JP6074255B2 - Radioactive waste processing apparatus and processing method - Google Patents

Description

  The present invention relates to a radioactive waste processing apparatus and a processing method.

Conventionally, a method for treating a radioactive waste containing a radioactive substance such as cesium has been proposed.
For example, in Patent Document 1, in a plasma melting treatment method for radioactive solid waste in which radioactive solid waste is melted by plasma heating, the radioactive solid waste is preheated at a temperature of 250 ° C. or higher and lower than the boiling point of cesium, and then A method for plasma melting treatment of radioactive solid waste characterized by performing plasma heating melting treatment is described. And it is described that such a treatment method can further contribute to the protection of radiation by preventing the environmental release of radioactive substances.

JP-A-10-26696

Since radioactive waste containing high concentrations of radioactive cesium needs to be shielded, it is important to reduce its capacity as much as possible.
However, in the conventional method, volume reduction of radioactive waste has been insufficient.

An object of the present invention is to solve the above-described problems.
That is, an object of the present invention is to provide a processing apparatus and a processing method capable of processing radioactive waste containing cesium and requiring shielded storage to obtain a more reduced radioactive waste.

The present inventor has intensively studied to solve the above-described problems and completed the present invention.
The present invention includes the following (1) to (6).
(1) A combustion section that combusts radioactive waste containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and discharges combustion bodies and exhaust gas;
Cooling the exhaust gas to a cooling temperature of 500 ° C. or less, and recovering cesium-containing dust from the exhaust gas;
The radioactive waste processing apparatus which collects the said combustion body as a decontamination processing waste.
(2) Furthermore, it has a high temperature dust collection part between the said combustion part and the said cooling part,
In the high-temperature dust collection unit, the exhaust gas discharged from the combustion unit is collected to discharge dust collection dust and post-dust collection gas,
In the cooling unit, the dust-collected gas is cooled to the cooling temperature as the exhaust gas, and cesium-containing dust is recovered from the dust-collected gas,
The radioactive waste processing apparatus according to (1), wherein the dust collection dust is recovered as the decontamination processing waste.
(3) In the above (1) or (2), the combustion unit burns the radioactive waste in the reducing atmosphere, and then burns the radioactive waste in an oxidizing atmosphere to discharge the combustion body and the exhaust gas. The radioactive waste processing apparatus as described.
(4) A combustion process in which radioactive waste containing cesium is burned in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and a combustion body and exhaust gas are discharged;
Cooling the exhaust gas to a cooling temperature of 500 ° C. or less, and recovering cesium-containing dust from the exhaust gas;
And a method for treating radioactive waste, wherein the combustion body is collected as decontamination waste.
(5) The exhaust gas discharged from the combustion process is dust-collected, and a high-temperature dust collection process for discharging dust collection dust and post-dust collection gas is further provided between the combustion process and the cooling process,
In the cooling step, the dust-collected gas is cooled to the cooling temperature as the exhaust gas, and cesium-containing dust is recovered from the dust-collected gas,
The radioactive waste processing method according to (4), wherein the dust collection dust is recovered as the decontamination processing waste.
(6) The above (4) or (4), wherein the combustion step is a step of burning the radioactive waste in the reducing atmosphere, and further combusting in an oxidizing atmosphere to discharge the combustion body and the exhaust gas. 5. A method for treating radioactive waste according to 5).

  ADVANTAGE OF THE INVENTION According to this invention, the processing apparatus and the processing method which can process the radioactive waste which contains cesium and needs shielding storage, and can obtain the radioactive waste further reduced in volume can be provided.

It is the schematic which shows the apparatus of this invention. It is the schematic which shows the preferable aspect of the apparatus of this invention. 1 is a schematic view of an apparatus used in Example 1. FIG. 2 is a schematic view of an apparatus used in Comparative Example 1. FIG.

The present invention will be described.
The present invention combusts radioactive waste containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and cools the exhaust gas to a cooling temperature of 500 ° C. or lower. And a cooling unit for recovering cesium-containing dust from the exhaust gas, wherein the combustor is recovered as decontamination waste.
Hereinafter, such a processing apparatus is also referred to as “the apparatus of the present invention”.

