JP2018179896A - Radioactive cesium volatilization acceleration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a volatilization acceleration method of radioactive cesium stuck to an object to be processed so that volume reduction processing of the object to be processed is stably performed regardless of radioactive cesium concentration of the object to be processed.SOLUTION: A volatilization acceleration method of radioactive cesium stuck to a radioactive material contaminated waste charged into a shaft furnace type gasification melting furnace 11 by adding calcium chloride to the waste substance comprises: a step of obtaining a relationship between a chlorine amount added to the radioactive material contaminated waste charged into the shaft furnace type gasification melting furnace 11 and a radioactive cesium elution ratio of the radioactive cesium stuck to fly ash generated when performing melting processing of the waste substance in the shaft furnace type gasification melting furnace 11 eluted into water; a step of calculating the chlorine amount added to the radioactive material contaminated waste charged into the shaft furnace type gasification melting furnace 11 based on the relationship using the radioactive cesium elution ratio in the fly ash cleaning process; and a step of calculating addition amount of the calcium chloride based on the calculated chlorine amount.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of adding calcium chloride to radioactive substance contaminated waste charged in a shaft furnace type gasification melting furnace to promote volatilization of radioactive cesium attached to the waste.

  On March 11, 2011, a 9.0-quake subduction-zone earthquake with an epicenter off the coast of Sanriku in the Pacific Ocean (the Tohoku-Pacific Ocean earthquake) occurred. The massive earthquake and the subsequent massive tsunami triggered a large number of facilities damage at the nuclear power plant built on the Pacific coast of Fukushima Prefecture, and a large amount of radioactive material was released to the atmosphere. As a result, a large amount of radioactive material-contaminated waste such as rubble contaminated with radioactivity is generated.

According to the “Policy on Disposal of Disaster Waste in Fukushima Prefecture” published by the Ministry of the Environment, it is possible to safely incinerate disaster waste that may be contaminated with radioactive materials, It is said that safe landfill disposal is possible for main ash and fly ash generated with incineration. Specifically, main ash with a radioactive cesium concentration (total value of cesium 134 and cesium 137) less than 8,000 Bq / kg can be landfilled at a general waste final disposal site (managed final disposal site) In addition, it is considered appropriate to temporarily store primary ash with a radioactive cesium concentration of more than 8,000 Bq / kg and 100,000 Bq / kg or less, until the safety of disposal is confirmed by the country. ing. In addition, it is considered desirable to store main ash with a radioactive cesium concentration of over 100,000 Bq / kg in a facility where radiation can be appropriately shielded.
As for the fly ash, as with the main ash with a radioactive cesium concentration exceeding 8,000 Bq / kg, temporary storage is appropriate until the safety of the disposal is confirmed by the country, and the radioactive cesium concentration is It is considered desirable to store fly ash in excess of 100,000 Bq / kg in facilities where radiation can be properly shielded.

  As described above, it is important to secure a storage place in the treatment of radioactive material contaminated waste, but since the storage place is limited, it is necessary to reduce the volume of main ash and fly ash. For example, in Patent Document 1, a radioactive cesium separating and concentrating method and radioactive cesium separating and concentrating apparatus capable of effectively separating and concentrating radioactive cesium contained in a treated material such as soil or incineration ash and reducing the volume largely. Technology is disclosed. According to the technology described in Patent Document 1, radioactive cesium is volatilized and separated from molten slag by adding a chlorine-based auxiliary agent and a melting point depressant (basicity adjuster) to an object to be treated and melting it in a reducing atmosphere.

JP, 2013-242194, A

  However, in the technique described in Patent Document 1, in order to make the radiation dose remaining in slag and the radiation dose contained in fly ash fall below a predetermined level, a melting furnace is used based on the radiation dose contained in the object to be treated The input amount per unit time of the object to be input must be adjusted (see paragraph [0077] of Patent Document 1). That is, in the technique described in Patent Document 1, when the radioactive cesium concentration of the object to be treated is high, the input amount of the object to be treated must be reduced so that the radioactive cesium concentration of the slag falls below a predetermined level. It is difficult to stably perform the volume reduction process of the object.

