JP6009849B2 - Decontamination equipment and decontamination method for wood contaminated with radioactive substances - Google Patents

Description

  The present invention relates to a technical field of a decontamination apparatus and a decontamination method for wood contaminated with a radioactive substance such as radioactive cesium.

In general, it is considered that radioactive materials diffuse into the atmosphere due to damage to nuclear reactors installed at nuclear power plants and the like. As radioactive materials diffused in this way, iodine 131, cesium 134, cesium 137, Representative examples include rhodium 106, cobalt 60, strontium 90, radium 226, uranium 234, uranium 235, uranium 238, and plutonium 239. Among such radioactive substances, cesium 134, cesium 137, and strontium 90, which are generated in large quantities, have a long half-life of about 30 years, which is a problem. Since the boiling points of these radioactive substances are 671 ° C. for cesium and 1382 ° C. for strontium, and the boiling point of cesium is low, it is considered that radioactive cesium diffuses in the air in a wide range.
The diffused radioactive material adheres to wood such as standing trees and timber, and when the attached wood is used as it is as a building material for a building, not only the building itself is contaminated but also the attached radioactive material is washed away by rainwater into the river. The environmental water contaminated with radioactive material will flow into the sea area and the contamination will spread further. It is necessary to prevent exposure.
As a technique for removing such radioactive substances, it has been proposed to decontaminate by a decontamination method suitable for each material after separation for each material such as metal, ceramics, and rubber products (for example, Patent Document 1). .

Japanese Patent Laid-Open No. 2001-21687

  However, since the thing of the said patent document 1 is targeting the pollutant which generate | occur | produced in the nuclear facility, the pollutant is preset to the thing preferable for decontamination in the said facility, and it accompanies damage of a nuclear reactor. If wood that normally exists around the reactor and around the pollutant diffusion area from the reactor is contaminated with radioactive materials, the contaminated water used for decontamination will contain contaminated solids if the contaminated wood is decontaminated. Substances (solid pieces attached to wood pieces and wood) are mixed, and it is necessary to remove them effectively. However, there is no specific method for removing them. There is a problem to be solved by the invention.

