JP2014066560A - Method for decontaminating biomass contaminated by radioactive substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for decontaminating biomass contaminated by a radioactive substance, which can achieve efficient separation of the radioactive substance from the biomass absorbed the radioactive substance, so that the biomass after the separation is used as resources.SOLUTION: A method for decontaminating biomass contaminated by a radioactive substance includes: a step of immersing the biomass contaminated by the radioactive substance in an alkaline solution; and a step of separating the biomass from the alkaline solution. The radioactive substance is desorbed in the alkaline solution after the separation of the biomass.

Description

  The present invention relates to a wood decontamination method for separating radioactive materials from biomass contaminated with radioactive materials such as radioactive cesium, for example, rubble wood.

  Radioactive materials that have diffused into the atmosphere fall to the surface of the ground due to rainfall, and have settled in various locations such as soil, asphalt, and the leaves of mountains. In particular, all timber such as rubble timber produced from wooden houses, timber houses and timber furniture that has been prevented from collapsing, will also be contaminated by radioactive materials.

  There are two possible methods for treating rubble wood, etc., to which radioactive substances are attached, such as incineration and extraction of radioactive substances.

  Incineration is a method of converting rubble wood into chips and disposing them in an incinerator (Patent Document 1). In this method, radioactive materials adhering to the wood are vaporized by incineration, so thorough treatment and management of exhaust gas is important. Moreover, since radioactive substances are concentrated in the incineration ash generated by incineration, explosion protection from the incineration ash and proper disposal are required. In addition, when there is combined contamination with radioisomeric substances and salt water, it is necessary to pay attention to the prevention of dioxins synthesized during incineration.

  The radioactive substance extraction process is a method of chemically extracting radioactive substances from rubble wood or the like. As an extraction method, there are a method using 6N cold hydrochloric acid, a method using 6N hot hydrochloric acid, 6N hot nitric acid and hot aqua regia (Non-patent Document 1). In this method, a radioactive substance is extracted (ionized) from rubble wood or the like with these strong acids, and the water-soluble radioactive substance is trapped by an adsorbent material such as zeolite. However, in the treatment with these strong acids, lignin and cellulose, which are wood components, are also subjected to acid hydrolysis, and water-soluble organic substances are dissolved to the solution side. For this reason, there exists a possibility that adsorption | suction to the zeolite etc. of a radioactive substance may be inhibited with these water-soluble organic substances. Furthermore, not only the acid component but also many organic substances are dissolved in the waste water after the extraction treatment, and the waste water treatment becomes very difficult. In addition, in research on extraction of radioactive substances from soil with these acids, the extraction efficiency is about 60% in one treatment, and several washings are required to further increase the efficiency.

  There is no clear previous study on the adsorption characteristics of radioactive materials on wood. However, in Non-Patent Document 1, cesium 137 was mixed with lignin (reagent), the main component of wood, and the adsorption characteristics were examined. As a result, water-soluble cesium 137 was 12.2%, substituted cesium 137 was 68.8%, fixed state It has been reported that cesium-137 is 31.2%, and most of it is adsorbed on solid lignin as well as soil. In summary, the adsorption characteristics of radioactive materials to timber such as rubble timber are considered to be firmly established in lignin and other wood components, and high extraction efficiency cannot be expected even with strong acids. It is done.

  Although it is not a decontamination technique for radioactive materials adsorbed on wood, for example, Non-Patent Document 2 discloses salt waste generated in dry reprocessing of metal fuel as a method for decontamination of halides containing radioactive elements. A method is disclosed in which the sucrose is passed through a zeolite column, the radionuclide in the salt waste is adsorbed onto the zeolite using ion exchange of the zeolite, and decontaminated. Furthermore, although not a decontamination technique for radioactive materials adsorbed on wood, Patent Documents 2 and 3 describe a method for treating radioactive waste of halides. Furthermore, although it is not a decontamination technique for radioactive materials adsorbed on wood, Patent Document 4 discloses that the same kind of acid as that generated when the neutral salt in the waste liquid is decomposed before the radionuclide is removed from the waste liquid. The acid is added to adjust the pH of the waste liquid, the radionuclide in the waste liquid is coprecipitated by adding a coprecipitation agent, the precipitate is removed from the waste liquid, the radionuclide is removed from the waste liquid, and the radionuclide in the waste liquid is removed. A method is disclosed in which a neutral salt of a waste liquid after being removed by ion exchange and radionuclide is decomposed into an acid and an alkali by electrodialysis.