  The present invention has been made in view of the above circumstances, and the volatilization of radioactive cesium adhering to the object to be treated is stable in order to stably perform the volume reduction treatment of the object regardless of the radioactive cesium concentration of the object to be treated Aims to provide a way to promote

In order to achieve the above object, according to a first aspect of the present invention, calcium chloride is added to radioactive substance contaminated waste charged in a shaft furnace type gasification and melting furnace to promote volatilization of radioactive cesium attached to the waste. And
The amount of chlorine added to radioactive material contaminated waste charged in the shaft furnace type gasification and melting furnace, and the radioactivity attached to fly ash generated when the waste is melted and processed in the shaft furnace type gasification and melting furnace Determining the relationship between the cesium release rate and the radioactive cesium elution rate into water;
Calculating the amount of chlorine to be added to the radioactive substance contaminated waste charged in the shaft furnace type gasification melting furnace by setting the radioactive cesium elution rate in the fly ash cleaning treatment from the relation;
And calculating the amount of added calcium chloride from the calculated amount of chlorine.

The second invention is a method of promoting the volatilization of radioactive cesium attached to the waste by adding calcium chloride to radioactive material contaminated waste charged in a shaft furnace type gasification and melting furnace,
The amount of chlorine added to radioactive material contaminated waste charged in the shaft furnace type gasification and melting furnace, and the radioactivity attached to fly ash generated when the waste is melted and processed in the shaft furnace type gasification and melting furnace Determining the relationship with the concentration of cesium;
The amount of increase in radioactive cesium concentration of fly ash to the incremental amount of chlorine added to radioactive material contaminated waste is determined from the above relationship, and the amount of decrease in radioactive cesium concentration of slag corresponding to the amount of increase in radioactive cesium concentration of fly ash A process to calculate
Estimating the radioactive cesium concentration of the slag after the melting process from the radioactive cesium concentration of the radioactive material contaminated waste charged into the shaft furnace type gasification and melting furnace;
The difference between the estimated value of the radioactive cesium concentration of the slag and the target value is divided by the reduced amount of the radioactive cesium concentration of the slag and added to the radioactive substance contaminated waste charged in the shaft furnace type gasification melting furnace Calculating the amount of chlorine;
And calculating the amount of added calcium chloride from the calculated amount of chlorine.

The present inventors are radioactive cesium of the amount of chlorine and fly ash to be added to radioactive material contaminated waste (hereinafter, may be simply referred to as "object to be treated") charged in a shaft furnace type gasification melting furnace. There was a positive correlation with the elution rate, and it was found that there is a proportional relationship between the amount of chlorine added to the object to be treated and the radioactive cesium concentration of fly ash.
In the present invention, the volatilization of radioactive cesium adhering to the object to be treated is promoted by melting the radioactive substance contaminated waste under the high temperature and reducing atmosphere of the shaft furnace type gasification and melting furnace. At that time, in the first invention, utilizing the positive correlation between the amount of chlorine added to the object to be treated and the radioactive cesium elution rate of fly ash, the desired radioactive cesium elution rate as fly ash washing treatment The amount of calcium chloride added to the object to be treated is adjusted so that In the second aspect of the invention, the proportionality between the amount of chlorine added to the object to be treated and the radioactive cesium concentration of fly ash is used, so that the radioactive cesium concentration of the slag becomes the target value. Adjust the amount of calcium chloride added to the treatment.

  In the radioactive cesium volatilization promotion method according to the first and second inventions, the fly ash is stored in a washing tank, and the fly ash is washed with washing water in the washing tank, and the washing of the fly ash. It is preferable to include the steps of: adding an adsorbent to the washing wastewater used in the step b) to recover radioactive cesium in the washing wastewater.