The present invention was created in order to solve these problems in view of the above circumstances, and the invention of claim 1 is a decontamination method for decontaminating wood whose surface is contaminated with radioactive substances. The decontamination apparatus includes a cleaning apparatus for decontaminating radioactive material adhering to the surface of the wood using cleaning water to the wood whose surface is contaminated with the radioactive substance, and the contamination used for the decontamination. Separation device for separating contaminated solid material from water, contaminated water storage tank for storing contaminated water mixed with fine contaminated solid material that has passed through the separation device, and the stored contaminated water is made of an inorganic metal salt A contaminated water treatment tank that stirs the mixture added with the flocculant at high speed to mix water and the flocculant, and generates floc containing the finely contaminated solid substance and radioactive substance, The generated flock is supplied with pressurized water. , Said pressurized water applied a floc separation tank which is floated floc separated from the water by fine bubbles generated from adhering to the flock when supplied, dehydrated floc was withdrawn from the flock separation tank dewatering An apparatus for decontaminating wood contaminated with radioactive material, characterized in that the apparatus is configured to include the apparatus.
According to a second aspect of the present invention, there is provided a first return flow path for returning the separated water dehydrated in the dehydrator to the contaminated water storage tank, a circulation tank to which the separated water separated from the flock in the flock separation tank is supplied. A radiation dose measuring device for measuring the radiation dose of the separated water supplied to the circulation tank, and when the radiation dose of the separated water exceeds a reference value, the separated water is returned to the contaminated water storage tank, The radioactive material according to claim 1, further comprising a second reflux channel branched so as to circulate as cleaning water for the cleaning device when the reference value is below the reference value. Wood decontamination equipment.
According to a third aspect of the present invention, in the contaminated water treatment tank, flocs containing radioactive material are grown greatly by stirring rapidly after adding a flocculant to the contaminated water, and further gently stirring. It is configured to be able to take in soluble radioactive substance, solid substance or non-soluble radioactive substance suspended in water, and contaminated with radioactive substance according to claim 1 or 2 This is a wood decontamination device.
The invention according to claim 4 is the decontamination apparatus for wood contaminated with the radioactive substance according to any one of claims 1 to 3, wherein the radioactive substance is at least radioactive cesium.
Invention of Claim 5 is a decontamination apparatus of the wood contaminated with the radioactive substance in any one of Claims 1-4 with which zeolite is further mixed in the flocculant.
The invention of claim 6 is a decontamination method for decontaminating wood whose surface is contaminated with a radioactive substance, wherein the wood whose surface is contaminated with a radioactive substance is supplied to a cleaning device, and the wood is cleaned using cleaning water. A decontamination process for decontaminating radioactive substances adhering to the surface of the solid, a solid-liquid separation process for separating solid substances mixed in the contaminated water used for the decontamination with a separator, and a fine process that has passed through the separator After adding a flocculant made of an inorganic metal salt to a contaminated water storage tank in which contaminated water containing solid substances is stored, the mixture is stirred at high speed, and then slowly stirred to mix the fine solid substances and radioactive materials. A flock generating step for generating a floc containing a substance, the generated flock is supplied to a flock separation tank together with the pressurized water, and the fine bubbles generated when the pressurized water is supplied adhere to the flock to float. It is decontamination method of contaminated wood radioactive material, characterized in that the lock comprises a floc separation step of separating the water.
According to a seventh aspect of the present invention, the floc separated in the flock separation step is dehydrated and the dewatered separated water is returned from the first recirculation flow path to the contaminated water storage tank, and separated from the flock by the flock separation tank. The separated water is supplied to a circulation tank and the radiation dose of the separated water is measured using a radiation dose meter. If the radiation dose of the separated water exceeds a reference value, the separated water is returned to the second reflux. 7. The radioactive material according to claim 6, further comprising a reflux step of returning from the flow path to the contaminated water storage tank and returning to the cleaning device from the second return flow path as cleaning water when the flow rate is below the reference value. This is a decontamination method for wood contaminated with substances.

  By setting it as invention of Claims 1-7, a radioactive substance can be efficiently removed from the wood contaminated with the radioactive substance.

It is a flowchart figure of embodiment of this invention. It is a flowchart figure of embodiment of this invention.

In carrying out the present invention, radioactive materials that can be decontaminated include iodine 131, cesium 134, cesium 137, rhodium 106, cobalt 60, strontium 90, radium 226, uranium 234, uranium 235, uranium 238, and plutonium 239. Representative examples of decontamination in the present invention are not only those elements and compounds containing these elements that are insoluble (these insoluble substances are suspended as fine particles in contaminated water). Also included are those that are dissolved into ions.
As washing water for washing wood, not only water but also heated water (hot water) can be used, and a detergent may be mixed therein if necessary.
Further, as the aggregating agent to be used, aluminum sulfate, sodium carbonate, sodium hydrogen carbonate, calcium carbonate, aluminum carbonate, calcium oxide, polyaluminum chloride, ferrous sulfate, ferric sulfate, ferric chloride and the like are usually known. Examples of the inorganic flocculant, and generally known polymer flocculants such as anionic, nonionic, and cationic are exemplified, and one kind or two or more kinds are selected from these flocculants. The flocculant secures a high decontamination function by incorporating the contaminated solid substance contaminated by the radioactive substance and the insoluble radioactive substance suspended in water into the floc.
In addition to radioactive materials, flocculants are not only heavy metals such as arsenic, lead, cadmium and mercury, but also solid materials adhering to the surface of wood and rubble, but they are still mixed in decontaminated water. Since the fine solid substance to be agglomerated can also be aggregated, it can be used for contaminated water mixed with these heavy metals, which is preferable.
In this case, the flocculant may contain zeolite as an adsorbent. Then, the zeolite is agglomerated by the flocculant to be flocked, and separation and recovery are facilitated. The zeolite may be either natural zeolite or artificial (synthetic) zeolite. Natural zeolites are typified by mordenite and clinoptilolite, and artificial zeolites are typified by A, X, and Y types, and one or more of these are selected and used. can do. Zeolite has the function of adsorbing radioactive substances dissolved in contaminated water, and the adsorbed zeolite is taken in and removed from the floc, thus supporting a high decontamination function. It becomes.
After adding the flocculant to the contaminated water, it is possible to grow flocs containing radioactive material by rapidly stirring to promote mixing and then gently stirring to grow these flocs. In the process, a soluble radioactive substance dissolved in water and a solid substance or an insoluble radioactive substance suspended in water can be efficiently taken into the floc.

