On March 24th, the staff explained the principle of nuclear power generation to media representatives. On the same day, at the invitation of Daya Bay Nuclear Power Operation Management Co., Ltd., more than 50 journalists from various media in Hong Kong formed a visiting group to visit Daya Bay Nuclear Power Station and held discussions with nuclear safety and emergency experts. Nuclear safety experts at Shenzhen Daya Bay Nuclear Power Base said that the power station of Daya Bay Nuclear Power Base has both site selection and design.
This is a panoramic view of Daya Bay Nuclear Power Station taken on March 24th. Xinhua News Agency reporter Li Qiuchan photo
The recent nuclear accident at Fukushima nuclear power plant has caused serious consequences. As the first large-scale commercial nuclear power plant in China, Daya Bay nuclear power plant has naturally attracted more attention: Can it resist extreme natural disasters such as earthquake and tsunami?
In this regard, relevant experts pointed out that Daya Bay Nuclear Power Station has five barriers, and its safety level and overall response capacity to serious accidents are significantly higher than those of Fukushima Nuclear Power Station, and there will be no consequences similar to those of Fukushima Nuclear Power Station in extreme accidents.
First, the technical route is different. Boiling water reactor has no steam generator, and the steam generated by boiling water directly drives the steam turbine. During normal operation, the steam is radioactive, and once it fails, the radioactivity will increase, making inspection and maintenance difficult. According to Pu Jilong, an expert from the National Nuclear Power Major Special Committee, the accident unit of Fukushima nuclear power plant adopts the old-fashioned single-layer circulating boiling water reactor, and the cooling water is directly introduced into the seawater cooling primary circuit, which belongs to the early nuclear power technology built in the late 1960s and early 1970s.
Pu Jilong said that Daya Bay nuclear power plant adopts pressurized water reactor technology, which fully draws lessons from the experience of the accident of Three Mile Island nuclear power plant in the United States in 1979 and the accident of Chernobyl nuclear power plant in the Soviet Union in 1986. The technology has been greatly improved, with the characteristics of high safety, advanced and reliable technology and so on. It belongs to a relatively advanced nuclear power plant built after the 1990s. At present, there are more than 70 similar units in operation all over the world, and accumulated more than 1000 years of experience in the operation of the same type of nuclear power units.
Second, special safety facilities are different. Pu Jilong said that the Fukushima nuclear power plant used the technology 40 years ago, and the reactor containment space was small, only about 3,400 cubic meters. In the case of serious accidents, the booster process was fast and hydrogen explosion was prone to occur.
The containment of Daya Bay Nuclear Power Station is composed of reinforced concrete cylinders with a space of 49,000 cubic meters, which can effectively reduce and dilute the hydrogen concentration and delay the pressurization time of the containment. At the same time, a hydrogen elimination system is installed in the containment, and dozens of hydrogen recombiners to deal with hydrogen risks can eliminate the risk of hydrogen explosion caused by hydrogen accumulation in the containment under serious accidents.
In addition, Daya Bay Nuclear Power Station is also equipped with a sand filter. Under extreme working conditions, if the containment pressure exceeds the design value, the sand filter can discharge the gas in the containment to the atmosphere, and the sand filter can retain most of the radionuclides in the gas to prevent the radioactive substances in the primary circuit from being released to the environment directly out of control.
Third, the geological conditions are different. According to Li Zhongcheng, an expert from the National Energy and Nuclear Power Engineering Technology Research and Development Center, Japan is located at the junction of the Asia-Europe plate and the Pacific plate, where the Pacific plate is subducting to the Asia-Europe plate, and the crustal movement is active. Strong earthquakes mainly occur in the plate subduction and collision zones.
The site of Daya Bay Nuclear Power Base was selected from more than 10 alternative sites in the coastal areas of Guangdong Province. It is located in the coastal zone in the southeast of Eurasian plate, far from the south-north tectonic belt with strong structural deformation and the subduction zone of Philippine Sea plate. There is no fault zone near the site, and the crust is safe and stable. There has never been an earthquake exceeding magnitude 5 on the Richter scale in history.
