Steam generator (nuclear power)

A steam generator is an important piece of equipment used in nuclear power plants. It acts like a heat exchanger, taking heat from a nuclear reactor and using it to turn water into steam. This steam can then be used to spin turbines and create electricity.

Steam generators are used in many types of nuclear reactors, including pressurized water reactors, liquid metal cooled reactors, pressurized heavy-water reactors, and gas-cooled reactors. In a typical pressurized water reactor, water flows through the reactor core, picking up heat from the fuel rods. This hot water then moves into the steam generator, where it passes its heat to another amount of water. That second amount of water is allowed to boil, creating the steam needed to make power.

These machines are key to safely turning the heat from nuclear reactions into usable energy, helping power our homes and cities.

Purpose

In some nuclear reactors called boiling water reactors (BWRs), the water that cools the reactor boils right in the reactor core, and the steam goes directly to the turbine. However, this can make maintenance harder because the water becomes radioactive and gives off radiation that makes it unsafe for people to be near the turbine.

In another type of reactor called pressurized water reactors (PWRs), a special part called a steam generator keeps the radioactive water separate from the water that goes to the turbine. This way, people can safely work near the turbines while the reactor is running, which helps keep things running smoothly and saves money on maintenance.

Description

In nuclear power plants, steam generators are important machines that turn water into steam. They are used in many kinds of nuclear reactors. Each steam generator is very tall and heavy, and inside it are many small tubes.

The water that comes from the nuclear reactor is very hot but kept under high pressure so it doesn’t boil. This hot water flows through the tubes in the steam generator. On the outside of these tubes, cooler water is turned into steam. The steam is then used to spin turbines that make electricity. After giving off its heat, the steam is cooled and turned back into water to start the process again.

Steam generators are also used in other types of reactors, such as those that use heavy water or liquid metal to keep the reactor cool. The tubes in a steam generator keep the water from the reactor separate from the water that makes steam, which helps keep things safe.

History

The first steam generators for nuclear power were made to power the first nuclear submarine, the USS ‘‘Nautilus’’ (SSN-571). After that, this technology was used in commercial power plants. In 1960, one of the first of these plants, the Yankee Rowe Nuclear Power Station, began operating in the United States. Since then, many companies have helped build and improve nuclear steam generators for power plants around the world.

Types

Westinghouse and Combustion Engineering designs have special tubes that stand straight up, with other tubes turned upside down for the water. Many suppliers in Canada, Japan, France, and Germany also use this upright design. In Russia, VVER reactors use steam generators that lay flat, with the tubes placed sideways. Babcock & Wilcox plants, like Three Mile Island, have smaller steam generators that push water from the top and pull it back out the bottom. The flat design is better at staying strong over time compared to the upright design.

The materials used to build the parts of a nuclear steam generator are very special. They are made to handle the heat and radiation from the reactor. The tubes that carry water must also stay strong against corrosion from the water for many years. In American reactors, the pipes are made from a special metal called Inconel, either Alloy 600 or Alloy 690. Alloy 690 has extra chromium, and most places heat-treat this metal to help it stay strong against heat and corrosion. Both Alloy 600 and Alloy 690 are good at handling acids, stress, and high temperatures because they have a lot of nickel.

Typical operating conditions

Steam generators in a typical pressurized water reactor (PWR) in the USA have specific conditions they need to work under.

Tube material

Different strong metals and special alloys are used to make the tubes in steam generators. These include type 316 stainless steel, Alloy 400, Alloy 600MA (mill annealed), Alloy 600TT (thermally treated), Alloy 690TT, and Alloy 800Mod. These materials help the tubes stay strong and safe when dealing with heat and pressure.