The present invention also includes a combustion process in which radioactive waste containing cesium is burned in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and a combustion body and exhaust gas are discharged; and the exhaust gas is cooled to a cooling temperature of 500 ° C. or lower. And a cooling step of recovering cesium-containing dust from the exhaust gas, and recovering the combustion body as a decontamination treatment waste.
Hereinafter, such a processing method is also referred to as a “processing method of the present invention”.

  The treatment method of the present invention is preferably carried out by the apparatus of the present invention.

  In the following description, “the present invention” means both “the apparatus of the present invention” and “the processing method of the present invention”.

<Radioactive waste>
The radioactive waste to which the present invention is applied includes soil and sewage sludge among wastes containing cesium. In addition, for example, silt and clay separated from soil correspond to radioactive waste. A mixture of soil and sewage sludge also corresponds to radioactive waste.
Since cesium tends to concentrate in silt and clay in the soil, it is preferable to classify the soil and treat only the resulting silt and clay as radioactive waste in the present invention.

  A radioactive waste should just contain cesium. The cesium content in the radioactive waste may be, for example, 3000 Bq / kg or more.

The radioactive waste preferably contains a combustible material. This is because the amount of energy used for heating the combustion device (fuel furnace, etc.) can be reduced in the combustion section. For example, since sewage sludge contains combustible material, it can be preferably used as radioactive waste. Here, the combustible means a component that contributes to combustion in the furnace, and specifically means carbon, hydrogen, nitrogen, sulfur, and oxygen as the main components in the dry solid.
In order to reduce the amount of energy, the combustible content in the radioactive waste is, for example, preferably 60% by mass or more, and more preferably 70% by mass or more.
For example, by adding a combustible material such as sewage sludge to the soil, a radioactive waste adjusted to a preferable range of combustible material content can be obtained.

The radioactive waste may contain moisture. When the amount of water is large (when the amount of water is approximately 80% by mass or more. Especially when the amount of water is high and the amount of flammable materials is small), the device of the present invention preferably has a drying section before the combustion section. Moreover, it is preferable that the processing method of this invention is equipped with a drying process before a combustion process.
When the radioactive waste is sewage sludge, it contains about 70 to 83% by mass of water. However, when reducing the amount of energy, some or all of the radioactive waste is dried in a drying section, etc. It is preferable to burn in the combustion section after making the amount 75% by mass or less. As the drying unit, for example, a conventionally known dryer can be used.
Hereinafter, the radioactive waste after drying in the drying section is also referred to as a dry body.

The present invention will be described with reference to FIG.
FIG. 1 is a schematic diagram of the apparatus of the present invention.
In FIG. 1, the apparatus (apparatus 10) of the present invention has a combustion section 14 and a cooling section 18.

<Combustion part, combustion process>
In the apparatus 10, the combustion unit 14 burns the radioactive waste 1 containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and discharges the combustion body 5 and the exhaust gas 7.
Moreover, when it has a drying part as mentioned above, the said drying body is burned in the reducing atmosphere adjusted to the said combustion temperature, and the combustion body 5 and the waste gas 7 are discharged | emitted.
The combustion body 5 is collected as the decontamination waste 11 (in FIG. 1, the combustion body 5 may be considered as the decontamination waste 11 itself).

In the combustion part 14, the apparatus which can combust in the reducing atmosphere which adjusted the said radioactive waste to the combustion temperature of 900 degreeC or more, and can discharge the combustion body 5 and the waste gas 7 can be used. For example, a conventionally known fluidized bed reduction furnace or rotary kiln can be used.
For example, when a rotary kiln is used as the combustion section, necessary radioactive gases such as fuel, air, steam, and nitrogen are fed into the furnace, and the radioactive waste is burned by adjusting the inside of the furnace to a reducing atmosphere of 900 ° C or higher. The combustion body 5 and the exhaust gas 7 can be discharged.

