Disposal of radioactive waste. Radioactive waste is very polluting to our earth, but it will also be produced in the process of chemical production. Many people are curious about how to deal with radioactive waste. Next, I will take you to know more about radioactive waste treatment.
Disposal of radioactive waste 1
introduce
The operation process of changing the physical and chemical state of radioactive waste in advance for the safe and economical final disposal of radioactive waste, including collection, concentration, solidification, storage and waste transfer.
Radioactive waste sometimes produces new waste in the process of treatment, which is called secondary waste. For example, when dealing with radioactive waste liquid, it is often necessary to treat it many times by flocculation and precipitation, ion exchange and other methods. The specific activity can reach the level of allowable discharge, and the sludge precipitation and waste resin produced in the treatment process belong to radioactive secondary waste. These wastes still need further treatment.
The treatment effect of radioactive waste is usually expressed by decontamination coefficient and volume reduction ratio. Because radioactivity can only be weakened by the decay of radionuclides, the process of radioactive waste treatment is essentially just a process of dividing radioactive waste into two parts, one part is small but concentrates most radioactive substances in the original waste, and the other part is large but has low specific activity (or radioactive concentration). The treatment goal of the latter part is to make the radioactivity reach the allowable standard, so that it can be treated as general waste in the next step, and its treatment effect is often measured by decontamination coefficient. Decontamination coefficient, also known as purification coefficient, is defined as the ratio of specific activity (or radioactive concentration) before and after waste treatment. For the former, the treatment effect is usually measured by the volume reduction rate, because its treatment goal is to minimize the final disposal volume. Volume reduction rate, also known as volume reduction factor, is defined as the ratio of waste volume before and after treatment. Volume reduction ratio usually refers to the volume ratio of solid waste before and after compression treatment or liquid waste after solidification treatment.
Collection of radioactive waste
All kinds of radioactive wastes should be collected at the place where they are produced and stored in temporary storage facilities with different receiving methods and transportation equipment. The purpose of classified collection is to facilitate separate treatment and disposal by different methods. Usually, wastes are divided into liquid, solid and gas wastes according to their physical state, and then further divided into high, medium and low radioactive wastes according to their specific activity (or radioactive concentration), which is referred to as high, medium and low radioactive wastes for short. Some special radionuclides should also be collected separately, such as tritium-containing wastes and transuranic wastes (see transuranic elements). Solid waste can also be divided into combustible waste, noncombustible waste and compressible waste.
Volume reduction of radioactive waste
Concentration and volume reduction of radioactive waste liquid include flocculation and precipitation, ion exchange, adsorption and evaporation. According to specific activity, chemical composition, waste liquid volume and treatment requirements, one or more methods can be used in combination. In general, the decontamination coefficients of evaporation method, ion exchange method and flocculation precipitation method can reach 103 ~ 106, 10 ~ 103 and102 respectively. Radionuclides in the treated raw waste liquid are concentrated in a small amount of evaporation residue, waste resin and precipitation mud. Volume reduction of solid waste is usually treated by incineration or compression. The volume reduction rate of combustible waste after combustion can reach 40 ~100; Noncombustible waste is reduced in volume by cutting and compressing, and the volume reduction ratio can reach 2 ~ 10.
Solidification of radioactive waste
In order to safely store and reduce environmental pollution, it is necessary to convert radioactive waste liquid or its concentrate into solid. The basic requirements of radioactive waste solidification are: stable physical and chemical properties, sufficient mechanical strength, large volume reduction rate and low leaching rate in water; The operation process is simple and easy, and the treatment cost is low. Different types of waste can be solidified by different methods, among which cement solidification, asphalt solidification, plastic solidification and glass solidification have been applied in practice.
Storage of radioactive waste
Unsolidated radioactive waste liquid and concentrate, as well as radioactive wastes such as solidified bodies for which the final disposal scheme has not been selected, should be stored in special containers at fixed locations, and attention should be paid to safety during storage to prevent leakage of radioactive wastes. Wastes with different specific activities need different storage tanks. For example, when storing alkaline medium and low level radioactive waste liquid, carbon steel storage tanks are generally used; Double stainless steel tanks must be used to store acidic high-level radioactive waste liquid. Compared with the high-level radioactive waste liquid storage tank with high activity and large heat release, there are particularly strict requirements: the material should be corrosion-resistant, the structure should be firm and reliable, and there should be ventilation and heat dissipation devices, leak detection systems, feed liquid conveying devices and so on. , it should be monitored.
Transshipment of radioactive waste
The key to the transfer of radioactive waste is the packaging container of waste. Safety inspection should be done in advance, and strict regulations should be made on the strength, shielding protection, sealing system and packaging marks of containers. Safe transportation is required to prevent radioactive waste from leaking and polluting the environment due to fire, container subversion and packaging damage.
