JP2006071322A - Method and system for disposing of radioactive metal waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conveniently prepare radioactive metal waste bodies which do not emit any gases. <P>SOLUTION: A method and a system in this invention have processes of: (3) pouring radioactive metal waste 2 into a waste container 1; (4) drying the inside of the waste container 1 after the process 3; (6) drying particulates 5 made of inorganic substances; and (7) pouring the particulates 5 into the waste container 1 after the processes 4 and 6 and filling the interstices of metal waste 2 in the waste container 1 with the particulates 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and system for treating radioactive metal waste generated from nuclear facilities and the like.

Radioactive metal wastes generated from nuclear facilities include wastes that are activated by long-term neutron irradiation, such as channel boxes and hulls, resulting in high radionuclide concentrations. A treatment method for these radioactive metal wastes is currently being studied, but has not yet reached a practical stage. In general, cement solidification, glass solidification, melt solidification, and the like are assumed as a solidification treatment method for forming a radioactive waste waste. Among these, since the cement solidification method is inexpensive and easy to process, application to the solidification of many wastes is assumed (for example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2003-307592

  However, if the concentration of radionuclide contained in the radioactive waste is high, there is a concern that the pore water or crystallization water present in the filled cement solidified material is decomposed by radiation and generates a radiolytic gas. . In order to suppress the release of gas from the solidified container, it is conceivable to seal the container, but there is a concern that the internal pressure will increase during long-term storage. Therefore, it is difficult to say that cement solidification is appropriate as a treatment method for making wastes such as channel boxes and hulls containing high concentrations of radioactivity.

  On the other hand, since melting and solidification are high temperature processing, long-term heat resistance is required for the material of the melting furnace, and radionuclide processing equipment that moves to the gas phase at high temperatures is difficult and expensive. There is a problem. Therefore, there is a demand for a waste body preparation method that is simple and does not generate gas.

  In view of the above problems, an object of the present invention is to provide a method for easily producing a radioactive metal waste body in which gas generation is suppressed and a system therefor.

  In order to achieve the above object, a radioactive metal waste treatment method according to the present invention includes a waste charging step of charging a radioactive metal waste into a waste container, and drying the inside of the waste container after the waste charging step. After the waste drying step, the powder drying step for drying the inorganic powder, and the waste drying step and the powder drying step, the powder is put into the waste container, And a filling step of filling the gaps between the metal wastes in the waste container with the powder particles.

  Further, the radioactive metal waste treatment system according to the present invention includes a waste container that receives the radioactive metal waste, a waste drying means that dries the inside of the waste container that receives the radioactive metal waste, and an inorganic powder. A hopper for temporarily storing the body; a powder drying means for drying the inside of the hopper receiving the powder; and the powder drying means in a waste container after being dried by the waste drying means And filling means for charging the powder particles into the gap between the metal wastes in the waste container.

  According to the present invention, it is possible to easily produce a radioactive metal waste body that generates no gas or generates little gas.

  Embodiments of a radioactive metal waste processing method and a system therefor according to the present invention will be described below with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  FIG. 1 is a flowchart of an embodiment of a radioactive metal waste treatment method according to the present invention. The radioactive metal waste 2 is introduced into the waste container 1 (waste input process 3), and a drying process is performed to remove the moisture in the waste container 1 (waste drying process 4). On the other hand, a drying process is performed outside the waste container 1 with respect to the granular material (particles or powder, or a mixture thereof) 5 made of an inorganic material (powder drying step 6).

  Next, this dried granular material 5 is put into the waste container 1 to fill the gap between the radioactive metal wastes 2 with the granular material 5 (filling step 7). Next, the waste container 1 is sealed (sealing step 8) to form a waste body 9.

  According to this embodiment, since there is no water in the waste body 9, generation of gas due to radiolysis does not occur, and the pressure in the waste container can be kept constant.

  Next, an example of an experiment conducted by specifically simulating the waste drying step 4 (FIG. 1) will be described with reference to FIG. A simulated waste 13 that simulates the metal waste 2 is placed in a 50 L drum 12 that simulates the waste container 1. In the example of this experiment, as simulated waste 13, stainless steel piping (diameter 24.5 mm, meat pressure 2 mm, length 400 mm) was set to 22.1 kg in total, and these were disposed after draining. The drum can 12 was covered with a temporary lid 14, and the humidity was measured with a hygrometer 30. At this time, the humidity was 82% at room temperature (24.3 ° C.).

  Next, the pressure was continuously reduced by the pressure reducing pump 15 so that the pressure became 100 Torr or less. After 8 hours, the inside of the drum 12 was returned to normal pressure, and then the humidity was measured again at room temperature (24.5 ° C.). At this time, the humidity was reduced to 7%, and it was confirmed that the moisture in the container was reduced by the reduced pressure.

  In an experiment in which the pressure was reduced to 1000 Torr, the humidity when the temperature was returned to room temperature was 18%, which was not sufficient drying. For this reason, it is preferable to reduce the pressure to 100 Torr or less.

