 |
AP1000 reactor nuclear power plant model.
Nuclear power station, but also not?
After the nuclear accident in Fukushima, Japan, people had unprecedented fears of nuclear power stations and their safety was generally questioned. But in the face of the temptation of the most efficient and zero-emission energy sources so far, where can we go? Fortunately, the two new types of nuclear power plant designs can largely dispel people's doubts.
After the nuclear disaster in Fukushima in Japan in March this year, the world’s enthusiasm for nuclear power plants fell to a minimum—even lower than the period after the Chernobyl nuclear accident. Countries such as Germany, Switzerland, and Italy have completely stopped nuclear power plant projects. Other countries including China have also conducted comprehensive safety inspections of existing nuclear power plants. However, none of the renewable energy efficiency can be compared with nuclear power plants. The energy generated by a nuclear power plant that covers an area of ​​one square kilometer is equivalent to a solar power station with an area of ​​20 square kilometers, or 1200 wind power generators. If a country wants to significantly reduce its dependence on fossil fuels, it will need to build more nuclear power plants. But the key question is how to ensure the safety of nuclear power plants?
From the construction of Qinshan Nuclear Power Plant, the first nuclear power station in our country, to its 30-year history in 1985, engineers have repeatedly increased the safety of nuclear power plants many times. The latest 3-generation half-nuclear power plants have already come out. (First-generation nuclear power plants refer to early prototypes; second-generation nuclear power plants refer to nuclear power plants built in the early 1960s to the end of the 1990s. Fukushima nuclear power plants belong to this generation; third-generation nuclear power plants refer to the 1990s. Nuclear power plants that were put into operation since the end were mainly located in Japan, France, and Russia.) Unlike previous designs, most of the 3rd generation nuclear power plants have a passive elemental safety layer that prevents the reactor from melting in the event of a power outage. The construction of the first 3-generation half-nuclear power plant is currently underway in Europe. The nuclear power plants currently under construction and planned in China also belong to the 3rd-generation half-nuclear power plant. In the United States, Southern has also recently begun construction of the first three-generation half-nuclear power plant, the Voghtle Nuclear Power Plant, in Augusta, Georgia. The first of the two reactors will be put into use in 2016.
Like some of the other 20 nuclear power stations planned, the Voghtle nuclear power plant will also use the Westinghouse AP1000 reactor. As a light water reactor, AP1000 uses uranium 235 to generate a chain reaction that produces high-energy neutrons. High-energy neutrons heat water into steam, which in turn drives turbines to generate electricity.
The biggest danger of a nuclear power plant is reactor melting - the core of the reactor is overheated, melted, and the shell ruptures, eventually leading to leakage of radioactive material. Like most reactors, the AP1000 also needs to rely on electricity to drive cooling water and fans to cool down, but it also has a passive safety system that can harness the natural forces of gravity, condensation, and evaporation to power the reactor in the event of a power failure. cool down.
At the heart of the passive safety system is a 3,000-cubic-meter tank that sits directly above the sealed enclosure. The valve of the tank requires power to remain closed. In this way, once the power supply to the reactor fails, the valve will open and the water in the tank will flow out to the sealed enclosure. Vents also passively draw cold air from the outside and allow it to flow through the core structure for further cooling.
If the situation deteriorates further, the technician can manually open another tank in the sealed housing and submerge the reactor core. Evaporated water condenses on the top of the shell and falls, and the core is repeatedly cooled. Most of the standby power supplies for today's nuclear power plants can only last for 4 to 8 hours after the grid power supply is interrupted, and the AP1000 can operate safely for at least 3 days without power intervention and manual intervention.
Although the safety has greatly improved, in theory, the 3rd generation of nuclear power plants may still melt, and some experts in the nuclear industry are currently working on the design of newer and safer fourth-generation nuclear power plants. One of the fourth-generation reactors, the molten salt reactor (MSR) fueled by helium, replaces the solid-state uranium used in today's nuclear power plants with liquid helium. This change completely eliminates the problem of melting.
The concept of a molten salt reactor was proposed and constructed at the Oak Ridge National Laboratory in Tennessee, USA, in the 1960s and operated 22,000 hours between 1965 and 1969. "It's not just a reactor in theory, nor is it experimental." Mark Kutcher, head of the Nonprofit Energy Alliance, said: "They are real and can run." At present all In the fourth-generation reactor design, the MSR was the only one that was actually tested outside the computer model. "Although it was not a complete system built at the time, it did prove that the MSR was a design that could be run successfully," said Jesse Giesing, senior project manager for the Nuclear Technology Project Office at Oak Ridge National Laboratory.
In terms of safety, MSR's design has two main advantages: its liquid fuel storage pressure is much lower than the pressure of solid fuel in light water reactors, which greatly reduces the kind of hydrogen explosion like the Fukushima nuclear power plant. possibility. Second, in the event of a power outage, the solid salt in the reactor melts and the liquid fuel flows into the reservoir and solidifies, ending the fission reaction. “The molten salt reactor is safe even if it is left unattended,†said Kuchi. “Even if the asteroid hits Earth, the end of the world, it will cool and solidify itself, even if it is abandoned and there is no electricity supply.â€
Although molten salt reactors can also use uranium or plutonium as fuel, the use of low-level elemental plutonium as fuel, with a small amount of uranium or plutonium as a catalyst, will be economical and safe. The reserve of thorium is 4 times that of uranium and it is easier to exploit - partly because it is less radioactive. In addition, the efficiency of cockroaches is much higher than that of uranium. “In traditional reactors, only 3% to 50% of uranium is used,†said Kuchi. “In a molten salt reactor, 99% of the plutonium is used.†The result is that 1 kilogram of plutonium produces energy equivalent to 135 kilograms of uranium, or 1.6 million kilograms of coal.
Due to the high efficiency of fuel utilization, the nuclear waste produced by the helium-fired molten salt nuclear power plant is also much less than today's nuclear power plants. Uranium-based nuclear waste remains hazardous for thousands of years, and the hazardous life of antimony waste is only a few hundred years. In addition, there is also a benefit that é’ is difficult to be made into nuclear weapons. "Even if a country stores 1,000 kilograms of plutonium, there is nothing to worry about," Cooch said.
Because there is no need for a large cooling tower, the molten salt reactor is smaller than the traditional light water reactor regardless of its floor space or power generation capacity. Today's nuclear power plants have an average generating capacity of 1,000 megawatts, while the thorium fueled molten salt reactors have only about 50 megawatts of power. Smaller, more numerous nuclear power plants can reduce the loss of electricity during transmission (in today's power grids, transmissions cause losses of up to 30%). The U.S. military expressed strong interest in using molten salt reactors to supply power to military bases. Google Inc., which needs stable power to ensure its server operations, also hosted a conference on the theme of the U.S. last year. “They hope to build a 70-80 MW molten salt reactor near the data center,†said Kuchi.
However, even with the support of the military and large enterprises, the transition to new nuclear power plants will be very slow. But in our country, this speed may be much faster. In January this year, China started a molten salt reactor project that uses thorium as fuel. "The Chinese Academy of Sciences has already confirmed that it will deploy the molten salt reactor in the near future - maybe less than 10 years," said Giesing. The launch of this project may play an exemplary role in the world. (text - Thompson/photo - Hande)
Linear High Bay,Garage Light Linear Highbay,Led Linear Highbay Light,High Lumen Linear High Bay Light
Fuonce-Lighting , https://www.szfuoncelighting.com