JPH0565837B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an iodine removal method, and particularly to an iodine removal method suitable for application to reprocessing plants and the like where effective iodine is generated. [Background of the Invention] At nuclear power facilities, various measures are taken to reduce the amount of radioactivity released into the surrounding environment in order to prevent surrounding residents from being exposed to radiation. Of these, radioactive iodine is selectively absorbed by the human thyroid and increases radiation exposure, so particularly strict measures are taken to reduce the amount of radioactivity released. As a measure to reduce exhaust gas, it is common practice to install an iodine removal filter filled with an adsorbent having a diameter of about 1 to 2 mm. Typical nuclear facilities include nuclear power plants and nuclear fuel reprocessing plants. In the former case, impregnated charcoal filters have been used for a long time. On the other hand, in the latter nuclear fuel reprocessing plant, a silver-impregnated adsorbent is used as an iodine removal filter. Although they are the same iodine removal filter, the performance required of the two filters is significantly different. In other words, in the former nuclear power plant, the target radioactive iodine has a short half-life.
¹³¹ I (half-life 8 days) and has an extremely low iodine concentration of 0.1 ppb. On the other hand, in the reprocessing plant, the target radioactive iodine is ¹²⁹ I (half-life 1.7×10 ^{7 )} , which has a long half-life.
year), and the iodine concentration is 50ppm, 500,000 times higher than in the former. From the above, the following three requirements are required for adsorbents for treating exhaust gas from reprocessing plants. That is, (1) ¹²⁹ I can be removed with high efficiency in order to reduce the amount of radioactivity released from the blunt. (2) The iodine adsorption capacity of the adsorbent is large and the amount of used adsorbent as waste is small; and (3)
There are three points: ¹²⁹ I can be stored semi-permanently as a chemically stable compound. From this point of view, the following two methods are currently being researched and developed or put into practical use. An outline of these two methods is shown in FIGS. 1 and 2. The system shown in FIG. 1 consists only of an adsorption tower 1 filled with a silver-impregnated adsorbent. This method has already been put into practical use because of its simple system, but it has the problem of using a large amount of expensive silver because the used silver-impregnated adsorbent is directly disposed of. The method shown in Figure 2 uses a silver-impregnated adsorbent to adsorb and remove iodine with high removal efficiency, then regenerates the silver-impregnated adsorbent with _H2 , and uses the iodine generated by the regeneration as a material that is cheaper than silver. It is intended to be adsorbed onto a lead-impregnated adsorbent. This system consists of two adsorption towers 1 filled with a silver-impregnated adsorbent, an adsorption tower 2 filled with a lead-impregnated adsorbent, a heater 3 for heating _H2 , a cooler 4, and an _H2 circulation pump 5. Ru. One of the adsorption towers 1 allows a process gas to flow therethrough and adsorbs and removes iodine. On the other hand, the adsorption tower 1 is regenerated with H ₂ (500° C.) heated by the heater 3. At this time, iodine is desorbed from the silver-impregnated adsorbent as HI (hydrogen iodide). Contains iodine passed through adsorption tower 1
The H ₂ is cooled to 150°C by a cooler 4 and sent to an adsorption tower 3 filled with lead-impregnated adsorbent via an H ₂ circulation pump 5.
, where iodine is adsorbed. The adsorption tower 1 that has been regenerated is placed in a standby state because it is used again to adsorb and remove iodine from the process gas, and the lead-impregnated adsorbent that has adsorbed iodine is discarded. Therefore, in this method, the consumption of expensive silver is reduced to 1/10 to 1/20 compared to the method shown in FIG. 1, since the amount of expensive silver consumed is limited to the silver-impregnated adsorbent generated as a result of regeneration deterioration. However, since the system becomes complicated, problems arise such as a large initial investment in equipment and complicated operation. Therefore, there is a need for an iodine removal device that has a simple system and consumes less silver. [Object of the Invention] An object of the present invention is to provide an iodine removal method that can achieve a high iodine removal rate with less silver consumption. [Summary of the Invention] The present invention is characterized in that the relative humidity of a gas containing iodine is set to 40% or less, and the gas having a relative humidity of 40% or less is impregnated with a metal containing at least either metallic copper or metallic lead. The gas is introduced into a first stage adsorption tower filled with adsorbent and whose adsorption temperature is 170°C or less, and the gas flowing out from the first stage adsorption tower is supplied to a second stage adsorption tower filled with an adsorbent impregnated with a silver compound. [Embodiments of the Invention] The present invention was made based on the following experimental results. Table 1 shows the results of measuring the adsorption amount of iodine for three types of metals selected from various elements.

〔Effect of the invention〕

According to the present invention, a gas containing iodine with a relative humidity of 40% or less is filled with an adsorbent impregnated with a metal containing at least either metallic copper or metallic lead, and the adsorption temperature is 170°C or less. Since it is sequentially supplied to the column and the subsequent adsorption column filled with an adsorbent impregnated with a silver compound, a high iodine removal rate can be obtained and the amount of silver consumed can be significantly reduced.
The amount of silver consumed is approximately 1/20th that of the device shown in Figure 1.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the flow of an iodine removal device using only an adsorption tower filled with a conventional silver-impregnated adsorbent, Figure 2 is a diagram showing the flow when a conventional silver-impregnated adsorbent is used repeatedly, and Figure 3 4 is a diagram showing the relationship between the amount of iodine adsorbed by the adsorbent of the present invention impregnated with metallic copper and adsorption temperature, and FIG. 4 is a diagram showing the influence of water vapor on the amount of iodine adsorbed by the adsorbent impregnated with metallic copper. , FIG. 5 is a basic flow diagram showing one embodiment of the present invention, FIG. 6 is a diagram showing an example of the adsorption distribution of iodine in an adsorption tower filled with an adsorbent impregnated with metallic copper, and FIG. The figure is a diagram showing the basic flow of another embodiment of the present invention. 1... Adsorption tower filled with silver-impregnated adsorbent, 2...
Adsorption tower filled with lead-impregnated adsorbent, 3... heater,
4...Cooler, 5...Circulation pump, 6...Adsorption tower filled with copper-impregnated adsorbent, 7...Heater, 8...
...dehumidification tower.

Claims (1)

[Claims] 1 In a method for removing iodine from gas,
The relative humidity of the gas containing iodine is set to 40% or less, and the gas with a relative humidity of 40% or less is filled with an adsorbent impregnated with a metal containing at least either metallic copper or metallic lead, and the adsorption temperature is 170
A method for removing iodine, characterized in that the gas is introduced into a first adsorption tower at a temperature of 0.degree.