Uses an original noble gas filter plus an organic iodine filter to minimize impact on the external environment
The HI-ABWR (Highly Innovative Advanced Boiling Water Reactor)*1 developed by Hitachi-GE Nuclear Energy, Ltd. (“Hitachi-GE”) will be equipped with a radioactive substance containment system consisting of a noble gas filter and an organic iodine filter with improved removal effectiveness, in addition to the conventional filter vent system*2 (Figure 1, center). Up to now, radioactive noble gases*3 that are one class of radionuclides have undergone decay prior to release; but the decay process has the problem of requiring a large amount of equipment. Hitachi, seizing on the difference in polarity and molecular size*4 between radioactive noble gases and the steam and hydrogen released from a plant, is developing technology using an original membrane filter to separate and remove the radioactive gases (Figure 1 (a)). For radioactive organic iodine,*5 Hitachi developed organic iodine adsorption technology with improved removal efficiency, by replacing the conventional zeolite*6 adsorbent with an ionic liquid-based material*7 (Figure 1 (b)). Making use of electrostatic interaction*8 with the ionic liquid, organic iodine can be selectively removed. Moreover, since solid zeolite material is not used, pressure drop in the filter vent system are reduced and the noble gas filter (membrane filter) can be made compact. It is expected that the combination these technologies enables this system to be installed in the limited space in existing nuclear power plants while minimizing the impact on the external environment.
Hitachi intends to continue working closely with Hitachi-GE, contributing to enhanced nuclear safety through the realization of HI-ABWR with its low environmental impact.
Development of the organic iodine filter in this project was partially funded by a grant from the Agency for Natural Resources and Energy of Japan’s Ministry of Economy, Trade and Industry, given for technology development contributing to enhanced nuclear safety.
Figure 1. Radioactive substances containment system
*1 Highly Innovative ABWR (HI-ABWR):
: https://www.hitachi-hgne.co.jp/en/activities/advanced_reactor/hi_abwr/pdf/brochure_hi-abwr.pdf
*2 Filter vent system: Equipment that removes most FP with long-term impact from gases released external environment the plant to protect the plant in case of an accident.
*3 Radioactive noble gases: Xenon, krypton and other noble gas radionuclides discharged at nuclear facilities in an accident.
*4 Difference in polarity and molecular size: Separation making use of differences in polarity of molecules, a property indicating their electrical bias (steam has strong polarity whereas noble gases have neutral polarity), or of differences in molecular size (noble gases are large and steam is small).
*5 Radioactive organic iodine: A highly volatile gaseous substance formed by chemical bonding of iodine with methyl iodide and other organic matter generated at nuclear facilities in an accident.
*6 Zeolite: The general name for various microporous, crystalline aluminosilicate materials. Among their functions are as molecular sieves, ion exchangers, catalysts, and adsorbents.
*7 Ionic liquid: An organic salt in liquid state, consisting entirely of ions. It has electrolyte, lubricant, and adsorbent functions among others.
*8 Electrostatic interaction: Electromagnetic forces acting between molecules, such as ion bonding, hydrogen bonding, and dipole interaction.
*9 FP: Fission products generated in the combustion of nuclear fuel. The main fission products include iodine and cesium. The radioactive noble gases xenon and krypton are also included.
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