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Nuclear industry uranium mining and tailings operation experience and accident lessons
I. Overview
Of hydrometallurgical techniques using plant extract and purification of uranium collectively uranium mill plant. In the early days of the nuclear industry, the CPC Central Committee and the State Council were very concerned about the safety and health of professionals and the residents around the nuclear facilities. Premier Zhou repeatedly instructed to do a good job in safety and health. To this end, in 1959, the Second Machinery Department put forward the policy of “production is not moving, protection firstâ€. In order to implement the principle of “protection firstâ€, the construction of tailings facilities was very important in the initial stage of the construction of uranium water smelting plant. On the basis of drawing on the experience of construction, management and operation of tailings facilities such as non-ferrous metals, ferrous metals and chemical mines at home and abroad, aiming at preventing and reducing radiation hazards as far as possible in view of the characteristics of wastewater and waste generated by uranium hydrometallurgical plants Under the first batch of uranium hydrometallurgical plants in China, there are complete and reliable tailings facilities for design and construction. According to China's specific national conditions, with the development of uranium mining and metallurgy industry, uranium mining and tailings facilities have accumulated rich experience in scientific research, design, construction and management, and trained a large number of engineering and technical personnel to develop a suitable nuclear industry. Regulations, regulations, rules and regulations for the investigation, design, construction and management of tailings facilities. In order to strengthen the inspection and supervision of the tailings pond project, in 1992, the Nuclear Industry Corporation established the “Nuclear Industry Tailing Dam Engineering Safety Technology Supervision Stationâ€, which is responsible for inspecting, supervising and guiding the safe operation of the tailings storage of the nuclear industry uranium mining and metallurgy system. .
With the publication of the National Environmental Protection Law, the environmental awareness of the whole people has been greatly enhanced. In accordance with the requirements of the late Prime Minister Zhou Enlai's “Protection Firstâ€, the nuclear industry has designed a complete and reliable tailings water treatment facility in the construction of the tailings bank of the second batch of smelting and smelting plants. The advanced flow bed ion exchange demineralization process has been widely adopted, the wastewater treatment has been strengthened and the purification efficiency has been improved, and the wastewater reuse capacity of the water and metallurgical plant has been continuously increased, and the discharge capacity has been decreasing year by year, thus ensuring the normality of the tailings pond. Excess water is discharged into the natural water system after being chemically treated to meet the national emission standards. In this way, the pollution of natural water bodies by uranium mining and tailings ponds is reduced to the minimum.
With the easing of the international situation and the reduction of the country's demand for uranium products, most of the tailings ponds of the nuclear industry uranium hydrometallurgical plant are being “closed†(collectively referred to as the tailings decommissioning in China). In order to protect the environment and prevent pollution, the China National Nuclear Corporation has issued a series of standards, regulations and notices for decommissioning nuclear facilities and radioactive waste management work by drawing on foreign experience and combining with national conditions. It is required that the decommissioned uranium tailings pond must be decommissioned. The purpose of decommissioning is to carry out various after-treatment treatments for the permanently terminated uranium mining and tailings facilities, so that the tailings pond and the surrounding environment can be restored to their natural state to ensure the public is protected from residual radioactive exposure. It is also necessary to ensure the stability and safety of the tailings pond in the next 100 years or even hundreds of years. Decommissioning and remediation projects are arduous, and the cost is surprising, often exceeding the investment in new tailings ponds.
Second, the status quo of uranium mining and tailings reservoir in China's nuclear industry
(1) Characteristics of uranium mining and tailings in China
The characteristics of uranium ore in China are characterized by low grade, many types and associated elements. After uranium extraction by chemical process, the uranium tailings produced have distinct characteristics compared with ferrous and non-ferrous metal tailings. Expressed as:
1. High tailings yield
Due to the low grade of uranium ore in China, most of them are around 0.1, so the tailings yield is very high. In addition, uranium ore adds a large amount of chemicals such as acid, alkali and ammonia in the process of water, so that the amount of tailings discharged from the uranium hydrometallurgical plant is generally greater than the amount of raw ore processed. The tailings of uranium mining and metallurgy in China is about 110% of the original ore. This is one of the more obvious characteristics of uranium mining and metallurgy in China. Therefore, the treatment of uranium tailings is a prominent problem in the construction of uranium mining and metallurgy in China. At present, uranium mining and metallurgy has begun experimenting with not taking ore from the ground, but injecting the leachate into the ore layer and directly extracting qualified liquid to produce uranium. China calls this method “ground dipâ€, so that tailings are no longer produced. . But this is just the beginning. If the test is successful, it can fundamentally improve the environmental conditions of the uranium hydrometallurgical plant. As far as the current situation is concerned, in the construction of uranium mining and metallurgy, it is still impossible to get rid of the technical means of using tailings reservoirs to store tailings. Therefore, the construction and management of the uranium tailings pond is still of special importance in the development of China's uranium mining and metallurgy industry.