  In this configuration, radioactive cesium in the washing wastewater is adsorbed by the adsorbent and concentrated until the radioactive cesium concentration reaches several million Bq / kg to minimize the radioactive cesium-containing waste body. On the other hand, fly ash after cleaning can be excluded from designated waste (radioactive cesium concentration is over 8,000 Bq / kg).

  In the present invention, the volatilization of radioactive cesium adhering to the object to be treated is promoted by melting the radioactive substance contaminated waste under the high temperature and reducing atmosphere of the shaft furnace type gasification and melting furnace. At that time, the amount of calcium chloride to be added to the object to be treated is adjusted so that the radioactive cesium elution rate desired for the fly ash cleaning treatment can be obtained, or the radioactive cesium concentration of the slag becomes a target value. It is not necessary to reduce the input amount of the processing object regardless of the radioactive cesium concentration of the processing object, and the volume reduction processing can be stably performed.

It is a flow figure of the fusion processing equipment which enforces the radioactive cesium volatilization volatilization concerning the 1st and 2nd embodiment of the present invention. It is a flowchart of a fly ash washing process. It is the graph which showed the relationship between the amount of chlorine added to a processed material, and the radioactive cesium elution rate of fly ash. It is the graph which showed the relationship between the amount of chlorine added to a thing to be processed, and the radioactive cesium concentration of fly ash.

  Next, embodiments of the present invention will be described with reference to the attached drawings for understanding of the present invention.

  The melt processing equipment which implements the radioactive cesium volatilization volatilization which concerns on the 1st and 2nd embodiment of this invention is shown in FIG.

  The radioactive material contaminated wastes to be melt-processed are disaster wastes 10a and decontamination wastes 10b with radioactive cesium concentration of several hundred to 100,000 Bq / kg, and stored in sealed receiving yard 10 . The disaster waste 10 a is cut into a size of 80 cm or less before being carried into the receiving yard 10, and is charged into the shaft furnace type gasification melting furnace 11. The decontamination waste 10b is charged in the shaft furnace type gasification melting furnace 11 while being packed in the flexible container bag.

  Coke, limestone and calcium chloride are added to the shaft furnace type gasification and melting furnace 11 together with radioactive substance contaminated waste. The amount of coke added is 150 to 250 kg per ton of the waste charge, and the amount of limestone added is 150 to 400 kg per ton of the waste charge. The addition amount of calcium chloride will be described later.

  The radioactive substance contaminated waste is completely melted under the high temperature (melting zone temperature: 1700-1800 ° C.) and reducing atmosphere of the shaft furnace type gasification and melting furnace 11 and volatilization of radioactive cesium adhering to the waste Promoted.

  The molten material is discharged from the outlet 11a in a state in which the fluidity is sufficiently enhanced by the basicity adjusting action of limestone, and is introduced into the water crushing apparatus 19 through a weir. The water pulverizing apparatus 19 includes a casing 19a for storing cooling water for cooling and solidifying the melt discharged from the shaft furnace type gasification and melting furnace 11, and the melt discharged from the shaft furnace type gasification and melting furnace 11. It has a jet nozzle (not shown) for jetting water to finely disperse the melt, and a scraper type conveyor (not shown) installed in the casing 19a. The molten material finely dispersed by the jetted water is cooled and solidified in the casing 19a to become molten slag or the like, and is carried out of the casing 19a by a conveyor. The harmless molten slag and the like are stored in the flexible container bag 20 and then stored.

  Fly ash generated in the shaft furnace type gasification and melting furnace 11 is discharged from the discharge port 11 b together with the exhaust gas and introduced into the combustion chamber 12. In the combustion chamber 12, the combustible gas is completely burned at a high temperature of 850 ° C. or more. The high temperature fly ash and the exhaust gas discharged from the combustion chamber 12 are cooled by the gas cooling tower 13 and then further cooled by the temperature reducing tower 14.

