Method for reducing amount of radioactivity in liquid

Abstract

To provide means for solving the problem on radioactive contamination by applying hydrogen water to applications that are different from an application of removing a radioactive substance from soil and that appropriately exhibit functions of hydrogen water with unique properties.SOLUTION: In a method for reducing an amount of radioactivity in liquid containing a radioactive substance by dissolving hydrogen in the liquid, hydrogen may be dissolved in the liquid by mixing a substance containing a radioactive substance with hydrogen water containing hydrogen of 1.0 ppm 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. [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 various 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 spraying means for spraying the produced hydrogen water in the form of a water flow. It is said that such a device can efficiently remove (decontaminate) radioactive materials attached to soil and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-78836 A 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 problems related to 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 amount of radioactivity in a liquid containing a radioactive substance, characterized in that hydrogen is dissolved in the liquid. As described above, radioactive cesium strongly binds to substances that constitute soil, so that it is not easy to separate radioactive cesium from soil even if hydrogen water with high reducing power is used. However, as a result of the inventor's investigation, it has become clear that hydrogen water in which radioactive cesium is dissolved, that is, a liquid in which radioactive cesium, which is a radioactive substance, is dissolved, hydrogen is actively dissolved, and water is used as a medium, significantly reduces the amount of radiation in a short period of time compared to a liquid in which radioactive cesium is dissolved, hydrogen is not actively dissolved, and water is used as a medium. The reason for this is unclear, but there is a possibility that the presence of hydrogen in the vicinity accelerates the decay of radioactive substances such as radioactive cesium.

[0007] For example, the radiation (beta rays, gamma rays) generated when radioactive cesium in hydrogen water decays may interact with the hydrogen in the hydrogen water, ionizing the hydrogen molecules. The hydrogen bonds caused by ions based on these hydrogen molecules may affect radioactive cesium (such as cesium hydroxide) dissolved in the aqueous solution, making it easier for them to aggregate. When radioactive cesium that is dissolved uniformly in the aqueous solution aggregates, it becomes easier for the radioactive cesium to affect each other. Specifically, gamma rays generated 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 become more likely to occur, promoting the conversion of radioactive cesium (such as cesium-137) to non-radioactive substances (such as barium-136). In this way, hydrogen dissolved in the aqueous solution may promote the aggregation of radioactive cesium, reducing the radiation level of the aqueous solution in a short period of time.

[0008] From the viewpoint of stably obtaining the effect brought about by the presence of hydrogen, hydrogen may be dissolved in the liquid by mixing the substance containing the radioactive material 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 containing radioactive material such as tap water.

[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. Effect of the Invention

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

[0011] The effects of the present invention will be described 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 to collect the cleaning solution after cleaning. The surface contamination density of the concrete slab was measured after the cleaning solution was collected, 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 concrete slab as a cleaning solution, and then 250 L of tap water was poured and collected. The surface contamination density of the concrete slab before the cleaning solution was sprayed was 4218 cpm as an average of five measurement points. The time required for spraying the cleaning solution was one hour, and the time required for collection was one hour.

[0016] The surface contamination density of the concrete slab after the cleaning solution and tap water were collected 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 the radioactivity concentration of the recovered cleaning solution was significantly reduced in a short period of time when hydrogen water was used as the cleaning solution compared to when hydrogen peroxide solution was 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 for a predetermined period of time in a state where it is not in contact with the substance containing the radioactive material (except when an organic polymer coagulant is added to the liquid during the predetermined period of time).

2. The method according to claim 1 , wherein the liquid is a cleaning liquid recovered after cleaning 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 according to 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.