NRC Reactor Concepts (R-100)
Total Page：16
File Type：pdf, Size：1020Kb
NRC Reactor Concepts (R-100) Welcome to the Nuclear Regulatory Commission's Reactor Concepts (R- 100) web-based training. This course is open to all NRC personnel and provides a baseline of knowledge of what NRC does in relation to nuclear power plants and how it maintains the protection of people and the environment. The mission of NRC is to license and regulate the Nation's civilian use of byproduct, source, and special nuclear materials in order to protect public health and safety, promote the common defense and security, and protect the environment. After completing the course, you will be able to speak knowledgeably and with confidence to the general public in relation to the mission of NRC. Begin Course Videos Acronyms Glossary Resources Training Page NRC Reactor Concepts (R-100) Training Course Nuclear Power for Electrical Generation Chapter Introduction Go To Top Chapter Overview The purpose of a nuclear power plant is to generate electricity from steam created by nuclear heat. It should not be surprising, then, that a nuclear power plant has many similarities to other electrical generating facilities using steam. Conversely, nuclear power plants have some significant differences from other plants. Throughout this chapter, we will examine: how to generate electricity using steam energy, the most common ways for producing commercial electricity in the United States (U.S.), and the significant ways that nuclear power plants differ from other power plants. We will also explore the differences and similarities between the two types of commercial nuclear plants in the U.S. Objectives After completing this chapter, you will be able to: • Describe the role of nuclear power in generating commercial electrical power in the U.S. • Describe the process for generating electrical power using steam. • Identify the most common sources and costs of commercial electrical power generation in the U.S. • Identify characteristics unique to nuclear power generation. • List the barriers to the escape of fission products from the fuel. • Identify the types of nuclear power plants used for commercial electrical power generation in the U.S. 6/14/2017 2 NRC Reactor Concepts (R-100) Training Course Estimated time to complete this chapter: 35 minutes Basic Electrical Generation Using Steam Commercial Generation of Electricity Commercial generation of electricity requires large-scale production of electricity in an economical and cost- effective manner. As both a primary consumer and producer of electricity, the U.S. has multiple options and methods for producing electricity. By far, the most prevalent is a steam electric power plant. 6/14/2017 3 NRC Reactor Concepts (R-100) Training Course The steam supply system includes the boiler. The boiler provides the heat that produces the steam. All steam electric power plants have a boiler, regardless of the nature of the fuel used to generate the steam. The main turbine provides the force used to turn the rotor of the electrical generator. The turbine includes a rotary engine made with a series of curved vanes on a rotating shaft. Turbines are considered the most economical means to turn large electrical generators. The electrical generator is an electromagnetic device that converts mechanical (rotational) energy into electrical energy. The electrical generator includes the rotor and the stator. The main condenser is a large heat exchanger designed to cool exhaust steam from a turbine to below the boiling point so that it can be returned to the heat source as water. The heat removed from the steam by the condenser is transferred to a circulating (cooling) water system and is exhausted to the environment, either through a cooling tower or directly into a body of water. The position of the throttle valve allows the operators to control the amount and rate of steam going to the turbines. The position of the throttle valve is directly related to the amount of electricity a plant produces at any given time. The feedwater pump guarantees that cool water continuously enters the boiler. Most of the water comes from the condenser, while additional water may be added from an outside source. Components of a Steam Power Plant First, let’s consider the basics of a steam power plant. All steam power plants, regardless of fuel type, have the same basic functionality and use many of the same components. Select the components of a basic steam power plant for an explanation of its function or role. Video Electrical Generator Steam electric power plants can use a number of fuels to create the steam, but all require an electrical generator to produce the electricity. In most large-scale electrical generators, a magnet (rotor) revolves inside a stationary 6/14/2017 4 NRC Reactor Concepts (R-100) Training Course coil of wire (stator). The magnetic lines of flux ‘cut,’ or flow, through the stator and create a flow of electrons inside the wire. This flow of electrons is electricity. Some mechanical device (wind turbine, water turbine, steam turbine, diesel engine, etc.) must be available to provide the force for turning the rotor. Select Play to view an electrical generator creating electricity. (View transcript.) Show me a rotor and stator used in commercial power plants. The rotor (magnet) is centered in the coiled wires of the stator. An outside force spins the magnet within the stator, creating a magnetic field, which in turn generates an electric current. 