  Next, for the apparatus according to the present invention, an apparatus for industrially removing radioactive substances was developed, not at the laboratory stage. Then, when removing radioactive materials using this device, preliminary experiments were conducted to confirm whether non-radioactive cesium could be removed by a flocculant, and after the accident at Fukushima Daiichi NPS, Attempts were made to remove radioactive cesium contained in contaminated water collected from an elementary school pool, and it was confirmed that it could be removed with high efficiency.

<Preliminary Experiment Example 1>
When the ion concentration was measured for an aqueous solution having a non-radioactive cesium ion concentration of 1.0 mg / L, the aqueous solution had a non-radioactive cesium ion concentration of 1.0358 mg / L. To this aqueous solution, 1.0 g of natural zeolite produced in Shimane Prefecture and 1.0 g each of calcium carbonate and aluminum sulfate as flocculants were added, shaken for 24 hours, then centrifuged and filtered to adjust the concentration of cesium ions in the water. When measured, it was 0.0011 mg / L and the removal rate was 99.89%. For comparison, 1.0 g of zeolite alone was added to the prepared aqueous solution, and after the same treatment, the concentration of cesium ions in the water was measured. As a result, the non-radioactive cesium ion concentration was 0.0038 mg / L. The rate was 99.63%. From this, it was confirmed that 2.7 μg / L of non-radioactive cesium was removed more when the zeolite and the flocculant were added than when only the zeolite was added.

<Preliminary Experiment Example 2>
When the ion concentration was measured for a 3.5% NaCl aqueous solution having a non-radioactive cesium ion concentration of 1.0 mg / L, the non-radioactive cesium ion concentration was 1.0530 mg / L. To this aqueous solution, 1.0 g of natural zeolite produced in Shimane Prefecture and 1.0 g of calcium carbonate and sodium hydrogen carbonate as flocculants were added and treated in the same manner as in Preliminary Experimental Example 1, and then the concentration of cesium ions in the water When measured, it was 0.2412 mg / L and the removal rate was 77.09%. For comparison, 1.0 g of zeolite was added in the same manner, and the non-radioactive cesium ion concentration was measured for the same treatment. As a result, it was 0.2543 mg / L and the removal rate was 75.85%. It was. From this, it was confirmed that 13.1 μg / L of cesium was removed more when the zeolite and the flocculant were added than when only the zeolite was added.

From these preliminary experiments, it was confirmed that the addition of the zeolite and the flocculant removed more cesium than the addition of zeolite alone. When this is converted into radioactive cesium, 1.0 becquerel can be regarded as 0.31 picog of radioactive cesium, and in the case of the preliminary experiment example 1, the added flocculant is about 8.7 million becquerel more than the zeolite. It was confirmed that radioactive cesium can be removed, and in the case of Preliminary Experimental Example 2, about 42 million becquerels can be removed.
In addition, when another preliminary experiment was repeated, it was preferable that the flocculant was a mixture of two or more kinds rather than one kind, and zeolite was further mixed with the flocculant rather than the case of only the flocculant as an additive. It was confirmed that the one can remove more cesium.