JP 61-233399 A Japanese Patent Laid-Open No. 8-110397 Japanese Patent Laid-Open No. 10-213697 JP-A-8-271692

Tsumura, Komamura, Kobayashi, Soil and research on the behavior of radioactive strontium and cesium in soil-plant systems, Agricultural Research Report B, 36, 57-113 (1984) M. A. Lewis et al., J. Am. Ceram. Soc., 76 (11), p. 2826-2832 (1993)

  However, as described above, when a biomass such as rubble wood or rice straw adsorbs a radioactive substance, the radioactive substance can be separated more efficiently than the biomass, and the separated biomass can be used as a resource. The current method is not known. Therefore, in view of such circumstances, the present invention can efficiently separate the radioactive material from the biomass adsorbed with the radioactive material, and can use the separated biomass as a resource, and the biomass contaminated with the radioactive material. The purpose is to provide a decontamination method.

  As a result of intensive studies by the present inventors to achieve the above-mentioned object, it was found that the biomass surface can be detached together with the radioactive substance by immersing the biomass contaminated with the radioactive substance in an alkaline solution. The invention has been completed.

  The present invention includes the following.

(1) A radioactive material comprising a step of immersing biomass contaminated with a radioactive substance in an alkaline solution and a step of separating the biomass from the alkaline solution, wherein the radioactive substance is separated from the alkaline solution after the biomass separation. A decontamination method for biomass contaminated with substances.
(2) A step of separating the precipitated sludge from the alkaline solution after separating the biomass, a step of adding a flocculant to the solution containing the separated precipitated sludge to form the agglomerated sludge, and a step of dehydrating the obtained agglomerated sludge The decontamination method according to (1), further comprising:
(3) The decontamination method according to (1) or (2), wherein the aqueous solution obtained in the step of dehydrating the agglomerated sludge is added to the alkaline solution and / or the precipitated sludge.
(4) The decontamination method according to any one of (1) to (3), wherein the alkaline solution in which the biomass is immersed includes a surfactant.
(5) The method according to (2), further comprising the step of adsorbing the radioactive material contained in the aqueous solution to the porous material by bringing the liquid obtained in the step of dewatering the aggregated sludge into contact with the porous material. Dyeing method.
(6) The decontamination method according to any one of (1) to (5), wherein the biomass is at least one selected from the group consisting of rubble wood, wood, house waste, rice straw, and dead leaves .

  ADVANTAGE OF THE INVENTION According to this invention, the decontamination method of biomass which can isolate | separate a radioactive substance efficiently from the biomass which adsorb | sucked the radioactive substance can be provided. By applying the biomass decontamination method according to the present invention, biomass that has been unusable because it has been contaminated with radioactive substances can be used as a resource. Moreover, according to the biomass decontamination method of the present invention, the amount of radioactive waste containing separated radioactive substances can be greatly reduced.

It is a schematic diagram for demonstrating a state when the biomass which adsorb | sucked the radioactive substance is alkali-processed. It is a schematic block diagram of the processing system which implements the decontamination method concerning this invention. It is a characteristic view which shows the result of having measured the particle size distribution when carrying out the ball mill process of the cellulose. It is a characteristic view which shows the result of having measured the particle size distribution when carrying out the alkali process of a cellulose. It is a characteristic view which shows the result of having analyzed the component about the liquid collect | recovered after carrying out the alkali treatment of wood. It is the photograph which imaged the jockey which put the cut pruned branch. The left side is a photograph after the pruned branch is immersed in an alkaline solution, and the right side is a photograph after the pruned branch is immersed in tap water. The left side is a photograph after the sun-dried pruned branch immersed in an alkaline solution, and the right side is a photograph after the sun-dried pruned branch immersed in tap water.

