JP2017110972A - Method for processing concrete debris polluted with radioactive cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing concrete debris polluted by cesium.SOLUTION: According to the method, concrete debris polluted with radioactive cesium is heated to a temperature in the range of 200-400°C, is put on a net electrode, and is classified by the net electrode while being broken by an electric pulse applied by a high-voltage rod-like electrode from a pulse-power generator in a water tank. After that, a slurry having passed through the net electrode is processed by a finer sieve than the net electrode and residues of discharge processing in the slurry are separated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating concrete rubble contaminated with radioactive cesium.

Currently, debris-like concrete waste contaminated with radioactive cesium is generated. A large amount of contaminated concrete waste is also expected in the decommissioning of nuclear power plants. Although it has been confirmed that the existing method is effective for decontamination of flat concrete that remains in the form of floors and walls, etc., studies have not been made on how to properly treat rubble-like contaminated concrete.

Unlike slab concrete, debris-like contaminated concrete has a contaminated portion that is distributed in a complicated manner, and cannot be uniformly removed by suspension or blasting from the surface. Therefore, a method of decontamination can be studied while the rubble lump surface is worn away.

For example, in the process of crushing the waste concrete material and then heating and recovering the recycled coarse aggregate, the fine aggregate raw material is taken out by sieving and the fine aggregate raw material is stirred in the dry first stirrer. After the surface is abraded, the “scrubbing method” such as a mechanical friction method (Patent Document 1) that agitates in the second agitator and abrades the surface to remove the paste adhering to the surface. Application can be considered.

However, this method includes a dry agitation process for collecting the aggregate, and there is a possibility that the cement paste part and the aggregate part may be worn away, increasing the amount of contaminated fine powder and scattering it. In addition, there is concern that secondary contamination may occur due to rubbing between the contaminated portion of concrete and the non-contaminated portion.

The application of the attempt to regenerate the coarse aggregate from the concrete block by the pulse power method using electrical pulses (Non-patent Document 1) can also be examined.

However, the coarse aggregate separated without applying an appropriate pulse to peel the cement paste from the aggregate in concrete has a lower dry density and surface dry density compared to the original coarse aggregate in the specimen preparation stage. However, the water absorption rate may increase. In addition, compared with the original coarse aggregate, the coarse aggregate separated by the impact of the pulse power has a tendency to become finer, and this method requires the precise control of the crushing conditions. It is also conceivable that a fine volume fraction separated and recovered is increased due to destruction of the material and the like, and a high volume reduction rate cannot be obtained.

Japanese Patent Laid-Open No. 8-91893

Shigeishi et al. “Utilization of Electric Pulse Power for Recycling Technology of Coarse Aggregate for Concrete” The 60th Annual Scientific Lecture (September 2005) 781-782

Therefore, the cement paste recovered as coarse aggregate, fine aggregate and sludge is separated and recovered from the concrete rubble which was generated by the Fukushima Daiichi Nuclear Power Plant accident and was contaminated with cesium. The problem was to realize a safe treatment method that can reduce the volume of pollutants from concrete debris by separating the radioactive cesium-contaminated part that has penetrated into the cement paste part of the concrete from the aggregate as sludge.

After heating concrete rubble contaminated with radioactive cesium to 200-400 ° C,
Placing on the mesh electrode and classifying with the mesh electrode while crushing with an electric pulse applied by a high voltage rod electrode from a pulse power generator in a water bath; and
There is provided a method for treating concrete rubble, characterized in that the slurry that has passed through the mesh electrode is treated with a sieve having an opening smaller than that of the mesh electrode, and the discharge treatment residue in the passed slurry is separated.

After heating concrete rubble contaminated with radioactive cesium to 200-400 ° C,
Placing on the first mesh electrode and classifying with the first mesh electrode while crushing with an electric pulse applied by a high voltage rod electrode from a pulse power generator in a water bath; and
Classifying the crushing portion in the slurry that has passed through the first mesh electrode while crushing with an electric pulse applied by a high voltage rod-shaped electrode from a pulse power generator in a water tank in the second mesh electrode; A method for treating concrete rubble, characterized in that the slurry that has passed through the second mesh electrode is treated with a sieve having an opening smaller than that of the second mesh electrode, and the discharge treatment residue in the passed slurry is separated. ,I will provide a.