<Experimental example 1>
Radioactive cesium-contaminated water (36200 Bq / kg (breakdown: cesium 134 16900 Bq / kg, cesium 137 19300 Bq / kg)) 1.0 L collected in an elementary school pool in Fukushima Prefecture and aluminum carbonate as a flocculant Then, 1.0 g each of aluminum sulfate was added and stirred for 10 minutes, and then left for 5 minutes to generate flocs. After that, the flocs were separated by filtration, and the radiation amount of the separated liquid was analyzed. It was below the limit value (detection limit value: 10.0 Bq / kg).
<Experimental example 2>
Furthermore, 100 g of zeolite and 100 g each of aluminum sulfate, sodium hydrogen carbonate, and calcium carbonate as flocculants were mixed with radioactive cesium-contaminated water (250 Bq / kg) 1.0 m ³ and stirred for 1 minute, and then 24 hours. The floc was generated by allowing it to stand, and then the floc was separated by filtration, and when the radiation dose was measured for the separated liquid, it was below the detection limit (detection limit: 10.0 Bq / kg).

<Experimental example 3>
In addition, 300 g of aluminum carbonate as a flocculant was added to 1.0 m ^{3 of} radioactive cesium-contaminated water (250 Bq / kg) and stirred for 1 minute, and then allowed to stand for 24 hours to generate floc. Was separated by filtration, and the radiation dose was measured for the separated liquid, which was 88.4 Bq / kg.

  From these facts, it was confirmed that radioactive cesium can be efficiently removed from the contaminated water using the flocculant containing the zeolite. Therefore, since it is considered possible to remove radioactive cesium from contaminated water decontaminated by using the flocculant containing the zeolite, the following removal device was developed and actually Attempts were made to remove contaminated water contaminated with radioactive cesium.

Hereinafter, an apparatus according to an embodiment of the present invention will be described with reference to FIGS. In the figure, 1 is wood (raw wood or lumber), and the surface of the wood 1 is contaminated with radioactive cesium, and this wood is transported by a belt conveyor 2a and decontaminated by an automatic cleaning device 2 ( This corresponds to the “decontamination step” of the present invention). The automatic cleaning device 2 is for decontaminating radioactive cesium adhering to the surface of the wood 1 by spraying water or hot water (water or hot water may contain a detergent) at a high pressure, Radiocesium adhering to the wood 1 by the decontamination is 4.0 Bq / cm ² or less, which is an allowable limit defined in the Ionizing Radiation Hazard Prevention Regulations, and such decontaminated wood uses a truck or the like. Are carried out.

The water (contaminated water) used for decontamination in the automatic cleaning device 2 contains radioactive cesium and contaminated solid substances (solid substances attached to wood pieces and wood) 4, and from this contaminated water, radioactive cesium and It is necessary to remove the contaminated solid material 4. This contaminated water has a radioactivity concentration of about 100,000 to 500 Bq / kg. This contaminated water is passed through the separation device 3, whereby most of the contaminated solid material 4 (wood chips and the like having a size of approximately 1.00 mm or more) is separated and recovered (corresponding to the “solid-liquid separation step” of the present invention). .) The collected contaminated solid substance 4 is transported to a temporary storage place for radioactive substances and stored.
On the other hand, the contaminated water that has passed through the separation device 3 is not only contaminated water but also finer (approximately 1.00 mm or less) contaminated solid material (non-dissolvable suspended in water) than the collected contaminated solid material 4. Including radioactive materials). These are once stored in the contaminated water storage tank 5, and the stored contaminated water is supplied to the contaminated water treatment tank 6 by the pump 5a. The contaminated water treatment tank 6 is partitioned into first and second treatment tanks 6a and 6b, and the supplied contaminated water is first supplied to the first treatment tank 6a. Is provided with a high-speed stirrer 6c that stirs the coagulant quickly throughout the contaminated water and promotes mixing, and the coagulant supply device 7 supplies the coagulant. Yes. And this flocculating agent collects the radioactive cesium and the mixed fine contaminated solid substance as a floc to be described later.