  Hereinafter, a decontamination method for biomass contaminated with radioactive substances according to the present invention will be described in detail with reference to the drawings.

  In the present invention, the radioactive substance means a substance containing a radionuclide. The radioactive substance may be a substance composed of a single element or a mixture containing a plurality of elements or substances. Here, the radionuclide means a nuclide having radioactivity, and an element having a stable isotope is also called a radioisotope. Radionuclides include naturally occurring radionuclides that exist in nature (such as uranium 238, potassium 40 and radium 226) and artificially produced artificial radionuclides (cesium 134, cesium 137, iodine 131, xenon 133, strontium 89, strontium 90 and krypton 88). The artificial radionuclide is not limited to the specific radioisotope described above, but includes all radioisotopes that can be generated in nuclear reactors, nuclear fuel recycling, nuclear explosion experiments, and the like.

  The biomass contaminated with such a radioactive substance means a biomass that can be used as a resource for various uses before being contaminated with a radioactive substance. Here, the cause of contamination by radioactive materials is not limited in any way. Contamination by a small amount of radioactive materials released during normal operation of a nuclear reactor or nuclear fuel cycle, and release due to the transfer and storage of nuclear fuel and nuclear waste Pollution caused by a small amount of radioactive material, and contamination by radioactive material released due to an accident in a facility handling radioactive material such as a nuclear power plant.

  In the present invention, the biomass means a plant-derived resource. Examples of biomass include, but are not limited to, rice straw, wheat straw, rice husks, forest land remnants (thinned wood, damaged trees, etc.), resource crops, feed crops, starch crops, dead leaves, and the like. In particular, the biomass may include wood contained in rubble (hereinafter referred to as rubble wood), processed wood products such as furniture, and building materials made of wood. The biomass is not limited to those exemplified as long as it is derived from a plant and can be used as a resource. “Available as a resource” means, for example, that it can be used as a material for biofuel and can be used as another energy source.

  In particular, in the present invention, it is preferable to use woody biomass generated as a residual material such as a lumber mill, construction generated wood, and forest land residual material. The woody biomass is not limited to the above-mentioned generation sources, and for example, road obstruction trees, dam drift trees, pruned branches such as park trees, roadside trees, fruit trees, waste pallets, and the like may be used. When using woody biomass as a resource, for example, a method of generating power by combustion or gasification, or a method of using heat by burning chips or pellets can be mentioned. Woody biomass can also be used as a raw material in biomass fuel production using fermentation technology.

  In the decontamination method according to the present invention, a biomass contaminated with a radioactive substance is immersed in an alkaline solution to separate the radioactive substance from the biomass into the alkaline solution. When biomass contaminated with a radioactive substance is immersed in an alkaline solution, the surface of the biomass is destroyed and the surface is made fine as shown in FIG. As a result, the radioactive substance fixed on the biomass surface can be separated in an alkaline solution in a state where it is fixed on the fine particles derived from the biomass surface. Moreover, about the biomass after isolate | separating a radioactive substance, as shown in FIG. 1, it can utilize as a resource as mentioned above. Furthermore, as shown in FIG. 1, the fine particles on the biomass surface to which the radioactive substance is fixed can be separated and collected as a dehydrated cake by, for example, aggregating or dehydrating.

