Airborne contamination radioactive materials

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

For purposes of emergency planning, EPA-520/1-75-100 provides Protective Action Guides (PAGs) for exposure to airborne radioactive materials, contaminated foodstuff or water, and contaminated property or equipment. (Ref. 6)... 

Radioactive needles contaminated with infectious agents or blood should be autoclaved as described above, and then incinerated on site or shipped to a low-level radioactive waste site. To prevent injuries, it is important that hypodermic needles and other sharps be kept in waste containers that are puncture-resistant, leak-proof, and closable from the point of discard through ultimate disposal. To prevent airborne radioactive materials, destruction of needles by grinding or a similar means is not recommended. 

Terrorism by way of radioactive materials can come in several forms. If the radioactive isotope is a fissionable material (material that can be used to create a chain reaction that could result in a nuclear explosion), such as some plutonium and uranium isotopes, it is possible that it could be combined into a nuclear weapon. Otherwise the radioactive material might be dispersed by a conventional explosion or by airborne means such as a powder or spray from an aircraft. A building could be contaminated by placing finely ground radioactive particles or powder in the ventilation system. The material could also be spread by hand (more dangerous for the terrorist) or mailed in a package or envelope. 

Exposure of a person may be external or internal and may be incurred by various exposure pathways (see Section 9.3). External exposure may be due to direct irradiation from the source, airborne radionuclides in the air (immersion or exposure to an overhead plume), or radionuclides deposited onto the ground and onto a person s clothing and skin. Internal exposure follows from the inhalation of radioactive material either directly from a plume or resuspended from contaminated surfaces, from the ingestion of contaminated food and water, or through contaminated wounds. Total effective dose can be calculated by taking into account all dominant exposure pathways by which persons were exposed. 

Bioassay measurements are subsequently taken at periodic intervals and at termination to detect if unsuspected intakes have occurred. If an intake is suspected, additional special monitoring should be used. An intake may be suspected if the individual has entered an airborne radioactive material area, has contamination on the face or nose, other skin contamination, or other unusual event. 

The primary purpose of anti-C clothing is to prevent skin contamination and the spread of contamination. In most instances, the use of anti-C clothing precedes the use of respirators. It is more common for areas to be contamination areas, indicating that there are surfaces and structures in the area with removable contamination, than it is for an area to be an airborne radioactive material area. Any airborne radioactive material area is automatically a contamination area because it is not possible to have a high concentration of airborne radioactive material without having removable contamination on the surfaces and structures in that area. 

Air Sampling The collection of samples of air to determine the presence of and the concentration of a contaminant, such as a chemical, aerosol, radioactive material, airborne microorganism, or other substance by analyzing the collected sample to determine the amount present and calculating the concentration based on the sample volume. 

Waste sorting should be done to the extent possible at the place of waste generation. If this is not possible the incineration facility shall have a sorting area where material not suitable for incineration can be removed. Depending on the radioactivity level of the wastes and the potential for airborne contamination, the wastes may or may not be sorted by hand. Alpha bearing wastes shall be sorted in a sealed glove box. 

The coatings of fuel storage ponds and fuel handling ponds, as well as the equipment used in these areas, will become contaminated. When the water level in such ponds is lowered, surfaces may dry out, and this may cause a hazard due to airborne radioactive material. Systems should be provided for decontaminating such surfaces before they dry out. Systems should also be provided for decontaminating, before they dry out, fuel transport flasks and components that may have to be removed from the ponds for repair. 

A.164S. Ground contamination. This section shall discuss possible ground contamination, by eidier direct dispersion of particulate radioactive material or deposition from airborne or aqueous releases. The surface contamination by radionuclides shall be estimated and the doses (due to ground shine and ingestion) assessed. 

Radioactive contaminants in filters, planchets, detectors, and shields may be primordial radionuclides and their progeny in aluminum (e.g., thorium), lead (e.g., uranium progeny), and filters C K). Materials with low radionuclide content should be selected from carefully screened supplies. Man-made radionuclides have contaminated steel and other metals during processing (from airborne fallout radionuclides) or reprocessing (from radioactive tracers or medical irradiation sources such as °Co, Cs, or Ra). 

In a situation where the only problem is the generation ofairborne radioactivity, individuals should leave the space in which the airborne activity is present,closing the doors behind them and turning off any ventilation in the area, if the controls are in the room. If the ventilation controls are inaswitchroomorbreakerroomelsewhere, they can be turned off from this location. If the accident occurs in or near a fume hood that would vent the material from the laboratory, it may be appropriate to allow the hood to remain on to reduce the airborne concentration of activity within the room however, this would depend uponthe radioactive toxicity ofthe material involved. If it is one ofthe more toxic materials,it would usually be preferable to avoid dispersal into a public area even if the levels are low, because of the possible concerns of exposure to persons in theseareas.Even ifthe potential forexposure is minuscule,many persons will become very alarmed. The laboratory represents a controlled space that can be decontaminated and, in general, the best approach is to restrict the contaminated area as much as possible. 

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