Materials Used for Building Construction

Buildings can provide some shielding from extraterrestrial radiation and from 7 radiation from rocks and soil outside the buildings. However, certain materials of construction (e.g., stone, especially granite), containing uranium or a high potassium content, can raise the dose of ionizing radiation received by the occupants of a building.

In the 1950s it was shown that the concentration of radon could reach 1.1kBq/m3 (30 pCi/liter) in the air of a residence that was heated by radiant heating from concrete floors containing crushed Chattanooga shale having about 0.008% uranium. In Florida, phosphate rock (ore), which can contain about 0.004% uranium, is mined for the production of fertilizer. Conversion of the ore to fertilizer reduces the concentration of uranium and its decay product 226Ra in the fertilizer. However, use of the mill tailings as fill around basements of buildings has resulted in elevated radon levels. In addition gypsum, CaS04 • 2H20, a by-product that may be contaminated with 226Ra, is used to manufacture plaster of paris and wallboard for building construction. Finally, cinder blocks manufactured from coal ash containing 226Ra also are a potential source of radon in houses and other buildings.

In the United States, following World War II, uranium was mined in 10 states: Arizona, Colorado, Idaho, New Mexico, North Dakota, Oregon, Pennsylvania, Texas, Utah, and Wyoming. Some of the approximately 24 million tons of tailings, a fine silt produced in the mining and milling of the ore, was used in several western states in concrete and as fill around the foundations of at least 5000 buildings that included private residences, schools, and public and commercial buildings. A similar situation occurred in Ontario Province in Canada. In the tailings that remain after the uranium has been leached from the ore, the 226Ra activity can be as high as 3.7-37MBq/kg (0.10-1.0 ^Ci/g). Concrete made from the tailings not only raised the level of 7 radiation, but also provided a concentrated source of radon within the buildings. Remedial action has been very costly. Treatment of mill tailings as radioactive waste is discussed in Section 14.12.2.4.

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