Although EDM services all nuclear plant designs, a typical Boiling Water Reactor is provided as a representative example.
The major difference between a Boiling Water Reactor (BWR) and other types of nuclear power generating systems is the steam void formation in the reactor core. A mixture of steam/water is created when very pure water moves upward through the core absorbing heat inside the boiling water reactor. This steam-water mixture exits the top of the core and enters two stages of moisture separation. Water is removed before the steam goes into a steam line. The steam then enters a main turbine where is turns the turbine and an electrical generator. Excess steam that is not used is exhausted to a condenser that changes it back to water. A series of pumps send the water back to the reactor vessel. Jet and recirculation pumps allow an operator to vary the flow of coolant through the core and change the power generated by the reactor.
Permits passage of workers and equipment into containment building, while managing the air exchange and maintaining integrity of the building.
The BWR containment building houses the reactor vessel, recirculation pumps, steam and coolant piping and associated safety systems. In the event of an accident, the containment building is the last line of defense in containing release of radioactivity into the environment.
The function of the cooling tower is to remove heat from the water discharged from the condenser so that the water can be expelled to the river or recirculated and reused. Cooling towers are of two types, mechanical draft and natural draft towers. Mechanical draft towers use fans to force air through the towers whereas natural draft relies on temperature differences between inside and outside to naturally pull air through the tower.
Standby Diesel Generator provides emergency power if needed. The cooling water jacket is kept warm and circulated at all times for quick start-up.
The High Pressure Coolant Injection (HPCI) system operates independently from the core cooling system and doesn’t require auxiliary ac electricity, a plant air system or an external water-cooling system. It supplies (makeup) water to the reactor to provide cooling during cooling accidents of small and intermediate loss of coolant. The HPIC is capable of supplying (makeup) water above the rated reactor pressure or below the point where the low-pressure emergency core cooling system can inject.
The Automatic Depressurization System (ADS) opens selected safety, relief valves via redundant logics that depressurize the reactor during small and intermediate accidental losses of coolants when the HPCI system is not available or cannot recover the water level in the reactor.
The Low Pressure Emergency Core Cooling (LPCI) system functions as an integral part of the residual heat removal process. It is made up of two, isolated and independent sub-systems – the Core Spray and the Low Pressure Coolant Injection (LPCI) systems.
The Core Spray system sprays water on top of the fuel assemblies via two pumping loops – either of which may supply water from the suppression pool to the reactor.
The LPCI system supplies (makeup) water to the reactor core during accidental cooling conditions.
The residual heat removal system serves multiple functions and uses the same major components of equipment depending on the mode in which it is employed. The LPCI is primary and normal configuration of valve lineup. The LPCI automatically kicks in to restore and maintain the coolant in the reactor vessel to prevent fuel-cladding temperatures in excess of 2200°F by supplying coolant to the reactor vessel from the suppression pool.
The Reactor Core Isolation Cooling (RCIC) system is made up of a turbine-driven pump and piping with valves. When the main steam lines are isolated and the normal water supply to the reactor is lost, the RICI system delivers water to the reactor.
Steam from the main steam lines drives a turbine and the exhaust is vented to a suppression pool. The turbine also drives a pump that provides (makeup) water from a condensate storage tank via a feedwater piping. The flow rate normally achieves approximately the same rate as the steaming rate 15 minutes after shutdown. This function can be automatically achieved at low water level in the reactor vessel or manually by an operator.
The Turbine Building houses the main turbine as well as the generator and associated auxiliary systems. The main turbine converts the thermal energy of the reactor steam into mechanical rotational energy which drives the main generator to produce electrical energy.
The main turbine lube oil system provides lubricating oil to the main turbine generator and exciter bearings. The system can supply oil to the over-speed mechanical trip devices, thrust bearings, and thrust bearing wear detectors and hydrogen seal oil system. The system has one major flow-path with various pump combinations available to supply it.