Separation and recovery of radioactive waste
In the late 1940s, the research on separation and recovery of fission product nuclides from high-level radioactive waste liquid began. From the late 1950s to the early 1960s, some countries established "intermediate factories" to separate and recover fission products and nuclides. The separation process has developed from early precipitation-extraction method to solvent extraction and ion exchange method (especially inorganic ion exchange materials). Compared with precipitation method, solvent extraction method and ion exchange method have higher recovery rate, better separation and purification effect, and are convenient for large-scale continuous operation and remote control. The following are the separation and recovery methods of various common radioactive wastes.
Strontium is a mature separation and extraction process. The organic extractant bis (2- ethylhexyl) phosphoric acid (HDEHP) was used to extract from high-level radioactive waste liquid under acidic conditions, or it was separated and recovered by ion exchange displacement chromatography.
Cesium in high-level radioactive waste liquid was separated by precipitation-extraction process in the early stage, but the radiation resistance of organic extractant was not ideal. The process of separating and extracting cesium from high-level radioactive waste liquid with inorganic ion exchange materials such as zeolite and zirconium phosphate has low recovery cost and good radiation resistance.
The process of separating and recovering promethium from high-level radioactive waste liquid is to extract and separate rare earth nuclides and transuranic nuclides with HDEHP, and then separate promethium and rare earth nuclides with ion exchange displacement chromatography.
Precious metals mainly adsorb technetium, rhodium and palladium from neutral or alkaline high-level radioactive waste liquid by ion exchange method, and then recover them with different eluents.
Neptunium 237 in transuranic radionuclide high-level radioactive waste liquid can be separated and extracted by extraction or ion exchange. When americium and curium are separated, HDEHP can be used to extract with rare earth nuclide * * * under the condition of low acidity (pH 1 ~ 2), and then the rare earth nuclide can be separated by extraction or ion exchange displacement chromatography.
Radioactive waste treatment is an important measure of radioactive waste management. The selection of treatment methods should be based on technical feasibility, economic rationality and code permission. The treatment process should prevent environmental pollution and minimize the generation of secondary waste. In addition, comprehensive utilization of radioactive waste should be actively carried out.
Treatment and preparation of radioactive solid waste
There are many kinds of radioactive solid waste, which can be divided into wet solid (evaporation residue, precipitation mud, waste resin, etc.). ) and dry solids (contaminated labor protection articles, tools, equipment, waste filter elements, activated carbon, etc.). ). More than 40% of solid waste from nuclear power plants is combustible or compressible. In order to reduce the volume and be suitable for transportation, storage and final disposal, solid waste should be burned, compressed, purified, solidified or fixed.
(1) Incineration refers to the oxidation of combustible waste into ashes (or residues). Incineration can achieve great volume reduction and weight reduction (10 ~ 100 times), and can convert wastes into inorganic substances; Avoid the danger of thermal decomposition, decay, fermentation and fire; Incineration can also recover useful substances, such as plutonium and uranium.
Incineration is divided into two categories, namely dry incineration (such as excess air incineration, controlled air incineration, pyrolysis, fluidized bed, molten salt furnace, etc.). ) and wet incineration (such as acid digestion and hydrogen peroxide decomposition, etc. ). For the incineration of radioactive waste, it is required to adopt a specially designed incinerator with adequate protective measures and maintain a certain negative pressure in the incinerator. After incineration, more than 70% of radioactive substances enter the furnace ash. Ash should be solidified or directly put into a highly integrated container for treatment.
(2) Compression Compression depends on mechanical force to densify waste and reduce waste volume. Although the volume reduction coefficient obtained by compression treatment is relatively low (2 ~ 10), compared with incineration treatment, compression treatment is simple in operation, with lower equipment investment and operating cost, so compression treatment is widely used in nuclear power plants. At present, there are many kinds of compressors used in various countries, some of which are compressed in barrels, and some are packed in barrels after flattening. High-pressure compressors with pressures of tens, hundreds and thousands of tons can compress metal scrap to near theoretical density.
(3) Decontamination Decontamination is to completely or partially remove unwanted radionuclides. Decontamination can reuse contaminated equipment or components or treat them as non-radioactive waste to reduce the amount of waste; After decontamination, the radiation level can be reduced, the harm to human body can be reduced, and it is convenient for maintenance, accident treatment or decommissioning. Decontamination activities of nuclear power plants include periodic and irregular decontamination of loops, accidental decontamination and decommissioning decontamination.
There are many decontamination methods, and different methods should be selected according to the treatment object and requirements, pollution degree and objective conditions. Commonly used methods are: ① Chemical method: using acid, alkali, redox agent, complexing agent, surfactant, corrosion inhibitor, etc. to prepare decontamination solution, foaming agent, paste, etc. The decontamination process includes soaking method, circulating washing method and spraying method. ② Mechanical methods: including vacuum cleaning, manual or mechanical wiping, high-pressure water or steam spraying, abrasive spraying (such as sand, steel grit, alumina, boron oxide, dry ice particles), ultrasonic decontamination, etc. ③ Electrochemical methods: such as electrolytic decontamination. In addition, after melting, most of the polluting nuclides enter the slag and can be reused after monitoring.