  In the decontamination method according to the present invention, the alkaline solution preferably contains a surfactant. By using an alkaline solution containing a surfactant, a more excellent decontamination effect can be achieved. Here, the surfactant is not particularly limited, but anionic (anionic) surfactant, nonionic (nonionic) surfactant, amphoteric surfactant and cationic (cationic) surfactant. An agent can be mentioned. Examples of anionic (anionic) surfactants include fatty acid surfactants such as sodium and potassium fatty acids, linear alkylbenzene surfactants such as sodium linear alkylbenzene sulfonate, alkyl sulfate sodium and alkyl ether sulfates. Mention may be made of higher alcohol surfactants such as sodium ester, alpha olefin surfactants such as sodium alpha olefin sulfonate, and normal paraffin surfactants such as sodium alkyl sulfonate. Nonionic (nonionic) surfactants include fatty acid surfactants such as sucrose fatty acid ester sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester and fatty acid alkanolamide, and higher alcohols such as polyoxyethylene alkyl ether. There may be mentioned system surfactants. Examples of zwitterionic surfactants include amino acid surfactants such as sodium alkylamino fatty acid, and amine oxide surfactants such as alkylamine oxide. Furthermore, examples of the cationic (cationic) surfactant include quaternary ammonium salt surfactants such as alkyltrimethylammonium salts and dialkyldimethylammonium salts. On the other hand, as an alkaline solution containing a surfactant, a commercially available alkaline detergent can be used. Although it does not specifically limit as a commercially available alkaline cleaning agent, For example, the brand name dynamic cleaner by MDI Corporation can be used.

  A processing system for carrying out the decontamination method according to the present invention is schematically shown in FIG. The treatment system shown in FIG. 2 includes an alkaline treatment tank 1 for immersing biomass by filling an alkaline solution, a coagulation sedimentation tank 2 for coagulating the sludge extracted from the alkaline treatment tank 1, and a coagulation sedimentation And a press machine 3 for performing dehydration treatment on the coagulated sludge formed in the tank 2.

  The alkali treatment tank 1 includes a stirring blade 4 for stirring the alkaline solution filled therein, a motor 5 for rotating the stirring blade 4, and a pump device 6 for extracting sludge precipitated inside. The agglomeration sedimentation tank 2 includes an agitation blade 7 for agitating the precipitate introduced therein together with the solution, a motor 8 for rotating the agitation blade 7, and a pump device 9 for extracting the agglomeration sludge condensed inside. With.

  Specifically, in the decontamination method according to the present invention, first, biomass such as rubble wood or the like is charged into an alkaline treatment tank 1 filled with an alkaline solution by a heavy machine. The alkaline solution preferably has a concentration that can destroy the biomass surface to make fine particles. The alkaline solution is, for example, 1 to 20% by weight sodium hydroxide solution, desirably 3 to 15% by weight sodium hydroxide solution. By maintaining this state for, for example, 1 to 2 days, the alkaline solution permeates the biomass surface such as rubble wood, and the biomass surface is plasticized and micronized. Since the radioactive substance contaminating the biomass is fixed to the finely divided biomass component, it is separated from the biomass. In addition, although it is not necessary to heat the aqueous alkali solution in the alkali treatment tank 1, it may be heated.

  At this time, the contact between the input biomass and the alkaline solution can be promoted by stirring the alkaline solution using the motor 5 and the stirring blade 4. Moreover, the flow of the stirred alkaline solution can make it easy to peel off the micronized biomass component.

  By the treatment in the alkali treatment tank 1 as described above, the finely divided biomass component containing the radioactive substance can be separated from the biomass. The micronized biomass component containing the radioactive substance is precipitated at the bottom of the alkali treatment tank 1. On the other hand, the biomass after separating the radioactive substance adhering to the surface is recovered from the alkali treatment tank 1 and dried by sun drying or a dryer. At this time, since the alkaline solution or moisture does not penetrate into the biomass such as rubble wood, it can be dried in a relatively fast time. Thereafter, the biomass can be effectively used as a biomass resource, such as making chips into an appropriate size, using a flooring material, and using fuel.

