Can the latest generation of nuclear power plants

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Whether the new generation of nuclear power plants can prevent future accidents

it is said that the new generation of nuclear power plants have the function of avoiding "serious accidents" by adopting various safety technologies. Reactors capable of disposing plutonium have also been developed. It is also possible to reduce the burden of final disposal. So, can we avoid another unprecedented accident like the Fukushima Daiichi nuclear power plant of Tokyo Electric Power Company in the future

before 2015, invest about 30billion yen to build a demonstration reactor for a new generation of reactors - China announced a schedule for the practicality of the new generation reactor "thorium molten salt reactor" in 2011. It is also reported that the demonstration reactor will be completed in 2030, and China plans to invest 200billion yen, which is of extraordinary seriousness

after a major accident that greatly exceeded the design standard at the Fukushima Daiichi nuclear power plant of Tokyo Electric Power Co., Ltd., that is, a "serious accident", enterprises should pay attention to: 1. The growth rate of automobile production and sales volume with the largest weight in the total industrial volume is picking up; 2. The cumulative order volume of key enterprises in the machinery industry has warmed up, and the safety myth of nuclear power plants has collapsed. In Japan, the time is ripe to reduce nuclear power plants in the future. Looking at the world, Germany has made it clear to go to nuclear power. The construction boom of nuclear power plants, known as the "nuclear renaissance", seems to have cooled significantly

on the other hand, emerging market countries such as China and India, which are expected to increase energy demand, still have high hopes for nuclear power. Fukushima Daiichi nuclear power plant was built more than 40 years ago. During this period, how much has the safety technology of nuclear power plants improved? Can the nuclear power plants built in the future avoid serious accidents

it can shut down automatically even in case of serious accidents

the development of a new generation of nuclear power plants is roughly divided into two trends. One is to transform most of the reactors that have been put into commercial use, namely "light water reactors". The other is the thorium molten salt reactor targeted by China and the "sodium cooled fast neutron reactor" adopted by the prototype fast neutron breeder "Manjusri" (Tunga City, Fukui Prefecture, Japan), which is different in concept and principle from the reactor of light water reactor

reactor structure comparison

from the first generation to the third generation are light water reactors. The pressure vessel is filled with water, and the energy generated by the nuclear fission of uranium is used to generate steam for power generation. BWR and PWR in the second generation have been improved to become the third generation. The fourth generation is different from light water reactor in structure and principle. For example, the thorium molten salt reactor uses liquid fuel with thorium and plutonium added to the "molten salt" liquid

first of all, from the light water reactor. Light water refers to ordinary water. Light water reactor is a reactor that uses water to absorb the energy released during nuclear fission of uranium and other nuclear fuels and applies it to power generation

representative light water reactors include "boiling water reactor (BWR)" manufactured by Toshiba, Hitachi and General Electric (GE) and "pressurized water reactor (PWR)" manufactured by Mitsubishi Heavy Industries and Westinghouse Electric (WH)

The principle of

bwr is to fill the pressure vessel with fuel with water, which boils and turns into steam with the progress of nuclear fission. Steam is used to directly drive the turbine to generate electricity. Fukushima Daiichi nuclear power plant belongs to BWR. After the earthquake, due to the loss of external power, the water pump stopped, the water in the pressure vessel could not be replenished, and the fuel overheated, which led to the core meltdown

on the other hand, the principle of PWR is basically the same. However, the pressure capacity multi limb chain should be tested for section. Although the water in the apparatus will reach high temperature and high pressure, it will not form steam. Instead, through the heat exchanger, the water called "secondary system" that does not contact the fuel boils to form steam

the U.S. Nuclear Regulatory Commission (NRC) designates the reactor according to data such as construction period (refer to the figure below). The first generation is the experimental reactor developed by the United States and other countries in the mid-1960s. After the second generation, commercial reactors were built before the mid-1990s, with BWR and PWR as the center. Fukushima Daiichi nuclear power plant also belongs to the second generation

the third generation is a reactor that enlarges the reactor before the second generation and strengthens the safety function by providing multiple water pumps and power supplies. Among them, the reactor to be built in the future is called "generation 3.5". "In order to cope with the earthquake, we are still studying the use of isolation devices," said yoshindahong, vice president of the Atomic Energy Technology Department of Mitsubishi Heavy Industries, which is developing such an improved PWR

