WO2022064081A1

WO2022064081A1 - Industrial ex situ wet soil washing plant for the decontamination of soils affected by medium and low level radionuclides

Info

Publication number: WO2022064081A1
Application number: PCT/ES2020/070579
Authority: WO
Inventors: Arsenio DE LA VEGA MARTÍNEZ
Original assignee: Sereco Gestion, S.L.
Priority date: 2020-09-28
Filing date: 2020-09-28
Publication date: 2022-03-31

Abstract

Ex situ wet soil washing is an effective technique in the remediation of contaminated soils. The technique is based on the difference in particle size and density of the materials, washing and separating the different fractions. The pollutants contained in the interstices of the affected material are separated therefrom and transferred from the granular fractions (gravel and sand) to the finer fractions (silts). This requires a combination of washing, screening, hydrocycloning, attrition, agitation and dewatering techniques. In a first phase, the soils are washed with water and then separated into the three fractions defined above: gravels, sands and silts. The sand is beaten with an energetic washing process; the gravel with simple desanding, attrition and double-stage cyclone sand washing; and the silt with conditioning, thickening, homogenisation and dewatering.

Description

INDUSTRIAL WET EX SITU SOIL WASHING PLANT FOR DECONTAMINATION OF LAND AFFECTED BY MEDIUM AND LOW INTENSITY RADIONUCLIDES.

DESCRIPTION

Technical sector

The present invention relates to a soil washing and granulometric separation plant, which releases the contaminating compounds (radionuclides of medium and low intensity) from most of the land, remaining decontaminated and concentrating that contamination only in the fine fraction of the soil. (silt).

Due to the demand by the organizations of the countries in charge of the management of waste from the dismantling of nuclear power plants, in 2014 the company SERECO GESTIÓN requested the Spanish Center for the Development of Industrial Technology (CDTI) the financing of the project of R+D+l for the decontamination of land with medium and low activity radioactive isotopes and materials from the demolition of radiological facilities.

The Utility Model to be registered can be applied to land or waste that has radiological contaminants with a granulometric curve or gravel, sand and fine content of around 40%, 40% and 20% respectively or similar.

The utility model presented is intended to obtain the following technological and industrial advantages:

° Use of the available systems and technologies for the decontamination of soils affected by conventional contaminants, in order to develop a technology for the reduction of contamination generated by nuclear activity.

° Application and optimization of radiological processes, techniques and methodologies for declassification, storage and control of nuclear waste.

° Obtain a technology that reduces the volume of radioactive waste storage in ATC (Centralized Temporary Storage). Currently, contaminated soils are stored as waste in their entirety and the application of the technique described in this document would cause only the fine fraction to be stored, being able to reduce up to 80% the material sent to nuclear landfill. • Development of a product applicable to problems arising from nuclear activity, which other companies in the sector do not have.

• Generation of a specific line of business that does not currently exist.

Background of the invention

Normally, the radioactive waste from the land where the nuclear power plants are located is of low or medium activity, but represents a considerable volume within the residual material generated in the dismantling processes. It is important, therefore, to distinguish between waste materials that are highly active radioactive and therefore require conditioning and storage under particularly stringent conditions, and waste materials with low enough activity that they can be decontaminated, if necessary, and be treated as conventional waste or as materials that can be recycled.

The conditions that must be taken into account and the limitations that exist to undertake the dismantling of a nuclear power plant are, among others, the capacity and availability of the storage facility to manage high-level waste, as well as for the high volume of waste of low activity, the radiological load associated with the dismantling tasks and the availability of financial funds to undertake the work with a sufficient guarantee of safety.

Radioactive waste from nuclear power plants is one of the main problems that exists in advanced global industry. Current technology has known how to control nuclear energy and takes advantage of its results, but it does not know how to neutralize and destroy its residues, the only applicable solution currently being to isolate them in drums and bury them at certain depths (mines abandoned and reused for this purpose and lately in underground silos).

There are also other non-nuclear radioactive waste of varying intensity from radiological medicine, research, the arms industry, etc.

There are currently three ways to proceed for the management and control of waste generated by nuclear activity:

° Open Cycle: The waste is encapsulated and stored retrievably in deep and stable geological formations, known as ATC (Centralized Temporary Storage). The geological isolation and confinement capacity is combined with artificial barriers made specifically so that the whole (geological formation + artificial barrier) ensures the confinement and isolation of the radioactive waste and radionuclides they contain according to the periods design of the storage facility and that it is tens of thousands of years old.

