Iodine filters

In aqueous solution, one is faced with the scattering of pure water (9), which is a strong scatterer below 200 cm-l with some broad structure around 150 cm-- -. Since water scattering is not an instrumental artifact, one does not evade this problem in going from a double to a triple monochromator or by using the iodine filter technique. The rotating divided-cell technique (10)... 

Rodgers, S.J., Udavcak, R.J., and Mausteller, J.W. (1965). Development of medium flow rate, high-purity, particulate, and iodine filters. Intern. Symp. Fission Prod. Release Transport Accident Conditions, Oak Ridge, Tenn., 1204-15. 

The gaseous waste treatment system prowdes storage of radioactive effluent until it decays down to a value allowable for discharge to the environment through the HEPA filter and iodine filter into the plant stack. 

Pathways for venting the containment atmosphere may be provided for a number of reasons, and these pathways may be equipped with filters to remove iodine from the vented gas. Filters for iodine removal can be present in both passive systems (in which flow continues only as long as there is a pressme difference) and active systems (in which there is a continuous forced flow at a controllable rate). Dry filters intended for the removal of aerosol particles are not likely to be effective for the removal of gaseous forms of iodine, especially organic iodides. Even if gaseous iodine will absorb on the filter mediiun, heat loads on the filter medium caused by radioactive decay can lead to revaporization of the absorbed iodine. Filters that involve water must be maintained at high pH to avoid the formation of volatile forms of iodine by processes identical to those that occur in reactor containment smnps. 

Following a loss-of-coolant accident, a fraction of the radionuclides released from the primary circuit remains airborne in the containment atmosphere, as was discussed in the preceding sections. In order to reduce the airborne activity concentrations, standby filters are installed in the annulus of the German PWR plants, consisting of aerosol filters and iodine filters. In the German RSK Guidelines a retention efficiency of 99.9% for particulate iodine, of >99.99% for h and of >99% for organoiodides is required under accident conditions. In certain other countries, the specified iodine species as well as the required retention efficiencies differ somewhat from these values. 

Aerosol iodides are also retained by the HEPA filters very efficiently, h and HI present in gaseous form in the atmosphere are to a part trapped on the surfaces of aersosol particles, with the responsible mechanisms being adsorption or chemical reaction. However, early on it was recognized that a fraction of the adsorbed iodide may desorb again from these filters (e. g. Adams and Ackley, 1968), due to reactions of reversibly bound iodine with the flowing air, the water vapor or the impurities present in it. Thus, at higher concentrations of particulate iodine in air a special iodine filter has to be added to the particulate filter. 

Under extreme filtration conditions (temperature >150°C), impregnated charcoals suffer from an increasing desorption of radioiodine. For such severe conditions other iodine filter materials have been developed such as silver-containing inorganic sorbents which exhibit a very low desorption of iodine even under extreme conditions, since the adsorbed iodine is bound as the very stable chemical compound Agl. However, such conditions are far more severe than those to be expected in design basis accidents there is no need, therefore, to replace the impregnated charcoals by these expensive materials. 

Wilhelm, J. G. Iodine filters in nuclear installations. Report Commission of the European Communities, Contract No. 1175-80-12 LA (1982)... 

Finally, the standby filters of the annulus air extraction system will act as an additional barrier, preventing the release of radionuclides from the annuli to the environment. The comparatively high humidity of the off-gas under accident conditions does not adversely affect the function of the aerosol filters, but potentially reduces the efficiency of the iodine filters. Nonetheless, a retention efficiency of >99% for I2 and of >90% for CH3I can be assumed, even under such unfavorable conditions. 

At Temeh n NPP, there is an emergency ventilation system of the MCR. Therefore, the ventilation system is equipped with ZFA aerosol and iodine filters. A study is elaborated for the case of emergency ventilation and habitability of the ECR. The study will be used as a basis for the implementation of possible modification. 

The Local Technical Centre (LTC) evaluates the situation of the incident and the possible development that might be foreseen. The LTC is located near the control room. This centre has ventilation systems protected by aerosol and iodine filters. It is also equipped with emergency power supply and communication means are available for all communication channels necessary with redundant backup. There is an emergency communication system based on the INMARSAT satellite communication... 

Airborne iodine and particulate radioactive material should be measured by passing air samples through combined particulate and iodine filters, on which gamma ray spectroscopy can then be carried out either with mobile equipment or with equipment in a laboratory that is operable under accident conditions. Provision should be made in advance for the transport of mobile monitoring equipment. 

The low frequency Raman spectra of these crystals have been reported by Peticolas et al. (65) using the iodine filter technique described above. 

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