Radioactive Waste Disposal Methods
Radioactive Waste Disposal Methods. I believe that you are not unfamiliar with radioactive waste, which is some sort of thing that is harmful to nature, and the country needs to get rid of it properly. The next step is for me to take you to learn more about radioactive waste disposal methods.
Radioactive Waste Disposal Methods 1
Introduction
The process of operations to change the physical and chemical state of radioactive waste in advance for safe and economical final disposal of radioactive waste, including collection, enrichment, solidification, storage, and transshipment of waste.
Radioactive waste sometimes generates new waste during disposal, and this newly generated waste is called secondary waste. For example, when dealing with radioactive waste liquids, often need to use flocculation and precipitation, ion exchange and other methods for many times, the specific activity in order to reach the level of permissible emissions, and the treatment process generated by the mud sediment, waste resin, etc. are with radioactive secondary waste. These wastes still require further treatment.
The treatment effect of radioactive waste is usually expressed in terms of decontamination coefficient and volume reduction ratio. As radioactivity can only rely on the decay of radionuclides themselves and weakened, the process of radioactive waste treatment, in essence, is only the radioactive waste into two parts of the process, a small but concentrated in the original waste in the vast majority of the radioactive material, the other part of the volume of a large but the specific activity (or radioactivity concentration) is very low. The objective of the treatment of the latter part is to bring the radioactivity up to the permissible standard so that it can be treated as general waste in the next step, and the effectiveness of the treatment is often measured by the decontamination factor. The decontamination factor, also known as the clean-up factor, is defined as the ratio of the specific activity (or radioactivity concentration) of the waste before and after treatment. For the former part, since the treatment objective is to minimize the volume for final disposal, the treatment effect is often measured by the volume reduction ratio. The volume reduction ratio, also known as the volume reduction factor, is defined as the ratio of the volume of waste before and after treatment. The volume reduction ratio usually refers to the ratio of the volume of solid waste compressed or liquid waste solidified before and after treatment.
Collection of radioactive waste
Radioactive waste should be collected in situ at the site where it is generated, and the waste should be sorted and concentrated in a temporary storage facility using different acceptance methods and transportation equipment. The purpose of separate collection is to facilitate separate treatment and disposal by different methods. Usually, the waste is first divided into liquid, solid and gaseous wastes according to its physical state, and can be further divided into wastes with high, medium and low levels of radioactivity according to their specific activity (or radioactivity concentration), referred to as high-, medium- and low-emission wastes. Certain special radionuclides should also be separately categorized and collected, such as tritium-containing wastes, transuranic wastes (see transuranic elements), and so on. For solid waste can also be divided into combustible waste, non-combustible waste, compressible waste, etc..
Reduction of radioactive waste
Concentration and reduction of radioactive waste liquids are used with flocculation and precipitation, ion exchange, adsorption, evaporation and other methods. According to the specific activity of the waste liquid, chemical composition, the amount of waste liquid and processing requirements can choose a method or several methods of joint use. In general, evaporation, ion exchange and flocculation precipitation method of radioactive waste liquid treatment decontamination coefficients of up to 103 ~ 106, 10 ~ 103 and 10 ~ 102, respectively. radionuclides in the treatment of the original waste liquid is concentrated in a small amount of evaporation residue, waste resin and precipitation slurry. Volume reduction of solid wastes is generally treated by incineration or compression. Combustible waste after incineration bypassing the volume reduction ratio of up to 40 ~ 100; non-combustible . Waste by cutting and compression capacity reduction, the reduction ratio of up to 2 ~ 10.
Curing of radioactive waste
In order to safely store, reduce the pollution of the environment, radioactive waste liquid or its concentrate shall be converted to solid. Radioactive waste solidification of the basic requirements are: the physical and chemical properties of the solidified body is stable, there is enough mechanical strength, the reduction ratio is large, in the water leaching rate is low; the operation process is simple and easy to carry out, low treatment costs, etc.. For different types of waste can be used in different curing methods, including cement curing, asphalt curing, plastic curing and glass curing has been practically applied.
