JPS6147597A - Method for removing radioactive iodine from exhaust gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for removing radioactive iodine compounds from exhaust gas emitted from nuclear facilities, and particularly relates to an adsorbent (hereinafter referred to as (referred to as "silver adsorbent").

[Background of the invention]

At nuclear facilities, various measures are taken to reduce the amount of radioactivity released into the surrounding environment in order to prevent the surrounding residents from being exposed to radiation. Among these, radioactive iodine is selectively absorbed by the human thyroid gland, increasing exposure to radiation, 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. Regarding methods for removing iodine from nuclear fuel reprocessing plant exhaust gas, several methods have been researched and developed or have been put into practical use.One of them is to remove iodine from a silver adsorbent that has absorbed iodine at 500p in a hydrogen atmosphere. There is a way to play it below and use it repeatedly.

This conventional method will be explained using FIG. 1. The iodine removal and adsorption devices (adsorption towers) 1 and 2 are of a two-unit switching system, and are switched when iodine exceeds the level. Hydrogen heated to 500C by the heater 3 is vented into the adsorption tower 2 where the adsorption operation has been completed. Iodine adsorbed as silver iodide is desorbed as hydrogen iodide. Meanwhile, at the same time, the silver adsorbent is reduced and regenerated into silver (Ag) by hydrogen.

The hydrogen iodide-containing gas leaving the adsorption tower 2 is cooled to 150C by the cooler 4 and vented to the iodine fixation device 5. Hydrogen iodide in the gas is adsorbed and fixed on a fixing adsorbent (for example, lead zeolite) in the iodine fixing device 5. However, the silver adsorbent regenerated by the above method is
The drawback is that it cannot adsorb organic iodine. Approximately 5% of organic iodine, mainly methyl iodide, is in the reprocessed exhaust gas.
Therefore, when applying a silver adsorbent regeneration system using hydrogen gas to reprocessed exhaust gas, it is necessary to install an additional adsorption tower 6 to adsorb and remove organic iodine after adsorption tower 1゜2. There is. For this reason, the regeneration process of silver adsorbents using hydrogen gas has the problem of increasing consumption of expensive silver and complicating the process.

[Purpose of the invention]

An object of the present invention is to provide a method for regenerating a silver adsorbent so that it can also adsorb organic iodine, in order to solve the above-mentioned problems.

[Summary of the invention]

The present invention was made with the focus on the point that when a silver adsorbent is regenerated with ozone and the regenerated form is made into silver oxide, the silver adsorbent becomes capable of adsorbing even organic iodine such as methyl iodide. .

[Embodiments of the invention]

Preferred embodiments for carrying out the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows the basic flow of a preferred embodiment for carrying out the present invention. The iodine adsorption and removal devices (adsorption towers) 7 and 8, which are of a two-unit switching type, are filled with silver adsorbent. The adsorption tower is switched when the iodine content is exceeded. Oxygen-nitrogen mixed gas (regeneration gas) with an oxygen concentration of about 30% is passed through the ozone generator 9, and the ozone concentration in the mixed gas is adjusted to several inches. , a mixed gas containing several ozone is vented into the adsorption tower 8 where the adsorption operation has been completed for regeneration.
゜Silver iodide on the silver adsorbent is oxidized to silver oxide and regenerated by the following reaction. On the other hand, the iodine adsorbed on the adsorbent is desorbed as elemental iodine gas (I2).

2AgI+03→AgzO+Iz+Oz ・・・・
(1) Most of the ozone is consumed to oxidize silver iodide to silver oxide according to the reaction formula (1).

The trace amount of ozone remaining in the regeneration gas is completely decomposed by the ozone decomposition device 10 filled with a platinum catalyst. In addition, the iodine in the regeneration gas is absorbed into the steel by impregnating copper with alumina.
The iodine fixation device 11 filled with 99.9
% or more are chemotactic. Figure 3 shows that when the regeneration gas is heated, the iodine content W' is
We will investigate how WE changes and show the results. As shown in Figure 3, if the regeneration gas temperature is kept below 150C, it is possible to regenerate the silver-absorbed 714 material with ozone gas.
Furthermore, it was found that the iodine contained in the regeneration gas could be immobilized on the copper adsorbent.

According to this embodiment, a silver adsorbent impregnated with silver sulfate for removing organic iodine such as methyl iodide becomes unnecessary,
Since organic iodine can also be removed with the regenerated silver adsorbent (present as silver oxide), the amount of silver adsorbent used is significantly reduced, which has the effect of reducing the consumption of valuable silver sources. In addition, the regeneration gas temperature is 150C or less, and the regeneration gas temperature due to hydrogen is 5.
Since it can be regenerated at a relatively low temperature compared to 00C,
Energy can be saved. Furthermore, since hydrogen gas is not used as the regeneration gas, it is safe and the apparatus is simple. As described above, according to this embodiment,
You can play around with a number of effects.

In the previous embodiment, it is also possible to use pure oxygen as the regeneration gas instead of the oxygen/nitrogen mixture. In this case, even if an oxygen/nitrogen mixed gas is used, the efficiency of ozone generation is improved, and the regeneration speed of the silver adsorbent that has adsorbed iodine is increased, so the regeneration time can be shortened.

In addition, the same effect as ozone can be obtained by using a combination of hydrogen peroxide, which can generate oxygen in the original ribs, instead of ozone.

〔Effect of the invention〕

According to the present invention, when regenerating a silver adsorbent that has adsorbed iodine, it is possible to regenerate it so that even organic iodine compounds can be adsorbed by a simple method.

[of the drawings] νj′j Simple explanation FIG. 1 is a flow diagram for explaining the conventional embodiment, and FIG.
The figure is a flowchart for explaining the invention in detail, and FIG. 3 is a diagram showing the results of an embodiment of the invention.

1.2... Iodine removal adsorption device, 3... Heater, 4
... Cooler, 5 ... Iodine fixation device, 6 ... Adsorption tower for removing organic iodine, 7, 8 ... Iodine removal adsorption device, 9 ... Ozone generator, 10 ... Ozone Decomposition device, 11...Figure 1

Claims (1)

[Claims] 1. In a method of regenerating and repeatedly using an adsorbent for removing iodine in which silver is impregnated on a carrier, silver iodide, which is a reaction product on the adsorbent, is removed by oxygen in a nascent state. A method for removing radioactive iodine from exhaust gas, which is characterized by oxidation and regeneration. 2. In claim 1, the oxygen in the nascent state is ozone and the oxygen/nitrogen mixed gas at 150°C or less,
The ozone generator, the iodine removal device filled with silver adsorbent that has adsorbed iodine, the ozone decomposition device, and the iodine fixation device filled with the fixation adsorbent are ventilated in this order, and then the ozone is removed again. A method for removing radioactive iodine from exhaust gas, which is characterized by oxidizing silver iodide to silver oxide in the process of returning it to a generator.