Radioactive waste disposal
Radioactive waste disposal, we all know that radioactive waste can not be handled indiscriminately, because it will pollute the environment, but how do we deal with them? Here I bring you a brief understanding of radioactive waste disposal.
Radioactive waste disposal1The methods used so far to deal with uranium-containing tailings are stacking and disposal, or backfilling of mine shafts. Some countries are working on radical solutions. For example, in hydrometallurgical processing, underground leaching and in situ heap leaching techniques are proposed, whereby only the leach solution is sent to a hydrometallurgical plant to extract uranium metal. In addition, also studied the tailings slag solidification and granulation technology; the use of various chemicals and vegetation to make the tailings dam layer stabilization.
Disposal of radioactively contaminated artifacts For a variety of artifacts contaminated with artificial or natural radionuclides, their specific radioactivity is divided into two categories of high level and medium and low level; their properties are distinguished as combustible and non-combustible. The main treatment and disposal methods for this type of solid waste are:
Decontamination Radioactively contaminated equipment, utensils, instruments, etc., if the use of appropriate detergents, complexing agents or other solutions in a certain part of the wipe or impregnation decontamination, most of the radioactive material can be cleaned down. Although this treatment produces radioactive waste liquid that needs to be disposed of, the volume may be reduced if properly operated, and the decontaminated artifacts can continue to be used. In addition, the use of electrolysis and spray plating methods can also eliminate the radioactivity of some contaminated surfaces.
Compression Compressible radioactive solid waste is put into metal or non-metallic containers and pressed with a compressor. The volume can be significantly reduced, waste paper, broken cardboard shells, etc. can be reduced to 1 / 3 to 1 / 7. Glassware first broken, metal objects are first cut, and then put into the container compression, can also reduce the volume, easy transportation and storage.
Incineration Combustible solid waste such as paper, cloth, plastic, wood products, etc., after incineration, the volume can generally be reduced to 1/10 to 1/15, up to 1/40. incineration to be carried out in the incinerator. The incinerator should be corrosion-resistant, and there should be a perfect exhaust gas treatment system to collect the escaping particles with radioactive, volatile aerosols and soluble substances. After incineration, the vast majority of the radioactive material is accumulated in the ash, and the residual ash and embers should be properly managed to prevent them from being blown away by the wind. The collected ash is generally placed in sealed metal containers or mixed into media such as cement, asphalt and glass. Incineration method due to the control of radioactive contamination surface requirements are very high, the cost is very large, the practical application of certain restrictions.
Burial The principles for selecting a burial site are: the impact on the environment within the permissible range; can be regularly monitored; the area shall not be productive activities; buried in the trench or groove can be covered with soil or concrete, and so on. Geological conditions of the site must meet: ① buried in the absence of surface water; ② buried groundwater does not lead to surface water; ③ pre-measured radioactivity in the soil retention time of several hundred years, its hydrological system is simple and reliable predetermined retention period; ④ buried should be higher than the highest groundwater level of several meters.
In some countries, natural salt beds are considered to be more suitable as repositories for such wastes. The reason is that the salt layer of good hygroscopicity, less corrosive to the container, easy to excavate, time, it is possible to form a sealed whole, more secure for long-term storage. German Federal **** and the country is an abandoned Arthur salt mine for the test, the U.S. National Oak Ridge Laboratory (ORNL) proposed an ideal model of salt cavern repository.
Ocean Disposal Offshore countries use ocean disposal by drumming waste into deep water and off the continental shelf. Containers are required to have sufficient sinking weight to withstand impacts on the seafloor, resist high pressure in deep water, and prevent corrosion and reduce the amount of radioactive leaching. It has been practically recognized that disposal areas must be located away from coasts, tidally active areas and aquaculture farms. This method poses a potential hazard to the high seas and is internationally controversial.