• Conventional Closed Cycle: The uranium and plutonium separated by reprocessing are burned in commercial nuclear reactors in the form of mixed oxides. After several reprocessing cycles, the final irradiated fuel is managed and stored in an underground facility similar to that of the open cycle.

• Advanced Closed Cycle: Advanced reprocessing of irradiated fuel is carried out, separating actinides, long-lived radioactive chemical elements, and fission products to generate new fuels that can be burned in next-generation reactors or transmutation systems.

The final irradiated fuels resulting from the closed cycle will have a lower volume and lower radiotoxicity and will be stored in an underground geological storage facility following the open cycle concept, but for a lower volume, lower radiotoxicity and different classification.

Some low-level radioactive waste is disposed of very diluted by dumping it into the atmosphere or water in concentrations so small that they are not harmful and the law allows, since the radiation rates that these discharges give are lower than those that many natural substances usually give. or some everyday objects such as home electronics.

Medium or low level waste is placed in special containers that are stored for a time on the surface until they are taken to security dumps. The definitive warehouses for this waste are, in general, underground, ensuring that they will not suffer water leaks that could drag radioactive isotopes out of the dump. In Spain, the facility prepared for this is El Cabril (Córdoba) where up to 50,000 m ³ of medium and low level waste can be stored.

High level waste is the most difficult to treat. The volume of spent fuel remaining in normal nuclear power plants can be greatly reduced if it is reused in special plants. This is done in some cases, but it presents the difficulty that a very dangerous substance has to be transported from one plant to another.

The residues that remain are usually vitrified (melted together with a vitreous mass) and placed in special containers capable of resisting highly corrosive agents, fire, earthquakes, big crashes etc. These containers would be stored in permanent landfills that must be built deep underground, in very stable geological locations (clay deposits, salts or granite massifs) and well refrigerated because radioactive isotopes emit heat.

The management of this highly active radioactive waste is the real aspect on which the nuclear energy debate is currently focused and on which research and development efforts are having an impact.

The scientific community has been studying the feasibility of geological storage of high-level waste for several decades. Interestingly, there is a deposit generated naturally long before the appearance of the human being; 2,000 million years ago, in the Precambrian, a vein of mineral especially rich in the isotope ²³⁵ U of Uranium spontaneously initiated a chain reaction, which lasted for a period of 500,000 years, giving rise to what is known as the Oklo natural fission reactor in Gabon. Its radioactive waste, some 5 tons of fission fragments and 1.5 tons of plutonium, have remained geologically immobilized in the area.

The geological storage of radioactive waste is a solution that offers the necessary guarantee so that the effects of waste on the biosphere and man are very low and less than those produced by natural radiation, although its application is questioned by some of the population when assigning geographical locations.

Due to the fact that the generation of energy through the nuclear industry will increase continuously due to the demand of our current society, it will be necessary to progressively increase the storage capacity of the waste generated, so it seems opportune to think about the need to investigate alternative solutions to geological storage.

However, regardless of the future increase in the use of nuclear energy, it is necessary that the waste already generated be managed without prejudice to future generations. It is unacceptable that an advanced society, with the opportunity to develop alternative techniques, chooses to transfer it to future generations for purely political or economic reasons, which is why the countries that have nuclear power plants are investigating how to minimize the generation of radioactive waste and reduce drastically the final storage capacity. The solutions currently proposed are grouped into three large areas:

• Techniques for reducing the volumes to be managed and stored in the long term.

• The separation of waste into different components and the transmutation of a fraction of these as part of a nuclear fuel, thus transforming an environmental problem into a source of energy.

• Development of new advanced reactors, with greater efficiency and degree of fuel burning, which make it possible to reduce the amount of long-lived waste per unit of energy generated.

Explanation of the invention

Ex situ wet soil washing is an effective technique in contaminated soil remediation processes, applicable in the case of contamination by a diverse range of organic and inorganic contaminants. In order to be applied to radiological contaminants of medium and low intensity, different techniques, stages and processes must be applied to concentrate said contaminants in the silt.

