JP2586927B2 - Tritium-contaminated concrete treatment method and apparatus - Google Patents

Description

The present invention relates to a method and an apparatus for treating tritium-contaminated concrete, which heats concrete waste generated when dismantling and removing a tritium handling facility and evaporates and separates tritium. It is about.

"Prior art" The Radiation Council recently approved a report entitled "About the unregulated dose for shallow land disposal of radioactive solid waste" compiled by its basic group. In this report, the “exempt doses” for extremely low-level radioactive waste
And for solid waste at lower doses,
The idea is to "exclude regulations from the perspective of preventing radiation hazards."

In other words, if this policy is established, even for radioactive waste, if the degree of contamination is below a certain level, it is necessary to consider that there is no need to consider the specialty of radioactive waste. Like general waste, it can be disposed of by burying it in shallow ground.

By the way, especially in a tritium handling facility such as a nuclear reactor such as a heavy water reactor, a spent nuclear fuel reprocessing facility, and a nuclear fusion research facility, tritium (a radioactive isotope of hydrogen) is contained in water vapor existing in the air in the facility. Tritium water (HTO) containing T) is contained in a very small amount, so that the tritium water in the air is free water, capillary water and crystal water in the concrete that forms the floors and walls of the facility. It is known to substitute with structural water or the like to permeate and fix in concrete. Therefore, if such a tritium handling facility reaches the end of its life and needs to be dismantled and removed, a large amount of tritium-contaminated concrete will be generated when the facility is dismantled and removed.

However, on the other hand, by separating tritium water from this tritium-contaminated concrete and disposing only the tritium water recovered thereby as radioactive waste, concrete, which accounts for the majority of waste, is reduced to the same level as ordinary waste. Is considered to be disposed of,
The tritium separation method used for that purpose is disclosed in Japanese Patent Application No. 59-21.
No. 1073 filed as "Method of Disposing of Concrete Structures in Tritium Handling Facility".

The method for disposal of concrete structures in the tritium handling facility is to crush the concrete structures in the tritium handling facility, collect the evaporated water while heating the crushed concrete mass to evaporate the water in the concrete mass. Then, the heated concrete mass is discarded.

"Problems to be Solved by the Invention" By the way, in the above-mentioned disposal treatment method, it is specified that "the heating condition should be maintained at a high temperature of, for example, 500 ° C. or more for several hours."

However, tritium water present in concrete is included as water in several different existing states such as free water, capillary water, crystal water, and structural water. The required minimum heating temperature is different. In addition, since the proportion of water present in each state is not disclosed, it is not possible to determine the minimum heating temperature required to remove the water in the concrete to a predetermined removal rate. For this reason, even if heated at 500 ° C., for example, not all moisture in concrete is removed, and if it is not necessary to remove all moisture in concrete, heating at a temperature of 500 ° C. or less is required. Even so, it is considered that water may be removed to a required removal rate, and it is considered uneconomical to heat uniformly to 500 ° C. or higher.

The present invention, when decontaminating tritium-contaminated concrete, by heating at a minimum heating temperature that can remove tritium water in the concrete to a predetermined level,
It aims at separating tritium in concrete effectively at low cost.

[Means for Solving the Problems] The method for treating tritium-contaminated concrete according to the present invention comprises heating tritium-contaminated concrete to evaporate water in the concrete, thereby converting tritium contained in the concrete to tritium. In the method of treating tritium-contaminated concrete separated as steam, a heating temperature is set in advance according to a desired tritium removal rate, and the concrete is heated at the heating temperature.

Further, another method for treating tritium-contaminated concrete according to the present invention is the method for treating tritium-contaminated concrete, wherein tritium in the concrete is removed to a predetermined removal rate by measuring the amount of water generated from the concrete. Is to be detected.

Further, the apparatus for treating tritium-contaminated concrete according to the present invention includes a heating furnace for heating concrete contaminated with tritium and evaporating water containing tritium water from the concrete; A tritium-contaminated concrete treatment device provided with a moisture collector for collecting the gas, wherein a thermal conductivity measuring device for measuring the thermal conductivity of the gas to detect the amount of moisture in the gas is provided. is there.

[Operation] In the method for treating tritium-contaminated concrete of the present invention, tritium contained in the concrete is separated as tritium water vapor by heating the concrete contaminated with tritium to evaporate the water in the concrete. At this time, a heating temperature corresponding to a desired tritium removal rate is set in advance, and the concrete is heated at the heating temperature, whereby the tritium in the concrete is reliably removed to a desired removal rate.