  Moreover, the radioactive substance density | concentration can be measured with respect to the biomass collect | recovered from the alkali treatment tank 1 with a conventionally well-known apparatus and method. For example, the concentration of cesium 137 can be calculated by gamma ray spectrum analysis using a germanium semiconductor detector. Thereby, safety | security can be ensured by measuring the radiation dose of the biomass after a process, and using only the biomass which is a radiation dose below various regulation values as a resource.

  On the other hand, the sludge precipitated at the bottom of the alkali treatment tank 1 is extracted by the pump device 6 and transferred to the coagulation sedimentation tank 2. At this time, the alkali treatment tank 1 and the coagulation sedimentation tank 2 can be connected by piping via the pump device 6 to reduce the influence of radiation during the transfer of sludge. In the coagulation sedimentation tank 2, water necessary for the sludge is added and adjusted to a pH suitable for coagulation with an acid as appropriate. Next, a coagulant is added to the coagulation sedimentation tank 2. As the flocculant, any substance used as a flocculant for sludge may be used. Examples of the flocculant include polyaluminum chloride (PAC), a polymer flocculant, a combination of PAC and a polymer flocculant, or a crosslinked polyglutamic acid. In particular, a polyglutamic acid cross-linked product is the most desirable flocculant because the applicable pH ranges from 4 to 12 in a wide range.

  Next, the coagulated sludge precipitated and separated in the coagulation sedimentation tank 2 is pulled out by the pump device 9 and transferred to the press machine 3. At this time, the coagulation sedimentation tank 2 and the press machine 3 can be connected by piping through the pump device 9 to reduce the influence of radiation during the transfer of sludge. In addition, as the press machine 3, you may use what kind of apparatus is used for the dehydration of sludge. As the press machine 3, for example, a filter press apparatus can be used.

  In the press machine 3, moisture contained in the coagulated sludge is removed, and the coagulated sludge is used as a dehydrated cake. The dehydrated cake contains radioactive substances and should be disposed of under proper management. Disposal of dehydrated cake includes incineration and storage in a state that prevents leakage of radiation.

  The liquid dehydrated and separated by the press machine 3 can be reused as water for the next alkali treatment or coagulation sedimentation treatment. However, when a radioactive substance is contained in the liquid dehydrated and separated by the press machine 3, the radioactive substance can be removed from the liquid by contacting with a porous material such as zeolite. Thus, when a radioactive substance is contained in a liquid component, after removing the said radioactive substance, it is preferable to recycle as water for alkali treatment or coagulation sedimentation treatment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the technical scope of this invention is not limited to a following example.

[Example 1]
In this example, commercially available cellulose was subjected to ball mill treatment and alkali treatment, and it was verified how the particle size of cellulose was changed by each treatment. In the present example, as a commercially available cellulose, trade name: cellulose manufactured by Aldrich was used.
In the ball mill treatment, commercially available cellulose was ground for 1 minute and 3 minutes. For the ball mill treatment, a device name: desktop ball mill manufactured by Seiwa Giken Co., Ltd. was used. In the alkali treatment, a 3% by weight aqueous sodium hydroxide solution was added so that a commercially available cellulose had a slurry concentration of 5%, and stirred for 24 hours.

  After collecting and drying commercially available cellulose after ball milling and alkali treatment, a predetermined amount is put into an ethanol solution, dispersed for 10 minutes with an ultrasonic cleaning device, and then with a microtrac particle size analyzer (SRA method; manufactured by Nikkiso Co., Ltd.). The particle size distribution was determined.

  The particle size distribution of the commercially available cellulose after the ball mill treatment is shown in FIG. 3, and the particle size distribution of the commercially available cellulose after the alkali treatment is shown in FIG. 3 and 4 show the particle size distribution of commercially available cellulose before each treatment.