the idea of "passive safety" is adopted. When an accident occurs in operation, there is no need for the operator to handle it. A reactor that can automatically prevent the dispersion of radioactive substances has also been invented. Westinghouse's "AP1000" and Ge Hitachi nuclear's "esbwr" have huge pools above the containment. Once the temperature in the container rises sharply, the valve will automatically open and spray water downward under the action of gravity. So as to cool the reactor and prevent serious accidents

another trend of the new generation of nuclear power plants is to strive to put the fourth generation reactors into operation after 2030. The sodium cooled fast neutron reactor in Manjusri and the thorium molten salt reactor that China is trying to promote the practicality belong to this category

the structure of sodium cooled fast neutron reactor is similar to PWR, but metal sodium is used for core cooling instead of water. Uranium is used as fuel in light water reactors. If uranium plutonium mixed oxide (MOX) is used, it can become a "fast breeder reactor" with no reduction in fuel during power generation

Japan has put forward the policy of implementing the "nuclear fuel cycle". The spent fuel produced by light water reactors contains plutonium that can be used as raw material for nuclear weapons and nuclear fission products with extremely high radiation levels, which is often referred to as "dead ash". Japan is ready to reprocess these spent fuels and apply uranium and plutonium to fast breeder reactors. Fission products are separated and disposed of as high-level radioactive waste

however, Manjusri, who carried out the demonstration of rapid breeder reactor, has been shut down due to failure. Moreover, sodium metal will catch fire after contacting with air, which is very inconvenient to use. In addition, breeder reactors need to cost a lot of development costs. Countries such as the United States and Britain have given up, emerging market countries and France are still developing, while in Japan, there are still disputes about whether breeder reactors can be developed

the Japanese government may publish a new "basic energy plan" this summer. From the orientation of nuclear power to the nuclear fuel cycle, and even the development direction of rapid breeder reactor, various discussions are still being carried out

in terms of thorium molten salt reactors, the United States completed the operation of experimental reactors in the 1970s. After the light water reactor took the lead, the thorium molten salt reactor was once far away from the stage of nuclear power development, but in recent years it has begun to receive attention again. In addition to the trend of China, nuclear power countries that do not know how to deal with the plutonium produced by the operation of light water reactors for many years have also begun to show interest

it can be used for plutonium disposal

thorium molten salt reactor is characterized by the use of liquid fuel with thorium and other substances added to the liquid called "molten salt". Thorium is a by-product of rare earth mining. China and other countries with prosperous rare earth development are worried about how to deal with the huge amount of thorium. Moreover, its resource reserves are said to be 4-5 times that of uranium

mixing plutonium and fission products in liquid fuel may also make them disappear, so as to solve the problem of Nuclear Non-Proliferation of plutonium and the disposal of high-level radioactive waste

molten salt is different from water. Even in high-temperature environment, it is under normal pressure in the container, so it is not easy to leak from the container. When the temperature rise is detected, the valve will open to make the liquid fuel fall into the special container at the lower part of the reactor, so as to stop the reaction. The reactor core does not need water cooling, and the success rate of avoiding accidents is high

but the subject also exists. Dawo Yama, an honorary professor at the University of Tokyo, commented that this kind of reactor "although highly safe, it is difficult to realize practicality without tens of billions of yen in development funds". Therefore, "the fast practical process may be the new reactor of American TerraPower and other enterprises with development funds funded by Bill Gates, the founder of Microsoft in the United States"

terrapower develops a "traveling wave reactor" that uses the deteriorated uranium that cannot be used in ordinary light water reactors as fuel. The modified light water reactor is large-scale and expensive, and in some countries and regions, the power produced cannot be fully utilized. Focusing on these markets, many enterprises such as TerraPower are developing small and medium-sized reactors

as a result, Toshiba is developing a super small sodium cooled fast neutron reactor "4S" due to the viscoelastic failure mechanism. The purpose is to apply it to seawater desalination and other equipment. When leaving the factory, it will be equipped with fuel that can be used for decades, and there is no need to replenish fuel. From the perspective of the use method buried deep underground, the safety seems to be very high

Johnson Matthey believes that all countries are developing new generation nuclear power plants. Compared with the Fukushima Daiichi nuclear power plant built 40 years ago, the safety has been improved. But there is no 100% safety in the world. No matter how to improve safety, the risk of accidents cannot be zero. How should nuclear power plants be used in the future? What we need to do now is to solve the complex equations involving accident risk, cost, stable energy supply and global warming. (Nikkei Business Week: Yamamoto light snow) (end)

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