The first dust collection unit 15 and the second dust collection unit 16 are provided in series in the rear stage of the temperature reducing tower 14. Activated carbon is injected into the first dust collector 15. In the first dust collector 15, the fly ash in the exhaust gas is adsorbed to the activated carbon and collected. Further, slaked lime is injected into the second dust collection unit 16. In the second dust collector 16, the exhaust gas is neutralized by slaked lime, and salts generated by the neutralization reaction are collected by the second dust collector 16.
The exhaust gas cleaned by the second dust collector 16 is emitted from the chimney 18 to the atmosphere by the induction fan 17.

The fly ash collected in the combustion chamber 12, the gas cooling tower 13, the temperature reducing tower 14, the first dust collection device 15, and the second dust collection device 16 is washed.
The radioactive cesium attached to the fly ash is soluble in water, and the fly ash is washed with water to dissolve the radioactive cesium in the water and separate the radioactive cesium from the fly ash.

The fly ash cleaning process will be described using the flow chart of FIG.
(1) Cleaning Step Fly ash is stored in the washing tank 21, and the fly ash is washed in the washing tank 21 with washing water.
(2) Dewatering Step The fly ash dissolved water is solid-liquid separated using the dehydrator 22 to separate it into the washing wastewater 24 (filtrate) in which the radioactive cesium is dissolved and the wash fly ash 23 (dehydrated cake). The washing fly ash obtained here is transported to the existing controlled disposal site because the radioactive cesium concentration is significantly reduced and the leaching ability is also reduced.

(3) Adsorption Step The separated washing wastewater 24 is subjected to adsorption treatment using the adsorption device 25. By the adsorption treatment, radioactive cesium in the washing wastewater 24 is adsorbed to the adsorbent and recovered, and the treated water 26 from which the radioactive cesium is removed is obtained. The radioactive cesium concentrate is stored in an intermediate storage facility, and the treated water 26 is subjected to the same post-treatment as leachate in the final disposal site.
Examples of the adsorbent include inorganic adsorbents such as zeolite, ion exchange resins that adsorb cations, or metal ferrocyanides such as cobalt ferrocyanide, copper ferrocyanide, or ferric ferrocyanide. Compounds etc. can be used.

Next, a method of determining the addition amount of calcium chloride to be added to the shaft furnace type gasification melting furnace 11 will be described.
[Method of promoting radioactive cesium volatilization according to the first embodiment]
(STEP-1) Amount of chlorine to be added to radioactive substance contaminated waste charged in shaft furnace type gasification and melting furnace 11 and fly generated when the waste is melted and processed in shaft furnace type gasification and melting furnace 11 Determine the relationship with the radioactive cesium elution rate at which the radioactive cesium attached to the ash is eluted into water.

The present inventors conducted a calcium chloride addition test using the above-described melt processing equipment.
The relationship between the amount of chlorine added to the object to be treated and the radioactive cesium elution rate of fly ash obtained by the calcium chloride addition test is shown in FIG. The radioactive cesium elution rate of fly ash was based on the elution test according to Ministry of the Environment notification No. 46.
The definition of the radioactive cesium elution rate of fly ash is as follows.
Radiocesium elution rate of fly ash [%] = Radiocesium elution amount of fly ash [Bq / L] × liquid-solid ratio [L / kg] / radiocesium concentration of fly ash [Bq / kg] × 100
The amount of radioactive cesium eluted was determined by γ-ray spectrometry using a Ge semiconductor detector. In addition, the liquid-solid ratio was 10 L / kg.

(STEP-2) As shown in FIG. 3, there is a positive correlation between the amount of chlorine added to the object to be treated and the radioactive cesium elution rate of fly ash. Therefore, the radioactive cesium elution rate in the fly ash cleaning process is set, and the amount of chlorine to be added to the radioactive substance contaminated waste charged in the shaft furnace type gasification and melting furnace 11 is calculated from the above relationship. For example, when the radioactive cesium elution rate in the fly ash cleaning process is 70% or more, the amount of chlorine added to the radioactive substance contaminated waste charged in the shaft furnace type gasification melting furnace 11 is 3 mass% or more according to FIG. Become.