  The combustion temperature is 900 ° C. or higher, preferably 1000 ° C. or higher. This is because cesium can be efficiently separated from the radioactive waste. Moreover, it is preferable that combustion temperature is 1500 degrees C or less. With such a combustion temperature, the durability of the refractory in the furnace is preferable because it has a practical life.

The reducing atmosphere in the combustion section means an atmosphere that is incompletely combusted due to insufficient oxygen relative to carbon, hydrogen, or the like supplied to the combustion section.
In the combustion section, the air ratio in the reducing atmosphere is preferably less than 1.0. The air ratio is preferably 0.5 or more. With such an air ratio, an appropriate reducing atmosphere can be maintained.

The combustion body 5 discharged from such a combustion part means a solid part remaining after burning the radioactive waste as described above. Moreover, the part discharged | emitted as gas from a combustion part is called exhaust gas 7. FIG.
By treating with the combustion part 14, many parts of the cesium contained in this radioactive waste can be contained in the exhaust gas 7 and separated. Since the exhaust gas 7 is at a high temperature (approximately 900 ° C. or higher), it is considered that cesium is contained as a gas. Therefore, the concentration of cesium in the combustor 5 decreases. The cesium concentration of the combustor 5 is, for example, about 5,000 to 6000 Bq / kg because when the sewage sludge of about 10,000 Bq / kg is treated as radioactive waste, the radioactive concentration is about 50 to 60%. It may be. In this case, the combustor 5 need not be shielded.

  The combustion section burns the radioactive waste in a reducing atmosphere adjusted to the combustion temperature, but then preferably burns in an oxidizing atmosphere to discharge the combustion body and the exhaust gas. This is because a relatively safe exhaust gas can be discharged by completely burning the unburned portion and the unburned gas at the subsequent stage of the combustion section.

Here, the oxidizing atmosphere in the combustion section means an atmosphere that is in a state where oxygen is theoretically sufficient with respect to carbon, hydrogen, or the like supplied to the combustion section and is completely burned. It can also be said that the air ratio is 1.0 or more.
In the combustion section, the air ratio in the oxidizing atmosphere is preferably 1.2 or more. The air ratio is preferably 1.4 or less. This is because it is possible to efficiently achieve complete combustion of unburned gas and unburned gas.

As a case where the combustion part can further burn in an oxidizing atmosphere as described above, there is an aspect in which the combustion part is divided into a preceding reduction part and a subsequent oxidation part.
For example, when a fluid type reduction furnace is used as the combustion part, the inside of the reduction furnace can be used as the reduction part, the required amount of air can be supplied from the exhaust gas duct, and the inside of the exhaust gas duct can be used as the oxidation part. For example, when using a rotary kiln as a combustion part, the front | former stage in a furnace can be used as a reduction | restoration part, and a back | latter stage can also be adjusted to an oxidation part. Further, in the case of a rotary kiln, by dividing the furnace into three parts and adjusting the atmospheric temperature and the air ratio, the foremost stage can be a drying part, the next can be a reducing part, and the next can be an oxidizing part.

  The combustion unit may be composed of two devices, a reduction furnace and an oxidation furnace.

  The combustion process in the processing method of this invention can be performed using such a combustion part. A preferable combustion temperature or the like in the combustion process can be the same as that in the above-described combustion section.

<Cooling part, cooling process>
In the apparatus 10, the cooling unit 18 cools the exhaust gas 7 to a cooling temperature of 500 ° C. or less, and recovers the cesium-containing dust 15 from the exhaust gas 7.
As described above, since the exhaust gas 7 discharged from the combustion unit 14 is high temperature, cesium exists as a gas in the exhaust gas 7, but when the exhaust gas 7 is cooled to the cooling temperature by the cooling unit 18, The cesium changes to a solid and is recovered as cesium-containing dust 15 in the cooling unit 18 together with the fly ash contained in the exhaust gas 7.
The cesium-containing dust 15 is a very small amount with respect to the radioactive waste 1 processed in the combustion unit 14, and cesium is concentrated. Specifically, when the mass of the radioactive waste 1 processed in the combustion unit 14 is 100 parts by mass, the cesium-containing dust 15 can be about 1 part by mass. Moreover, when the mass of the cesium contained in the radioactive waste 1 processed in the combustion part 14 shall be 100 mass parts, the cesium contained in the cesium containing dust 15 can also be about 97 mass parts.