Classifying the crushing portion in the slurry that has passed through the second mesh electrode while crushing in the water tank with an electric pulse applied by the high voltage rod-shaped electrode from the pulse power generator in the third mesh electrode; A method for treating concrete rubble is provided, wherein a discharge treatment residue in a slurry that has passed through the third mesh electrode is separated.

Here, the separation of water and the discharge treatment residue in the slurry can be based on decantation, specific gravity separation, sieving in water or drying. The discharge residue is isolated as is or after stabilization. Radioactive cesium is concentrated in the residue (sludge) after the slurry is dehydrated. However, radioactive cesium is fixed to sludge and can be safely stored without any special treatment. In particular, when the contamination density is high and there is a concern about elution of radioactive cesium, it is possible to apply a method of storing the mixture after immobilization and stabilization by mixing with zeolite, bentonite, other clay minerals, or the like.

The pulse power technology is a technology for generating, controlling and transmitting a large amount of power in a very short time. For example, after charging multiple capacitors connected in parallel, using a Marxbank pulse power generator that discharges these capacitors in series through a discharge gap, place concrete rubble on a wire mesh electrode submerged in a water tank. Then, it can be pulverized by generating an electric pulse from the tip of the rod electrode on it.

In the present invention, it is essential to heat concrete rubble contaminated with radioactive cesium as a pretreatment for pulse power crushing. The heating temperature is preferably 200 to 400 ° C. If the heating temperature is too low, even when reclaiming aggregates from concrete using the pulse power method, the crushing properties will differ depending on the strength of the aggregate and cement haste used in the rubble concrete, and the optimum processing conditions for aggregate recovery will be selected. Becomes difficult. When the heating temperature is low, the strength of the cement paste is high, and when the strength of the aggregate is low, the aggregate paste is crushed simultaneously with the pulverization of the cement paste by pulse power, and the aggregate recovery rate decreases. Reduce the quality of recovered aggregates. If the heating temperature is too high, the energy required for the decontamination treatment of the aggregate increases and the efficiency is deteriorated.

When the heating temperature is selected at 200 to 400 ° C., even when a wide range of concrete rubble is processed under a relatively low energy discharge condition, the recovery rate of the decontaminated aggregate is increased, and the contaminated portion is non-aggregate. Concentrated in part, volume reduction of pollutants can be achieved.

It was found that the effect of heating concrete rubble can be enhanced synergistically with pulse power crushing. The reason is not clear, but it seems that the heating action selectively weakens the cement paste part and greatly affects the separation properties of the aggregate and the cement paste.

Heating is dry, and an ordinary electric furnace, burner furnace, or the like can be used. A closed furnace capable of preventing dust from leaking to the outside or a furnace provided with a dust collector in the exhaust gas is preferable. No vapor scattering of the cesium compound due to heating was observed.

FIG. 1 shows a processing flow of the present application. The concrete rubble contaminated with radioactive cesium is heated to 200 to 400 ° C., and then classified by the mesh electrode while crushing the electric pulse on the mesh electrode, and the non-passed portion is used as a recycled aggregate. The slurry that has passed through the mesh electrode is treated with a sieve having a mesh smaller than that of the mesh electrode, and the non-passed portion is further made into recycled aggregate, and the passed slurry separates water and the discharge treatment residue. This is because radioactive cesium is concentrated in the discharge treatment residue.

FIG. 2 schematically shows the configuration of the pulse power crusher. The heated rubble 20 was placed on the mesh electrode 13 in the water tank 10 of the pulse power crusher 100 and crushed with an electric pulse applied by the high-voltage rod electrode 12 from the pulse power generator 11. The crushing is carried out in the water tank 10, and the mesh electrode 13 is used as a cathode as a ground 14, and selective crushing is possible by peeling and destroying the contaminated cement paste portion by discharge between the rod-like high voltage electrode 12. It is.

Since the pulse power crushing is performed on the mesh electrode, an object to be crushed which has become smaller than the mesh falls into the water in the water tank, and the mesh electrode itself becomes a classifier having the mesh opening as a classification point. For example, if the opening of the first mesh electrode is 5 mm, the classification point is 5 mm, and a coarse aggregate larger than 5 mm is obtained on the mesh electrode, and the crushing portion smaller than 5 mm passes through the first mesh electrode. And recovered as a slurry. The crushed material on the first mesh electrode is collected as a coarse aggregate that has been decontaminated.

