V. L. Novichenko

Metal-Containing Zeolites as Sorbents for Localization of Radioiodine and CsI Aerosols from Vapor-Air and Aqueous Phases

New sorbents for efficient sorption of radioiodine and radiocesium from the vapor-gas phase and aqueous solutions were prepared by treatment of Cu+- and Ag+-substituted NaX and NaA zeolites with acetylene in aqueous solution. The distribution factor Kd of radioiodine and radiocesium between the modified sorbents and aqueous solutions is higher than 103-104 ml g-1. Decontamination factor of the vapor-gas phase with respect to radioiodine and 137CsI aerosols exceeds 102-103 and 103, respectively. The sorption properties of the modified sorbents in both aqueous solutions and the vapor-gas phase are better than those of the initial sorbents. However, localization of radioiodine from the vapor-gas phase with the Cu+-containing sorbents is less efficient than with the Ag+-containing zeolites. At the same time, in aqueous solutions the sorption capacity of the Cu+-containing sorbents for radioiodine is appreciably higher than that of the Ag+-containing sorbents. The sorption properties of the modified sorbents were studied as influenced by various factors. Paracomplexes of univalent copper and silver with C2H2, H2O, and anions present in the solution are probably formed during modification of the metal-containing zeolites. The dependence of Kd of radioiodine on the metal concentration in the sorbent, the free pore volume of the sorbent, and the anion nature was revealed.

Oxidative Hydrolysis in Water Vapor-Air Phase of CsI Radioaerosols Produced by CsI Sublimation from Metallic Surface

Behavior of CsI radioaerosols produced by CsI sublimation from a platinum support in argon, air, and water vapor-air mixture was studied. During 10-12 min of the vaporization at 900-1570 K, CsI radioaerosols undergo oxidative hydrolysis with atmospheric oxygen and water vapor to form CsOH aerosols and I2. The cesium-to-iodine ratio determined in various fractions shows that oxidation of CsI in argon is minimal and is caused by the presence of oxygen and water traces. Oxidative hydrolysis of CsI strongly increases with increasing water vapor content in the vapor-gas flow. The degree of oxidative hydrolysis of CsI in the gas flow depends not only on the content of water vapor and oxygen but also on the initial CsI/O2 molar ratio.

The Effect of Hydrophobization of Ag-Containing Zeolites on Absorption of CH3131I from the Water Vapor-Air Phase

The effect of hydrophobization of Ag-containing nonmodified and acetylene-modified zeolites with poly(vinyl chloride) (PVC) on sorption characteristics of sorbents with respect to CH3131I was studied. The PVC coating on the sorbent results in increased absorbtion of CH3131I from a water vapor-air flow at a humidity of up to approximately 70 vol %; the decontamination factor of approximately 105 is reached. The sorbent modified with PVC retains radioiodine at heating to 300°C and can be proposed for practical purposes.

Cocrystallization of Radioiodine Compounds from the Gas Phase

The study of the behavior of 137Cs131I in the presence of MCl (M = NH4+, K+, Ag+, and Cu+) in the water vapor-gas phase showed that CsI aerosols are localized in the MCl matrix owing to both agglomeration cocrystallization [137Cs131I-MCl systems (M = K+, Ag+, NH4+)] and agglomeration capture [137Cs131I-CuCl system]. The main advantage of the first process is formation of crystalline globules encapsulating radioiodine in their bulk, which prevents transformation of radioiodine into elemental iodine and methyl iodide.

Sorption of CH3131I from the Gas Phase on Modified Metal-Substituted Zeolites Containing Copper and Silver Ions

Sorption of CH3131I from vapor-gas flow with acetylene-modified Cu+- or Ag+-containing zeolites in argon atmosphere was studied. The decontamination factor of the gas flow from radioiodine with the sorbent containing 7% of Ag+ is considerably higher than that of the Cu+-containing zeolite and reaches more than 104 at the bed height of 6.5 cm and contact time of 3.4 s. The sorbent capacity is more than 9 mg of CH3I per 1 g of the sorbent. In treatment of the sorbent with water after absorption of CH3I, 131I is not noticeably desorbed to aqueous phase.

Sorption of CH3131I from Steam-Gas Phase on Modified Ag-Containing Zeolites

Sorption of CH3131I from the steam-gas phase on Ag-containing zeolites modified with acetylene was studied. The radioiodine adsorption in a column depends on the silver concentration in the sorbent, humidity of the steam-gas flow, and the temperature. The modified sorbents AgX-m containing ∼30-57% silver efficiently localize CH3I at the humidity up to ∼80% and sorption temperature from 120 to 195°C. Under these conditions the decontamination factor of a gas flow with respect to CH3131I at 7.5-cm height of the sorbent bed and a ∼0.2 s gas-sorbent contact time exceeds 99.99%. The sorption properties of the modified Ag-containing sorbents are better that those of the nonmodified sorbents and known Ag-substituted zeolites.

Modified Cu+-Containing Zeolites as Sorbents for Localization of Radioiodine and Radiocesium Aerosols

New sorbents for efficient sorption of radioiodine and radiocesium from aqueous solutions and vapor-gas phase were prepared by treatment of Cu+-containing NaX and NaA zeolites with acetylene in aqueous solution. The modified zeolites sorb radioiodine and radiocesium from aqueous solution with the distribution coefficient more than 104 and from a vapor-gas flow with the decontamination factor higher than 102 and 103, respectively.