Disposal of solid waste from radioactive waste streams The solidification of radioactive waste streams is converted into radioactive solid waste, which some countries prefer to dispose of by burying them, believing that this ensures safety. Depending on the self-generated heat of the contained radioactivity, low-level waste can be buried directly in a trench. Medium-level waste is buried in vertical concrete or steel pipes in the ground. High-level solid waste can generate up to 430 kcal/hour or more per cubic meter, and must be buried using a multiple barrier system: the first barrier is to transform the waste into an inert, insoluble solidified body, the second barrier is to place the solidified body in stable, impermeable containers; and the third barrier is to choose to be buried in favorable geological conditions.
Final Disposal The fundamental issue in radioactive solid waste management is final disposal. Currently being explored methods of final disposal of high-level radioactive waste include: placing important 'radionuclides such as (cesium, (strontium, (krypton and (iodine, etc., in reactors to irradiate them and convert them into short-lived nuclides that decay as quickly as possible, or into stable nuclides; using long-distance rockets to carry the radioactive material into space outside the Earth's gravity; or placing it on the Antarctic ice and using the heat it releases to dissolve the ice to form a well cavern and seal the waste. The idea is to use the heat released to dissolve the ice to form a well to confine the waste, and so on. These ideas, involving international treaties and technical and economic difficulties, are difficult to realize in the near future.
Recycling of radioactive solid waste For uranium ore and waste slag, the main thing is to improve the recovery rate of uranium, radium and other resources and recycling of chemicals used in the refining process, etc.. As for a large number of fission products and the recovery of some transuranic elements must first be separated from the waste liquid or ash leachate, and then according to the nature and abundance of nuclides separately or uniformly purified, as a source of energy irradiation or other heat, light source, etc. to use, but also to consider the high level of radioactive solid wastes made of solid radiation sources for industry, agriculture and health.
Radioactive Waste Disposal 2The residue and remaining portion of radiopharmaceuticals after use is known as radioactive waste. Radioactive waste has a solid, liquid and gas three, so called "radioactive waste". "Three wastes" improper handling will cause radioactive contamination of the environment, affecting the staff and the health of the surrounding residents, and therefore the proper handling of "three wastes" is very important. The purpose of this provision is to regulate the handling of radioactive waste, prevention of radioactive contamination.
1. All radioactive waste generated during the operation of nuclear medicine shall not be disposed of as general garbage. Must be collected by the relevant departments, unified in accordance with national regulations sent to the radioactive waste disposal site.
2. Solid radioactive waste can be temporarily stored in a special bucket, the bucket must be switched with a foot pedal, and in the periphery with lead bricks or lead skin to protect. Solid waste should be regularly collected in specialized containers, in the container outside the indication of radionuclide categories, half-life (multiple nuclides to the longest half-life shall prevail), sealed in a designated location. Waste storage area should be far away from the work area, the walls and doors should be protected, preferably without windows, the door should be locked, and have a strict management system and specialized management.
3. Liquid radioactive waste can be treated as follows
(1) ion exchange resin treatment: anion exchange resin about 1kg (wet base) into the infusion bottle, the bottle wrapped in protective lead jacket, the bottle under the mouth of the rubber tube, through the sewer. Usage: The syringes, medicine cups, pipettes and other glassware stained with radionuclides are washed with water, and the washing solution is injected directly into the upper port of the infusion bottle, and then discharged into the sewer after exchange. Resin saturation regeneration treatment: anionic resin with 4 times the volume of 8% sodium hydroxide solution can be reused after soaking 2h.
(2) such as liquid radioactive waste containing radionuclides with a half-life shorter than 15d, can be sent to the decay pool sealed until more than the longest half-life of which more than 10 times the radioactive activity of the water is less than 3700Bq / L or less, and then discharged into the sewer.
(3) If the half-life of the radionuclides contained in the liquid is longer than 15d, and the treatment of resins mixed with a high ratio of radioactive liquid, must be sealed in a special, sealed containers, sent to the radioactive waste disposal site.
4. radioactive waste gas treatment. Any volatilization, evaporation possibility of radionuclides and operations, must be in a dedicated place with adequate ventilation. Exhaust should be activated carbon or other effective filters. Filter content should be depending on the workload and radioactive load of regular replacement, replacement of radioactive filters in accordance with the solid radioactive waste disposal.
5. After the use of radionuclides, patient excreta treatment, with liquid radioactive waste 2, 3 treatment.