Byproducts of power generation

Byproducts of power plant operation need to be considered in both the design and operation. Waste heat due to the finite efficiency of the power cycle must be released to the atmosphere, often using a cooling tower, or river or lake water as a cooling medium. The fuel gas from combustion of the fossil fuels is discharged to the air; this contains carbon dioxide and water vapor, as well as other substances such as nitrogen, nitrous oxides, sulfur oxides, and (in the case of coal-fired plants) fly ash and mercury. Solid waste ash from coal-fired boilers is removed. Ash generated can be re-used for building materials.

Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 5.7% of the world's energy and 13% of the world's electricity. In 2007, the IAEA (International Atomic Energy Agency) reported there were 439 nuclear power reactors in operation in the world, operating in 31 countries. Also, more than 150 naval vessels using nuclear propulsion have been built.

There is an ongoing debate about the use of nuclear energy. Proponents, such as the World Nuclear Association, the IAEA(International Atomic Energy Agency) and Environmentalists for Nuclear Energy contend that nuclear power is a sustainable energy source that reduces carbon emissions. Opponents, such as Greenpeace International and Nuclear Information and Resource Service believe that nuclear power poses many threats to people and the environment.

Nuclear power plant accidents include the Chernobyl disaster (1986), Fukushima Daiichi nuclear disaster (2011), and the Three Mile Island accident (1979). There have also been some nuclear-powered submarine mishaps. Research into safety improvements is continuing and nuclear fusion, believed to be safer, may be used in the future.

China has 25 nuclear power reactors under construction, with plans to build many more, while in the US the licenses of almost half its reactors have been extended to 60 years, and plans to build another dozen are under serious consideration. However, Japan's 2011 Fukushima Daiichi nuclear disaster prompted a rethink of nuclear energy policy in many countries. Germany decided to close all its reactors by 2022, and Italy has banned nuclear power. Following Fukushima, the International Energy Agency halved its estimate of additional nuclear generating capacity to be built by 2035.

In 2011 nuclear power provided 10% of the world's electricity. In 2007, the IAEA reported there were 439 nuclear power reactors in operation in the world, operating in 31 countries. However, many have now ceased operation in the wake of the Fukushima nuclear disaster while they are assessed for safety. As of December 2009, the world had 436 reactors (including inactive ones). Since commercial nuclear energy began in the mid 1950s, 2008 was the first year that no new nuclear power plant was connected to the grid, although two were connected in 2009.

The United States produces the most nuclear energy, with nuclear power providing 19% of the electricity it consumes, while France produces the highest percentage of its electrical energy from nuclear reactors—80% as of 2006. In the European Union as a whole, nuclear energy provides 30% of the electricity. Nuclear energy policy differs among European Union countries, and some, such as Austria, Estonia, Ireland and Italy, have no active nuclear power stations. In comparison, France has a large number of these plants, with 16 multi-unit stations in current use.

In the US, while the coal and gas electricity industry is projected to be worth $85 billion by 2013, nuclear power generators are forecast to be worth $18 billion.

Many military and some civilian (such as some icebreaker) ships use nuclear marine propulsion, a form of nuclear propulsion. A few space vehicles have been launched using full-fledged nuclear reactors: the Soviet RORSAT series and the American SNAP-10A.

International research is continuing into safety improvements such as passively safe plants, the use of nuclear fusion, and additional uses of process heat such as hydrogen production (in support of a hydrogen economy), for desalinating sea water, and for use in district heating systems.

Дата добавления: 2015-08-03