Mechanism Research On Aerosol Filtration In Containment Vessel By MEMS Inertial Impactor

Normally, the concentration of natural radioactive aerosols in the vessel atmosphere plant is very low and in balance. But when there is a serious nuclear accident, the concentration of radioactive aerosols in the containment will increase rapidly. It will increase the risk of accident and cause a serious damage to the atmospheric environment if such radioactive aerosols directly release. So the filter used for adsorbing radioactive aerosols is necessary.At present, the common aerosol filters use mesh structures or filter papers, which need filter papers replacement and can significantly increase the flow resistance in the course of aerosol deposition and retard the containment pressure relief following the nuclear accidents. What’s more, it has been a technical problem to replace filter papers under the highly radioactive condition, in addition, the used filter papers will become new radioactive wastes.This paper proposes and studies MEMS (Micro Electro Mechanical Systems) inertial impactor filter that filtrates and collects radioactive aerosols without replacing filter papers, and won’t cause new radioactive liquid or solid wastes at the same time. Micro Electro Mechanical Systems belongs to micro device technology, which has many potential advantages, such as higher performance, low power dissipation, rapid response and low cost. Moreover, the device has a small volume and simple working principle. The new device can achieve aerosol collection under the premise that not retard the step-down velocity of containment. In past twenty years, the MEMS technology has made lots of progress. But according to the survey, there is no inertial impact device based on MEMS technology, not to mention the precedent that use MEMS technology to collect plant aerosols. This study of MEMS device aims at filtering and collecting aerosols within 1 to 3 microns, which is a new attempt both on the design concept and technology.The study designs MEMS inertial impactor filter based on the actual environment of nuclear power plant accident cases. Getting the vessel air flow field using CFD (computational fluid dynamics) software and calculating the trajectory of aerosol particles in the flow field based on DPM model (discrete phase model). Finally, we determine whether the particles are collected according to the result. After a lot of simulation test, we can find parameters which affect collection efficiency, so the suitable size of inertial impact for the aerosol filtration can be determinated. And then, we design simulation experiments to obtain the collection efficiency of the impactor, and validate its feasibility.What’s more, take the practical engineering application into account, this article also compare the collection efficiency of the each impact under different shapes bottoms, and analyses the different effects from different bottoms on collection efficiency. In the end, get the most suitable aerosol filtration device type after comprehensive study.