2. The physical and mechanical properties of tailings are specific
Uranium ore adds chemical agents such as acid and alkali to the smelting process, which makes the uranium tailings have special physical and mechanical properties. The dry bulk density of the uranium tailings ore stored in the tailings pond is very low, and the dry bulk density is generally 0.5-0.7t/m 3 . The water content is high and the void ratio is large, resulting in a low total dry bulk density. It is said that the tailings storage of the same volume has less tons of uranium tailings.
(II) Current status of uranium tailings reservoir
1. Number and type of uranium tailings storage
Since 1958, China's uranium mining and metallurgy industry has built 15 tailings ponds with a total storage capacity of tens of millions of tons. Most of them are valley-type tailings ponds, and there are also hillside mines in the hilly area that have been upgraded and become the flat-type tailings reservoir of the surrounding dam center drainage. It is surrounded by nine dams, so there are 24 uranium mines. Tailings dam. The tailings dam is piled up by the upstream method to continuously increase the storage capacity of the tailings pond.
(1) Initial dam: The initial dam of the uranium mining and tailings reservoir is constructed using local materials - soil and stone. The dam type of the initial dam was originally a single homogeneous earth dam. China's first large-scale uranium hydrometallurgical plant was one of the former Soviet Union's aid projects. The design of its tailings facility was completed under the guidance of experts from the former Soviet Union. The initial dam and the dam of the tailings pond are all compacted earth dams. After the Soviet Union broke down the support in August 1960, it completely relied on China's own technical strength to design and construct the tailings facilities of the second and third batch of uranium hydrometallurgical plants in China. The dam type of the initial dam began to transition to multiple types. According to China's specific national conditions and actual conditions, dam types suitable for local conditions and economical and reasonable are constantly appearing, such as: water fill dam type, permeable rockfill dam type, multiple soil combination dam type, soil water injection dam type, etc. In the project of uranium mining and tailings storage. [next]
The initial dam height of the uranium mining and tailings warehouse is generally about 20m, the highest is 32m, and the lowest is the slope type tailings pond on the Gobi Desert in Xinjiang, h=8.0m.
(2) Tailings accumulation dam: The uranium mining and smelting tailings reservoir is constructed by upstream method tailings after the initial dam is filled. Design maximum dam height (including initial dam) -90m. At present, there are 4 seats with a height of more than 60m and two with a height below 30m. The others are between 40 and 60m. At different heights of the tailings accumulation dam, an drainage facility is provided to reduce the immersion line of the dam body to avoid the occurrence of swamping of the downstream slope during the operation of the tailings pond.
In order to prevent pollution and improve the environment, the tailings accumulation dam of the uranium mining and tailings reservoir is basically covered with the natural soil material to cover the outer slope with the pile height , and the grass is protected in time to prevent the wind and rain from accumulating the outer slope of the dam. Erosion.
2. Safety status of uranium tailings pond
(1) The engineering grade of the uranium tailings pond is high: the engineering grade and design standard of the uranium mining and tailings reservoir developed by the nuclear industry are 1-2 higher than the reservoir and non-ferrous metal and ferrous metal tailings ponds of the same scale. The engineering facilities are perfect, and there is no disease and dangerous reservoir project that insists on working with the disease.
(2) The uranium tailings reservoir has strong flood resistance: due to the higher engineering grade, the corresponding flood design standards are higher. The storm flood generated in the catchment area of ​​the tailings pond is an important factor affecting the safety of the tailings pond. There are many examples of catastrophes in the tailings pond due to poor storm flooding. In the initial stage of uranium mining and metallurgy, on the basis of summarizing the experience and lessons of the tailings reservoirs at home and abroad, taking into account the special requirements of radiation protection safety, we have formulated policy measures to improve the flood control design standards for uranium tailings ponds, ensuring uranium for 30 years. There has never been a flood safety accident in the operation of the tailings pond. The maximum catchment area of ​​the 15 tailings ponds of uranium mining and metallurgy is 14.4km 2 , and the smallest one is only 0.4km 2 , which is generally about 1~3km 2 . Its design flood standards are designed in a hundred years and once in the millennium. In case of special circumstances, check with the maximum possible rainfall flood. Compared with the same storage capacity of the reservoir and colored, black flood standard beneficiation plant tailings grade increased by 1 to 2, uranium tailings drainage structures to ensure flood safety of tailings.
3. Accidents of uranium mining and tailing facilities in the nuclear industry
The tailings storage of uranium mining and metallurgy has a short operating history, and the engineering grade and design standards are relatively high. No accidents have occurred. The use unit can timely expand (renovate) the technical measures for the construction and renewal of the tailings pond before the tailings pond has reached the designed service life and the accumulated elevation. Therefore, the tailings reservoir of uranium mining and metallurgy can work under normal operating conditions, but there have been two large dam landslide accidents in the tailings pond.
