Li Di Chen Ke
Nuclear Energy Nuclear Power Series Report ③
Irradiation processing has been widely used in many fields such as sterilization, food preservation, and material modification due to its advantages of energy saving, environmental protection and high efficiency. It has gradually replaced traditional processing methods and has become a recognized new generation of high-efficiency green environmental protection and energy saving. -Type technology processing method.
Peng Chaorong, President of Sichuan Institute of Atomic Energy
It has been 10 years since the Fukushima nuclear accident in Japan.
According to foreign media, the Japanese Atomic Energy Commission released the latest investigation report on March 10 and brought bad news: The internal pollution of the Fukushima nuclear power plant far exceeded expectations, and there is a risk of another explosion.
The Fukushima nuclear accident was a major disaster in the history of nuclear energy development.
This has caused many people who do not know much about nuclear science to have anti-nuclear, nuclear fear, and even talk about nuclear discoloration.
But in fact, nuclear technology now has a wide range of applications in industry, agriculture, and health.
So, how does human beings guarantee safety in the process of using nuclear energy?
Four barriers to ensure the safety of nuclear power plants
People's fear of nuclear is largely due to the radiation it produces.
But in fact, radiation is not a unique product of nuclear reactions.
There are three main types of radiation encountered by human beings, namely nuclear radiation, space radiation and environmental radiation.
Both space radiation and environmental radiation exist objectively, and they are inevitable radiation sources for human beings.
For example, in summer, the reason why people feel the "spicy" of sunlight is related to the increase in the intensity of the sun's radiation.
Solar radiation specifically includes electromagnetic waves and particle streams emitted by the sun into space.
"What we usually call nuclear radiation mainly refers to the radiation caused by nuclear facilities, radioactive materials produced by artificial activities and artificial devices." said Professor Duan Tao, Dean of the School of National Defense Science and Technology of Southwest University of Science and Technology.
The same is radiation. Why does nuclear radiation sound so terrible?
"Nuclear radiation is a kind of ionizing radiation, and its ionization effect can damage the body. After the biological body absorbs the energy of nuclear radiation, on the one hand, the molecules and atoms of the cell material in the body are ionized and excited, which leads to the breaking and destruction of polymer bonds in the body; On the one hand, water molecules in the body (water accounts for about 70% of an adult's body) ionize to form free radicals, which can cause cell degeneration and even death, until it causes material metabolism and energy metabolism disorders." said Professor Yang Yushan from the National Defense Science and Technology College of Southwest University of Science and Technology.
Yang Yushan pointed out that the degree of damage caused by nuclear radiation depends on factors such as the type of radiation, the amount of energy, and the sensitivity of human organs to radiation.
"Because the human body has the most complex structure and the highest sensitivity to radiation, it has the worst radiation resistance. The radiation safety of the human body must be guaranteed in nuclear industrial production and nuclear radiation practice."
Nuclear power plants are an important way of using nuclear energy.
"Nuclear power plants, as energy facilities, have added multi-level and overlapping protection measures in the design process, and their radiation to the environment is minimal, let alone a'nuclear explosion'." Duan Tao introduced that as a source of nuclear energy, nuclear power plants have four Heavy measures to prevent the spill of radioactive materials, these four measures constitute the isolation system of the nuclear reactor.
The four major barriers to ensure the safety of nuclear power plants are: uranium oxide ceramic pellets for nuclear fuel, which can absorb more than 95% of the reaction products; fuel cladding made of lead alloy, which can seal the nuclear fuel core rod; pressure pipes and cooling Reagent system, which can seal nuclear fuel core rods in a high-pressure system to prevent radioactive materials from leaking out of the reactor; a containment vessel with a thickness of 1 meter in the reactor can prevent radioactive objects from entering and exiting the reactor and causing radiation diffusion.
Duan Tao said that with these four layers of barriers, the nuclear power plant has no radiation to the surrounding residents, and there is no need to worry about the safety of nuclear power.
Nuclear power plants can provide energy for people without radiation.
"Ground gas" nuclear technology applications are everywhere
In recent years, my country's nuclear technology application industry has entered a period of rapid development, with more than 10,000 scientific research institutions, universities, and enterprises engaged in nuclear technology applications.
The application of nuclear technology not only plays an irreplaceable role in industry, agriculture, and life and health, but is also an indispensable part of national defense construction and the sustainable development of the national economy.
Unexpectedly, nuclear technology also has a "down-to-earth" side: the delicious and storage-resistant pickled chicken feet are inseparable from nuclear technology.
In the process of production and processing, a special sterilization technology-irradiation processing technology is added, so that the taste and taste of the food can be preserved for a long time.
Some people can't help wondering: "How can food be processed so dangerous as nuclear radiation?" "Is irradiated food harmful to the body?" "Is irradiated food even more unpalatable?"...
In this regard, the expert's opinion is that there is no need to worry.