That is, in general, water in concrete exists in several different existing states such as free water, capillary water, crystal water, and structural water, and the water in each of these existing states is the minimum necessary for evaporating. The heating temperatures are different.
For this reason, if the minimum heating temperature required to evaporate the moisture in each existing state and the proportion of the moisture present in each existing state in the concrete are known, it is necessary to evaporate the desired proportion of the moisture from the concrete. The minimum heating temperature can be determined. Similarly, if the minimum heating temperature required to evaporate the water in each state and the proportion of tritium water present in each state in the concrete are known, the desired proportion of tritium water can be evaporated from the concrete. The minimum required heating temperature can also be determined. Then, this minimum heating temperature is the minimum heating temperature necessary for removing tritium in concrete to a desired removal rate.

If the concrete is heated to such a minimum heating temperature and held for an appropriate period of time, one or more existing moistures corresponding to the minimum heating temperature will evaporate. The tritium water present in the state also evaporates by a rate equal to the proportion of the total tritium water contained in the concrete.

Further, in the method for treating tritium-contaminated concrete, when the amount of water generated from the concrete is measured to detect that the tritium in the concrete has been removed to a predetermined removal rate, the presence of the corresponding tritium is determined. It is possible to detect that all of the moisture in the state has evaporated from the concrete, and thereby it is possible to detect that the tritium in the concrete has been removed to a desired removal rate.

Further, in the apparatus for treating tritium-contaminated concrete of the present invention, a heating furnace for heating concrete contaminated with tritium and evaporating water containing tritium water from the concrete, A moisture collector for collecting moisture, and a thermal conductivity measuring device for measuring the thermal conductivity of the gas to detect the amount of moisture in the gas. Can be heated at the same time, all the water present in the state corresponding to the heating temperature can be separated by evaporation, and further, all the water separated by evaporation and the tritium water contained in the water are collected. I can do it. In addition, the thermal conductivity measuring device detects that the water in the existing state has completely evaporated from the concrete, thereby detecting that the tritium in the concrete has been removed to a desired removal rate. it can.

Embodiment An embodiment of the present invention will be described below.

The apparatus for treating tritium-contaminated concrete of this embodiment uses an electric furnace 2 as a heating furnace for heating concrete 1 contaminated with tritium, and discharges gas in the electric furnace 2 to the electric furnace 2. A gas discharge pipe 3 was connected, and the gas discharge pipe 3 passed through the thermal conductivity measuring device 4 for measuring the thermal conductivity of the gas and measuring the amount of water in the gas, and the thermal conductivity measuring instrument 4. A moisture adsorber 5 (moisture collector) for adsorbing moisture contained in the gas is provided. In addition, an air inlet 6 for taking in air into the electric furnace 2 is provided at an upper part of the electric furnace 2, and a water droplet condensed and flowing down in the electric furnace 2 is collected at a lower part in the electric furnace 2. A water drop recovery port 7 is provided.

The thermal conductivity measuring device 4 is a kind of gas chromatography, and samples a gas supplied through the gas discharge pipe 3 to measure the thermal conductivity of the gas and to measure the thermal conductivity of the reference gas. Is measured and compared with the thermal conductivity to continuously measure the amount of water in the gas. Then, based on the measured value, it is detected that the release of moisture from the concrete 1 in the electric furnace 2 has been completed.

When processing the concrete 1 contaminated with tritium by using such a processing apparatus, a heating temperature corresponding to a desired tritium removal rate is set in advance. That is, for example, when setting the tritium removal rate to 70%,
For example, the proportion of tritium water present as free water and capillary water in the concrete 1 is 70% of the total tritium water contained in the concrete 1, and the free water and the capillary water are all evaporated from the concrete 1. Assuming that the required minimum heating temperature is 200 ° C., the heating temperature is set to 200 ° C.

After setting the heating temperature in this way, the concrete 1 to be treated is put into the electric furnace 2 and then the electric furnace 2 is heated to raise the temperature of the entire concrete 1 to the heating temperature. And the heating temperature is maintained. At this time, the amount of water in the gas discharged through the gas discharge pipe 3 is constantly and continuously measured by the thermal conductivity measuring device 4. And the concrete 1
Is heated at a constant heating temperature, and moisture that evaporates and separates from the concrete 1 is collected by a moisture adsorber 5 or the like, and the thermal conductivity measuring device 4 is discharged through the gas discharge pipe 3. When it is detected that the moisture is no longer measured from the gas to be heated, the heating is stopped immediately.

