Finding and evaluating potential radiological problems in the vicinity of uranium milling sites

The Oak Ridge National Laboratory (ORNL) has been performing radiological surveys at former uranium and thorium milling and processing sites since 1975. Tailings at inactive milling sites usually have a low frequency of human occupancy but continuously generate 222Rn into the atmosphere. Thus, independent 222Rn surveys are conducted at the inactive mill sites and their environs by the Mound Facility. Measurements of airborne 222Rn and 222Rn flux are made on the sites to define the tailings source term. Concurrently with these measurements, an ambient 222Rn monitoring network is established off-site and a meteorological station is established at or near the mill site. Unfortunately, tailings are not always confined to the milling site. Radioactivity can migrate to areas outside of site boundaries by wind and water erosion, groundwater transport, spillage of incoming ore, and removal of tailings or other material for private purposes. In order to identify and assess off-site radioactivity on properties in the vicinity of milling sites, a combination of aerial and ground-level radiological monitoring techniques are used. The ground mobile gamma-ray scan is conducted using a vehicle equipped with sensitive gamma-ray detectors. The detectors are shielded so that gamma radiation input is viewed through only one side of the vehicle. This system is capable of precisely locating properties which have anomalously high gamma radiation levels caused by the presence of tailings. Subsequently, these properties are identified as candidate vicinity properties and are scheduled for radiological surveys subject to the property owner's consent. The comprehensive radiological surveys conducted at these vicinity properties determine the amount, type, and location of tailings materials