(4) Solidification of wet solids such as fixed sludge, evaporation residue and waste resin, and dry solids such as incinerator ash are dispersive substances, which are not suitable for safe transportation, long-term storage and final disposal and need to be solidified. The cured product should be a solid block. Pressure resistance, impact resistance, firmly containing radioactive nuclides, leaching resistance, radiation resistance and decay heat resistance, no corrosion to packaging containers, insensitive to bacterial erosion. Many curing methods have been developed and studied. In addition, the polluted waste filter element and the polluted equipment which are cut and disintegrated are packed in steel drums or boxes, and cement mortar or molten asphalt needs to be poured to fill the pores and fix them.
Disposal of radioactive waste 2. Removal of radioactive pollution
brief introduction
Radionuclides are used in exploration logging, pipeline manufacturing, installation, use and equipment container construction in petroleum industry. In the process of using radioactive substances, due to lack of protection or violation of operating rules or accidents, human surfaces and other objects are often polluted, which not only affects the health of operators, but also pollutes the surrounding environment. Measures should be taken as soon as possible. Cleaning up pollution is one of the important means to prevent radiation damage. The sooner you clean up pollution, the better the effect.
classify
When hands and skin are polluted, wash them immediately with soap, detergent, potassium permanganate, citric acid, etc. Or mix 1% calcium diethylamine tetraacetate with 88% water and scrub. If your hair is polluted, wash it with warm water and soap. For those who inhale radionuclides, 0.25% epinephrine can be sprayed on the upper respiratory tract or 1% ephedrine can be used to constrict blood vessels, and then a large amount of physiological saline can be used to wash the nose and rinse the mouth, or expectorants (ammonium chloride and potassium iodide) can be used to eliminate phlegm. Eyes, nostrils and ears should also be washed with normal saline. It is not easy to use organic solvents and strong pickling hands, which will promote pollutants to enter the body. When cleaning the pollution on work clothes, if the pollution is not serious, you can use ordinary cleaning methods in time; When the pollution is serious, it is necessary to use an efficient detergent, which is not suitable for hand washing, such as a mixture of oxalic acid and sodium phosphate. If you can't find these cleaners for a while, you can seal the contaminated clothes in a large plastic bag to avoid large-scale pollution.
In addition to polluting the surface of objects, such as glass and ceramic utensils, they should be washed with water first, then soaked in hydrochloric acid or citric acid solution for one hour, and then washed with water after being taken out. If the pollution cannot be eliminated, they should be immersed in the compound solution for 15 minutes, and then taken out and washed with water; Rinse the metal utensils with water first, then immerse them in citric acid solution 1 hour, then rinse them with water and dry them. It is not advisable to use strong acid lotion to avoid corrosion of metal surface. Plastic and rubber products can be washed with water or soap first. If it cannot be decontaminated, it should be cleaned with dilute hydrochloric acid, nitric acid or citric acid, and then washed with water.
After the surface of the studio is polluted, the proper cleaning method should be selected according to the nature and pollution of the surface materials. Generally, first scrub with water and washing powder or soap. If the pollution is serious, consider cleaning with dilute hydrochloric acid or citric acid solution, or scraping the surface or replacing materials.
Treatment of eating radioactive nuclides by mistake
Those who eat radionuclides by mistake should immediately induce vomiting, gastric lavage, enema and laxative. If you eat radioactive nuclides with high solubility such as strontium or radium by mistake, you should immediately give precipitant, such as barium sulfate, to form insoluble barium sulfate precipitate to prevent absorption and discharge. Taking potassium iodide can block the absorption of radioactive iodine by thyroid. Licorice and Smilax glabra have a good effect on promoting strontium excretion.
Other methods
We must actively do a good job in safety protection to prevent the pollution area from expanding after pollution, and seriously deal with radioactive waste liquid. It can be treated by dilution method or coagulation and precipitation method according to national regulations.
Related patents
An electrolytic decontamination method for removing radioactive pollution on metal surfaces includes connecting the parts to be decontaminated to the positive pole of a power supply, connecting the parts to be decontaminated to the negative pole of the power supply, and adding electrolyte into a decontamination device for electrolytic decontamination. The electrolyte formula used is HNO3 with mass percentage of 3% ~ 10%, NaNO3 with mass percentage of 5% ~ 20%, and the rest is water. The current density during electrolysis is 0. 1~ 0.6A/cm/cm, and the electrolysis temperature is 20 ~ 50℃. This method can be widely used for electrolytic decontamination of radioactive pollution on the metal surface of nuclear facilities, so that a large amount of metal waste generated when nuclear facilities are decommissioned can be degraded or recycled.