"Because of its advantages in energy saving, environmental protection, and high efficiency, irradiation processing has been widely used in many fields such as sterilization, food preservation, material modification, etc., and has gradually replaced traditional processing methods, becoming a recognized new generation of high-efficiency green environmental protection and energy saving. -Type technology processing methods." Researcher Peng Chaorong, Dean of Sichuan Institute of Atomic Energy, introduced.
Irradiation technology uses the interaction between rays and substances, ionization and excitation of activated atoms and activated molecules to cause a series of physical, chemical, and biochemical changes to the substance, leading to degradation, polymerization, cross-linking, and modification of the substance. Sex.
Among them, the electron accelerator, as an irradiation device that provides high-energy electron beams, plays an important role in the irradiation process.
Peng Chaorong introduced that the use of electron beams generated by electron accelerators for irradiation processing technology is safer, more efficient and economical, and has become the development trend of the irradiation processing industry.
"In terms of safety, electron beam irradiation does not need to dispose of waste sources, and there is no hidden danger of environmental pollution. The generation and stop of electron beams are realized by the on/off technology of the electron accelerator. After the electron accelerator is shut down, no radiation will be emitted. And controllability is greatly improved."
Duan Tao further explained that the radiation processing technology mainly uses radioactive high-energy gamma rays or electron beams generated by electron accelerators as the radiation source. The ray energy is relatively high and is a type of device with greater potential harm.
"However, because the country has formulated the "Regulations on Radiation Protection of Radioisotopes and Radiation Devices" (hereinafter referred to as the "Protection Regulations"), the safe application of radiation processing technology has rules and laws to follow. Therefore, workers in radioactive activities and the surrounding public The health and safety of the country are guaranteed."
The "Protection Regulations" clarified that the location of the irradiation processing device should fully consider the hydrogeological structure and the surrounding environmental conditions. The irradiation device must be installed in a separate building, and the shielding design of the irradiation room must comply with the national radiation protection optimization principle. Strictly control the annual dose equivalent limit; it is required that the irradiation room must be equipped with full-time (part-time) radiation health protection personnel, install good ventilation facilities, install multi-channel interlocking devices, emergency landing devices and fixed dose monitoring instruments, etc. , To ensure the safety in the application of irradiation processing technology, so that nuclear technology can better serve the national economy.
The nuclear waste transformation program is receiving attention from the international nuclear energy community
"Nuclear waste generally refers to the no longer needed and radioactive waste produced in the production and processing of nuclear fuel and used in nuclear reactors. The increase in the number of nuclear power plants has led to a large increase in nuclear waste. Nuclear waste is radioactive and causes radiation hazards to the human body. It is an important radiation source and environmental pollution source that pollutes the environment. The treatment of nuclear waste is an important part of radiation protection and environmental protection.” Duan Tao said.
According to reports, among all kinds of nuclear waste, nuclear waste with high level of radioactivity has become a worldwide problem in the safe and effective treatment and disposal of nuclear waste due to its strong radioactivity, high toxicity, long half-life, complex processing technology, and high processing cost.
"The radioactivity of nuclear waste cannot be eliminated by general physical, chemical and biological methods. It can only be reduced by the decay of the radionuclide itself. Current technology cannot reduce the radioactivity cycle of nuclear waste. In addition, because nuclear waste contains many elements, Elements have their own half-lives, so the same treatment will waste resources. However, if you want to separate the isotopes, the chemical methods are extremely demanding." Peng Chaorong explained.
Nuclear reactors can only burn less than 1% of nuclear fuel, and the rest is mostly nuclear waste, which is very radioactive.
To realize the value-added and evolution of nuclear fuel, scientists have found that accelerator-driven subcritical transmutation system (ADS) is an effective and best choice.
In fact, the system is a "combination" of an accelerator and a reactor, consisting of a medium-energy high-current accelerator (mainly a proton accelerator), an exogenous neutron generation target and a subcritical reactor.
"In the ADS system, the proton beam produced by the accelerator bombards the heavy metal spallation target set in the subcritical reactor, causing a spallation reaction, providing exogenous neutrons for the subcritical reactor, and keeping the subcritical cladding system in a chain Reaction in order to obtain energy and use excess neutrons to multiply nuclear materials and transmutate nuclear waste.” Yang Yushan said, currently, the ADS proton linear accelerator developed in my country adopts the superconducting linear accelerator structure, and the front end uses two identical, parallel injections. The devices are hot backup to each other to ensure their reliability.
"Long-lived nuclear waste that is harmful to the environment can be transformed into short-lived nuclear waste through this system, thereby reducing the amount of radioactive waste and its hazards. Therefore, the ADS system generates a small amount of nuclear waste during the production process, which is the most potential. China’s nuclear waste transformation program is receiving more and more attention from the international nuclear energy community,” said Duan Tao.