Development of an Organic Iodine Filter for Filtered Containment Venting Systems of Nuclear Power Plants

Abstract

A design for an organic iodine filter was developed for filtered containment venting systems of nuclear power plants. After the Fukushima Dai-ichi nuclear accident, filtered containment venting systems were developed and installed at nuclear power plants in Japan employing aerosol filters, which are typically combinations of alkaline water scrubbers and metal fiber filters. Using silver zeolite, the newly designed filter absorbs organic iodine, which cannot be captured with alkaline water scrubbers and metal fiber filters. Methyl iodide absorption performance tests were conducted with various gas velocities and compositions, which covered the operating conditions of filtered containment venting systems. The test results demonstrated that the decontamination factors of the silver zeolite were over 50 if an appropriate gas contact time was ensured, even though steam condensation and the existence of hydrogen during vent startup had negative effects on the absorption performance. It was also revealed from the tests that intermittent venting might dampen the silver zeolite and reduce its absorption performance. Flow control of the vent gas was found to be an effective countermeasure to maintain the performance even under such conditions. Filter unit tests and numerical analyses of the gas flow within the filter vessel confirmed that the gas contact time was uniform in the filter and appropriate for achieving a decontamination factor of 50.

Effects of Zeolitic Parameters and Irradiation on the Retention Properties of Silver Zeolites Exposed to Molecular Iodine

“…By comparison with organic or hybrid materials such activated carbons/charcoals and Metal Organic Frameworks, silver zeolites are more robust under oxidizing/ionizing conditions. 6 Nowadays, works are ongoing to develop new FCVS with silver zeolites 18 but many scientific gaps still persist, for instance about the relationships existing between the zeolite characteristics and their filtration behavior. Despite hundreds structural types of zeolites exist, most of academic and industrial studies have focused on Ag/X and Ag/MOR types.…”

“…By comparison with organic or hybrid materials such activated carbons/charcoals and metal organic frameworks, silver zeolites are more robust under oxidizing/ionizing conditions, and are also believed to be more selective for iodine under representative accidental conditions . Nowadays, works are ongoing to develop new FCVS with silver zeolites but many scientific gaps still persist, for instance data about the relationships existing between the zeolite characteristics and their filtration behavior. Despite the existence of hundreds of structural types of zeolites, most academic and industrial studies have focused on Ag/X and Ag/MOR types. ,,− These latter materials are also those sold for iodine retention (FCVS and fuel reprocessing applications) by commercial suppliers (for instance under the Ionex trademark).…”