  Examples of the cooling unit 18 include a heat exchanger, a cooling tower, a bag filter, or an exhaust gas treatment tower. The cooling unit 18 preferably includes a heat exchanger, a cooling tower, a bag filter, and an exhaust gas treatment tower in this order. For example, by adjusting the temperature of the exhaust gas 7 to be about 250 ° C. immediately after passing through the heat exchanger and 150 to 200 ° C. immediately after passing through the cooling tower, cesium from the heat exchanger, cooling tower, and bag filter is adjusted. The contained dust 15 can be recovered.

  The cooling process in the processing method of the present invention can be performed using such a cooling unit. Preferable processing conditions and the like in the cooling step can be the same as those in the cooling unit.

Next, a preferred embodiment of the present invention will be described with reference to FIG.
A preferred mode (device 20) of the present invention shown in FIG. 2 is a mode having a high temperature dust collecting part 16 in addition to the mode of the device (device 10) of the present invention shown in FIG.

  As shown in FIG. 2, the apparatus of the present invention combusts radioactive waste containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and discharges a combustion body and exhaust gas. A high-temperature dust collecting unit that collects the exhaust gas discharged from the exhaust gas and discharges the collected dust and the post-dust collection gas; and the post-dust collection gas is cooled to a cooling temperature of 500 ° C. or less; And a cooling unit that collects cesium-containing dust from gas, and is preferably a radioactive waste treatment apparatus that collects the combustion body and the dust collection dust as decontamination treatment waste.

Further, the treatment method of the present invention combusts radioactive waste containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and discharges combustion bodies and exhaust gas, and is discharged from the combustion process. A high-temperature dust collecting step for collecting the exhaust gas and discharging the dust dust and the gas after dust collection, cooling the gas after dust collection to a cooling temperature of 500 ° C. or less, and containing cesium from the gas after dust collection. It is preferable that it is a radioactive waste processing method, comprising a cooling step of collecting dust, and collecting the combustion body and the dust collection dust as decontamination processing waste.
Such a preferred embodiment of the treatment method of the present invention is preferably carried out by the preferred embodiment (apparatus 20) of the present invention shown in FIG.

FIG. 2 shows a preferred embodiment of the apparatus of the present invention, but the same components as those shown in FIG. 1 are given the same reference numerals.
Below, the suitable aspect of the apparatus of this invention is demonstrated centering on a different point from the aspect shown in FIG.

<High temperature dust collection section, high temperature dust collection process>
In the apparatus 20 of the present invention, the high temperature dust collection unit 16 collects the exhaust gas 7 discharged from the combustion unit 14 and discharges the dust collection dust 6 and the post-dust collection gas 9.
The high-temperature dust collection unit 16 treats the exhaust gas 7 discharged from the combustion unit 14 at a high temperature (the temperature at which cesium is a gas. For example, more than 700 ° C. and 900 ° C. or less) to treat dust contained in the exhaust gas 7. A device capable of collecting dust can be used. For example, a ceramic dust collection filter, a high-temperature cyclone, or the like can be used.

  In the high-temperature dust collection unit 16, the exhaust gas 7 is collected at a high temperature (temperature at which cesium is a gas), so that cesium contained in the exhaust gas 7 is not collected in principle. Therefore, cesium is not substantially contained in the dust collection dust 6 collected in the high temperature dust collection unit 16.

  In the device of the present invention of the preferred embodiment shown in the device 20, the decontamination waste 11 containing the dust collection dust 6 and the combustion body 5 is recovered, but the concentration of cesium contained in this is low, for example, radioactive waste When sewage sludge of about 10,000 Bq / kg is treated as a product, the radioactive concentration is about 50 to 60%, so it may be 5,000 to 6000 Bq / kg. Accordingly, in this case, it is not necessary to shield and store the decontamination waste 11.