Fourth, the ability to cope with the tsunami is different. The Fukushima nuclear power plant in Japan was safe and controllable after the earthquake, and the related plants and facilities were basically complete. According to the current accident analysis, the tsunami flooded the diesel engine, which led to the uncontrollable accident and gradually deteriorated. Therefore, whether Daya Bay Nuclear Power Station can cope with similar tsunami is a concern of the outside world.
Li Zhongcheng said that Daya Bay belongs to the marginal sea. Because the seawater is not deep enough, it is only 20 to 30 meters, and the spread of tsunami requires a water depth of nearly 1,000 meters. Generally, there is an "island arc" between the marginal sea and the open sea. The "island arc" is a series of island chains, and the tsunami caused by seismic waves can only be transmitted from the gaps in the island chains, with limited energy. The highest tsunami recorded on the coast of China is below 0.5 meters, so there will be no strong tsunami similar to that in Japan at the Daya Bay nuclear power plant site.
The biggest natural disaster risk faced by nuclear power plant sites in China’s coastal areas is super typhoon. Daya Bay Nuclear Power Station is located in an area where tropical typhoons often occur. The design benchmark flood control water level of the plant site is the sum of astronomical high tide level exceeding the probability of 10%, possible maximum storm surge water increase and sea level rise during the life of the power plant.
Secondly, Daya Bay Nuclear Power Station’s ability to cope with tsunami is also higher than that of Fukushima Nuclear Power Station. Even if the Daya Bay Nuclear Power Station loses all the power sources inside and outside the plant, it can use the steam generated by the secondary loop through the core waste heat to drive the steam-driven feed pump related to nuclear safety to supply water to the steam generator. At the same time, the secondary loop is equipped with an atmospheric exhaust system, which can cool the reactor core through natural circulation after power failure and discharge heat to the atmosphere to avoid the continuous rise of temperature and pressure in the reactor pressure vessel. In addition, Daya Bay Nuclear Power Station is equipped with two emergency diesel engines for each unit according to the standard, and a fifth diesel engine is also equipped for standby. In addition, the problem of mobile power supply is also being considered.
Fifth, long-term adherence to the nuclear safety culture of "safety first". Jiang Xinghua, director of Daya Bay Nuclear Power Station, said that the principle of "safety first, quality first" has always been implemented in the production and construction process of Daya Bay Nuclear Power Station, which regards safety as the lifeline of nuclear power and respects and guards nuclear safety with a spirit of being highly responsible to the country and society. When other work elements conflict with safety, they must give way unconditionally. At any time and under any circumstances, we should put safety and quality first, and do not exchange quality for progress or safety for power generation. For example, shortly after the start of Daya Bay Nuclear Power Station in September 1987, quality inspectors found that some steel bars were leaked from the raft foundation of the nuclear island. In order to ensure the quality of engineering construction, Daya Bay Nuclear Power Station has been rectified for one month at the cost of $1 million per day of shutdown. In February, 1995, when Unit 1 of Daya Bay Nuclear Power Station carried out the rod drop test, the staff found that the rod drop time of a few control rods was different from the design standard. Although the test results were within the safety margin and did not affect the unit operation, Daya Bay Nuclear Power Station decisively stopped the unit, opened the reactor pressure vessel for treatment five times, thoroughly found out the reasons for the deviation and made proper improvements before starting the unit operation. The handling of this incident lasted for five months, and it paid a great economic price, but in exchange for the good reputation of Daya Bay Nuclear Power Station, such as safety first, seriousness, conservative decision-making, "zero tolerance, zero defects and zero mistakes".
Daya Bay Nuclear Power Station is located in Dapeng Peninsula, Longgang District, Shenzhen City, Guangdong Province. Construction started in 1987 and it was put into commercial operation in 1994. It is the first large-scale commercial nuclear power station in China. Since the unit was put into production, it has maintained safe and stable operation. Since 1999, Daya Bay Nuclear Power Station has won 21 first prizes in 64 international safety performance challenges of similar units. (Reporter Peng Yong)