The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world's largest power station in terms of installed capacity (22,500 MW) since 2012. The dam generates an average 9520 TWh of electricity per year, depending on annual amount of precipitation in the river basin. After the extensive monsoon rainfalls of 2020, the dam's annual production nearly reached 112 TWh, breaking the previous world record of 103 TWh set by Itaipu Dam in 2016.
The dam body was completed in 2006. The power plant of the dam project was completed and fully functional as of July 4, 2012, when the last of the main water turbines in the underground plant began production. Each main water turbine has a capacity of 700 MW. Coupling the dam's 32 main turbines with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of the dam is 22,500 MW. The last major component of the project, the ship lift, was completed in December 2015.
A large dam across the Yangtze River was originally envisioned by Sun Yat-sen in The International Development of China, in 1919. He stated that a dam capable of generating 30 million horsepower (22 GW) was possible downstream of the Three Gorges. In 1932, the Nationalist government, led by Chiang Kai-shek, began preliminary work on plans in the Three Gorges. In 1939, during the Second Sino-Japanese War, Japanese military forces occupied Yichang and surveyed the area. A design, the Otani plan, was completed for the dam in anticipation of a Japanese victory over China.
During the 1980s, the idea of a dam reemerged. The National People's Congress approved the dam in 1992: out of 2,633 delegates, 1,767 voted in favour, 177 voted against, 664 abstained, and 25 members did not vote, giving the legislation an unusually low 67.75% approval rate. Construction started on December 14, 1994. The dam was expected to be fully operational in 2009, but additional projects, such as the underground power plant with six additional generators, delayed full operation until May 2012. The ship lift was completed in 2015. The dam had raised the water level in the reservoir to 172.5 m (566 ft) above sea level by the end of 2008 and to the designed maximum level of 175 m (574 ft) by October 2010.
Funding sources include the Three Gorges Dam Construction Fund, profits from the Gezhouba Dam, loans from the China Development Bank, loans from domestic and foreign commercial banks, corporate bonds, and revenue from both before and after the dam was fully operational. Additional charges were assessed as follows: Every province receiving power from the Three Gorges Dam had to pay 7.00 per MWh extra. Other provinces had to pay an additional charge of 4.00 per MWh. The Tibet Autonomous Region pays no surcharge.
The first north side main generator (No. 2) started on July 10, 2003; the north side became completely operational September 7, 2005, with the implementation of generator No. 9. Full power (9,800 MW) was only reached on October 18, 2006, after the water level reached 156 m.
The 12 south-side main generators are also in operation. No. 22 began operation on June 11, 2007, and No. 15 started up on October 30, 2008. The sixth (No. 17) began operation on December 18, 2007, raising capacity to 14.1 GW, finally surpassing Itaipu dam (14.0 GW), to become the world's largest hydro power plant by capacity.
As of May 23, 2012, when the last main generator, No. 27, finished its final test, the six underground main generators are also in operation, raising capacity to 22.5 GW. After nine years of construction, installation and testing, the power plant was fully operational by July 2012.
During the November to May dry season, power output is limited by the river's flow rate, as seen in the diagrams on the right. When there is enough flow, power output is limited by plant generating capacity. The maximum power-output curves were calculated based on the average flow rate at the dam site, assuming the water level is 175 m and the plant gross efficiency is 90.15%. The actual power output in 2008 was obtained based on the monthly electricity sent to the grid.
The Three Gorges Dam reached its design-maximum reservoir water level of 175 m (574 ft) for the first time on October 26, 2010, in which the intended annual power-generation capacity of 84.7 TWh was realized. It has a combined generating capacity of 22.5 gigawatts and a designed annual generation capacity of 88.2 billion kilowatt hours. In 2012, the dam's 32 generating units generated a record 98.1 TWh of electricity, which accounts for 14% of China's total hydro generation. Between 2012 (first year with all 32 generating units operating) and 2021, the dam generated an average of 97.22 TWh of electricity per year, higher than Itaipu dam's average of 89.22 TWh of electricity per year during the same period. Due to extensive monsoon of 2020 year with heavy rainfalls, the annual production reached 112 TWh that year, which broke the previous world record of annual production by Itaipu Dam equal to 103 TWh of 2016 year.
