Method for reducing the amount of radioactivity in a liquid

Abstract

To provide one of means for solving a problem related to radioactive contamination by applying hydrogen water to a use different from removal of a radioactive substance from soil, that is, a use for appropriately exhibiting a function of hydrogen water having a unique property.SOLUTION: In the method for reducing the amount of radiation of the liquid material containing the radioactive materials by dissolving hydrogen in the liquid material, hydrogen may be dissolved in the liquid material by mixing the material containing the radioactive materials with hydrogen water containing hydrogen of 1. 0ppm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for reducing the amount of radioactivity in a liquid body. [Background technology]

[0002] Water containing hydrogen (also referred to as "hydrogen water" in this specification) has a high reducing power, and therefore attempts are being made to apply it to a variety of uses. For example, Patent Document 1 describes a radioactive decontamination device that is characterized by comprising a hydrogen supply means for supplying hydrogen gas, a hydrogen water production means for dissolving the hydrogen gas in raw water to produce hydrogen water, and a spray means for spraying the produced hydrogen water in the form of a water flow. It is said that this device can efficiently remove (decontaminate) radioactive materials attached to soil and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-78836 Summary of the Invention [Problem to be solved by the invention]

[0004] However, according to the results described in the examples of Patent Document 1, the difference between decontaminating soil using tap water and decontaminating it using hydrogen water is not necessarily clear, and it has been shown that even when hydrogen water is used, it is not easy to remove radioactive materials, particularly radioactive cesium such as cesium-137 and cesium-134, from soil.

[0005] The present invention aims to provide one of the means for solving the problems associated with radioactive contamination by applying hydrogen water to a purpose other than removing radioactive materials from soil. [Means for solving the problem]

[0006] One aspect of the present invention is a method for reducing the radioactivity of a liquid containing radioactive material, characterized by dissolving hydrogen in the liquid. As mentioned above, radioactive cesium binds strongly to soil constituents, making it difficult to separate radioactive cesium from soil even with hydrogen water, which has high reducing power. However, the inventors' studies have revealed that hydrogen water containing dissolved radioactive cesium, i.e., a liquid containing dissolved radioactive cesium and actively dissolved hydrogen, and containing water as the medium, significantly reduces the amount of radiation in a short period of time compared to a liquid containing dissolved radioactive cesium and not actively dissolved hydrogen, containing water as the medium. Although the reason for this is unclear, it is possible that the presence of hydrogen nearby accelerates the decay of radioactive materials such as radioactive cesium.

[0007] For example, the radiation (beta rays and gamma rays) emitted when radioactive cesium in hydrogen water decays may interact with the hydrogen in the hydrogen water, ionizing the hydrogen molecules. The hydrogen bonds formed by these ions based on hydrogen molecules may facilitate the aggregation of radioactive cesium (e.g., cesium hydroxide) dissolved in the aqueous solution. When radioactive cesium dissolved uniformly in the aqueous solution aggregates, it becomes more likely to interact with other radioactive cesium. Specifically, gamma rays emitted by the decay of some of the aggregated radioactive cesium are more likely to collide with other radioactive cesium. As a result, photonuclear reactions of radioactive cesium occur more easily, promoting the conversion of radioactive cesium (e.g., cesium-137) to non-radioactive substances (e.g., barium-136). Thus, hydrogen dissolved in the aqueous solution may promote the aggregation of radioactive cesium, thereby rapidly reducing the radiation level of the aqueous solution.

[0008] To stably obtain the effect brought about by the presence of hydrogen, hydrogen may be dissolved in the liquid by mixing the substance containing the radioactive substance with hydrogen water containing 1.0 ppm or more of hydrogen. Alternatively, hydrogen may be dissolved in the liquid by supplying hydrogen under pressure to a liquid such as tap water containing radioactive substances.

[0009] Acceleration of decay by hydrogen is particularly evident when the radioactive material is radioactive cesium, particularly when it contains at least one of cesium-137 and cesium-134. [Effects of the Invention]

[0010] According to the present invention, a method for reducing the amount of radioactivity in a liquid containing radioactive substances, which is one of the problems related to radioactive contamination, is provided by applying hydrogen water. DETAILED DESCRIPTION OF THE INVENTION

[0011] The effects of the present invention will be explained below with reference to examples and comparative examples.

[0012] (Example) A cleaning solution was sprayed onto a concrete slab contaminated with radioactive materials, including radioactive cesium, and the radioactive materials were dissolved in the cleaning solution. The surface contamination density of the concrete slab was measured, and the average of five measurement points was 3734 cpm. The cleaning solution was water (hydrogen water) with approximately 1.3 ppm of dissolved hydrogen. 120 L of cleaning solution was used. It took one hour to spray the cleaning solution.

[0013] It took one hour for the cleaning solution to be collected. After the cleaning solution was collected, the surface contamination density of the concrete slab was measured, and the average of the five measurement points was 2068 cpm. Therefore, the decontamination rate (unit: %, [surface contamination density before cleaning - surface contamination density after cleaning] / surface contamination density before cleaning x 100) was 45%.

[0014] 22 hours after the recovery work was completed, the radioactivity of the recovered cleaning solution was measured and found to be 32,640 Bq. Since the recovered volume was 120 L, the radioactivity concentration of the recovered solution was 272 Bq / L.

[0015] (Comparative Example) The concrete slab was cleaned in the same manner as in the above example, except that 12 L of 3% hydrogen peroxide solution was sprayed onto the slab as a cleaning solution, followed by 250 L of tap water, which was then collected. The surface contamination density of the concrete slab before spraying the cleaning solution was 4218 cpm, averaged over five measurement points. The time required for spraying the cleaning solution was one hour, and the collection time was one hour.

[0016] After the cleaning solution and tap water were collected, the surface contamination density of the concrete slab was measured and found to be 2406 cpm on average at five measurement points. Therefore, the decontamination rate was 43%.

[0017] 24 hours after the recovery work was completed, the radioactivity of the recovered cleaning solution was measured and found to be 225,300 Bq. Since the recovered volume was 250 L, the radioactivity concentration of the recovered solution was 901 Bq / L.

[0018] From the above examples and comparative examples, it was confirmed that hydrogen water and hydrogen peroxide solution have the same ability to remove radioactive materials from concrete slabs, but that the radioactivity concentration of the recovered cleaning solution is significantly reduced in a short period of time when hydrogen water is used as the cleaning solution compared to when hydrogen peroxide solution is used.

Claims

1. A method for reducing the amount of radioactivity of a liquid containing a radioactive substance, the liquid being obtained by mixing hydrogen water containing 1.0 ppm or more of hydrogen with a substance containing a radioactive substance, comprising: Hydrogen is dissolved in the liquid, A method characterized in that the liquid is maintained in a state where it is not in contact with the substance containing the radioactive material for a predetermined period of time (except when an organic polymer flocculant is added to the liquid while maintaining the state for the predetermined period of time).

2. The method according to claim 1 , wherein the liquid is a recovered cleaning liquid used to clean the material containing the radioactive material.

3. 3. The method according to claim 1, wherein the amount of dissolved hydrogen in the cleaning solution before cleaning is 1.0 ppm or more.

4. The method of any one of claims 1 to 3, wherein the predetermined period of time is 22 hours or more.

5. 5. The method of claim 1, wherein the radioactive material comprises radioactive cesium.