The Composite Materials for Localization of Volatile Radioactive Iodine Forms from Steam-Air Phase during Severe Accidents at NPPs

Abstract

The safety of NPPs is currently a problem of particular concern in all industrially developed countries throughout the world. The various science and technology projects being developed in this area seek to minimize the possibility of accidents. During severe accidents the formation of large quantities of gaseous products, which leads to an abrupt increase in pressure inside the containment (protective casing) take place. Eventually, there is a risk of destroying the containment as such. Besides, such accidents may cause contamination of the nuclear power plant closed areas, such as the intercontainment area, technical and service corridors, reactor area, et cetera, due to leakage through non-airtight sectors of the containment. It was established that such a leak of the air-and-steam mix out of the containment can reach a rate of 0.3 to 1.0 % per 24 h. Today, in order to prevent environmental pollution in the event of severe accidents, the operational nuclear power plants are equipped with emergency valves that can be activated to reduce the pressure inside the containment, in which case the air-and-steam flow, carrying radioactive aerosols and volatile fission products, is forced through special decontamination systems (Asmolov, 1994; Particulate Filtration in Nuclear Facilities, 1991; Containment Systems and Components for LOCA and Severe Accident Mitigation, 1993; Rogers, 1990). The all systems, excepting sand bed and gravel filter, have a high efficiency of localization of aerosols, and some of them have a high efficiency relative to molecular form of iodine. However, these systems, excepting Germany system, including the filter based on molecular sieve, practically do not localize the organic form of iodine, such as methyl iodide. WWER-440/V-230 NPPs are first-generation Russian NPPs that have been operated for more than 25 years now. As the engineering of the designs of these stations was realized long before severe accidents at Three Mile Island and Chernobyl NPPs, all system of localization of accidents was plotted on the concept of impossibility of severe accidents at NPPs. However now point of view varies and the concept of improvement of a protection system of Russian WWER-440/V-230 NPPs with allowance for possibilities of severe accidents is now considered. All modifications of Russian WWER-440/V-230 NPPs belong to this first generation (Kovalevich et al., 2000; Dragunov et al., 2006).