Chapter 4—Monitoring Accidental Radiation Releases ¢ 6] larly from the ingestion of contaminated milk.3 The whole-body dose is the main concern. However, deposition of radioactive material on pastures can lead to concentration in milk obtained from cows that graze on those pastures. The infantthyroid doses from drinking milk from family cows is also assessed.* The Department of Energy’s criteria for conduct- ing a test are: Fortests at the Nevada Test Site, when considering the event-day weatherconditions and thespecific event characteristics, calculations should be made using the most appropriate hypothetical release models which estimate the off-site exposures that could result from the most probable release scenario. Should such estimates indicate that off-site populations, in areas where remedial actions to reduce whole-body exposures are not feasible, could receive average whole-body dose in excess of 0.17 R/year (170 mR/year), the event shall be postponed until more favorable conditions prevail. In addition, events may proceed only where remedial actions against uptake of radionuclidesin the food chain are practicable and/or indications are that average thyroid doses to the population will not exceed 0.5 R/year (500 mR/year).5 Thesecriteria mean that a test can only take place if the estimate of the fallout from an accidental release of radioactivity would not be greater than 0.17 R/year in areas that are uncontrollable. i.e., where ‘‘remedial actions to reduce whole-body exposures are not feasible.’’ Thus, tests are not conducted when the wind is blowing in the general direction of populated areas considered to be uncontrollable, except under persistent light wind conditions that would limit the significant fallout to the immediate vicinity of the NTS. Areas considered to be uncontrollable by EPA are shownin figure 4-2. recommended remedial actions, and where remedial actions against uptake of radionuclides in the food chain are practicable. The controllable area is the zone within approximately 125 milesof the test control point (see figure 4-2) for which EPA judgesthat its remedial actions would be effective. Within this area, EPA has the capability to track any release and perform remedial actions to reduce exposure, including sheltering or evacuation of ail personnel (as needed): controlling access to the area; controlling livestock feeding practices, i.e., providing feed rather than allowing grazing; replacing milk; and controlling food and water. In the case of the controllable area, a test may be conducted if the fallout estimate implies that individuals in the area would not receive whole-body doses in excess of 0.5 R/year and thyroid doses of 1.5 R/year. If winds measured by the weather service indicate that the cloud of radioactive debris produced by the assumed venting would drift over controllable areas, such as to the north, thetest is permitted when EPA’s mobile monitors are in the downwind areas at populated places. EPA must be ready to measure exposure and to assist in moving people under cover or evacuating them. if necessary, to keep their exposures below allowable levels. As a consequence of the geometry of the controllable area, tests are generally not conducted if winds aloft blow toward Las Vegas or towards other nearby populated locations. In addition, the test will not be conducted if there is less than 3 hours of daylight remaining to track the cloud. ., those areas where trained rad-safe monitors are Prior to conducting test, detailed fallout projections are made by the weather service for the condition of ‘‘the unlikely event of a prompt massive venting.’ Predictions are made of the projected fallout pattern and the maximum radiation exposures that might occur. An example of such a prediction is shownin figure 4-3. The centerline is the predicted path of maximum fallout deposition for a prompt venting, marked with estimated arrival the exposure of each individual can be documented), where people can be expected to comply with side indicate the width of the fallout area. The two dashedlines indicate the 500 mR/year area and the The EPA and DOEhavealso defined a controllable area (figure 4-2), within which remedial actions are considered feasible. Criteria for the controllable area, as defined by the DOEare: available, where communicationsare effective (where times (in hours) at various distances. Linesto either 3See ‘‘Offsite Remedial Action Capability for Underground Nuclear Weapons Test Accidents,’’ U.S. Environmental Protecuon Agency. Environmental Monitoring Systems Laboratory—Las Vegas, NV, October 1988. 4In the case of an accident, however, the actual dose would be minimized because the milk would be replaced as much as possible. 5See ‘Offsite Remedial Action Capability for Underground Nuclear Weapons Test Accidents.’’ U.S. Environmental Protection Agency. Environmental Monitoring Systems Laboratory —Las Vegas, NV, October 1988.