When the concrete 1 is subjected to the heat treatment in this manner, for example, all the water existing as free water and capillary water in the concrete 1 is separated by evaporation, and at this time, the tritium water existing as the free water and the capillary water is also removed. The tritium in the concrete 1 evaporates by a rate equal to the proportion of the total tritium water contained therein, whereby the tritium in the concrete 1 is removed to a desired removal rate.

"Experimental example" Generally, water in concrete is contained in the paste portion, fine aggregate, and aggregate, but most of them are contained in the paste portion. For this reason, the experiment which investigated the general release behavior by heating of the moisture contained in the cement paste was performed.

In this experiment, a medium heat Portland cement with a water cement ratio of 0.55 was prepared, and this was cured for 69 days as a sample, and the sample was heated at each heating temperature, and the released gas was measured by a mass spectrometer. . FIG. 2 shows the relationship between each heating temperature and the number of molecules of each component in the generated gas.

As a result, the amount of generated water molecules peaks in two temperature ranges of 100 to 200 ° C. and 450 to 550 ° C., whereby
It is presumed that water in different existing states is released in four temperature ranges of -200 ° C, 200-450 ° C, 450-550 ° C, and 550-850 ° C. That is, in the temperature range of 200 ° C. or lower, free water and capillary water that are relatively easily released are released, and crystal water that is released next is 20%.
It is released in the temperature range of 0 to 450 ° C. In the temperature range of 450 to 550 ° C, calcium hydroxide (Ca (OH) ₂ ), which is easily released in structured water, is released. In the temperature range of 550 to 850 ° C, It is believed that other structural water is released. For this reason, the water released in each temperature range is classified into four groups,
Group, Group II, Group III and Group IV. Table 2 below shows the results.

The results shown in Table 1 are considered to be common characteristics to ordinary Portland cement, fly ash cement, and the like. By setting the heating temperature to the upper limit of each temperature range shown in Table 1, free water can be obtained. And only capillary water can be released, and up to crystal water or structured water can be released.

Also, when determining the time to maintain the predetermined heating time, the gas released from the concrete is collected,
By measuring the thermal conductivity of a gas collected by a thermal conductivity measuring instrument, which is a kind of gas chromatograph, and comparing it with that of a reference gas, the increase or decrease in the amount of water in the gas is continuously measured. Then, it is detected from the measured value that the release of water from the sample has been completed.

Next, by examining the proportion of water present in each state in the tritium-contaminated concrete, the minimum heating temperature required to remove water to a desired removal rate is determined, and the time during which the minimum heating temperature is to be maintained Was examined.

The samples used in this experiment were kneaded using pure water, cast in a mold, and cured for 28 days.There are two types, cement paste and mortar. Also had a cylindrical shape with a diameter of 45 mm and a height of 44 mm.

First, as shown in FIG. 3, each sample 8 was placed in an exposure box 7 kept at 20 ° C. After this, one end face of the sample was brought into contact with air (tritium concentration: 730 Ci / cm ³ ) containing 90% relative humidity (RH) containing tritium water vapor, and the other end face was put in relative humidity not containing tritium water vapor. (RH) By contacting with 10% air, tritium water was allowed to permeate from one direction and left for a certain period of time. After infiltrating tritium water into each sample in this manner, the sample is put into an electric furnace, and the heating temperature is sequentially increased according to a time schedule as shown in FIG. 4, and each sample is heated in four temperature ranges. At that time, water generated from each sample was continuously collected, and the concentration of tritium in the water was measured by a scintillation counter. The outline of the operation procedure is shown below.

1st stage (heated at ~ 200 ° C): Group I water capture → measurement ↓ 2nd stage (heated at 200-450 ° C): Group II water capture → measurement ↓ 3rd stage (heated at 450-550 ° C): III Group water capture → measurement ↓ 4th stage (heating at 550-800 ° C): Group IV water capture → measurement As a result of conducting the experiment as described above, the ratio of water present in each state in each sample and tritium water Was found to be as shown in Table 2 below.