(1) The initial dam landslide accident and treatment results of a mine
1, the accident passed
In early July 1992, torrential rains occurred in some areas of Guangdong Province. In the northern mountainous areas of Guangdong Province, there were two shallow landslides in the initial dam of the tailings reservoir of uranium hydrometallurgy, which slipped out of the earth. The landslide range is from a range above the downstream drainage prism to a maximum depth of about 2.0 m near the initial dam crest. There were no casualties, no impact on the downstream farmland, and no impact on the normal operation of the tailings pond.
After the accident, the technical experts of the Nuclear Corporation and the safety and technical supervision station of the nuclear industry tailings dam project immediately went to the site for command, research, rescue and repair. The head office allocated 2 million yuan, and the completion acceptance was completed in February of the following year. It is currently running normally.
2. Analysis of the cause of the accident
The two initial dams with shallow landslides are homogenous earth dams, and the downstream drainage ribs are turf surface protection. The reason for the analysis of the landslide is that the drainage of the dam's foot drain is not smooth, so that the rain from the side of the dam body rushes to the dam slope, and the lateral scouring forms a gully, resulting in a vacant surface parallel to the dam axis. The torrential rain caused the surface of the dam slope to be saturated and the strength decreased, which caused the dam slope to collapse along the airfront. This problem should have been discovered early, but because of the high height of the grass on the dam slope, the surface looks like a sullen cluster, in fact, the dam surface has been washed out criss-cross. Everything has a process from micro to macro, and that that is a major factor that hinders the discovery of its changing process.
3, the processing results
After analyzing the reasons and researching the treatment measures, it was decided to remove the mud, raise the downstream drainage prism, slow down the dam slope, and all the downstream slopes to set up the drainage drainage layer and the stone weight increase, and increase the lateral gully erosion dam to prevent the dam body. Technical measures such as the body's anti-shock wall. Two tailings reservoirs with landslide accidents were renewed after the rescue was completed. [next]
4. Loss situation
Because it is a shallow landslide, the scope of impact is small, there are no casualties and loss of tailings, no production is stopped, and the loss is only the cost of emergency reinforcement, which is about 2.3 million yuan.
5, lessons learned
Through the analysis of the causes of landslides, people realized that it is not a good thing to stir the grass on the outer slope of the earth dam. On the contrary, it hinders the inspection and inspection of the dam surface by the patrolling personnel. The following is the gully vertical and horizontal, the surface is the gloom of the jungle, giving people the illusion, which is the cause of the great disaster. Of course, the negligence of managers is the direct cause of the accident. To this end, the Nuclear Industry Tailings Dam Safety Technology Supervision Station has notified the units with tailings ponds that all weed shrubs on the downstream slope of the tailings dam must be removed, resulting in good conditions for inspection and inspection of the dam surface. Put the accident out of the initial stage.
(2) Other environmental pollution accidents
1. Environmental pollution caused by tailings conveying pipeline
After the earliest uranium hydrometallurgical plant was put into operation in the early 1960s, the most common safety accident in the tailings facility was that the slurry pipeline conveying the tailings was sprayed with slurry to cause pollution along the pipeline. Guided by the belief of the Chinese people's own construction roads, the scientific and technological personnel have the courage to explore and innovate, actively adopt new technologies and new equipment, and rely on their own strength to build a new batch of tailings facilities of the water and metallurgical plant, creating a suitable for China. Specific national conditions for the construction of uranium tailings.
In order to improve the environment and prevent pollution, in the late 1960s and early 1970s, China's uranium mining and metallurgy upgraded and upgraded the tailings conveying system of each uranium hydrometallurgical plant. The tailings conveying system is equipped with steel-lined cast stone conveying pipeline and high-lift oil-isolated mud pump , which eliminates the pollution along the uranium tailings conveying pipeline and greatly improves the environmental quality.
The steel-lined cast stone tailings conveying pipeline has a large investment, but the operation and operation cost is small, and the wear resistance and corrosion resistance are excellent. As long as the design, construction and installation are reasonable, the operation is proper, and the tailings can be completely eliminated during the transportation process. Run, take, drip,
Leakage phenomenon. The new uranium mining and tailings conveying system has not been polluted by the environment for more than 20 years.
2. The impact of the tailings pond on the environment:
So far, no catastrophic accidents have occurred in the uranium mining and tailings reservoir. Since the construction of the tailings dam can be adhered to with the increase of the pile, the measures for shielding and planting grass slopes are covered at any time, so the pollution of the solid tailings around the reservoir is not obvious.