The technique is based on the difference in the size of the particles and the density of the materials, washing and separating the different fractions. The polluting substances contained in the interstices of the affected material are separated from it and transferred from the granular fractions (gravel and sand) to the finer fractions (silt). For this, washing, screening, hydrocycloning, attrition, agitation and dehydration techniques must be combined.

In a first phase, the soils are washed together with water and later they are separated into the 3 previously defined fractions: gravel, sand and silt.

° On the one hand, the gravel fraction must subsequently be subjected to an independent energetic washing process in order to reliably remove the contamination still attached.

° For its part, the sand fraction is especially sensitive and special washes must be carried out to eliminate both the contamination and the silt present in them. This is not achieved with a simple desanding as it is usually done, but rather a simple desanding, an attrition phase and later a double cycloning stage sand washing for its complete washing must be equipped in series. In addition, the cycloning systems are usually conical with small granulometric cuts (<0.080 mm) with the consequent risk that the contamination is found in a slightly larger fraction and the sand cannot be decontaminated. For this reason, this plant equips the combination of conical cyclones and flat cyclones that allows choosing larger granulometric cuts that enable the declassification of sand as waste.

° Thus, all the contaminants extracted from both the gravel and the sand, together with the washing water, migrate and join the silt, which is the fraction with micrometric granulometry and with a high absorption of contaminants by its low porosity. In this third stage, the silt and contaminants have a high amount of water and are therefore subjected to adaptation, thickening, homogenization and dehydration processes in order to minimize the residue by eliminating the water and concentrating all the contamination in a single dry residue. .

Brief description of the figures

The written description is complemented, for easy understanding, with different figures where the following has been represented for illustrative and non-limiting purposes:

Figure 1: Bar Separator, shows a top perspective view of a bar separator.

Figure 2: Hopper and Belt Feeder, shows a bottom perspective view of a hopper and belt feeder.

Figure 3: Washing Trommel, is a bottom perspective view of the washing trommel.

Figure 4: Screens, shows a perspective view of the screens from above.

Figure 5: Stonewasher, shows a top perspective view of a stonewasher.

Figure 6: Desander, shows a bottom perspective view of a desander.

Figure 7: The sand trap is presented in the following scheme where:

1. Entry of sand and water into the tank

2. Suction mixes sand and water

3. Hydrocycloned

4. Sand outlet to drainer

5. Advance and exit of the sand in the drainer

6. Evacuation of water with fines

7. Valve and level float in the tank

Figure 8: Attrition tank, shows a bottom perspective view of an attrition tank.

Figure 9: Block diagram of an attrition tank, is a perspective view from above, partially cut away, of the attrition tank.

Figure 10: Two-stage sand washing group shows a bottom perspective view of a two-stage sand washing group.

Figure 11. Sludge thickeners, shows a top perspective view of two sludge thickeners.

Figure 12. Scheme of a sludge thickener, is a cutaway perspective view of a sludge thickener. The description of the operation of a settling-clarification equipment, where:

1. Flocculant preparation and dosage group, where water and flocculant are injected.

2. Sludge feeding

3. Box where the water with sludge is mixed with the flocculant.

4. Sludge scraper-concentrator.

5. Sludge suction cone.

6. Sludge pump.

7. Clear water outlet.

Figure 13: Filter presses, is a perspective view from below of sludge filter presses.

Figure 14: Diagram of a filter press, is a perspective view from profile, cut away, of the operation of the filter press.

Figure 15. Conveyor belts, shows a bottom perspective view of the conveyor belts.

Figure 16: Flow diagram of the different stages of the soil washing plant with radiological contamination in the wet process.

Preferred embodiment of the invention

Appropriate technology that allows the decontamination of land or waste with medium or low radioactivity affected by the activity of nuclear power plants or by any other source of radioactive energy includes the following equipment for washing aggregates and granulometric classification:

Gravel feeding and washing

Feed hopper: it is a device similar to a large funnel intended for the deposit and channeling of granular or pulverized materials, among others. Sometimes, it is mounted on a chassis that allows transport. Figure 2 shows the image of a feeding hopper.

Depending on the maximum size of the aggregate, it may be necessary to previously introduce a bar separator into the hopper, which is a vibrating device with bars separated by a distance to be determined in each case, which prevents improper elements and large volumes from entering the hopper. Figure 1 shows the image of a bar separator.