  When using a fluidized bed type reduction furnace and a rotary kiln as the combustion section in the apparatus of the present invention, the apparatus of the present invention preferably has a high temperature dust collecting section.

  Using such a high-temperature dust collection unit, the high-temperature dust collection step in the treatment method of the present invention can be performed. Preferred processing conditions and the like in the high temperature dust collection step can be the same as those in the case of the above high temperature dust collection unit.

<Example 1>
Sewage sludge (dehydrated cake) containing cesium is prepared, and this is processed by the apparatus (apparatus 60) of the present invention shown in FIG. The water content of sewage sludge is 70 to 83%. Here, the sewage sludge corresponds to the radioactive waste in the present invention.
In consideration of the reduction in the amount of energy, as shown in FIG. 3, first, the sewage sludge 41 is dried using a dryer 62. The temperature in the dryer 62 (drying temperature) is about 105 ° C. The moisture content of the sewage sludge after drying is about 20%, and it is mixed with undried sewage sludge to adjust the overall moisture content to 75% by mass or less to obtain a dry body 43 supplied to the combustion furnace 64. be able to. Here, the dryer 62 corresponds to the drying section in the present invention.

Next, the dry body 43 is processed using the combustion furnace 64. The inside of the combustion furnace 64 is adjusted to 1000 to 1500 ° C. Here, the combustion furnace 64 corresponds to the combustion section in the present invention.
In addition, the combustion furnace 64 is divided into a front-stage reducing section and a rear-stage oxidizing section. The front-stage section is a reducing atmosphere (air ratio = 0.5 to 1.0), and the rear-stage section is an oxidizing atmosphere (air ratio = 1. 2 to 1.3). Therefore, the combustion furnace 64 serves as a reduction furnace and an oxidation furnace.
The dry body 43 is reduced in the reduction section, passes through the oxidation section, and is then discharged from the combustion furnace 64 as the combustion body 45. Further, the exhaust gas 47 generated from the combustion furnace 64 is collected by a high temperature dust collector 66 while maintaining a high temperature (approximately 900 ° C. or higher). Here, a part of the combustion body 45 may be accompanied by the exhaust gas 47 and collected by the high temperature dust collector 66. And it is discharged | emitted from the high temperature dust collector 66 as the gas 53 after dust collection. Here, the high-temperature dust collector 66 corresponds to a high-temperature dust collection unit in the present invention.
The dust collection dust 49 and the combustion body 45 collected by the high temperature dust collector 66 are combined and collected as a decontamination treatment waste 51.

The dust-collected gas 53 passes through the heat exchanger 68, the cooling tower 70, the bag filter 72, and the exhaust gas treatment tower (scrubber) 74 in this order, and is diffused to the atmosphere. Here, the heat exchanger 68, the cooling tower 70, the bag filter 72, and the exhaust gas treatment tower 74 correspond to a cooling unit in the present invention.
The temperature of the dust-collected gas 53 is approximately 250 ° C. immediately after passing through the heat exchanger 68 and 150 to 200 ° C. immediately after passing through the cooling tower 70. In the heat exchanger 68, the cooling tower 70, and the bag filter 72, fly ash contained in the post-dust collection gas 53 is recovered as cesium-containing dust 55.

  In such an apparatus of the present invention (apparatus 60), when the sewage sludge 41 is treated, the mass ratio of the sewage sludge 41, the decontamination waste 51, and the cesium-containing dust 55 can be 100: 6: 1. Further, the mass ratio of cesium contained in each of the sewage sludge 41, the decontamination waste 51, and the cesium-containing dust 55 can be 100: 3: 97.

That is, when the sewage sludge 41 is processed by the apparatus (apparatus 60) of the present invention, 97% by mass of cesium contained in the sewage sludge 41 can be concentrated to the cesium-containing dust 55 reduced to 1% by mass.
Thus, the cesium-containing dust that has been reduced in volume to 1% by mass and further concentrated by 97% by mass of cesium may be shielded and stored. The decontamination treatment waste 51 corresponding to 6% by mass with respect to the sewage sludge 41 can reduce its cesium concentration from the radioactive waste, so it is necessary to shield and store it depending on the conditions of the waste to be treated. Can be eliminated.