As the water level in the sedimentation tank in the tailings pond is continuously increasing, the seepage area is enlarged, and the permeate water of the tailings dam flows out of the reservoir, which has certain influence on the downstream of the dam. In order to prevent this phenomenon, the uranium mining and tailings reservoir is common. The method adopted is to set up the seepage pump house, collect the seepage water, send it back to the tailings pond or send it to the sewage treatment plant.
For the discharge of normal excess water in the tailings pond, the second batch of uranium hydrometallurgical plants in China are equipped with a tailings water treatment plant (workshop) to ensure that the normal discharge of tailings water can meet the national emission standards.
Fourth, the particularity of uranium mining and tailings reservoir
(1) Large amount of tailings
Extracting uranium from uranium ore is not a physical process but a chemical process. Therefore, compared with the tailings of black mines and non-ferrous mines, uranium tailings have other physical and mechanical properties besides the special characteristics of residual radioactive materials, mainly due to the high water content of fine tailings. Dry weight is low. The amount of tailings in the water smelting plant is generally greater than the amount of raw ore processed. The amount of tailings discharged from non-ferrous mines and black mines is mostly smaller than the amount of raw ore processed.
(2) Residual radioactivity in tailings
During the smelting process of uranium ore, only the uranium in the radioactive isotope is leached and extracted, and the remaining nuclides remain in the tailings and discharged into the tailings pond, resulting in residual radioactivity in the uranium tailings pond.
V. Safety management system for uranium mining and tailings facilities in the nuclear industry
The uranium mining and metallurgy industry has formed a relatively complete tailings facility management system for 30 years. Each uranium hydrometallurgical plant is equipped with a tailings workshop or a tailings section, which is responsible for the operation and management of the tailings facilities. Radiation protection personnel regularly sample and monitor tailings water and air. The head office issued a series of notices, regulations, regulations and standards for the particularity of uranium mining and metallurgy, so that the tailings facilities of uranium mining and metallurgy have rules to follow from investigation and design to construction and operation. As early as 1978, the former second-machine department held the first tailings work conference, and enacted and promulgated the Regulations on the Management of Tailings Facilities. In 1992, the Nuclear Corporation established a safety technical supervision station for the nuclear industry tailings dam project, which is responsible for inspecting and supervising the safe operation of the tailings dam project.
More than 30 years of operational experience has led to a consensus among the governing bodies and various grassroots departments that scientific and standardized management is a key factor in ensuring the safety of uranium tailings facilities. With higher engineering standards, even the best engineering design only provides the basic conditions for engineering safety. If it is neglected, it will cause great disaster. [next]
In order to strengthen management and improve the level, the Chinese nuclear industry has issued the following ministerial regulations for the management of tailings facilities:
(1) Regulations on the Management of Tailings Facilities in Uranium Water and Metallurgical Plants 1978.
(2) “Several Problems in the Design of Mining and Metallurgical Enterprises of the Second Ministry of Machinery Industryâ€, 1981.
(3) “Safety Design Regulations for Tailings Reservoir of Uranium Water and Metallurgical Plant†(EJ794-93) 1993.
All factories and mines have established safety regulations and regulations for tailings facilities, and emergency flood control organizations have been established in the flood season.
Uranium mining and metallurgy pays more attention to the design, construction and management experience of tailings reservoirs in other industries, and it is used by me. Ministry of Water Resources and Electric Power "Design Code for Rolled Earth and Rock Dam", "Technical Specifications for Construction of Rolled Earth and Rock Dam", "Code for Seismic Design of Hydraulic Structures", etc., "Design Specification for Tailings of Mineral Processing Plants" of the Ministry of Metallurgy and Nonferrous Metals Corporation The “Management Regulations for Metallurgical Mine Tailings Facilities†are the specifications and standards for the implementation of uranium mining and tailings facilities.
6. Main problems affecting the safety of uranium tailings facilities
(1) Low quality of management personnel
The management personnel and treasury workers of the uranium tailings pond in the nuclear industry have not undergone special training. Most of them have groped, summarized and improved themselves in actual work, and gradually improved themselves. Although the management personnel have a high degree of education, they are limited by the knowledge of the professional boundaries of “earth mechanicsâ€, “hydraulics†and “hydraulic structureâ€. In recent years, although graduates of professional water conservancy colleges have allocated uranium plants and mines, it is difficult to take roots.
(2) It is necessary to establish a scientific, complete and whole-process management system, which is the weak link in the management of uranium mining and tailings.
(3) Social security factors need to be purified
Most of the uranium mining and tailings facilities are located in the barren hills and mountains, far from the plant area. The communication and lighting equipment of the tailings pipelines, pipe fittings and tailings ponds, and the observation equipment on the dam are seriously lost. Even some people in the area have even slope protection. The dry masonry has moved home to build a house. It is difficult for the management staff to maintain normal production.
This is a difficult point in the current safety management of uranium tailings ponds.