  The addition amount of the flocculant is preferably 0.001% by weight or more and 0.3% by weight or less with respect to 100 parts by weight of the contaminated water, and the addition form of the flocculant may be addition as a solid, It may be added as an aqueous solution.

  Then, the contaminated water is stirred at a high speed in a state where the flocculant is added in the first treatment tank 6a, and the contaminated water and the flocculant are quickly mixed as a whole. After adsorbing the substance adsorbed zeolite together with the pollutant not dissolved in the contaminated water (contaminated solid substance, non-dissolvable radioactive material suspended in water) and aggregating, it overflows the partition wall 6e As a result, the low-speed stirrer 6e in the second treatment tank 6b performs a gentle agitation so that the floc F is largely formed without being destroyed. The generation of floc (aggregate) F in which the substance, the insoluble radioactive substance suspended in water and the radioactive substance dissolved in the contaminated water) are taken in is promoted ("Flock life" of the present invention It corresponds to the process ".). The contaminated water in which the generation of the floc F is promoted in this way is supplied to the floating separation tank (corresponding to the “floc separation tank” of the present invention) 9. Pressurized water pressurized in the pressurized water tank 8 is mixed. In the levitation separation tank 9, it is preferable that the fresh water is pressurized to 0.2 to 1 MPa by supplying pressurized water from the pressurized water tank 8. In the levitation separation tank 9, fine bubbles are generated when pressurized water is supplied from the pressurized water tank 8, and the bubbles adhere to the flock and the flock F floats to separate from the water (the present invention). This corresponds to the “floc separation step” in FIG. In addition, the flocks F that have emerged become an aggregate and become huge.

  The floated flock F is pulled out from the upper first discharge port 9a, stored in the sludge storage tank 10, and then dehydrated by the dehydrating device 11. The dehydrated solid content is transported to a temporary storage place for radioactive substances. And will be stored. The dewatered water here is configured to return to the contaminated water storage tank 5 through the first reflux channel R1.

On the other hand, the separated water separated from the floc F in the floating separation tank 9 is supplied to the stationary tank 12 from the second discharge port 9b, and then supplied to the filtration device 13 to be separated into solids and filtrate. Although filtered, there are, for example, sand, plastic, paper, diatomaceous earth, cloth, and the like, and one kind or two or more kinds are appropriately selected from these filter media. Then, the filtered separated product is transported to a temporary storage place for radioactive material and stored. On the other hand, the filtrate is supplied to the circulation tank 14, and necessary inspections such as radiation dose, turbidity, pH, and conductivity are measured in the circulation tank 14, and these measured values exceed the reference value (allowable value). When the water is returned to the contaminated water storage tank 5 through the second recirculation flow path R2 and below the reference value, it is recirculated through the second recirculation flow path R2 as washing water of the automatic cleaning device 2 and reused It is like that. The second reflux flow path R2 is equal to or less than the reference value with the first branch flow path R3 through which the filtrate flows back to the contaminated water storage tank 5 when the measured value of the filtrate exceeds the reference value. In this case, the filtrate is branched to the second branch flow path R4 for allowing the filtrate to flow back to the automatic cleaning device 2. In addition, the process of refluxing water to an appropriate place through each of the flow paths R1 to R4 corresponds to the “reflux process” of the present invention.
And when the removal process of contaminated water was tried several times using the apparatus of this Embodiment, the radiation dose is 20 Bq / kg or less also in any treated water, and the effect at the time of implementing this invention was confirmed. It was.

  The present invention can be used in the field of removing radioactive substances from radioactive substance-containing water containing radioactive substances such as radioactive cesium.

