Impregnated charcoal filters

The retention systems which are installed in the Canadian Candu plants show a similar design (McArthur and Salaff, 1988). They consist of a combination of an aerosol filter with different pore sizes and an impregnated charcoal filter with an iodine retention efficiency of better than 99.9%. 

Diborane in air may be analyzed by passing air through a PTFE filter and oxidizer-impregnated charcoal. It is oxidized to boron and desorbed with 3% H2O2. Boron is measured by plasma emission spectrometry or ICP emission spectrometry (NIOSH. 1984. Manual of Analytical Methods, 3rd ed. Cincinnati, OH National Institute for Occupational Safety and Health). Boron hydrides can be analyzed by FTIR techniques. 

The realization that it was more economical to have a single respirator design for all three services led to the introduction of the General Service (GS) respirator, familiar to all those who served in the Second World War. Over 25 million of these respirators were made in the UK alone, and issued to all Commonwealth forces and Civil Defence Corps. The GS respirator consisted of a rubber facepiece with stockinette covering, flat circular eyepieces, a diver-type outlet valve, an elastic webbing harness and a filter canister fitted with an inlet valve. The canister, worn on the body and attached to the facepiece by a hose, was filled with activated charcoal granules, with a wool-asbestos mixture added later, and impregnated charcoal added even later. 

Analysis for diborane in air may be performed by NIOSH Method 6006 (NIOSH 1984). Air is passed through a polytetrafluoroethylene (PTFE) filter and oxidizer-impregnated charcoal at a flow of 0.5 -1 L/min. Diborane is oxidized to boron, which is desorbed with 3% H2O2 and analyzed by plasma emission spectrometry. Alternatively, boron may be analyzed by inductively coupled plasma atomic emission spectrometry (NIOSH 1984, Method 7300). 

The principle of reprocessing is as follows ( PUREX process ). The process starts with cutting the fuel rods in pieces of about 5 cm length. The fuel (UO2/PUO2) is dissolved in half-concentrated nitric acid. Radioactive aerosols and radio-iodine set free in the process are retained in filters (aerosols in mechanical filters, iodine in filters impregnated with silver nitrate). Fission rare gases (mainly Kr, Tin = 10.5 years) maybe condensed in cold charcoal filters and filled later into steel cylinders. 

Stationary filter stations requiring filter collection for measurement Gamma spectrometer in laboratory Radionuclide-specific Provides accurate results Sample collection, transportation, preparation, and measurement is time-consuming Experienced staff required Iodine sampling (eternal tary and organic) with impregnated charcoal and aerosol filters... 

In order to remove radioactive substances potentially present in the air flow, most of the ventilation systems are equipped with filter units consisting of high-efficiency particulate filters (HEPA filters, class S) and iodine adsorbers (activated charcoal, KI impregnated). These filters are monitored, either continuously or at regular intervals the filter efficiency of the iodine adsorbers is determined by taking charcoal samples from the filter beds at regular intervals and analyzing them in the laboratory (see Section 6.2.1.5.). 

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. 

Experimental work at Windscale indicated the best combination of filters and demisters and the appropriate impregnation for the charcoal for the clean-up plant in order to handle air of high relative humidity which would arise following a depressurization accident (refs 2, 3). With this Impregnated charcoal, decontamination factors for methyl iodide better than 105 can be achieved with laboratory scale plant. The work has also indicated the useful life to be expected from the charcoal when the clean-up plant is in continuous use as it is in the prototype reactor. Tests on the actual clean-up plants have shown decontamination factors for methyl iodide of about 105, which is nearing the practical limit of sensitivity for full scale tests. 

Daniel (Ref 1, p 599), under the title Papier explsible describes an expl prepd by impregnating filter paper with aqueous suspension of saltpeter 41.66, K chlorate 41.66, charcoal or coal dust 8.34 sawdust 8.34%, followed by drying some glue was dissolved in water to make the suspension adherent to the paper... 

As, Se, Sb, Br, I and Hg) were observed on the base-treated filters using the combined techniques of PGAA, INAA and IC. The base-treated filters proved to be very efficient collectors of the acidic gas-phase species, but apparently allow some elemental and organic species to pass through as shown by studies with activated charcoal-impregnated filters. 

A series of experiments were conducted with activated-charcoal impregnated filters being used in both side-by-side studies and in... 

The off-gas passes scrubber containing NaOH solution and filters with silver-impregnated zeolite or charcoal in which Ru and I are retained. Kr may be separated by condensation or adsorption on charcoal at liquid-nitrogen temperature. 

The filter can consist of up to three elements. The outer element is a particulate filter, often made of glass fibre paper, pleated to increase surface area. The inner element is a vapour adsorbent, usually activated granular charcoal. The third element comprises various chemicals impregnated on to the charcoal, such as copper, chromium, silver and triethylenediamine (TEDA), to react with volatile chemical agents such as hydrogen cyanide and cyanogen chloride that are poorly adsorbed. 

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