As a result, in both cement paste and mortar, when heated at 200 ° C, about 70% of the infiltrated tritium is released, and when the heating temperature is set to 450 ° C or 550 ° C, About 90% or 99.5 each
% Was found to be released. Further, considering FIG. 4 together with this result, in order to remove 70% of tritium, it is only necessary to hold the heating temperature at 200 ° C. for about 2.5 hours, and to remove 90% of tritium. After heating at 200 ° C for 2.5 hours, the heating temperature was further increased to 450
It was found that the temperature should be raised to ℃ and heated for about 1.5 hours.

According to the method for treating tritium-contaminated concrete of the present invention, a heating temperature is set in advance according to a desired tritium removal rate, and the concrete is heated at the heating temperature. Can be reliably removed to a desired removal rate.

That is, in this method for treating tritium-contaminated concrete, the minimum heating temperature required to evaporate the water present in each state of free water, capillary water, crystal water, structural water, etc., in the concrete and the above-mentioned respective states Investigate the proportion of tritium water present and determine the minimum heating temperature required to evaporate the desired proportion of tritium water from concrete based on the survey results, and determine the minimum heating temperature as the heating temperature. . Therefore, when concrete is heated at this heating temperature, one or two or more existing moistures corresponding to the heating temperature are all evaporated, and at that time, tritium water present in these existing states is also included in the concrete. Evaporates by a rate equal to the proportion of the total tritium water contained. For this reason, tritium in concrete can be reliably removed to a desired removal rate, and the amount of energy used can be minimized by heating at the minimum temperature necessary to remove to the removal rate. Energy can be saved, and equipment can be simplified,
Improvements in work efficiency can also be expected.

Further, in the method for treating tritium-contaminated concrete, when the amount of water generated from the concrete is measured to detect that the tritium in the concrete has been removed to a predetermined removal rate, the presence of the corresponding tritium is determined. It is possible to detect that the water in the state has completely evaporated from the concrete, and thereby it can be confirmed that the tritium in the concrete has been removed to a desired removal rate. For this reason, when tritium is removed to a desired removal rate, heating can be stopped immediately, thereby preventing heating for an unnecessarily long time and further saving energy.

Further, according to the apparatus for treating tritium-contaminated concrete of the present invention, a heating furnace for heating concrete contaminated with tritium and evaporating water containing tritium water from the concrete, A moisture collector for collecting the moisture, and a thermal conductivity measuring device for measuring the thermal conductivity of the gas to detect the amount of moisture in the gas. Can be heated at the same time, it is possible to evaporate and separate all the moisture present in the presence state corresponding to the heating temperature, and further collect all the evaporated and separated moisture and the tritium water contained in the moisture. I can do it. In addition, it is possible to detect that the water in the existing state has completely evaporated from the concrete, thereby detecting that the tritium in the concrete has been removed to a desired removal rate.
By immediately stopping the heating, energy can be saved.

[Brief description of the drawings]

1 to 4 are views showing an embodiment of the present invention. FIG. 1 is a schematic configuration diagram of an apparatus for treating tritium-contaminated concrete, and FIG. 2 shows the amount of water release at each heating temperature. Graph, FIG. 3 is a schematic diagram of the exposure box,
FIG. 4 is a graph showing a time schedule of the heat treatment experiment. 1 ... tritium-contaminated concrete, 2 ... heating furnace (electric furnace), 4 ... thermal conductivity measuring device, 5 ... moisture collector (moisture adsorber).

Claims (3)

(57) [Claims] 1. A method for treating tritium-contaminated concrete in which tritium-contaminated concrete is heated to evaporate water in the concrete to separate tritium contained in the concrete as tritium water vapor. A method for treating tritium-contaminated concrete, comprising setting a heating temperature according to the tritium removal rate of the above and heating the concrete at the heating temperature. 2. A method for treating tritium-contaminated concrete according to claim 1, wherein the amount of water generated from the concrete is measured to detect that tritium in the concrete has been removed to a predetermined removal rate. Tritium-contaminated concrete treatment method. 3. A heating furnace for heating concrete contaminated with tritium to evaporate water containing tritium water from the concrete, and a water collector for collecting the water from gas discharged from the heating furnace. A device for treating tritium-contaminated concrete, comprising: a device for measuring the thermal conductivity of the gas to detect the amount of moisture in the gas. apparatus.