  Next, an example of an experiment conducted by specifically simulating the granular material drying step 6 (FIG. 1) will be described with reference to FIG. A heater 22 was placed on the body of a conical screw type mixer (hopper) 21 having a screw 20, and the outside was covered with a heat insulating material (jacket) 23. Moreover, it was set as the structure which can inject the heated dry air 24 from the lower part. Sodium nitrate powder (about 150 kg) having a moisture content of 0.2 wt% was charged as the powdery granule 5 to a position of about half of the total height (160 cm from the bottom) in the conical barrel portion of this apparatus. As shown in the figure, the hygrometer 32 was disposed at a position where the tip was inserted into the granular material 5.

While controlling the temperature inside the hopper 21 to be 100 ° C., the screw 20 was rotated, and dry air 24 heated to 100 ° C. from the lower part was injected at a rate of 1 m ³ / Hr.

  After 4 hours, the internal sodium nitrate was collected and the water content was measured. As a result of the measurement, it was confirmed that the moisture content was 0.02 wt%, and it was confirmed that the granular material 5 could be dried with this apparatus configuration.

  In the above description, the temperature inside the hopper 21 is controlled to be 100 ° C., but the saturated vapor pressure of water is about 60 ° C. and about 10 times the saturated vapor pressure at room temperature (20 ° C.). Since drying can be expected, the temperature inside the hopper 21 is preferably controlled to 60 ° C. or higher.

  Next, an example of an experiment conducted by specifically simulating the filling step 7 (FIG. 1) will be described with reference to FIGS. As shown in FIG. 4 (a), the granular material 5 is uniformly introduced into the waste container 1, and then the waste container 1 is vibrated in the vertical direction as shown in FIG. 4 (b). As a result, as shown in FIG.4 (c), the granular material 5 is filled densely.

  The experimental conditions and results at this time are shown in FIG. That is, an acrylic container having a height of 2 m, an inner diameter of 10 mm, and a thickness of 1 mm was used as a container for simulating a waste container, and zirconia powder having a particle size distribution of 6 types (particle diameter of 1 to 1000 μm) was vibrated. Continuously charged. The zirconia powder was stirred and mixed in advance in a container under the conditions of 925 μm: 725 μm: 550 μm: 260 μm: 70 μm = 4: 2: 1: 1: 3.

  In this experiment, as a result of filling, the input amount of zirconia powder was 130 g, and the filling rate at this time was 82.5%.

  Next, another example of an experiment that specifically simulates the filling step 7 (FIG. 1) will be described with reference to FIGS. In this example, when the granular material 5 is put into the waste container 1, the waste container 1 is placed on a table (vibration table) (not shown) that can be moved up and down to vibrate the waste container 1. By doing so, the porosity is lowered and the filling rate is increased. This is the same as in the experiments of FIGS.

  The waste container 1 was 30 cm thick, 1 m wide, and 1.5 m high. As the simulated waste 13 simulating the radioactive metal waste 2, a stainless steel plate and piping with a gap of 80% was placed in the waste container 1. As the granular material 5, what preliminarily mixed silica sand Nos. 5, 6, and 7 defined by JIS (G5901) at a ratio of 1: 1: 1 was used. As described above, the powder body 5 preferably has at least three types of particle size distributions in order to reduce mutual voids and increase the filling rate. The granular material 5 was injected into the waste container 1 from above through an injection pipe (tube) 40. Here, in order to avoid clogging of the granular material 5 in the injection pipe 40, the inner diameter of the injection pipe 40 is preferably set to 10 times or more the maximum particle diameter of the granular material 5.

  In the experimental example (simple filling) of FIG. 6, the granular material 5 was injected (filled) in a state where the injection pipe 40 was fixed so that the outlet of the injection pipe 40 was positioned above the waste container 1. In this case, the porosity after filling was 51%.

  In the experimental example of FIG. 7 (drawing and filling), the injection pipe 40 was first inserted so that the outlet of the injection pipe 40 was positioned in the gap of the simulated waste 13 near the bottom of the waste container 1 (see FIG. 7A).

  Thereafter, the injection pipe 40 was gradually raised while injecting (filling) the granular material 5 (see FIG. 7B). The rising speed (drawing speed) of the injection pipe 40 was 5 cm / second. As a result of this experimental example, the porosity was improved to 30%.

  The experimental conditions and experimental results of FIGS. 6 and 7 are collectively shown in FIG.

  Next, in the filling step 7 (FIG. 1), when the powder body 5 is filled in the waste container 1, the amount of the powder body 5 filled in the waste container 1 is confirmed, and an appropriate amount is filled. A configuration for stopping the supply of the granular material 5 will be described with reference to FIG.

  For example, two ultrasonic transducers 44 are installed below the lid 42 at the top of the waste container 1. The ultrasonic transducer 44 includes an ultrasonic probe (not shown) that transmits and receives an ultrasonic wave having a required frequency and an ultrasonic transmitter / receiver (not shown) for the ultrasonic probe.