6/14/2017 5 NRC Reactor Concepts (R-100) Training Course Cooling with Circulating Water To operate properly, steam plants need a circulating water system to remove excess heat from the steam system. The steam exiting the turbines enters the condenser and its heat is transferred to the environment. The circulating water system pumps water through thousands of metal tubes in the plant’s condensers. Steam exiting a plant’s turbine is cooled and condensed back into water as it comes into contact with the much-cooler tubes. Since the tubes provide a barrier between the steam and the environment, there is no physical contact between a plant’s steam and the cooling water. The condenser is maintained at a vacuum since that will increase the amount of energy that the turbine can extract from the steam. Because a condenser operates at a vacuum, any tube leakage in this system will produce an inflow of water into the condenser rather than an outflow of water to the environment. There are three methods for cooling with circulating water. Select a tab for an explanation of each method. Body of WaterForced Draft TowerNatural Convection Tower 6/14/2017 6 NRC Reactor Concepts (R-100) Training Course Power plants located on large bodies of water often discharge their circulating water directly back to the ocean or other body of water under strict environmental protection regulations. The discharge water temperature and chemical composition is regulated by the states. The expected temperature increase from circulating water inlet to outlet is about 5 to 10 degrees Fahrenheit. Power plants located on large bodies of water often discharge their circulating water directly back to the source under strict environmental protection regulations. The discharge water temperature and chemical composition are regulated by the states. The expected temperature increase from circulating water inlet to outlet is about 5 to 10 degrees Fahrenheit. 6/14/2017 7 NRC Reactor Concepts (R-100) Training Course With a forced draft cooling tower, the circulating water is pumped into the top of the tower after passing through the condenser and allowed to splash downward transferring some of its heat to the air. Several large electrical fans, located at the top of the cooling tower, provide forced air circulation for more efficient cooling. The tall, hourglass-shaped, natural convection cooling towers do not require fans to transfer the excess heat from the circulating water system into the air. Rather, the natural tendency of hot air to rise removes the excess heat as the circulating water splashes down inside the cooling tower. These towers are typically several hundred feet tall. The "steam" vented from the top of a cooling tower is really lukewarm water vapor. As the warm, wet air from inside the cooling tower contacts the cooler, dryer air above the cooling tower, the water vapor that cannot be held by the cooler air forms a visible cloud. This is because the colder the air is, the lower its ability to hold water. The released cloud of vapor will only be visible until it is dispersed and absorbed by the air. However, that released water vapor represents a significant 'loss' of volume from the circulating water system. Plants need to make up tens of thousands of gallons of water per hour to accommodate these losses. 6/14/2017 8 NRC Reactor Concepts (R-100) Training Course Check Your Knowledge • Which items describe using steam to generate electrical power? Select all that apply, then select Done. 1. correct:Steam power is the most widely used method of large-scale power generation. 2. Steam power plants are very limited in the types of fuel that can be used to create the steam. 3. correct:Basic components of steam power plants include the steam supply system, the cooling system, the turbine and throttle valve, the electrical generator, and the feedwater pump. 4. The water used to create the steam and the water used for cooling mix freely in the cooling system. 5. Only nuclear power plants have environmental regulations regarding their cooling system. • Correct. Steam power is the most efficient means of large-scale power generation and can use a variety of fuels to create the steam. Regardless of the fuel used, the basic components of steam power plants include the steam supply system, the cooling system, the electrical generator, the throttle valve, and the feedwater.