Described by some people as a very terrible radioactive hazard, to put it bluntly, it is really minimal. Residents near the nuclear power plant only receive a radiation dose of 0.3 millirem per year. If we want to give you a perceptual comparison, then if a person smokes 1 cigarette, it is equivalent to absorbing 5 millirem, the radiation dose received by X-ray fluoroscopy is 20 ~ 100 millirem, and the radiation dose received by flying for one hour is 0.5 millirem. These figures fully show that the radioactive hazard of nuclear power plants need not be regarded as a scourge.
We pointed out the shortage of coal as energy earlier, and we don't want to cancel this traditional energy at present. On the contrary, coal is still one of the major energy sources in the world, including China. When formulating technical policies, China needs to build a coal energy base with Shanxi as the center. However, when and where nuclear energy must be developed, scientists must lose no time to provide scientific basis for decision-making.
Among the various sources of nuclear power materials, although there are similar hazards to the environment caused by coal in production, due to the high energy density of nuclear fuel, the harm range is much smaller, which has been comprehensively investigated. 1982, due to the use of Swiss nuclear power plants, the CO2 emission of the whole energy system in China was reduced by about 1/4.
But at present, when we choose power stations, we hear far less accusations against coal-fired thermal power than against nuclear power, which is a concrete reflection of people being bound by traditional concepts.
Now, we need to deeply analyze the safety performance of nuclear power and make a comprehensive evaluation after comparing with other energy systems.
What is the safety of nuclear power? In order to solve this problem, nuclear power plants in some countries are open to the outside world and people are organized to visit them. The fact shows that nuclear energy is not only safe, but also less dangerous than many other energy sources.
The nuclear-filled part of a nuclear power plant reactor will never explode like an atomic bomb, and its potential danger is the leakage of highly radioactive fission products, which will pollute the surrounding environment.
The atomic bomb consists of high-concentration (more than 93%) fissile material uranium -235 or plutonium -239 and a complex and sophisticated detonation system. Fission materials are pressed together by the detonation system, reaching the supercritical volume, and then a chain reaction of nuclear fission is suddenly formed, which releases huge nuclear energy in a very short time and produces a nuclear explosion. The structure and characteristics of a reactor are completely different from those of an atomic bomb. Most reactors use low-concentration fissile materials as fuel, and these fuels are dispersed in the reactor. Under any circumstances, it is impossible to press fuel together like an atomic bomb and cause a nuclear explosion. Moreover, the reactor also has various safety control measures to realize the controllable chain reaction of nuclear fission. In design, the reactor is always self-stable, that is, when the nuclear energy is accidentally released too fast and the core temperature rises too high, the chain reaction of nuclear fission will automatically weaken or even stop. Therefore, under any circumstances, the nuclear fuel part of the reactor will never explode like an atomic bomb.
In view of the danger of nuclear power plants, in order to prevent accidents, various safety measures have been taken in the design, the main starting point of which is to prevent abnormal temperature rise of fuel elements and a large number of fission products from escaping into the environment. If these two points can be achieved, the safety of nuclear power plants will be guaranteed. Specific safety measures are as follows:
(1) In order to prevent the leakage of radioactive materials, the nuclear power plant has set up four safety barriers.
The first barrier is nuclear fuel pellets.
The second barrier is zirconium alloy cladding tube.
The third barrier is the pressure vessel and the closed primary system.
The fourth barrier is the containment building. Due to the barrier of the containment plant, the impact on the environment and personnel outside the plant is minimal.
(2) Reliable control and protection system.
When the power of the reactor is too high, the temperature rises rapidly, the time required to increase the neutron number is too short, and the coolant flow rate is too low, the reactor can be stopped quickly or the power can be reduced by the control system to avoid damage to the core. Flow control, chemical compensation and liquid poison can also be used to achieve control and protection. Instruments, signals and control circuits are all working in a reliable state. There are three sets of independent monitoring devices for important parameters, which act according to certain principles. This can not only ensure accidental shutdown, but also avoid misoperation caused by instrument failure.
(3) Reliable cooling system.
The system can ensure that the reactor can take away the heat generated by fuel under normal working conditions or accidents, and avoid the combustion of fuel elements. For example, the accident of light water reactor losing cooling water is an imaginary serious accident. If the pipeline is broken, the most serious situation is that the pipeline with the largest diameter in the primary circuit is broken, causing two cracks and ejections, resulting in reactor water loss. The core will burn out and a large amount of radioactive materials may be released into the containment. At this time, the reactor automatically stopped and stopped in an emergency, and multiple safety facilities immediately played a protective role: first, due to the sudden drop of primary circuit pressure, the safety water injection tank in the emergency core cooling system immediately pushed open the check valve to inject emergency water into the primary circuit to compensate for the lost coolant in the system; Secondly, at the same time, the high and low pressure safety water injection pumps in the emergency core cooling system are started one after another, and the water in the water storage tank is continuously injected into the primary circuit of the reactor to ensure that the core is submerged and cooled. The containment spray pump is also started at the same time to spray water into the containment, so that the water vapor in the containment condenses, the pressure drops, and radioactive substances are absorbed by water; Thirdly, after the water in the water storage tank is used up, the safety water injection pump will immediately take water from the containment pit and circulate it back to the reactor to ensure the long-term cooling needs. The pressure-resistant sealing device is always tightly sealed to prevent leakage of radioactive materials.
The design and manufacturing standards of nuclear power plants are much higher than those of conventional industries, and the quality control and quality assurance to meet these standards are much stricter. Nuclear power plants even take the worst accident that is extremely unlikely to happen as the safety basis, and do deep defense to ensure safety. Nuclear power plant is the product of the comprehensive development of modern science and technology. Its scientific design, meticulous manufacturing, reliable operation and multiple safety measures make the possibility of major accidents much lower than other natural and man-made disasters (such as plane crash, fire, earthquake, dam break, hurricane, strong wind, etc.). ).
