Testing ground Degelen was used for medium- and small-yield nuclear tests. The site is situated in the Delegen mountain range, a dome-shaped elevation of 17-18 km in diameter. Its total area is about 300 km2. The underground nuclear tests were made in tunnels.
A tunnel is a horizontal excavation of length ranging from several hundreds of meters to 2 kilometers with 3-meters in diameter. In order to prevent release of radioactive products from explosions into the atmosphere, so-called stemming complex with high-strength sealed elements, damping facilities, gas blocking and other units was made.
On the whole, 209 nuclear tests were made in 181 adits in the period from 1961 to 1989. The last test was made in the adit 169/2 on November 4, 1989.
In order to eliminate possibility of secondary usage of tunnels for nuclear tests, in the period from 1996 to 1998 works on closure of all tunnels on the Delegen site were carried out. The operations were made in the framework of agreement on elimination of the infrastructure of nuclear weapons tests between the Defense Ministry of the USA and the Ministry of Energy and Mineral Resources of the Republic of Kazakhstan.
Radioecological surveying of the Delegen site showed that most of the territory does not have radioactive contamination as the main amount (over 90%) of radioactivity released during nuclear tests still remains in the adits. However, there are some places with high concentrations of radionuclides (soil, water, vegetation). Such areas were mainly formed in three ways: 1) emergency situations during nuclear tests, 2) unsealing of tunnels after tests, 3) carrying-out of radioactivity from tunnels by waterways.
Water transfer of radioactivity from adit cavities The most contaminated areas of the Degelen ground are near-portal areas of tunnels with watereffects. Long-term monitoring shows that carrying-out of radionuclides by water from cavities of nuclear explosions is still under way. The number of such adits on the Degelen testing ground varies from 8 to 12 depending on weather conditions in different years (the main influencing factor is atmospheric precipitations). On the banks and flood-lands of watershed streams there are places with concentration of 239+240Pu up to n*104 Bq/kg, 90Sr – n*104 to n*105 Bq/kg, 137Cs – from n*104 to n*106 Bq/kg. The main features of radioactive pollution caused by carrying out of radioactivity from tunnel cavities by water flows is rather high concentration of artificial radionuclides along waterways and in bottom sedimentations. As a rule, radioactive contamination has maximal values near the tunnel portal and decreases with increase of the distance from the tunnel. There is a clearly pronounced dependence of concentration of radionuclides in soil and water on the distance from the tunnel portal. As 239+240Pu and 137Cs have the lowest migration ability, the distance of their spreading along the riverbed in most cases is not more than a hundred meters from the source. Strontium-90 is transported by water at a distance of several hundreds of meters from the source, tritium is practically not retarded and its propagation distance may reach maximal values (several tens of kilometers and more). The main mechanism of radionuclide transfer beyond the mountain range is their migration along the
There is a clearly pronounced dependence of concentration of radionuclides in soil and water on the distance from the tunnel portal. As 239+240Pu and 137Cs have the lowest migration ability, the distance of their spreading along the riverbed in most cases is not more than a hundred meters from the source. Strontium-90 is transported by water at a distance of several hundreds of meters from the source, tritium is practically not retarded and its propagation distance may reach maximal values (several tens of kilometers and more). The main mechanism of radionuclide transfer beyond the mountain range is their migration along the Delegen waterways – streams which pass in the zone influenced by water flows from the adits. However, taking into account the fact that surface water flows dry up even on the territory of the Delegen site, ground waters provide the main way for carrying out artificial radionuclides beyond the mountain range. According to radio-ecological monitoring performed in 1998-2008, ground waters of fluorite deposit Karadzhal situated close to the Delegen testing ground contain trace concentrations of cesium-137 and strontium-90, whereas tritium concentration in water goes up to n*104 Bq/l. Therefore, one of the key directions of investigations will be studying of the fields of spatial distribution of artificial radionuclides by water flows beyond the territory of the SNTS testing sites.
In the waters of the Delegen ground in addition to artificial radionuclides, scientists registered anomaly high concentrations of rare-earth elements and heavy metals. For example, concentration of beryllium and molybdenum in some streams of the Delegen mountain range is tens of thousands of times higher than the maximal permissible concentrations (MPC). These facts show that high concentrations of some microelements better reflect peculiarities of geological structure of the mountain range than characteristics of tested nuclear devices. This problem as well as the “radiation” problem is now thoroughly studied, and it is quite possible that scientists will discover some areas or zones promising in terms of exploration and mining for some rare-earth chemical elements.