DESCRIPTION OF SYMBOLS 1 Wood 2 Automatic washing apparatus 3 Separation apparatus 4 Contaminated solid substance 5 Contaminated water storage tank 8 Pressurized water tank 9 Floating separation tank 11 Dehydration apparatus F Flock

Claims (7)

A decontamination device for decontaminating wood whose surface is contaminated with radioactive substances,
The decontamination device
A cleaning device that decontaminates radioactive materials attached to the surface of the wood using cleaning water to the wood whose surface is contaminated with radioactive materials,
A separation device for separating the contaminated solid material from the contaminated water used for the decontamination;
A contaminated water storage tank for storing contaminated water mixed with fine contaminated solid substances that have passed through the separator;
The stored contaminated water to which a flocculant composed of an inorganic metal salt is added is stirred at high speed to mix the water and the flocculant, and then gently agitated to mix the fine contaminated solid substance and the radioactive substance. A contaminated water treatment tank that produces floc containing
The generated flock is supplied together with pressurized water, and a fine bubble generated when the pressurized water is supplied adheres to the flock so that the flock floats and separates from the water,
A decontamination apparatus for wood contaminated with a radioactive material, comprising: a dehydrator for dehydrating a floc drawn from the flock separation tank. A first return flow path for returning water dehydrated in the dehydrator to the contaminated water storage tank;
A circulation tank to which separated water separated from the flock in the flock separation tank is supplied;
A radiation dose measuring device for measuring the radiation dose of separated water supplied to the circulation tank;
When the radiation amount of the separated water exceeds a reference value, the separated water is returned to the contaminated water storage tank, and when the amount is less than the reference value, the second water is branched to return as cleaning water for the cleaning device. The decontamination apparatus for wood contaminated with radioactive material according to claim 1, further comprising a reflux flow path.   In the contaminated water treatment tank, flocculant is added to the contaminated water, and then rapidly stirred, and further gently stirred to grow large flocs containing radioactive materials, and in the process, soluble radioactive materials in the flocs, 3. The decontamination apparatus for wood contaminated with radioactive substances according to claim 1 or 2, characterized in that it is capable of taking in solid substances and non-dissolvable radioactive substances suspended in water.   The decontamination apparatus for wood contaminated with a radioactive substance according to any one of claims 1 to 3, wherein the radioactive substance is at least radioactive cesium.   The decontamination apparatus for wood contaminated with radioactive substances according to any one of claims 1 to 4, wherein the flocculant is further mixed with zeolite. A decontamination method for decontaminating wood whose surface is contaminated with radioactive substances,
A decontamination process in which wood whose surface is contaminated with radioactive material is supplied to a cleaning device, and the radioactive material adhering to the surface of the wood is decontaminated using cleaning water;
A solid-liquid separation step of separating solid substances in the contaminated water used for the decontamination using a separation device;
After adding a flocculant made of an inorganic metal salt to a contaminated water storage tank in which contaminated water mixed with fine solid substances that have passed through the separation device is stored, the mixture is stirred at a high speed and then slowly stirred. And a flock generating step for generating a flock containing the fine solid substance and the radioactive substance,
The generated flock is supplied to the flock separation tank together with the pressurized water, and a flock separation step of separating the flock from the water by floating the flock by attaching fine bubbles generated when the pressurized water is supplied is provided. A method for decontamination of wood contaminated with radioactive material. While dewatering the floc separated in the floc separation step and returning the dehydrated water from the first reflux channel to the contaminated water storage tank,
The separated water separated from the floc in the floc separation tank is supplied to the circulation tank and the radiation dose of the separated water is measured using a radiation dose measuring device,
When the radiation amount of the separated water exceeds the reference value, the separated water is returned from the second reflux channel to the contaminated water storage tank, and when the amount is below the reference value, the second reflux stream is used as washing water. The decontamination method for wood contaminated with radioactive substances according to claim 6, further comprising a refluxing step of refluxing from the road to the washing device.

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