<Comparative Example 1>
The same sewage sludge (dehydrated cake) as in Example 1 is prepared, and this is treated with the apparatus (apparatus 100) shown in FIG.
First, as in the case of Example 1, the sewage sludge 81 is dried using the dryer 102. The temperature in the dryer 102 (drying temperature) is about 105 ° C. The moisture content of the dried body 83 which is the sewage sludge after drying is about 15%.

Next, the dried body 83 is processed using the melting furnace 104. The inside of the melting furnace 104 is adjusted to about 1450 ° C. and the air ratio = 1.2. The dried body 83 is oxidized and melted in the melting furnace 104 and discharged as slag 85.
Further, the exhaust gas 87 generated from the melting furnace 104 passes through the heat exchanger 108, the cooling tower 110, the bag filter 112, and the exhaust gas treatment tower (scrubber) 114 in this order, and is diffused to the atmosphere. The temperature of the exhaust gas 87 is approximately 250 ° C. immediately after passing through the heat exchanger 108 and 150 to 200 ° C. immediately after passing through the cooling tower 110.
In the heat exchanger 108, the cooling tower 110, and the bag filter 112, fly ash contained in the exhaust gas 87 is recovered as cesium-containing dust 88.

  In such an apparatus (apparatus 100), when the sewage sludge 81 is processed, the mass ratio of the sewage sludge 81 and the slag 85 can be 100: 3. Moreover, the mass ratio of cesium contained in each of the sewage sludge 81 and the slag 85 can be 100: 15 or more.

  In other words, when the sewage sludge 81 is processed by the apparatus (apparatus 100), the slag 85 and the cesium-containing dust 88 have a radioactivity concentration that is five times or more that of the sewage sludge 81. There is.

DESCRIPTION OF SYMBOLS 1 Radioactive waste 5 Combustion body 6 Dust collection dust 9 Gas after dust collection 11 Decontamination processing waste 14 Combustion part 15, 55, 88 Cesium containing dust 16 High temperature dust collection part 18 Cooling part 41, 81 Sewage sludge 43, 83 Drying Body 45 Combustion body 47, 87 Exhaust gas 49 Dust collection dust 51 Decontamination processing waste 53 Dust collection exhaust gas 62, 102 Dryer 64 Combustion furnace 66 High temperature dust collector 60 Device (device of the present invention)
68, 108 Heat exchanger 70, 110 Cooling tower 72, 112 Bag filter 74, 114 Exhaust gas treatment tower 85 Slag 100 Device 104 Melting furnace

Claims (4)

Combusting a radioactive waste containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and discharging a combustion body and exhaust gas;
A high-temperature dust collection unit that collects the exhaust gas and discharges the dust and the gas after dust collection;
A cooling unit for the dust collecting the gas after cooling to a cooling temperature below 500 ℃, recovering cesium-containing dust from the dust collector after the gas,
The radioactive waste processing apparatus which collects the said combustion body and the said dust collection dust as a decontamination processing waste. 2. The radioactive waste treatment apparatus according to claim 1, wherein the combustion unit burns the radioactive waste in the reducing atmosphere, and further burns the radioactive waste in an oxidizing atmosphere to discharge the combustion body and the exhaust gas. . Combusting a radioactive waste containing cesium in a reducing atmosphere adjusted to a combustion temperature of 900 ° C. or higher, and discharging a combustion body and exhaust gas;
A high-temperature dust collecting step of collecting the exhaust gas and discharging the dust and the dust-collected gas;
Cooling the post-dust collection gas to a cooling temperature of 500 ° C. or less, and recovering cesium-containing dust from the post-dust collection gas ;
A method for treating radioactive waste, comprising: collecting the combustion body and the dust collection dust as decontamination waste. The radioactive waste according to claim 3, wherein the combustion step is a step of burning the radioactive waste in the reducing atmosphere, and further combusting in an oxidizing atmosphere to discharge the combustion body and the exhaust gas. Processing method.

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