A Low Cost Radioiodine Air Sampling System for Nuclear Incidents: Experience at Three Mile Island

An air mover was developed to draw 5 ± .5 ft3 min-1 through a combined HEPA filter and absorber. The air mover can be operated on 110V alternating current or 12V direct current available from standard automotive electrical systems. Air mover cost was a major design consideration. The third (last) prototype was used to estimate production cost of 100 air movers. The overall unit cost for an air mover and a filter-canister assembly was between $157 and $107 in 1978 dollars. A 4% silver loaded silica gel adsorber was developed that would trap organic iodine, hypoiodous acid, and elemental iodine with better than 90% efficiency under severe ambient conditions, for a 5 minute collection cycle. The principal advantage of the 4% silver loaded silica-gel adsorber was low noble gas adsorption efficiency. Xenon adsorption efficiency was less than 5 × 10-3% at 55° C and 4 × 10-2% at 7° C. The last figure is about 200 times better than charcoal at the same temperatures. High photon efficiency G. M. detectors were tested for improved filter-adsorber readout sensitivity. A specially filtered Victoreen 6306 tube provided a sensitivity improvement of more than 10 times the standard CDV 700 probe. The new Victoreen probe was designed to be about a factor of 2 less sensitive to 135Xe than 131I. The standard CDV 700 probe is more sensitive to 135Xe than 131I. Three Mile Island provided an operational test of the air sampling system. The following observations and conclusions are offered: a.