(STEP-3) The addition amount of calcium chloride is calculated from the calculated chlorine amount.

[Method for promoting volatilization of radioactive cesium according to the second embodiment]
(STEP-1) Amount of chlorine to be added to radioactive substance contaminated waste charged in shaft furnace type gasification and melting furnace 11 and fly generated when the waste is melted and processed in shaft furnace type gasification and melting furnace 11 Determine the relationship with the concentration of radioactive cesium attached to the ash.

  The relationship between the amount of chlorine added to the object to be treated and the radioactive cesium concentration of fly ash obtained by the calcium chloride addition test is shown in FIG. Here, the radioactive cesium concentration of fly ash was determined by ICP mass spectrometry (ICP-MS).

(STEP-2) The amount of increase of the radioactive cesium concentration of fly ash with respect to the incremental amount of chlorine to be added to the object to be treated is determined from the above relationship.
As shown in FIG. 4, there is a direct proportional relationship between the amount of chlorine added to the object to be treated and the radioactive cesium concentration of fly ash. For example, the radioactive cesium concentration of fly ash increases by about 5,000 Bq / kg each time the addition amount of chlorine increases by 1% by mass.

(STEP-3) The reduction amount of the radioactive cesium concentration of the slag corresponding to the increase of the radioactive cesium concentration of fly ash is calculated.
The fact that the radioactive cesium concentration of fly ash increased means that the radioactive cesium concentration of slag decreased by the same amount. For example, when the generation ratio of slag to fly ash is 3: 1, the radioactive cesium concentration of the slag decreases by 5,000 Bq / kg to 3 = 1,667 Bq / kg when the addition amount of chlorine is increased by 1% by mass.

(STEP-4) From the radioactive cesium concentration of the radioactive substance contaminated waste charged in the shaft furnace type gasification and melting furnace 11, the radioactive cesium concentration of the slag after the melting process is estimated.
The radioactive cesium concentrations of slag and fly ash are calculated by the following equation.
Radioactive cesium concentration of slag = Radioactive cesium concentration of material to be processed x Transfer rate to slag-Slag generation ratio (1)
Radiocesium concentration of fly ash = Radiocesium concentration of treated material × Transfer rate to fly ash ÷ Fly ash generation ratio (2)

here,
Transfer rate to slag [%] = 100%-Volatilization rate of radioactive cesium [%]
Transfer rate to fly ash [%] = Volatilization rate of radioactive cesium [%]
In addition, the slag generation ratio is the amount of slag [kg] generated when the 1,000 kg of object to be treated is melt-processed, and the fly ash generation ratio is the amount of fly ash generated when the 1,000 kg of object to be treated is melt-processed ].

  The radioactive cesium concentration of the object to be treated can be estimated from the surface dose rate (μSv / h). It can also be measured and confirmed using a NaI scintillation detector or a Ge semiconductor detector.

  Table 1 shows a list of estimated values of the radioactive cesium concentrations of slag and fly ash calculated from the radioactive cesium concentration of the object to be treated from the formulas (1) and (2). However, the slag generation ratio is 300 kg / 1,000 kg of object to be treated, and the fly ash generation ratio is 100 kg / 1,000 kg of object to be treated.

