feedwater enters through the nozzles at the mid-height of the steam generator at a temperature of about 425F. The water flows downward outside a wrapper sheet to the area just above the tubesheet where the water turns and flows upward past the U-tubes. The water increases in temperature and turns to steam. A moist steam at about 510-547F with pressure of 720-1005 pounds per square inch is produced. The moist steam travels upward to steam separators (chevron separators and swirl vanes) which allow 99.75% purity steam to pass of the steam generator and the remaining water is directed back to the lower part of the steam generator. The reactor cooling system water enters the steam generator at ~590F and leaves at ~ 530F. That water then flows to the ...

Reactor Coolant Pump which pumps the water back to the reactor.

Pressurizer is used to control the pressure in the reactor cooling system so that boiling does not occur in the reactor. The pressurizer also is used to act as a surge tank for the system taking up the level variations in the system. Heaters are installed at the bottom of the pressurizer for heating the water to about 652F and 2250 pounds per square inch. Automated pressure control valves (called power operated relief valves) and safety valves, connected to the top of the pressurizer, can open to control and maintain pressure.

Secondary Systems line drawings illustrate the major sub-components in the non-radioactive part of the system where steam flows to the turbine, condenses in the condenser, then is pumped back to the steam generator first by condensate pumps, then by feedwater pumps. The feedwater heaters improve the efficiency of the cycle by recovering and reusing energy that would otherwise be lost. By doing so efficiency of the cycle is raised to 33%.