  As can be seen from FIG. 3, as the ball mill treatment time increased, a tendency to shift toward a smaller particle size as a whole was observed, but the ball mill treatment did not significantly change the cellulose particle size. On the other hand, it was found that the commercially available cellulose subjected to the alkali treatment clearly increased in the number of particles having a small particle size compared with that before the treatment. In particular, in the alkali treatment, many fine particles of 10 μm or less were confirmed. The median particle size (D50) was determined to be 23.0 μm before the treatment, 21.4 μm for the ball mill for 1 minute, 21.5 μm for the ball mill for 3 minutes, and 17.4 μm for the alkali treatment. As a result, it was found that the alkali treatment has an effect of making cellulose fine particles by hydrolysis of the cellulose surface.

[Example 2]
In the present Example, it verified about how the surface of the cellulose changed about the alkali treatment which had the effect of making the cellulose fine particles in Example 1. In this example, a commercially available cedar material was used as the wood.

  In this example, first, wood was immersed in a 3% by weight aqueous sodium hydroxide solution for 24 hours. Thereafter, the liquid was collected and filtered through a 0.45 μm membrane filter. Using the obtained filtrate, the eluted components were analyzed by liquid chromatography (manufactured by Waters, apparatus name: Alliance system). The chromatogram obtained as an analysis result is shown in FIG. As can be seen from FIG. 5, several peaks were detected in the eluted components, but vanillin and vanillic acid could be identified in particular. These components constitute lignin of wood, and this experiment suggested that the lignin of wood was destroyed by alkali treatment.

Example 3
From Examples 1 and 2, it was suggested that the surface of the woody biomass can be destroyed by alkali treatment of the woody biomass and the surface of the biomass can be made into fine particles. From this result, it was verified whether the biomass contaminated with radioactive material can be decontaminated efficiently in such a way that the biomass can be used effectively by alkali treatment.

  Specifically, pruned branches cut from the S city mountain forest were used. Among the pruned branches, those having a diameter of 1 to 1.5 cm were selected and cut to a length of 20 cm. As shown in FIG. 6, 275 g each of the pruned branches cut into two 5 L plastic jockeys was put. One jockey was mixed with 4 L of tap water, and the other jockey was mixed with 4 L of NaOH aqueous solution (55 g-NaOH / L) (set to 20% NaOH addition per pruned branch weight).

  As a result of standing at room temperature for 18 hours, a sample immersed in an aqueous NaOH solution (hereinafter referred to as alkali immersion) was discolored to black as shown in FIG. 7 (left: alkali immersion, right: water immersion). This is presumably because the pruned branch surface resin portion was eroded by alkali, and in particular, the alkali-soluble lignin was dissolved.

  The pruned branch was taken out from each jockey to another jockey, and 4 L of tap water was added and washed with a stirrer at a speed of 30 rpm for 5 minutes. Thereafter, the pruned branches washed with water were taken out and dried in the sun.

  FIG. 8 shows a pruned branch after drying in the sun. As shown on the left of FIG. 8, the pruned branches immersed in alkali had a bark surface changed to black. On the other hand, as shown on the right side of FIG.

  Next, each sun-dried pruned branch was processed into chips of about 5 mm with pruning scissors, and the radiation dose and moisture content were measured. The radiation dose was measured with a germanium semiconductor measuring device (manufactured by ORTEC, device name; food / environmental radioactivity measuring device SEG-EMS (germanium semiconductor detector GEM20P4-70)).

  The measurement results are shown in Table 1.

  As shown in Table 1, the radiation dose of the test pruned branch was 2,300 Bq / kg for Cs-134 and 3,600 Bq / kg for Cs-137. On the other hand, both the pruned branches immersed in water and alkali decreased the dose. In particular, the dose of pruned branches immersed in alkali was 510 Bq / kg for Cs-134 and 890 Bq / kg for Cs-137.

  In order to evaluate the reduction effect, the dose on a dry weight basis was calculated. The results are shown in Table 2.