Belt feeders The belt feeder is a piece of equipment used for transferring material continuously and regularly, from the feed hopper to the rest of the installation.

It is especially suitable for continuous granulometry products, such as natural gravel, concrete crushing material and detrital materials in general, also being applied in the feeding of granular soils. Compared to other types of feeders, such as vibrating or reciprocating feeding, it has enormous advantages in operating with wet materials.

Among its characteristics, the following can be highlighted:

° Belt widths from 500 to 1,400 mm.

° Feed rates of up to 100 m ³ /h in conventional models.

° There are models to work both horizontally and in an ascending position.

° Different feeder lengths.

° Manual and even electronic power regulation by installing frequency inverters. They are equipped with a regulation damper.

Head scrapers can be installed.

Figure 2 shows the image of a conventional band feeder.

Trommels: the trommels or "washing cylinders" are equipment intended for the energetic washing of rocks, gravel, minerals of coarse granulometry, disintegrating the coarsest fractions, through the impact of particles generated by the rotation of the drum, of the finest fractions.

Inside, the drum usually has elements that cause the turning and advancement of the material from the feeding to its exit. The friction that is generated inside, together with the necessary contribution of water, causes a washing effect that eliminates the remains of dirt-surface contamination that the material presents, as well as the fine particles of the matrix.

The intensity of the washing is linked to the necessary residence time according to the problem to be treated and varies with the diameter, length of the cylinder and its rotation speed.

There is a wide range of washing trommels on the market, with different performances, being equipment that can be designed and built to measure and even configured in series or parallel to increase performance and residence times. Figure 3 shows the image of a washing trommel.

Vibrating screens: A screen is equipment designed to separate the different fractions contained in a material, normally granular soil, by granulometrics. They are widely used equipment in gravel pits and quarries, allowing to obtain selected stockpiles of the desired sizes.

The equipment (see figure 4) consists of a metal structure on which a set of springs sit, connected to the screen body, which, due to the eccentric oscillation generated by a set of counterweights attached to the screen body, produce the vibration in the set.

Inside the sieve there are different mesh cloths with different light openings, depending on the granulometries that you want to obtain in the classification. From the output of each cloth, a collection of the different granulometries can be obtained.

Screening can be carried out dry or wet, by injecting water through a pressurized irrigation system that facilitates the separation of the fine fractions, generating a clarification of the screened material.

The dimensions of this equipment are variable, being able to go from 2.3 to 15 m ² of surface in commercial manufacture, although they can be designed, sized and manufactured specifically for each type of action.

There are other equipment for washing, classifying and handling aggregates, such as probabilistic screens, bucket elevators, shaking tables, Reichert cone, etc., which will be evaluated for their application in the case deemed appropriate.

After draining, two streams of material are generated:

- Material greater than 4 mm (gravel) with a humidity of less than 15-20% that is extracted by conveyor belt to the energetic gravel washing process.

- Material less than 4 mm (sand and silt) together with the washing water that is sent by gravity to the sand washing and treatment process.

washers of

: The stone washer, also called Log-washer, is a secondary type washing machine to treat granulometries between 2/3 mm and 90/100 mm.

In order to ensure the absence of contaminants, sand and fines in the thickest materials (greater than 4 mm), these will be subjected to a pressure washing process by passing them through gravel washing equipment.

It is a fundamental piece of equipment for the recovery of waste from quarries. The quality of the finished product in coarse materials is superior to that obtained in other machines such as screens, wet screens, washing ramps, etc.

The equipment is arranged in an inclined and ascending position, working against the current, that is, the washing water and the material circulate in the opposite direction, the effect of the washing is by attrition and shearing between the blades and the material. It is possible to eliminate the clay, chalk and slime that accompany the material, crumble the decomposed soft particles and clean the contamination adhered to the outside of the stone.

Figure 5 shows an image of a stone washer.

sand washing

The material from the fractions less than 4 mm classified in the screening process and also from the energetic gravel washing is sent together with the process water to the sand washing treatment.

This exhaustive washing of the sand with a grain size of less than 4 mm requires a double desanding in series (1st ^and 2nd washing stages ⁾ , where an attrition is inserted, to ensure its correct washing.