The slurry containing the crushing part that has passed through the first mesh electrode is taken out and subjected to the second pulse power discharge with the second mesh electrode. Here, the second mesh electrode can be processed in place of the sieve. The slurry under the sieve is separated by specific gravity, screened or dried in water, separated as a discharge treatment residue, or subjected to pulse power discharge at the third mesh electrode. This is because radioactive cesium is concentrated in the discharge treatment residue.

The crushing part on the second mesh electrode is crushed by the electric pulse applied by the high voltage rod-shaped electrode from the pulse power generator in the water tank, and at the same time, the crushed material is classified by the second mesh electrode. For example, if the opening of the second mesh electrode is 2.5 mm, the top of the sieve is collected as a fine aggregate of 2.5 mm to 5 mm.

The slurry containing the crushed portion that has passed through the second mesh electrode is passed through a sieve, taken out, and subjected to a third pulse power discharge with the third mesh electrode. Here, the third mesh electrode can be replaced with the sieve for processing. The slurry under the sieve is separated by specific gravity, isolated in water or dried and sieved to isolate the discharge treatment residue, or is subjected to pulse power discharge at the third mesh electrode, and the specific gravity together with the classified passing slurry. The discharge treatment residue is isolated by separation, sieving in water or drying and sieving. This is because radioactive cesium is concentrated in the discharge treatment residue.

The opening of the third mesh electrode is set to be smaller than the second mesh electrode (for example, 1.2 mm). Thus, for example, the discharge treatment residue in the slurry of 1.2 mm or less is treated as sludge. When pulse power crushing using the third mesh electrode is performed, there is an advantage that a finer fine aggregate (fine aggregate) without contamination can be obtained. This is because radioactive cesium is concentrated in the discharge treatment residue.

When the third mesh electrode treatment is not performed, for example, the fine aggregate of the particle fraction of 1.2 mm to 2.5 mm is relatively increased, and the contamination is concentrated, for example, the particle fraction of 1.2 mm or less is reduced. be able to.

Since the slurry that has passed through the third mesh electrode or the slurry that has passed through the sieve replaced with the third mesh electrode becomes a discharge treatment residue sludge in which radioactive cesium is concentrated, it is dehydrated and treated as a contaminant.

The size of the mesh may be first net electrode> second net electrode> third net electrode, but the first net electrode is about 5 mm, and the second net electrode is 2.5 mm. The third mesh electrode is preferably about 1.2 mm. When the concrete rubble to be treated is large, or when the maximum particle size of the coarse aggregate used is large, or in the case of mass treatment with a large apparatus, the first mesh electrode is set to about 10 mm, for example. It is also effective to ensure strength (durability).

When the aggregate used in the concrete to be decontaminated is an aggregate having a relatively smooth surface such as river gravel, the aggregate and the cement paste are easily peeled off. High decontamination by pulse power can be obtained by heating at a relatively low temperature. In such a case, an optimal pretreatment heating temperature condition is confirmed in advance. In addition, if the sludge generated by the treatment with the first mesh electrode is separated by specific gravity, sieving in water or drying and sieving to recover the discharge treatment residue enriched in radioactive cesium, treatment with pulse power is possible. The decontamination can be completed only with the first treatment.

From concrete rubble contaminated with cesium, it can be recovered at a high recovery rate while decontaminating coarse and fine aggregates. In addition, without increasing the sludge portion, for example, it can be concentrated as a contaminant in a particle size fraction of 1.2 mm or less. There is no scattering due to the heating of cesium, the treatment of the pulse power method is underwater, there is a radiation shielding effect from cesium, and the radiation dose of cesium in the treated water is very small and easy to treat, so concrete rubble This is a safe disposal method. Compared to conventional pulse power crushing alone, the number of discharges was reduced, and aggregates meeting JASS 5N regulations could be recovered while decontaminating.

JASS 5N is the standard for construction and quality control in reinforced concrete construction of major buildings of nuclear power plants, following the format of “Building Construction Standard Specification / Explanation JASS5 Reinforced Concrete Construction”. It is a stricter standard than the quality of aggregate. Fig. 3 shows the JASS 5N specified range (allowable range of absolute dry density and water absorption) for recycled coarse aggregate and recycled fine aggregate.

