JPH0626665B2 - Radioactive material collection material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radioactive substance scavenger that can be safely used without admitting ignition even when a highly dangerous semi-volatile or volatile radioactive substance is adsorbed. Is.

Conventional technology Nuclear fuels such as uranium produce 40 types of fission products by nuclear fission. Among them, volatile elements such as rare gas xenon and semi-volatiles such as ruthenium, technetium, iodine and cesium. Since it contains radioactive elements, it is necessary to take measures to prevent these elements from vaporizing and contaminating the external environment.

Especially with the recent development of nuclear power generation, which has become a major part of power supply, enormous amounts of radioactive materials are being produced. Therefore, it is desired to develop safer and more effective trapping materials to prevent accidents and to confine them in the fuel reprocessing process, waste processing, disposal process, etc. ["International Atomic Energy・ Agency Technical Report, No. 22
0, Vienna (International Atomic Energy Agency Te
chnical Report, No. 220, Vienna) ", (1982
Year)〕.

Activated carbon has been mainly used as a collector for such volatile radioactive elements (Japanese Patent Publication No. 46-3524).
No. 4), this is a combustible substance, and therefore, when treating an inflammable substance, there is a risk of causing a fire accident, so that it is gradually replaced by a non-combustible material.

However, these alternatives are far less practical than activated carbon due to their low collection ability, complicated operation, and high cost.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention contains activated carbon having a large adsorptive power as an adsorbent component, and makes it incombustible without impairing its adsorptive power to obtain a trapping material for dangerous semi-volatile or volatile radioactive substances. This is the purpose.

Means for Solving the Problem Ruthenium, which is one of the semi-volatile elements, is a problematic element because it produces nuclides with a lengthy half-life of about 10% due to fission by thermal neutrons such as uranium. is there. In addition, ruthenium has a complicated chemical property and is relatively easily oxidized to form a volatile tetraoxide even at room temperature, so ruthenium is considered to be an element requiring intensive measures. This ruthenium tetroxide is often adsorbed by activated carbon, but the activated carbon that adsorbed 20% by weight of this was burned explosively by itself ["US Nuclear Report (HW-32
175) ”, (1954)], activated carbon was no longer used as a trapping material.

The inventors of the present invention have conducted extensive studies mainly on this ruthenium as a means of preventing combustion when it is adsorbed on activated carbon, and as a result, unlike activated carbon itself, activated carbon mixed with colloidal soil is Even if one part ignites, it will be immediately blocked and will not spread to other parts, so no explosion or fire will occur, and ruthenium tetroxide, which is extremely flame retardant and dangerous, can be handled safely. It was confirmed for the first time that the present invention was completed based on this finding.

That is, the present invention provides a radioactive substance trapping material containing activated carbon and colloidal soil.

The activated carbon used in the present invention can be arbitrarily selected from those usually used as an adsorbent.

Further, the colloidal soil used in combination with this activated carbon is called Allophane in the chemical term, and is naturally produced as a modified product of aluminum silicate.

In the present invention, the activated carbon contains 80% by weight of the total amount of the mixture.
Ignition of ruthenium can be suppressed by incorporating a certain amount of colloidal soil, but it can be used in a smaller amount for radioactive substances other than ruthenium.

If the amount of activated carbon is reduced too much, the adsorption capacity will decrease, so it is preferable to increase the amount of activated carbon as much as possible without causing ignition.

The scavenger of the present invention is prepared, for example, by mixing activated carbon powder and colloidal earth powder in a predetermined ratio and granulating by a conventional method.

The scavenger thus obtained is not only highly safe, but also has a large adsorption of activated carbon, etc.
Activated carbon has been used so far, and it can be used for all applications for which improvement in safety is desired. For example,
It can also be used as a safe and highly efficient scavenger for volatile radioactive iodine and as a scavenger for volatile pertechnetate. In addition, since the reactor exhaust contains short-lived nuclides such as volatile radioactive noble gases such as xenon-138 and krypton-89, they are adsorbed through the activated carbon layer during the discharge process and are retained for a while. During this period, the radioactive gas having a short half-life is significantly attenuated, and when it is sequentially eluted, the radioactive concentration becomes lower than the permissible concentration, so that it can be released into the atmosphere. By using the trapping material of the present invention instead of the activated carbon, the risk of ignition or combustion of the activated carbon can be greatly reduced.

As described above, the trapping material of the present invention plays a major role in trapping semi-volatile and volatile radioactive substances which are extremely dangerous, but the utility of the trapping material is not limited to this. Non-radioactive ruthenium tetroxide, osmium tetroxide,
It is known that volatile oxygen acid compounds such as chromium trioxide and vanadium pentoxide have oxidizing power and are harmful to the human body, and it is necessary to remove them from the air in the workplace or living environment. Since the substance of No. 1 can be removed to a trace concentration without fear of ignition by the trapping material of the present invention, the range of use is extremely wide and the economical effect is great.

EXAMPLES Next, the present invention will be described in more detail with reference to examples.