In the first desanding stage, the particles smaller than 0.080 mm (silt) are separated by hydrocycloning, together with the water, from the particles between 4 and 0.080 mm (sand). The objective is to release the greatest amount of fines so that they drag the contamination with them and so that the subsequent sand attrition process is as effective as possible. This separation is carried out by means of two conical-bottomed cyclones and especially flat-bottomed ones that allow the effective cutting diameter to be adjusted by changing the configuration of the cyclones based on the analytics obtained in the sands, being able to sweep a range of 0.250 - 0.080 mm and thus be able to decontaminate the sands.

After sand removal, the water with this fine material is extracted by the overflow (upper part of the hydrocyclone) and sent to the thickening process. On the other hand, the fractions of the cut 4 - 0.080 mm are sent by the underflow (lower part of the hydrocyclone) to a drainer and with a humidity lower than 20% they will be introduced by gravity in the attrition cells.

Once the sand has been attritioned, it is reintroduced into a second desanding group which, in turn, has, unlike the previous one, 2 cyclone stages so that sand washing is as effective as possible. The equipment used in sand washing is described below.

Sand traps: They are equipment designed to wash sand without loss of fines and with reduced humidity at the end of the process, the sand and water are introduced into a tank through a side access. From the bottom of the tank, the mixture of water and sand is sucked in by means of a pump that drives the pulp towards a cyclone.

Due to the effect of centrifugal force, the clay particles are separated from the sand. The clays, together with the water, rise inside the cyclone and are expelled through the upper part of this element, while the sands leave the hydrocyclone to the drainer that the equipment incorporates.

The drainer causes the sand to advance towards its front part, allowing the water to filter through the grid (made of polyurethane or steel).

The water contained in the fines is evacuated for later treatment, balancing the water in the tank by means of a float valve.

Figure 6 shows a photograph of a sand trap. Figure 7 shows a diagram of the work and classification process that occurs in the sand trap.

There is a wide variety of manufacturers and types of sand traps on the market, with sand removal equipment available with cyclones from 450 mm to 750 mm.

Sand treatment capacities can be found between 5 Tm/h and 200 Tm/h and water intake capacity of between 10 m ³ /hour and 700 m ³ /hour.

Attrition tanks They are specific equipment designed to wash sandy materials, through a physical process that generates friction between the granular particles. This process needs a slight humidity to be able to be produced, so it is necessary to precisely adjust the humidity of the material before it enters the process. An excess of water would generate a lubrication effect between particles that would reduce the desired effect. Figure 8 shows an image of an attrition tank.

Figure 9 presents a block diagram of the treatment process within a attrition tank; The material is introduced into a first chamber in which, a double axis moved by an external motor, moves two propellers in the opposite direction, each one of them, generating the necessary friction movement and the displacement of the material inside the chamber.

The material passes into a second chamber on the inside of the tank, where it is stirred in reverse by another set of propellers that moves it outwards.

Equipment of different capacities can be found on the market, however, since they are very specific equipment, their manufacture is normally carried out under specific conditions for the specific application, being systems that are usually manufactured to order.

Two-stage washing group: A 2-stage sand washing group is a special configuration made up of 2 grit traps (1st ^and 2nd stage) ^with the particularity that the first one does not have a drainer and the sands, instead of After leaving the equipment, they go to the second sand trap where clean water is added for better washing.

In the first stage, the sand and water are introduced into a tank through a side access. From the bottom of the tank, the mixture of water and sand is sucked in by means of a pump that drives the pulp towards a cyclone.

Due to the effect of centrifugal force, the clay particles are separated from the sand. 80% of the clay, together with the water, rises inside the cyclone and is expelled through the upper part of this element, while the sand leaves the hydrocyclone and instead of draining, is sent to a second tank through a lateral access and clean water is added ⁽ 2nd stage).

In this second stage, this clean water falls directly on the sands that are already free of fines (only 20% of the fines remain) and therefore it is the greatest washing that can be done to some sands. Within this second stage, the operation is analogous to that of a conventional sand trap. Due to the effect of centrifugal force, the clay particles are separated from the sand. The clays, together with the water, rise inside the cyclone and are expelled through the upper part of this element, while the sands leave the hydrocyclone and are sent to a drainer.