  As shown in Table 2, the dose per dry weight of the pruned branch immersed in water and the pruned branch immersed in alkali decreased by 28% and 65% of the dose in the test pruned branch, respectively. From this result, it became clear that an extremely excellent decontamination effect can be achieved by immersing biomass contaminated with radioactive substances in an alkaline solution.

Example 4
In this example, a technique for further improving the decontamination effect was examined.

  First, weeds cut from S city forest were used. This was cut to about 5 cm with scissors. The moisture content of the cut weeds was 81.4%.

  50 g of weeds were put in three 1 L glass beakers, and 800 mL of each cleaning solution shown in Table 3 was mixed. No. 1 is tap water, and No. 2 is a NaOH aqueous solution adjusted to 1.5 g / L with tap water. No. 3 is a dynamic cleaner manufactured by MDI Corporation, which was diluted four times with tap water. The dynamic cleaner is a pH 12 detergent mainly composed of ethylene glycol monobutyl ether.

  Each beaker was set in a jar tester and stirring was continued at room temperature for 18 hours. After the completion, the contents of each beaker were passed through a stainless steel sieve having a 2 mm opening, and a 2 mm over portion was collected. Thereafter, the 2 mm over portion recovered on the sieve was washed with tap water, and used as a sample for analysis when the water was sufficiently removed.

  The moisture content and radiation dose of the obtained analytical sample were measured. In addition, the radiation dose was measured with the germanium semiconductor measuring device (the same apparatus as Example 3). Table 4 shows the measurement results. In the items Cs-134, Cs-137 and the reduction rate, the numerical values in parentheses are values based on dry weight.

  As shown in Table 4, in the test weed, 134 Bq / kg of Cs-134 and 380 Bq / kg of Cs-137 were detected per wet weight. In terms of dry weight, this is 1,183 Bq / kg for Cs-134 and 2,043 Bq / kg for Cs-137. On the other hand, in No. 1 washed with water, Cs-134 per wet weight was 56 Bq / kg, and Cs-137 was 100 Bq / kg. In No. 2 washed with NaOH aqueous solution, it was confirmed that Cs-134 per wet weight was significantly reduced to 19 Bq / kg and Cs-137 to 13 Bq / kg. Furthermore, in No.3 using the dynamic cleaner, which is an alkaline cleaner with a surface-active effect, both Cs-134 and Cs-137 are further reduced, and the lower limit of detection is less than 16 Bq / kg in terms of wet weight. It became. The result is a very high reduction rate of over 95% on a wet basis and over 89% on a dry basis.

  The cleaning fluid dynamic cleaner used in No. 3 is a cleaning agent that imparts surface activity to alkali. As described above, it was found that the decontamination effect more than the alkali cleaning can be exhibited by imparting the surface activity to the alkali.

DESCRIPTION OF SYMBOLS 1 ... Alkali processing tank, 2 ... Coagulation sedimentation tank, 3 ... Press machine, 4 ... Rotary blade, 5 ... Motor, 6 ... Pump apparatus, 7 ... Rotary blade, 8 ... Motor, 9 ... Pump apparatus

Claims (4)

  Contaminated with radioactive material, characterized in that it comprises a step of immersing biomass contaminated with radioactive material in an alkaline solution and a step of separating biomass from the alkaline solution, and the radioactive material is separated from the alkaline solution after biomass separation. Of decontaminated biomass.   A step of separating the precipitated sludge from the alkaline solution after the biomass separation, a step of adding a flocculant to the solution containing the separated precipitated sludge to form the agglomerated sludge, and a step of dehydrating the obtained agglomerated sludge. The decontamination method of Claim 1 containing.   The decontamination method according to claim 1 or 2, wherein the aqueous solution obtained in the step of dewatering the agglomerated sludge is added to the alkaline solution and / or the precipitated sludge.   The decontamination method according to any one of claims 1 to 3, wherein the alkaline solution in which the biomass is immersed contains a surfactant.

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