The dam was expected to provide 10% of China's power. However, electricity demand has increased more quickly than previously projected. Even fully operational, on average, it supports only about 1.7% of electricity demand in China in the year of 2011, when the Chinese electricity demand reached 4,692.8 TWh.
According to the National Development and Reform Commission, 366 grams of coal would produce 1 kWh of electricity during 2006.From 2003 to 2007, power production equaled that of 84 million tonnes of standard coal.
The dam discharges its reservoir during the dry season between December and March every year. This increases the flow rate of the river downstream, and provides fresh water for agricultural and industrial usage. It also improves shipping conditions. The water level upstream drops from 175 to 145 m (574 to 476 ft), preparing for the rainy season. The water also powers the Gezhouba Dam downstream.
The Three Gorges Dam is a steel-concrete gravity dam. The water is held back by the innate mass of the individual dam sections. As a result, damage to an individual section should not affect other parts of the dam. Zhang Boting, deputy secretary-general of China Society for Hydropower Engineering, suggested that concrete gravity dams are resistant to nuclear strikes. Sung Chao-wen, former Taiwanese Ministry of Defense advisor, called the notion of using cruise missiles to destroy the Three Gorges Dam \"ridiculous\". He cited missiles would only deliver minimal damage to the reinforced concrete, and any attack attempts would need to go through multiple layers of ground and air defenses.
Immediately after the first filling of the reservoir, around 80 hairline cracks were observed in the dam's structure; however, an experts group gave the project overall a good-quality rating and the 163,000 concrete units all passed quality testing, with normal deformation within design limits.
In the final analysis, the Fukushima accident does not reveal a previously unknown fatal flaw associated with nuclear power. Rather, it underscores the importance of periodically reevaluating plant safety in light of dynamic external threats and of evolving best practices, as well as the need for an effective regulator to oversee this process.
The accident at Fukushima Daiichi Nuclear Power Station on March 11, 2011, has put safety concerns front and center of the ever-contentious debate about nuclear energy. With large quantities of radioactivity released into the environment, over three hundred thousand residents evacuated from the vicinity of the plants,1 and a cleanup operation that will take decades and cost tens, if not hundreds of billions of dollars, critics have argued that nuclear power is too dangerous to be acceptable. But are they right Can nuclear power be made significantly safer The answer depends in no small part on whether nuclear power plants are inherently susceptible to uncommon but extreme external events or whether it is possible to predict such hazards and defend against them.
On March 11, 2011, at 2:46 pm local time, Japan was struck by a magnitude 9.0 earthquake, centered in the Pacific Ocean about 80 kilometers east of the city of Sendai, that set a powerful tsunami in motion.3 This was the largest earthquake ever recorded in Japan and, according to the United States Geological Survey, the fourth largest recorded worldwide since 1900.4
[d]uring the initial response, work was conducted in extremely poor conditions, with uncovered manholes and cracks and depressions in the ground. Work at night was conducted in the dark. There were many obstacles blocking access to the road such as debris from the tsunami and rubble that was produced by the explosions that occurred in Units 1, 3 and 4. All work was conducted with respirators and protective clothing and mostly in high radiation fields.17
As a result, we believe it would be unfair to apportion significant blame for the accident on the actions the operators took (or failed to take) after the tsunami, as the official investigation committee has done. Furthermore, given the potential challenges of a complete loss of AC power, it is clear that prevention is the best form of management. To this end, the key questions raised by the accident are why was the tsunami hazard at Fukushima Daiichi so dramatically underestimated And could changes in plant design (resulting from effective safety reviews) have prevented a severe accident in the event that a tsunami struck the plant The answers to these questions help shed light on whether the accident could have been prevented. 153554b96e