The drainer causes the advance of the sand towards its front part, allowing the filtering of the water through the grid (made of polyurethane or steel).

Figure 10 shows a photograph of a 2-stage sand washing group.

Both equipments are simultaneously and innovatively equipped with conical bottom cyclones and especially flat bottom cyclones that allow the effective cutting diameter to be adjusted by changing the configuration of the cyclones based on the analytics obtained in the sands, being able to sweep a range of 0.250 - 0.080 mm and thus be able to decontaminate the sands.

sludge adequacy

The stages described above cause a stream of water, silt and contaminants to be adequately treated (sludge). To do this, they are subjected to different stages of physical-chemical adaptation (coagulation-flocculation) and thickening.

Coagulation: The mixture of mud and water, coming from the gravel and sand washing equipment, is sent to a tank where the corresponding coagulant is added, starting the physical-chemical treatment process. This tank is equipped with an agitator to facilitate the mixing of the coagulating agent with the sludge. This additive is injected by means of an addition pump. Once mixed, a bottom pump sends the sludge to the thickener pre-feeder.

Flocculation: The sludge is sent to the thickener pre-feeder where the polyelectrolyte necessary for its flocculation is added. This reagent is prepared in a compact polyelectrolyte manufacturing plant with three chambers: preparation, maturation and dosing, and is added through a dosing pump controlled by an automatic flocculation verification system. The objective of carrying out the coagulation-flocculation process is to concentrate the solid particles as much as possible in such a way that it gives the material the appropriate density to precipitate and easily separate from the water. This is done inside the thickener.

Sludge thickener: The sludge thickener or decanter - clarifier is a tank, usually circular, whose mission is to separate the clays or sludge from the water, which are concentrated in the process and are extracted from the bottom of the tank, while the water clarified water overflows from the periphery and the upper part for later reuse.

The thickeners can be installed on a concrete base or elevated on a metal structure and can incorporate a centrifugal, volumetric or membrane pump, depending on their application. Figure 11 shows the image of a sludge thickener.

Clarification equipment can be found on the market with treatment capacities from 20 m ³ /h to 1,000 m ³ /h, with different dimensions and powers, although they are equipment that can be dimensioned and built to the needs of each project.

The description of the operation of a settling-clarification equipment is presented in figure 12.

Clear water: Through the upper part of the thickener, the clarified water is recovered by overflow, which is sent to a regulation tank from which water will be fed to all points of the plant by means of a pump in such a way that a closed circuit is generated.

Only water must be replenished due to the losses that there will be in the form of humidity in each of the stockpiles.

sludge dewatering

The sludge extracted from the bottom of the thickener contains the contaminants and is concentrated but still contains a significant volume of water. To minimize the volume of the waste and remove as much water as possible (up to 80% reduction), the sludge is dewatered. The equipment used in sludge dewatering is described below.

Press filters: they are the equipment designed to cause the greatest possible reduction of the volume of water contained in a sediment, by applying high pressure, consisting of a battery of successive square or rectangular plates facing each other in a vertical position arranged on a frame with one end fixed and the other mobile. The filter cloths are fitted on each of these plates.

There are different models and manufacturers of filter presses on the market that offer different sizes in number of plates and filter surface, which gives this dewatering element a diverse range adaptable to each case. They are, unlike other solutions (belt, centrifugation...) the equipment that confers the greatest dryness to a sludge.

In the filtering process, the plates are held together by hydraulic presses or mechanically actuated screws between the fixed and mobile ends. In this way they are hermetically adhered and can resist the pressure that is applied to them during filtration.

The filter circuit, consisting of ducts located in the central part and distributed between the spaces between the plates until these cavities are filled with wet mud. When the pressure is exerted, the liquid is forced to pass through the filter cloth and the outlet holes of the plates. In this way, the dehydrated material, called cake, remains between the plates. At this moment, the pressure is removed, and when the moving end moves, the plates separate and the mud cake falls off, reaching a dryness percentage of 55-65% and even higher (up to 90%) depending on the nature of the material. soil to treat.

The duration of the filtration cycle includes the time necessary to fill the filter press, maintain the pressure between the plates, open the filter and discharge the sludge cake, cleaning the filter cloths. Figure 13 shows an image of several press filters arranged in parallel and figure 14 shows the operating scheme of a press filter.

