Since the nuclear accident in Fukushima, the safety measures for nuclear power generation have been reviewed all over the world. Among these safety measures, the filtered venting system is highly desired as a final facility that prevents the diffusion of radioactive materials around the power plant.

 

Radioactive iodine is one of the most important nuclides to be prevented diffusion from a nuclear facility. The radioactive iodine can be divided into two forms. One is inorganic iodine, and another organic iodine compound. The inorganic iodine can be almost removed completely by a scrubber or metal fiber filter system.

 

However, it is very difficult to remove the organic iodine components such as methyl iodide because of their highly volatility. The proportion of organic iodine is estimated to be a few percent in iodine. But even if inorganic iodine can be removed completely by a scrubber system or metal fiber system, total removal efficiency of radioactive iodine for this equipment will be determined by the ratio of organic iodine.

 

Unlike inorganic iodine, methyl iodide is absorbed immediately by the lungs through breathing. With a single breath, about 75% of the methyl iodide that inhaled into the lungs is absorbed and immediately moves from the lungs to the blood. The methyl iodide will diffuse to thyroid within several minutes.

 

Currently, many nuclear power plants in the world are considering installing the filter vent facilities as the measures to remove organic iodine. In order to meet the needs of nuclear safety utilization, we have developed AgX adsorbent. It shows excellent adsorption performance of organic iodine even under the severe off-gas conditions. In addition, we also developed a new adsorbent AgR. It not only shows a very high adsorption efficiency of organic iodine, but it can also works very well in the atmosphere with a higher concentrations of hydrogen. Therefore, AgX is preferentially recommended for BWR and AgR for PWR.

 

In order to broaden the application range of AgX adsorbent, its low-temperature adsorption performance has been examined. The experimental   results show that AgX can keep a high adsorption efficiency as low as 40 degrees below zero. Furthermore, since AgX can play its role at high relative humidity, it is possible to build an air purification system that removes radioactive iodine from the outside air. This equipment can be designed very simple.

 

The purpose of this presentation is to describe in detail adsorption characteristics of organic iodine on AgX and AgR, and to introduce its applications to nuclear facilities, in particular to nuclear power plant.


Agx and Agr as Highly Efficient Adsorbents for Organic Iodine

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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