Storage of radioactive waste
Radioactive waste such as uncured radioactive waste liquids and concentrates as well as solidified bodies that have not yet been selected for final disposal should be stored in a fixed location in a special container, the storage process should pay attention to the safety of radioactive waste can not be made to leak. Different storage tanks are required for various specific activities of the waste. Such as the storage of alkaline medium and low discharge waste liquid generally use carbon steel storage tanks; storage of acidic high discharge waste liquid must be used double stainless steel tanks. For the storage of high specific activity, heat release of large high release of waste liquid storage tanks have particularly stringent requirements: the material should be corrosion-resistant, the structure should be solid and reliable, with ventilation and heat dissipation devices, leak detection systems and liquid transfer devices, etc., and must be monitored.
Transfer of radioactive waste
The key to the transfer of radioactive waste is the waste packaging containers, prior to a good safety inspection of the strength of the container, shielding protection, sealing system, packaging signs and so on, there are strict regulations. Requirements for safe transportation to prevent the occurrence of fire, container upheaval and packaging damage and radioactive waste leakage, pollution of the environment.
Separation and Recovery of Radioactive Waste
The separation and recovery of fission-product nuclides from high-level waste liquids began in the late 1940s, and the separation and recovery of fission-product nuclides from the end of the 1950s to the beginning of the 1960s, the separation and recovery of fission-product nuclides from the intermediate plants established in a number of countries. Separation process from the early precipitation - extraction method developed into solvent extraction and ion exchange and other methods (especially inorganic ion exchange material) based process. The solvent extraction and ion exchange methods have higher recovery rates and better separation and purification effects than the precipitation method, and facilitate large-scale continuous operation and remote control. The following is a variety of common radioactive waste separation and recovery methods.
Strontium The more mature, used in the production of strontium separation and extraction process flow, is the use of organic extractant bis (2-ethylhexyl) phosphoric acid (HDEHP) in acidic conditions from the high discharge waste liquid, or separation and recovery of strontium by ion exchange replacement chromatography.
Cesium In the early days, cesium in the high discharge waste liquid was separated by precipitation-extraction process, but the irradiation resistance of the organic extractant was not satisfactory. With inorganic ion exchange materials such as zeolite, zirconium phosphate, etc. from the high discharge waste liquid separation and extraction of cesium process, has the advantages of low recycling costs, material irradiation resistance.
Promethium The process of separating and recovering promethium from high release waste liquid is to use HDEHP to extract and separate the rare earth nuclides and transuranic nuclides, and then use ion exchange displacement chromatography to separate promethium from the rare earth nuclides.
Precious metals mainly use ion exchange method to adsorb technetium, rhodium, palladium, etc. from neutral or alkaline high discharge waste liquid, and then use different eluents to recover them respectively.
Transuranic nuclides Neptunium 237 can be extracted by extraction or ion exchange. Separation of nuclides such as americium and curium can be extracted with HDEHP and rare earth nuclides*** under low acid conditions (pH 1 to 2), and then separated from rare earth nuclides by extraction or ion exchange displacement chromatography.
Radioactive waste treatment is an important measure of radioactive waste management. Selection of treatment methods should be based on technically feasible, economically rational and standardized licensing. The treatment process should prevent environmental pollution and minimize the amount of secondary waste generated. In addition, radioactive waste should be actively carried out comprehensive utilization.
Radioactive solid waste treatment and preparation
Radioactive solid waste is a wide variety of types, which can be divided into wet solids (evaporation residue, sedimentation slurry, waste resin, etc.) and dry solids (contaminated labor supplies, tools, equipment, waste filter cores, activated carbon, etc.) two categories. More than 40% of nuclear power plant solid waste is combustible or compressible. In order to reduce the volume and suitable for transportation, storage and final disposal, solid waste should be incinerated, compressed, decontaminated, cured or fixed and other treatments.
(1) Incineration Incineration is the oxidation of combustible waste into ash (or residue). Incineration can obtain a large volume and weight reduction (10 to 100 times), can make the waste to inorganic transformation; eliminating thermal decomposition, decay, fermentation and fire and other hazards; incineration can also be recycled plutonium, uranium and other useful substances.
Incineration can be divided into two categories, namely, dry incineration (such as excess air incineration, controlled air incineration, cracking, fluidized bed, molten salt furnace, etc.) and wet incineration (such as acid cooking solution, hydrogen peroxide decomposition, etc.). The incineration of radioactive waste requires the use of specially designed incinerators, with adequate protective measures to maintain a certain negative pressure inside the furnace. After incineration, more than 70% of the radioactive material into the ash. The ash should be cured or directly loaded into a high degree of integrity of the container for disposal.