Which energy system is more dangerous to human health? To answer this question, we should not only look at its size and appearance, but also measure the danger caused by unit energy, that is, the total danger to human health divided by the net energy generated by the energy system. At the same time, we should also consider all the energy cycles. If we only calculate and compare the risks brought by some systems, it will not explain the problem.
The overall risk is evaluated according to the death, trauma and disease caused by the energy system, and the whole process of energy production, including the initial stage, the intermediate stage and the final stage, should be considered. For example, for nuclear power plants and solar collectors, we should not only consider the dangers in the process of construction and operation, but also consider the dangers in the process of mining raw materials such as sand, copper, iron and uranium and making them into glass, copper pipes, nuclear fuel rods and steel, and also consider the dangers in the process of transportation.
Comparing the harm caused by the unit energy generated by nuclear energy, coal, oil, natural gas and other energy systems, we can find that the harm of nuclear power plants is much lower than that of oil-fired or coal-fired power plants. At the same time, the calculation results show that the total risk of most unconventional energy systems such as solar energy, wind energy, ocean energy and wood alcohol is greater than that of conventional energy systems (coal, oil, natural gas, hydropower, etc.). ) and nuclear power.
1 1 Among the energy systems, natural gas power generation is the least dangerous, followed by nuclear power plants, and the third is unconventional ocean temperature difference power generation system. Most other non-traditional energy systems have many dangers. But the highest of all energy systems are coal and oil, which are about 400 times more dangerous than natural gas.
Unconventional energy systems are more dangerous because their unit energy output requires a lot of materials and labor. Solar energy and wind energy are divergent energy sources, which are weak. To accumulate a large amount of energy, a considerable collection system and storage system are needed. However, coal, oil and nuclear energy systems are concentrated forms of energy and require few equipment. Natural gas needs the least materials and the shortest construction time, while wind energy needs the most materials and solar photovoltaic cells need the longest construction time. Unconventional energy systems need a lot of materials, which means a lot of industrial activities, such as mining, transportation, processing and construction. Moreover, every kind of industrial activity will cause certain risks. When all the risks are added up, the risks of these unconventional energy systems are considerable.
Contrary to many people's intuition, unconventional energy systems, such as solar energy and wind energy, are much more harmful to human health than conventional energy systems (such as natural gas) and nuclear power plants.
The following will describe the operation safety and management of nuclear power plants that many people care about:
Decomposition of operational safety factor
From the point of view of operation, nuclear power plants can be divided into three parts: units, operators and management, in which management includes leaders and functional departments. The management holds both the unit and the operator, but the management can't directly interfere with the operation of the unit. Only the operator can change the operation state of the unit, thus forming two relationships in three aspects: one is the relationship between the operator and the unit, that is, the man-machine interface; On the other side is the relationship between management and operators, that is, everyone's relationship. In this way, when studying and managing operation safety, we must comprehensively consider the above three aspects and two relationships.
According to historical experience, operational safety problems are mainly caused by human factors, and operators are naturally the center of operational safety research and management. In layman's terms, everything in a power plant revolves around the operator. Factors related to operators include personnel selection and assessment, initial training, follow-up training, task assignment and reward and punishment incentives, among which task assignment is the relationship between everyone in the operation team. The overall goal is to have a qualified and capable operator to run the team.
As a power plant entity, the device provides the physical environment for operators to operate. Generally speaking, the unit has to go through several major processes such as design, manufacture, construction, installation, debugging and maintenance. Among them, the design and manufacture will give the unit enough safety margin and reliability to withstand a certain degree of failure and human error. In the operation stage, maintenance is the key to ensure that the unit is in the normal state specified in the design. Unit elements related to operational safety include power plant layout, identification, color coding, material condition and cleanliness. At the same time, we should also consider the harm of high temperature, noise, electricity and chemistry to the operator. Industrial safety factors.
Management is an essential environment for operators, as important as the physical environment. Management is service, including policy, system, outline, plan, coordination and guarantee.
In terms of man-machine interface, we should pay attention to the design of main control room (physical layout and environmental conditions), auxiliary diagnostic means, simulator, maintenance training facilities and operating procedures.
In interpersonal relationship, we should pay special attention to the cultivation of safety literacy, management attitude, resource allocation, self-study ability and communication channels.
Only with a good material environment, management environment and personnel environment, and mastered by qualified operators, a good unit can create a good operating record.
Operational safety management
Security cannot be directly managed. We can only manage the power plant conditions necessary to promote safety, including the attitude and commitment of senior management to safety, and promote the safety literacy of the whole plant.
Due to the development stage of nuclear power and the limitations of manpower, material resources and intelligence, so far, the management of nuclear power safety by the competent department of nuclear power plant and the National Nuclear Safety Administration mainly focuses on design and construction, as well as the evidence collection of operators, which is basically static and partial. In the future, in order to adapt to the situation that nuclear power plants are put into production, safety management should manage the relationship between units, operators and managers, man-machine and everyone, and realize organic all-round management.
The management method of operation safety is completely different from the management method of license review process. Between "yes" and "no", the content of management is more administrative than technical, and the management mode mainly depends on dialogue and consultation, encouraging owners to actively consider how to improve operational safety. Of course, for serious violations, the competent authorities still need to supplement certain sanctions.
It is very important to establish certain standards, establish the evaluation outline of the owner's performance system, check the management quality of the owner, and promote and support the owner to establish and maintain safety literacy.
As long as we work hard, security that cannot be trusted by the public is completely achievable.