[en] An integral step in the test procedure for determining the trapping efficiency of methyliodide at 25⁰C is the prehumidification of the impregnated charcoal. The specifications (1) direct that the prehumidification with air at 95 +- 2% RH be continued until the temperatures recorded at the entrance and exit of the charcoal bed are equal. Since this operation may require about five hours, it is convenient to allow the prehumidification to extent overnight (sixteen hours). This Note is concerned with the unexpected adverse influence on methyliodide trapping by exposures of charcoals to prehumidification at long contact times

[en] Traditionally, weathering data have been expressed in terms of removal efficiency as a function of time for a select number of bed depths. Variables include: (1) variations in the efficiency of the adsorbent when new; (2) guard bed design (bed depth, replacement schedule); (3) air quality; and (4) air velocity. This paper discusses the development of a single parameter, namely, the Effective Weathering Rate (EWR), its usefulness in correlating weathering data, and subsequent utilization during design. The effectiveness of the model was checked by analyzing several sets of data. Values of EWR were determined from the limited available experimental data for air which could be described only qualitatively as ranging from relatively clean to relatively dirty air from a heavily industrialized area. As quantitative data become available, it is expected that the EWR can be correlated with the character and concentration of air contaminants such as hydrocarbons, SO₂, NO/sub x/ and O₃. The EWR, determined from experimental data, can be used to predict adsorber efficiencies for conditions corresponding to a specific application. Some of the changes in conditions which can be treated by this method include: (1) bed depth of adsorbent, (2) addition of guard bed or depth of guard bed, (3) effectiveness of the carbon (new), (4) operating time, and (5) air velocity. Someparametric studies were performed analytically to demonstrate some applications of the weathering model. These included calculating the adsorber efficiency as a function of time and bed depth, for carbons having various efficiencies when new, and for guard beds of variable bed depth and having different replacement schedules for the guard bed material

[en] The adsorption of non-radioactive methyl iodide has been measured experimentally over a range of conditions of concentration, and temperature on an activated charcoal. This is of interest since methyl iodide is formed from iodine fission products in gas cooled nuclear reactors. A mathematical model has also been developed which describes the rate of adsorption, under isothermal and linear adsorption isotherm conditions in a recycle adsorber. This model takes into account the resistance to adsorption caused by the surface adsorption, as well as the external and internal mass transfer resistances. The solution to the model for the recycle adsorber was obtained using a semidiscretisation method to reduce the partial differential equations to a system of stiff ordinary differential equations, and the resulting differential equations solved by a standard numerical technique. (author)

No abstract available

[en] Experimental measurements have been made on the breakthrough behaviour of (non-radioactive) methyl iodide in a fixed bed of activated charcoal. The system is of interest since radioactive methyl iodide is present in the circulating gas in a nuclear reactor and charcoal beds are installed to adsorb volatile radioactive compounds in case the circulating gas has to be released to the atmosphere in an emergency. A mathematical model has been developed which, using the parameters obtained in the preceding paper, gives a good prediction of the breakthrough curves for particle sizes up to 8.6 x 10^-4m. Theory and experiment can be reconciled for larger particle sizes by allowing for their lack of sphericity through a shape factor. (author)

[en] An adsorption model to predict the time-dependent removal efficiency of methyl iodide by a triethylene-diamine-impregnated charcoal bed under various operating conditions is proposed. The mass transfer controlling step is pore diffusion. Under humid conditions, the reduction of equilibrium adsorption capacity and effective pore diffusivity is considered. The predicted values agree well with the experimental results

[en] A technique to determine the content of methyl iodide in dimethylcadmium is developed which lowers the minimum detectable concentration of methyl iodide by two orders (down to 10^-2 mol.%) due to dimethylcadmium fixation in mass spectrometer intake tube by adsorbed mercury

[en] A new and efficient synthesis of high specific activity TCH₂I containing one atom of tritium per molecule is reported. The precursors for this reagent, chloromethyl p-phenylbenzoate or bis-chloromethyl terephthalate, were prepared by the condensation of the corresponding acid chlorides with paraformaldehyde in the presence of zinc chloride. Tritiodehalogenation of the precursors with tritium gas and Pd-C(10%) in dimethylformamide afforded the desired tritioesters. Cleavage of the esters by lithium iodide at 180⁰C (SN₂ type reaction), or by HI at 140⁰C gave mono tritium labeled methyl iodide in more than 95% yield. The reaction of the latter with a number of amines yielded tritium labeled N-methylated products readily as was shown by Radio-HPLC. The specificity of the labeling in the final products was confirmed by tritium nmr spectroscopy. (author)

[en] Procedures have been developed for estimating, at a stated level of confidence, how long a trapping plant can be relied upon to perform its duties and for determining how this estimate depends on the values of the input parameters and their invariances. Analysis of the relationships involved has shown that the frequency with which plant has to be tested and the charcoal changed is reduced if: (a) the K-value of the charcoal in the as-received condition is high; (b) the bed stay-time is large; (c) provision is made for sampling the charcoal during service and measuring its K-value; and (d) the variances of the K-values for the charcoal of the bed stay-time are small. Attention is drawn to the advantages of continuously recording the gas flows through the sorbent bed as a function of time and of maintaining by-pass leakage at as low a level as possible. It has been shown that, in order to avoid having to renew the charcoal at the time of the first re-test, the K-value of the fresh charcoal and the value of bed stay-time must exceed definable limits. (author)

[en] Using a frequency stabilized CO₂ laser, the absorption coefficients of methyl iodide were measured, for more than 40 lines of the P and R branches in the 10.4μm and 9.4μm bands of CO₂. The Stark modulation in CH₃I was studied vs. pressure and applied electric field. The percentage modulation for the P(14) line has a maximum in the pressure range 16-20 torr and increases almost linearly with the Stark voltage (m = -2.7% at 4 kV/cm and 24 torr). We found that three new lines of the CO₂ laser can be modulated by CH₃I, namely P(18), P(22) and P(24), but with a smaller percentage modulation than that for the P(14) line. (author)