The filters used in the nuclear industry are called "nuclear-grade filters".
High efficiency filter:
To prevent the release of radioactive dust into the atmosphere, the exhaust system of nuclear power plants requires a large number of high-efficiency filters. The American standard stipulates that the efficiency of this high-efficiency filter is: 99.97% for 0.3mm DOP particles. Most countries have copied the American standard, and some countries have specified their own test methods, but the filter performance is equivalent to that measured by the US method.
The high-efficiency filters used in nuclear power plants in most countries are traditional forms of filters with partitions. Among them, the filter material is glass fiber filter paper, the separator is made of 0.038mm aluminum foil, and the outer frame is carbon steel or stainless steel. The adhesive between the two is silicone, PVC or other temperature-resistant materials. The windward and leeward sides of the filter have metal protective nets. Many performances of nuclear filters are usually "redundant performances", and those performances are considered for reliability in accidents.
France is the originator of partitionless filters. The French successfully replaced the traditional partitioned filters with partitionless filters in nuclear power plants. South Korea and China imported French nuclear power plants and each realized localization of filter production. In addition to these three countries, no one dared to use high efficiency filters without partitions in key parts of nuclear power plants.
The high-efficiency filters used in China's early nuclear reactors were similar to those in the United States. Later, China introduced nuclear power plants in France, Canada, and Russia. China has few nuclear-grade filters and many styles. Those interested in China's nuclear high-efficiency filter regulations can refer to the national standard GB / T17939-1999.
Activated carbon filter:
Methyl iodide and iodine are fission products of the radioactive element uranium. They are radioactive gases unique to the nuclear industry. In order to remove methyl iodide and iodine vapor from the air, nuclear power plants use a large number of activated carbon filters. Activated carbon materials for this purpose need to undergo a special chemical impregnation treatment to improve the adsorption capacity of methyl iodide and iodine. Traditionally, people refer to the activated carbon materials used in the nuclear industry as "nuclear-grade carbon" and the activated carbon filters as "iodine adsorbers".
Compared with ordinary activated carbon filters, the filters used in nuclear power plants have thick carbon layers, high adsorption efficiency, high temperature and seismic requirements.
Because adsorption is an exothermic process, too high temperature may ignite activated carbon, so there is a strict temperature resistance requirement for iodine adsorbers. The concentration of methyl iodide and iodine in nuclear fuel processing plants is very high. At this time, activated carbon can no longer be used, but other non-combustible porous adsorption materials are used to make iodine adsorbers.
In terms of consumption, the most used filters in nuclear power plants are general ventilation filters, reactors, auxiliary plant buildings, and office and service areas.
There are various forms of ventilation filters for nuclear power plants. It shouldn't have been so particular, but the specific specifications of the filters were determined in the early stages of construction, and the filter company must supply them according to the original specifications. Unless unexpected, owners and suppliers dare not easily change raw materials, manufacturing processes, test methods and supply channels.
The filters used in the nuclear industry are similar in principle and structure to those used in other industries. Nuclear industry filters do not seek high-tech, market economy, or bargaining.
Safety first, reliability first.
Compared with filters used in other industries, filters used in the nuclear industry have to undergo more testing items and undergo more certifications. Those inspections and certifications are often done by government-run specialized agencies related to the nuclear industry. In addition, filter suppliers must have reliable qualifications and credibility, receive more or less government support, and have considerable performance and corresponding technical strength.
The certification body of China's nuclear-grade filter is Zhengzhou Nuclear Fifth Research Institute, but the Nuclear Fifth Research Institute that manages and kills power has set up its own filter factory, so some competitors bypassed the Fifth Research Institute and sold the filters to nuclear power plants.
Iron rice bowl with limited capacity:
Because of stable customers and attractive prices, nuclear power plants have coveted many filter companies, but few manufacturers can really squeeze in.
If you count the total value of the filters, you will find that there are not as many filters used in nuclear power plants as people think. In developed countries, a reactor can only provide one or two employment opportunities for filter companies, but this is an "iron rice bowl" that has been owned for many years. According to the current domestic production level, a reactor can still provide ten rice bowls for domestic filter companies. As the production level increases, the number of rice bowls will continue to decrease.
The construction period of nuclear power plants is seven years; due to the shortage of nuclear fuel, China's nuclear power industry is difficult to reach the level of the nuclear powers in the United States and France. But these do not prevent hundreds or thousands of people from competing for the rice bowl of nuclear power plant filters, at least not preventing the filter sellers from thinking.