(2) Compression Compression is the use of mechanical forces to compact and reduce the volume of waste. Although the compression treatment can be obtained to reduce the volume of relatively low multiples (2 to 10), but compared with incineration, compression treatment is simple to operate, equipment investment and operating costs are low, so the compression treatment in the nuclear power plant is quite common. Now there are many kinds of compressors used in various countries, some of which are compressed in barrels, some of which are flattened and loaded into barrels. Pressure of tens of tons, hundreds of tons, there are thousands of tons of pressure of the high-pressure compressor, the metal scrap can be compressed to close to the theoretical density.
(3) decontamination decontamination is to make the unwanted presence of radionuclides part & gt; part or all removed. Decontamination allows contaminated equipment or components can be reused, or disposed of as non-radioactive waste to reduce the volume of waste; decontamination can reduce the level of radiation, reduce the harm to humans, so that easy maintenance, accident management or decommissioning operations. Decontamination activities in nuclear power plants include regular and unscheduled decontamination of the circuit, accident decontamination and decommissioning decontamination.
Decontamination methods are many, should be based on the object of treatment and requirements, pollution levels, objective conditions, etc., choose different methods, commonly used: ① chemical method: the use of acids, alkalis, oxidation - reducing agents, complexing agents, surfactants and corrosion inhibitors formulated into a decontamination solution, foam, paste, etc.. Decontamination process has a soaking method, cyclic rinsing method, spraying method. ② mechanical methods: including vacuum vacuum, manual or robotic wiping, spray high-pressure water or steam, spray abrasives (such as sand, steel grit, aluminum oxide, boron oxide, dry ice particles), ultrasonic decontamination and so on. ③ Electrochemical method: such as electrolytic decontamination. In addition, scrap metal after melt treatment, most of the contaminating nuclides into the slag, this melt treatment of scrap metal can be reused after monitoring and qualification.
(4) curing and fixing radioactive waste liquid treatment of slurry, evaporation residues and waste resin and other wet solids, incinerator ash and other dry solids, are diffuse substances, not suitable for safe transportation, long-term storage and final disposal, need to be cured. Cured products should be solid monolithic blocks. Resistant to pressure, impact resistance, firm inclusion of radionuclides, leaching resistance, resistance to irradiation and decay heat effects, non-corrosive packaging containers, less susceptible to bacterial erosion effects and so on. Many curing methods have been developed and researched. In addition, contaminated waste filter cores, cutting disintegration of contaminated equipment, mounted in steel drums or boxes, need to be filled with cement mortar or molten asphalt, fill the pores, for fixed treatment.
RADIOACTIVE WASTE DISPOSAL METHODS 2RADIOACTIVE WASTE DISPOSAL
BASIC PRINCIPLE
The basic principle of radioactive waste disposal is to construct a disposal system that will effectively contain the radioactive waste for a certain safety period. Even though the radioactive waste will migrate and dilute through natural processes in a number of diffuse forms, the diluted concentrations are not unacceptably hazardous. For uranium mine waste rock, in-situ backfill disposal is generally utilized for waste mine shafts, and for short-lived intermediate and low-emission wastes, near-surface disposal, cavern disposal, or hydraulic fracturing and deep-well injection are generally used, with the effective period of the disposal system ranging from 300 to 500 years; for high-emission wastes, d-wastes, spent fuels, and long-lived intermediate and low-effort wastes, cosmic disposal, deep-sea disposal, seabed disposal, ice-cap disposal, and rock-melting disposal have been proposed
Other definitions
Waste disposal is the placement of waste in an approved facility that uses a multiple shielding system combining engineered shielding and natural shielding to provide safe isolation of the disposed waste to ensure:
(1) decay of contained short-lived radionuclides to a harmless level;
(2) decay of contained long-lived radionuclides to a harmless level;
(3) decay of contained short-lived radionuclides to a harmless level. p> (2) Releases of contained long-lived radionuclides and other toxic materials are extremely low and enter the environment at acceptable levels.
Broadly speaking, disposal also includes the authorized discharge of airborne or liquid effluents directly into the environment, such as the discharge of treated wastewater into a body of water, and the discharge of treated exhaust gases into the atmosphere.