  The ultrasonic transceiver generates a transmission ultrasonic wave 46 having a required frequency from the ultrasonic probe by applying a pulsed electric signal to the ultrasonic probe. The transmitted ultrasonic wave 46 is reflected by the radioactive metal waste 2 or the granular material 5 in the waste container 1, and the reflected wave 48 is detected by the ultrasonic probe. The detected reflected wave 48 is converted into an electric signal by an ultrasonic transmitter / receiver, and is converted into an echo electric signal, which is sent to the processing calculation / flow rate control device 50. In this processing calculation / flow rate control device 50, the echo electric signal is subjected to data processing or calculation processing, and the highest position of the granular material 5 or the radioactive metal waste 2 in the waste container 1 can be detected without contact. When this position reaches a certain height or higher, the supply of the granular material 5 can be stopped automatically or manually.

The procedure flow figure showing one embodiment of the radioactive metal waste disposal method concerning the present invention. It is a figure which shows the example of the experiment which simulated the waste drying process of FIG. 1, Comprising: The typical longitudinal cross-sectional view of an experiment apparatus. It is a figure which shows the example of the experiment which simulated the granular material drying process of FIG. 1, Comprising: The typical longitudinal cross-sectional view of an experimental apparatus. It is a figure which shows the example of the experiment which simulated the granular material filling process of FIG. 1, Comprising: (a) at the time of injection | pouring, (b) at the time of filling vibration, (c) is an experimental apparatus which shows after filling vibration, respectively FIG. The table | surface which shows the experimental condition of FIG. 4, and the outline | summary of a result. It is a figure which shows the example of the other experiment which simulated the powder body filling process of FIG. 1, Comprising: The typical longitudinal cross-sectional view of an experiment apparatus. It is a figure which shows the modification of the example of an experiment of FIG. 6, Comprising: The typical longitudinal cross-sectional view of an experiment apparatus. The table | surface which shows the experimental condition of the example of an experiment of FIG. 6 and FIG. 7, and the summary of a result. It is a figure which shows the structure for confirming the amount of granular material in a waste container in the granular material filling process of FIG. 1, and stopping granular material supply at a time, Comprising: The typical longitudinal cross-sectional view of an apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Waste container 2 ... Radioactive metal waste 5 ... Granule 9 ... Waste

Claims (15)

A waste input process for putting radioactive metal waste into a waste container;
A waste drying step of drying the inside of the waste container after the waste charging step;
A granular material drying step for drying inorganic particles;
After the waste drying step and the powder drying step, filling the powder into the waste container, and filling the powder into the gap between the metal waste in the waste container,
The radioactive metal waste processing method characterized by having.   The radioactive metal waste treatment method according to claim 1, further comprising a sealing step of sealing the waste container after the filling step.   The powder particles are sand, gravel, crushed stone, excavation sludge, glass, silica, alumina, zirconia, slag, silicon nitride, boron nitride, boron carbide, or a combination of a plurality of these. The radioactive metal waste processing method of 1 or 2.   The radioactive metal waste treatment method according to any one of claims 1 to 3, wherein the granular material is composed of granular material having at least three kinds of particle diameters. The waste drying step
A temporary lid fastening step for fastening the temporary lid to the waste container;
A depressurization step of depressurizing the pressure in the waste container after the temporary lid tightening step;
The radioactive metal waste processing method of any one of Claims 1 thru | or 4 characterized by the above-mentioned.   6. The radioactive metal waste processing method according to claim 1, wherein the waste drying step includes a heating step of heating the inside of the waste container. The powder granule drying step includes a hopper charging step of charging the powder granular material into a hopper,
A hopper heating step of heating the hopper after the hopper charging step;
The radioactive metal waste processing method according to claim 1, comprising:   8. The radioactive metal waste processing method according to claim 7, wherein the powder particle drying step includes a step of monitoring humidity in the hopper.   The radioactive metal waste treatment method according to claim 1, wherein the waste drying step includes a step of monitoring humidity in the waste container. The filling step includes
Before introducing the granular material into the waste container, an injection pipe having an inner diameter much larger than the largest one of the particle sizes of the granular material and having an outlet end at the lower end is provided at the outlet end. Arranged near the bottom in the waste container,
Throwing the powder into the waste container while pulling up the injection pipe;
The radioactive metal waste processing method according to claim 1, comprising:   The radioactive metal waste treatment method according to claim 1, wherein the filling step includes a step of vibrating the waste container.   The radioactive metal waste processing method according to claim 11, wherein the step of vibrating the waste container includes a step of irradiating the waste container with ultrasonic waves.   12. The radioactive metal waste processing method according to claim 11, wherein the step of vibrating the waste container includes a step of vibrating a vibration table on which the waste container is placed.   The radioactive metal waste processing method according to any one of claims 1 to 13, wherein the filling step includes a step of measuring the height of the granular material in the waste container using an ultrasonic transducer. . A waste container for receiving radioactive metal waste;
Waste drying means for drying the inside of the waste container that has received the radioactive metal waste;
A hopper that temporarily accommodates inorganic particles;
A granular material drying means for drying the inside of the hopper receiving the granular material;
The granular material dried by the granular material drying means is put into the waste container after being dried by the waste drying means, and the granular material is inserted into the gap of the metal waste in the waste container. Filling means for filling,
A radioactive metal waste treatment system comprising:

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