For LMFBR fuel reprocessing plants, a required radioiodine retention factor of ^ 1()8 is projected. Also projected is a cumulative retention factor of ^ 10f or iodine fixation achieved upstream of the filter-adsorber assembly used for final off-gas treatment. Thus, this assembly will need to provide a decontamination factor (DF) of *v 102, but considerable reserve capability is desired. Certain silver-containing sorbents in a 2-in. depth at 100°C and/or 200°C have, in shortterm laboratory tests, exhibited DF T s of > 103 for iodine as methyl iodide or elemental iodine under conditions including 3 vol % water vapor and iodine loadings estimated equivalent to that for at least one year of operation. Present objectives are to obtain information on the effective service life of such sorbeuts and to ascertain the desirability of locating a catalytic oxidation bed upstream of the sorbents to minimize poisoning by organics and to convert organic iodides to l£. Accordingly, a laboratory facility for exposing sorbents to simulated fuel reprocessing off-gas is being operated. The main air stream is humidified to around 85% saturation (referred to room temperature). Elemental iodine (60-day 125l-labeled), dodecane, and nitric oxide are continuously injected at their anticipated concentrations. One group of sorbents is exposed to untreated off-gas while another group is exposed to off-gas which has traversed a Hopcalite bed at 350°C. Methyl iodide (12.3-hr 130i-labeled) is injected periodically to furnish short-term results, whereas long-term cumulative results are obtained with the I 2 .Sorbents investigated include three varieties of silver zeolite (designated AgX with the percent Ag + for Na + exchange denoted), GX135 (silver salt-treated alumina-silica), and a type of iodized charcoal. Sorbent depths are 2 in. Excellent performance (indicated 12 and CH3I DF's £ 10-?) has been observed thus far for the following test situations: 26% AgX, 1/16-in. pellets, at 200°C, both with and without Hopcalite upstream, 196 days exposure; 99% AgX, 1/16-in. pellets, 100°C, both with and without Hopcalite, 105 days; GX135 (8 x 16 mesh, U.S.), 200°C, with Hopcalite, 196 days; and GX135, 100°C, without Hopcalite, 119 days. (Data are not yet available for GX135, 100°C, with. Hopcalite.) Performances observed for other test situations ranged from poor to good. The importance of sorbent particle size was demonstrated by the less favorable performance of 88% AgX, 1/8-in. pellets, 100 and 200°C, relative to that for the 26% AgX, 1/16-in. pellets (200°C). The use of Hopcalite was observed highly beneficial in trapping iodine injected as CH3I; in trapping iodine injected as Io» its use was beneficial for 26% AgX, 99% AgX, and GX135 and deleterious for 88% AgX (l/8~in. pellets) and iodized charcoal (the latter at 66°C). This investigation is being continued.
Contamination of the atmosphere can be controlled by a disposal system based upon adsorption of gases by porous solids T m continuous release of fission product gases is a characteristic of circulating fuel nuclear reactors not found in heterogeneous solid fuel nuclear reactors. For reactor operation this is advantageous in that these fission gases can be removed from the system, and the concentration of xenon-135, a reactor poison, can be maintained a t l o~v concentrations. The yield of fission gases through fission of uranium-235 is high, and consequently the radioactivity of the gas mixture is of such magnitude that direct disposal into the atmosphere is prohibited. Special provisions must be made for the disposal of these gases.Two methods for the disposal of fission gases, other than direct release into the atmosphere, have been reported. One method, involving complete containment in gas storage tanks, has been applied a t the Shippingport Reactor Site ( 3 ) . A second method involving the absorption of fission gases by kerosinebase solvents has been proposed (5). TheoreticalI n the process of dynamic adsorption, the fission gases, krypton and xenon, are physically adsorbed from the carrier gas stream onto the surface of a solid adsorbent such as activated charcoal. ' 4 state of equilibrium exists a t every point, and fission gas molecules will be desorbed from the surface a t the same rate as others are being adsorbed from the gas stream. While the fission gas molecules are not permanently adsorbed, this adsorption process effectively increases the time required for a fission gas molecule to pass through a portion of the adsorber system relative to the passage time required for the carrier gas molecules.The longer the fission gases can be detained in the system, the lower will be the level of radioactivity issuing from the adsorber system because of radiodecay. The disappearance of the fission gas atoms through the process of radiodtscay renders the system self-regenerating.To analyze the experimental data a theoretical treatment of the dynamic adsorption process was developed ( 2 ) . I t is assumed that an adsorber column is divided into a number of theoretical dP -FAY P dt k'nz P.td If X' differential equations for the -Y chambers are solved simultaneously, setting k' equal to k/p,,d, the solution of the general equation for the Al-th chamber is :where k rn k' = partial pressure of fission gas, atm. = standard pressure (1 atm.) = amount of fission gas injected into first chamber, cc. at STP = number of theoretical chambers = flow rate of carrier gas, cc. min. = time after injection of fission gas = dynamic adsorption coefficient, = weight of adsorbent, grams = static equilibrium adsorption coefficient derived from linear portion of isotherm, cc./gramatm.pulse, min.cc./gram chambers* ' ' 3 and as gas enters each T h e time, t, , , , to reach maximum parchamber it is instantly distributed and brought to adsorption equilibrium Equation by setting dP/dt = o.through the theoretical chamber. The tial pressure,...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.