Example 1 The following experiment was conducted in a draft to confirm the difference in safety when capturing ruthenium tetroxide by using the trapping material of the present invention and activated carbon for comparison.

1 g of dried ruthenium tetroxide was placed in a washed and dried stoppered test tube, placed in a water bath heated to 30 to 40 ° C. to melt, and allowed to cool to solidify. If this test tube is held vertically and the stopper is removed and the activated carbon particles are dropped from above the test tube port at room temperature of 10 to 20 ° C, the tip end will collide with a large excess amount of ruthenium tetroxide. At the moment when the activated carbon particles reach the surface of the ruthenium tetroxide lump, it reacts with an explosive sound, and part of the activated carbon particles jumps out from the test tube port, and during this explosive reaction, Instant fires were often noted at.

On the other hand, in the case of the collecting material of the present invention in which allophane was mixed and granulated so as to contain 20% of powdered activated carbon, no explosive sound or ignition was observed at all even when dropped. In this way, the test tube in which the composite trapping material was laminated on the tenium tetroxide lump was left for a while, then placed in a water bath to gradually raise the temperature, and even if the temperature was raised to 100 ° C, no peculiar reaction occurred and it was safe. The sex was confirmed.

Example 2 9% of a mixed granulation of 20% by weight powdered activated carbon and allophane
A -12 mesh pellet was filled into a tube with an inner diameter of 8 mm and a length of 200 mm, which was filled with a breathable stopper at one end, to obtain a collection tube.

This collection tube is connected to a glass reaction vessel connected to an air filtering device via a glass air guide tube attached upward to the outlet of the vessel, and a second section is provided at the rear of the collection tube. The collector is connected, the rear of the second collector is connected to the third collector pipe, and the rear part thereof is connected to a device for sucking air at an arbitrary constant speed. A glass common incubator is used to airtightly connect each of the connectors up to the third collection tube.

Using such an apparatus, radioactive ruthenium dissolved in a predetermined amount of dilute hydrochloric acid is placed in a reaction vessel, and an oxidizing agent and dilute hydrochloric acid are added to generate radioactive ruthenium tetroxide. The device is operated to supply it to the collecting tube together with air and collect it.

The water vaporized during the reaction is condensed in an air guide pipe connected to the outlet and is returned to the reaction vessel.

After a predetermined time, the collection tube was removed and cut into a predetermined length, and the cut end was sealed with an adhesive to obtain a radioactivity measurement sample. This sample was placed at a predetermined distance on a germanium semiconductor detector in which lithium was diffused and connected to a wave height analyzer to measure radioactivity. Since the count value of γ-rays with energy of 497 KeV obtained at the predetermined measurement time corresponds to the radioactivity value of ruthenium-103, the amount of ruthenium collected can be quantified from this value.

The white circles in FIG. 1 are obtained by extrapolating this measurement result up to a length of 0 cm of the collection tube, standardizing this value as 10 ⁶ counts / 100 seconds · cm, and graphing it.

In such a trapping device, it is known that the trapping ability at a predetermined temperature depends on the velocity of the passing air. First
The white circles in the figure show the case where the space velocity is 300 (air 50 cc / min), but when using a collection material with such a large adsorption force, the collection curve does not change much even if the space velocity is increased a little. Even if the space velocity is doubled, it was found that 99% or more of the trapping layer of 2-3 cm and 99.999% or more of ruthenium were trapped in the layer of 10 cm or less. In addition, the radioactivity of ruthenium was detected from the second collection device and the third collection tube only to the extent of a measurement error even after long-term measurement.

As described above, when the trapping material of the present invention is used, ruthenium tetroxide can be trapped efficiently at room temperature.

Comparative Example 1 Example 2 except that bone charcoal was used instead of the trapping material of Example 2.
An experiment similar to the above was carried out, and the result is shown in FIG.

Example 3 A potassium iodide solution containing iodine-131 and dilute nitric acid were added to the reaction vessel of Example 2 and heated to generate radioactive volatile iodine, which was used in the same collection tube as in Example 2. And collected in the same way. Next, a measurement sample was prepared in the same manner as in Example 2, and the amount of iodine collected was measured from the radioactivity value of 364.5 KeV γ rays. Also in this case, radioactive iodine was found to be collected with extremely high efficiency.

Comparative Example 2 A commercially available activated carbon was used in place of the trapping material of Example 2, and the results of the same experiment are shown by the black circles in FIG.

As is clear from the above results, the trapping material of the present invention has a superior ability to trap radioactive substances even when compared with commercially available activated carbon or bone charcoal.

[Brief description of drawings]

FIG. 1 is a graph showing a collection curve for various collection materials.

Claims (3)

[Claims] 1. A radioactive material trapping material containing activated carbon and colloidal soil. 2. The radioactive substance trapping material according to claim 1, which contains at least 20% by weight of activated carbon. 3. The radioactive substance trapping material according to claim 1 or 2, which is formed into a granular shape.