[Embodiment]
Preparation of concrete rubble samples Concrete contaminated with radioactive cesium following the accident at the Fukushima Daiichi power plant was obtained by replacing the contaminated road gutter lid with a new gutter lid. The concrete cover is a JIS A 5345 road side cover, and the size is 500 × 412 × 95 mm. The collected concrete lid was cut into a 10 cm square and used for the test. The average radiation concentration was 233-758 Bq / kg.

The concrete lid of the side groove for cutting concrete was cut using a concrete cutter so that the contaminated surface was 10 × 10 cm. The radioactive cesium adhering to the concrete was fixed to the solid phase on the concrete surface, and it was confirmed that it did not elute into the water even after washing.

Evaluation of the contamination status of the concrete The distribution status (penetration status) of the radioactive cesium before treatment of the concrete used was measured by measuring the cross section of the cut concrete using beta-ray autoradiography using an imaging blade. confirmed. The distribution situation of radioactive cesium was implemented with respect to each of the concrete samples (three pieces) used for a test. The distribution state of radioactive cesium was measured by autoradiography using an imaging blade on a cross section of a concrete lid considered to have penetrated from the upper surface.

Pretreatment of the concrete rubble sample by pretreatment heating of the rubble sample was performed at 200 ° C., 300 ° C., and 400 ° C. in a closed-type atmospheric electric furnace.

Processing of concrete rubble samples and results The concrete crushing state by the pulse power method varies depending on the strength and deterioration of the concrete, and changes depending on the applied voltage, the number of shots of pulses, the mesh electrode openings and the processing sequence. The processing conditions of the pulse power method are as follows: the first mesh electrode, the second mesh electrode, and the third mesh electrode have a three-stage treatment of 5 mm, 2.5 mm, and 1.2 mm, respectively. Were sequentially pulsed with a fine mesh mesh electrode.

That is, it is placed on a 5 mm first mesh electrode, classified by the first mesh electrode while being crushed by an electric pulse applied by a high voltage rod-shaped electrode from a pulse power generator in a water tank, The slurry containing the crushing portion that has passed through the mesh electrode is subjected to water sieving on the 2.5 mm second mesh electrode, and then the water tank is placed on the second mesh electrode while the sieve on the second mesh electrode is placed on the second mesh electrode. In the above, the second mesh electrode was classified while being crushed with an electric pulse applied by a high voltage rod-shaped electrode from a pulse power generator, and the slurry containing the crushed portion that passed through the second mesh electrode was 1.2 mm. After water sieving with a third mesh electrode, the slurry was classified into a non-passing portion and a slurry that passed through the third mesh electrode while being crushed with an electric pulse applied by a high-voltage rod electrode from a pulse power generator.

FIG. 4 shows a conceptual diagram of a part of the processing flow of the present application including the above-described processing flow. The solid line arrow indicates the flow of the crushing part (solid), and the alternate long and short dash line arrow indicates the flow of the slurry. The broken line in FIG. 1 is water treatment.

The voltage applied by the pulse crushing method is 30 kV, the number of shots of the pulse is 170 times for the first mesh electrode condition of 5 mm, and 100 times for the second mesh electrode condition of 2.5 mm, and the third mesh of 1.2 mm. The electrode condition was 120 times.

The mass of the collected coarse aggregate of 5 mm or more, the fine aggregate of 2.5 mm to 5 mm and the fine aggregate of 1.2 mm to 2.5 mm was measured after drying for 24 hours with a dryer at 105 ° C. Each recovery rate was calculated. In the treatment of the third mesh electrode, the sample (slave under the sieve) that passed through the mesh was recovered, and the 1.2 mm sieve was dehydrated to recover the solid content.

In accordance with JIS A 1109 (fine aggregate density and water absorption rate test method) and JIS A 1110 (rough aggregate density and water absorption rate test method), recovered coarse aggregate of 5 mm or more, 2.5 mm to 5 mm The water absorption, surface dry density, and absolute dry density of the fine aggregate and the fine aggregate of 1.2 mm to 2.5 mm were measured, and the results are shown in Table 1.

When heated at 400 ° C, JASS 5N was satisfied, and the water absorption, surface dry density, and absolute dry density were all excellent as aggregates. In the case of non-heating conditions, fine aggregates that do not meet the requirements of JASS 5N can be obtained, suggesting that it is necessary to optimize pulse processing conditions in order to collect high-quality aggregates. doing. When the temperature is 400 ° C or higher, the cost for energy required for heating is required and the economic efficiency is lowered. It is necessary to adjust the optimum conditions.

