Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 32

Accidents at uranium mines have the same health consequences as those at all other mines and cannot therefore be identified as nuclear accidents. On the other hand, uranium mines, especially underground uranium mines, are areas where radiation sources are significant. This is owing, in particular, to radon concentrations that can exceed 100,000 Bq.m⁻³ [CCS 11]. This radon comes from the decay of elements of the families of uranium and thorium (mainly uranium 238), which give rise to various radon isotopes (mainly radon 222), which are in a gaseous state and accumulate in mine galleries. Radon isotopes decay in a cascade into various radionuclides that are in a solid state and when inhaled into the lungs are deposited as radioactive dust that may have health consequences (Figure 2.2).

Figure 2.2. The radioactive family of uranium 238 and its derivatives (according to AMI 13a]). For a color version of the figure, see www.iste.co.uk/amiard/industrial.zip

One of the few accidents with environmental and health impacts is one in Puerco, USA. In 1968, 27 km northeast of the town of Gallup, near the town of Church Rock, New Mexico, United Nuclear began operating the largest underground uranium mine in the United States. The mine waste was stored in three large ponds, each closed off by a dike of earth. Residents near the mine were almost entirely native Navajo and used the Puerco River as a source of water for their livestock. In the early morning hours of July 16, 1979, fewer than 4 months after the high-profile Three Mile Island accident was reported, one of the earth dams gave way near Church Rock Mill. The 6 m-wide dam released approximately 1,100 tons of radioactive waste, and 95 million gallons (360 million liters) of effluent reached the Puerco River in North Fork. In addition to the river, groundwater was affected up to more than 130 km downstream of the dike [BRU 07].