Stockpiles of material

Conveyor belts: The conveyor belt is an essential element in aggregate treatment facilities and in general in mining and industry. It is designed in most cases for each specific need, for which there are numerous typologies concrete:

• Fixed and mobile.

• Stakers, to make large circular stockpiles or to feed different online hoppers.

• Ripable, to rest directly on the ground without the need for a foundation.

• Movable on motorized wheels, etc.

There are different band widths ranging from 500 mm to 1,400 mm, and these can be smooth or ribbed. Figure 15 presents an aggregate installation with conveyor belts.

Continuous radioactivity detector This equipment is developed with the purpose of detecting the radioactive emission emitted by the material moved by conveyor belts and to be able to act immediately before it leaves them. In places where a large amount of product is moved at high speed, equipment with a fast response time is needed that can detect and signal the existence of an alarm to the outside in order to stop the belt in time without radioactive material being deposited. out of it and thus avoid contamination of other stockpiles.

To detect the radiation, a sensor is used that converts the radiation emissions into electrical pulses where the amplitude of said pulses will be proportional to the energy of the emissions.

The level of radiation that reaches the sensor is made up of two values. Firstly, we have the amount of radiation emitted by the sample to be controlled and secondly, a more or less constant value that is always present called "BACKGROUND" and that is due to radiation of natural or human origin. Natural radiation comes from many sources, such as the more than 60 naturally occurring radioactive materials in soil, water, and air. In order to increase the accuracy of the measurement, the background value is largely eliminated first with adequate shielding of the sensor and the rest with electronic methods that obtain the real value of the radiation produced by the sample to be measured. Therefore, the correct calibration of the equipment is necessary once it is located in the place where the measurements are to be carried out by specialized personnel. collection of leachate and losses (safety bucket)

One of the biggest problems that arise in the operation of aggregate classification and/or soil washing plants are losses and spills of effluents and granular materials. Given the type of contaminants that are going to be transferred, it is essential to provide for the provision of a concrete safety basin equipped with a drainage network (surface gutters) to collect and evacuate said materials to a spill box so that they are again pumped to head and reintroduced in the process.

Auxiliary facilities

ELECTRICAL INSTALLATION

The electrical installation has all the necessary instrumentation for its correct operation. In this sense, a general electrical panel is included that contains the protections and control of the equipment that compose it, including those of the intermediate panels, if applicable.

PNEUMATIC INSTALLATION

The supply of the installation includes a compressor from which compressed air will be supplied to all the elements of the installation that require it, making the connection to them.

Claims

1. INDUSTRIAL WET EX SITU SOIL WASHING PLANT FOR THE DECONTAMINATION OF LAND AFFECTED BY MEDIUM AND LOW INTENSITY RADIONUCLIDES. The industrial plant may consist of the following elements:

Bar Separator (figure 1).

- Hopper and belt feeder (figure 2)

- Trommel washing (figure 3).

- Screens (figure 4).

Stone washer (figure 5).

Sand trap (figure 6 and figure 7).

Attrition tank (figure 8 and figure 9).

Two-stage sand washing group (figure 10)

Sludge thickener (figure 11 and figure 12).

Press filters (figure 13 and figure 14).

- Conveyor belts (figure 15).

Continuous radiation detector.

Flow diagram of the different stages of the wet soil washing plant (figure 16).

2. Plant according to claim 1. Due to laboratory and pilot plant studies, we know that the joint operation of washing with flat bottom hydrocyclones plus attrition favors the migration of low and medium intensity radionuclides down to the smallest fractions (< 125 micrometers in diameter) being able to choose this size in the range 250-80 micrometers.

3. Plant according to claim 1. The particle size fractions greater than 125 microns once washed with different processes (stone washing in the case of gravels (figure 5) and sand washing in a group of 2 stages (figure 10) in the case of the sands) present activity values below the objective value of decontamination.

4. Plant according to claim 1. The continuous radioactive material detector located on the sand and gravel exit conveyor belts to stockpiles allows the detection of material that is not exempt from radioactive contamination.

5. Plant according to claim 1. The washing water used in the trommel (figure 3), screen (figure 4), stone washer (figure 5) and second stage of the sand washing equipment (figure 10), are recovered in order to reduce the consumption of clean water, making it an ecologically sustainable plant.