(STEP-5) The radioactive substance contaminated waste charged in the shaft furnace type gasification melting furnace 11 by dividing the difference between the estimated value of the radioactive cesium concentration of the slag and the target value by the reduction amount of the radioactive cesium concentration of the slag Calculate the amount of chlorine to be added to
For example, when the radioactive cesium concentration of the object to be treated is 10,000 Bq / kg, assuming that the transfer rate to the slag is 4.0%, the estimated value of the radioactive cesium concentration of the slag is 1,333 Bq / kg according to Table 1. . Assuming that the radioactive cesium concentration of the slag is 100 Bq / kg as a target value, the amount of chlorine added to the object to be treated is as follows.
(1,333-100) /1,667=0.74 [mass%]

In addition, when the radioactive cesium concentration of the material to be treated is 50,000 Bq / kg, assuming that the transfer rate to slag is 4.0%, the estimated value of the radioactive cesium concentration of slag is 6,667 Bq / kg according to Table 1. . Assuming that the radioactive cesium concentration of the slag is 100 Bq / kg as a target value, the amount of chlorine added to the object to be treated is as follows.
(6,667-100) / 1,667 = 3.9 [mass%]

(STEP-6) The addition amount of calcium chloride is calculated from the calculated chlorine amount.

  The embodiment of the present invention has been described above, but the present invention is not limited to the configuration described in the above-described embodiment, and considered within the scope of the matters described in the claims. And other embodiments and modifications. For example, the first embodiment and the second embodiment may be used in combination, and in this case, the one with the higher addition amount of calcium chloride may be adopted.

10: Receiving yard, 10a: disaster waste, 10b: decontamination waste, 11: shaft furnace type gasification melting furnace, 11a: outlet port, 11b: outlet, 12: combustion chamber, 13: gas cooling tower, 14 : Temperature reducing tower, 15: first dust collector, 16: second dust collector, 17: induction fan, 18: chimney, 19 water pulverizer, 19a casing, 20: flexible container bag, 21: washing tank , 22: dehydrator, 23: washing fly ash, 24: washing wastewater, 25: adsorption device, 26: treated water

Claims (3)

A method of adding calcium chloride to radioactive substance contaminated waste charged in a shaft furnace type gasification melting furnace to promote volatilization of radioactive cesium attached to the waste,
The amount of chlorine added to radioactive material contaminated waste charged in the shaft furnace type gasification and melting furnace, and the radioactivity attached to fly ash generated when the waste is melted and processed in the shaft furnace type gasification and melting furnace Determining the relationship between the cesium release rate and the radioactive cesium elution rate into water;
Calculating the amount of chlorine to be added to the radioactive substance contaminated waste charged in the shaft furnace type gasification melting furnace by setting the radioactive cesium elution rate in the fly ash cleaning treatment from the relation;
And d. Calculating the amount of added calcium chloride from the calculated amount of chlorine. A method of adding calcium chloride to radioactive substance contaminated waste charged in a shaft furnace type gasification melting furnace to promote volatilization of radioactive cesium attached to the waste,
The amount of chlorine added to radioactive material contaminated waste charged in the shaft furnace type gasification and melting furnace, and the radioactivity attached to fly ash generated when the waste is melted and processed in the shaft furnace type gasification and melting furnace Determining the relationship with the concentration of cesium;
The amount of increase in radioactive cesium concentration of fly ash to the incremental amount of chlorine added to radioactive material contaminated waste is determined from the above relationship, and the amount of decrease in radioactive cesium concentration of slag corresponding to the amount of increase in radioactive cesium concentration of fly ash A process to calculate
Estimating the radioactive cesium concentration of the slag after the melting process from the radioactive cesium concentration of the radioactive material contaminated waste charged into the shaft furnace type gasification and melting furnace;
The difference between the estimated value of the radioactive cesium concentration of the slag and the target value is divided by the reduced amount of the radioactive cesium concentration of the slag and added to the radioactive substance contaminated waste charged in the shaft furnace type gasification melting furnace Calculating the amount of chlorine;
And d. Calculating the amount of added calcium chloride from the calculated amount of chlorine.   The radioactive cesium volatilization promotion method according to claim 1 or 2, wherein the fly ash is contained in a washing tank, and the fly ash is washed with washing water in the washing tank, and the washing used for washing the fly ash. And a step of adding an adsorbent to the waste water to recover the radioactive cesium in the washing waste water.

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