Combined Filter for Purifying a Radioactive Steam-Gas Mixture

The design of a new fireproof combined filter for purifying a radioactive steam-gas mixture by removing volatile compounds of radioactive iodine during normal operation of NPP as well as during accidental depressurization of fuel rods is described. The filter consists of identical cylindrical sections, each of which possesses a top lid for anchoring spiral filtering elements with variable surface area and a bottom lid with a grid for anchoring sorbents. The first and closing sections along the course of the purified gas flow are filled with sorbent consisting of the inorganic material SiO₂–Cu⁰ or KSKG brand silica gel or a mixture of the two. A granulated sorbent based on SKT-3I brand activated charcoal or Fizkhimin inorganic granulated sorbent based on silica gel is used as a filler in each of the intermediate sections to catch volatile forms of radioactive iodine. The size of the pores in the spiral filtering elements with variable surface area decreases in a direction from the first to the closing section along the course of the purified gas flow; there are at least three sections equipped with sorbent for purifying gases by removing radioactive iodine-containing impurities.