Therefore, with the heating temperature fixed at 400 ° C., various data were obtained under the conditions shown in Tables 2 and 3 while adjusting the pulse power conditions to the conditions that allow actual operation for two samples as compared to the case of non-heating. I got it. The initial weight of the heated sample was 2079.6 g, the initial total radioactivity was 995.0 Bq, the initial weight of the unheated sample was 2157.1 g, and the initial total radioactivity was 1477.1 Bq.

The concentration of radioactive cesium contained in the solid content in the coarse aggregate, fine aggregate, fine aggregate and sludge recovered by the mesh electrode openings was quantified by wave height spectroscopic analysis using a germanium semiconductor detector.

Evaluation of decontamination performance In addition to the data of coarse aggregate, fine aggregate, and fine aggregate separated by the pulse power method, from the measurement results of dry mass and radioactive concentration of solids in sludge of 1.2 mm or less, The decontamination performance was evaluated from the recovery rate (wt%) of the entire solid content and the radioactive distribution (%). Table 4 is a sample heated at 400 ° C., and Table 5 is a non-heated sample.

When Table 2 to Table 5 are comprehensively evaluated, the sample heated at 400 ° C. has a relatively small number of discharges and is an energy-saving discharge treatment, but the aggregate performance can be sufficiently secured by the water absorption rate, etc. The aggregate recovery rate is high (heating: 51.6 wt%, non-heating: 44.5 wt%), and the radioactivity distribution in this aggregate part is reduced (heating: 8.5%, non-heating: 12. 0%). Although it is a partial aggregate part with a high yield, conversely, it can be seen that the radioactivity has a low distribution. Moreover, the recovery rate of 5 mm or more is high, and it can be confirmed that the cement paste can be separated without crushing the aggregate itself.

Concentration of radioactivity is also observed in the sludge portion of 1.2 mm or less by heating, and the distribution of radioactivity is increased especially in the particle size of 0.15 mm to 1.2 mm, and a volume reduction effect is observed. Heating at 400 ° C increases the recovery rate of aggregate parts with a particle size of 1.2 mm or more, while reducing the radiation distribution in this part and increasing the decontamination rate per unit energy used for pulsed radiation. .

It is the figure which showed the processing flow of this application. It is the figure which showed typically the structure of the pulse power crusher. It is the figure which showed JASS 5N regulation (absolute dry specific gravity and water absorption rate) of reproduction coarse aggregate and reproduction fine aggregate. It is the figure which illustrated a part of processing flow of the example of this application.

DESCRIPTION OF SYMBOLS 100 Pulse power crusher 10 Water tank 11 Pulse power generator 12 High voltage rod-shaped electrode 13 Net electrode 14 Ground 20 Contaminated concrete debris sample

Claims (3)

After heating concrete rubble contaminated with radioactive cesium to 200-400 ° C,
Placing on the mesh electrode and classifying with the mesh electrode while crushing with an electric pulse applied by a high voltage rod electrode from a pulse power generator in a water bath; and
A method for treating concrete rubble, characterized in that the slurry that has passed through the mesh electrode is treated with a sieve having an opening smaller than that of the mesh electrode, and the discharge treatment residue in the passed slurry is separated. After heating concrete rubble contaminated with radioactive cesium to 200-400 ° C,
Placing on the first mesh electrode and classifying with the first mesh electrode while crushing with an electric pulse applied by a high voltage rod electrode from a pulse power generator in a water bath; and
Classifying the crushing portion in the slurry that has passed through the first mesh electrode while crushing with an electric pulse applied by a high voltage rod-shaped electrode from a pulse power generator in a water tank in the second mesh electrode; A method for treating concrete rubble, characterized in that the slurry that has passed through the second mesh electrode is treated with a sieve having an opening smaller than that of the second mesh electrode, and the discharge treatment residue in the passed slurry is separated. . Classifying the crushing portion in the slurry that has passed through the second mesh electrode while crushing in the water tank with an electric pulse applied by the high voltage rod-shaped electrode from the pulse power generator in the third mesh electrode; 3. The method for treating concrete rubble according to claim 2, wherein a discharge treatment residue in the slurry that has passed through the third mesh electrode is separated.