The Ignalina NPP is located in the area of the East-European platform, at the junction of two large structure elements: the Baltic sineclize and the Mazur-Belorus antiklize. Therefore, the crystal foundation and sediment case are separated by a series of tectonic breaks. Some of these were discovered by geophysical methods and determined by data from drilling samples. Data of seismic prospecting and test drilling 10 km to the north-west from the Ignalina NPP show, that dimensions of tectonic blocks can not be large, in the neighborhood of 2 x 2 km. From the evidence of such tectonic disintegration of this area, the probability of availability of tectonic disintegration zones near the Ignalina NPP is sufficiently high.
The surface in the Ignalina NPP area is rough. Their absolute elevation-marks change from 150 m to 180 m and more. Glacial Quaternary sediments exist near the surface within a depth from 60 to 200 m, they are supported from below by Before-Quaternary, Devonian, Silurian, Ordovician, Kembrician and Upper-Protozoan sediment variety. At a depth of 700-750 m imbedded methomorphic and Crystal sediments of Upper Proterozoic and Archei are present.
Table 2.3 Filtration properties of glacial accretions of the ground-cover in the Ignalina NPP area [10]
|
Type of accretion |
Geological index |
Distribution, % |
Power, m |
Filtration coefficient, m/day |
Depth of water bed level, m |
Water yield coefficient |
|
Swampy |
bIV |
5 |
2 - 6 |
0.04 - 6 |
0.2 - 0.4 |
0.001 - 0.05 |
|
Alluvial |
aIV+III |
5 |
1 - 20 |
1 - 190 |
0.2 - 5 |
0.01 - 0.25 |
|
Limno-glacial |
lgIIInm3 |
5 |
4 - 6 |
0.2 - 8 |
0.5 - 2.5 |
0.0002 - 0.15 |
|
Fluvi-glacial |
fgIIInm3 |
5 |
10 - 15 |
5 - 20 |
2.5 - 5 |
0.05 - 0.35 |
|
Water-glacial |
agtIIInm3 |
|||||
|
agtIIInm1 |
30 |
5 - 10 |
10 - 20 |
2.5 - 5 |
0.05 - 0.35 |
|
|
Glucagon |
gtIIInm3 |
|||||
|
|
gtIIInm1 |
50 |
5 - 50 |
0.01 - 2 |
0.5 - 1.5 |
0.001 - 0.1 |
Table 2.4 Engineering-geological properties of glacial accretions of the ground-cover in the Ignalina NPP area [10]
|
Type of accretion |
Particle density, g/cm2 |
Soil density, g/cm2 |
Humidity |
Porosity coefficient |
Fluidity limit |
Plasticity limit |
Angle of friction, 0 |
Adhesion, MPa |
Young's modules, MPa |
|
Swampy |
1.57 |
0.89 |
6.76 |
13.3 |
- |
- |
- |
- |
0.5 |
|
Alluvial |
2.71 |
1.97 |
0.29 |
0.77 |
0.33 |
0.11 |
22 |
0.034 |
7 |
|
Limno-glacial |
2.71 |
1.94 |
0.21 |
0.82 |
- |
- |
14 |
0.011 |
5 |
|
Fluvi-glacial |
2.64 |
1.69 |
0.09 |
0.72 |
0.33 |
0.22 |
33 |
0.001 |
27 |
|
Water-glacial |
2.65 |
1.67 |
0.09 |
0.71 |
- |
- |
32 |
0.001 |
6 |
|
Glucagon |
2.70 |
2.24 |
0.13 |
0.34 |
0.19 |
0.14 |
23 |
0.028 |
30 |
Surface sediments in the area of Ignalina NPP are very inhomogeneous. They were formed during the retreat of the last glacier as a result of different glacial and water-glacial processes. Later on, alluvial, marsh and lake-sediments were formed.
The lithologycal structure, the filtration and engineering-geological properties of separate genetic types of surface sediments are not equal (Tables 2.3 and 2.4). Most prevalent are the permeable water-glacial sediments, which are located in direct proximity of lake Druksiai and the Ignalina NPP, Fig. 2.4. All surface sediments contain subsoil water, which range in depths from 0.2 to 7 m. Heterogenous supporting weight, the marsh, lake-marsh, lake-glacial and water-glacial sediments are located near the surface and at the level of the building foundations and other constructions. According to lithologycal classification this is peat, sand, gravel, sandy soil, sandy loam and clay.
The complexity of engineering-geological conditions of the platform in question is:
All these factors have an influence to the settlement of buildings and constructions. The deformation of the split slabs can be considerable - from 50 to 1000 mm - and can be highly irregular.
The Ignalina NPP territory is located in the area of a Before - Kembrician platform. In spite of this, the earth's crust is pulsating, even experiencing perceptible shocks. The predicted intensity of neotectonic motion in the area of Ignalina NPP is 3.5 mm per year. The district was affected by the Karpat earthquake, which had a predicted intensity of 5 on the Richter scale.
Construction and operation of the Ignalina NPP essentially widens the spectrum of technogenic influence on the geologic environment. The character and scales of the consequences depends on the geological situation such as power of the aeration zone and filtration, as well as from drainage conditions of the subsoil aquifer. From this point of view the territory of Ignalina NPP is located in unfavorable conditions. The depth of the aeration zone is from 1-2 m to 5-8 m and is insufficient to protect subsoil waters. It is composed of fine sands, the filtration coefficient of which is 5-20 m/day, the water-yield coefficient is 0.05-0.35, and for sandy loam, the filtration coefficient of which is 0.01-2 m/day, the water-yield coefficient is 0.001-0.1. Soils of the Ignalina NPP area can not guarantee a reliable localization of radionuclides during an accidental leak, and can not be a barrier, which prevents the migration of such radionuclides as 90Sr and 137Cs to the biosphere.
Fig. 2.4 Glacial accretions of the ground-cover in the Ignalina NPP area [10]
1 - swampy accretions (peat, slimy sand), 2 - alluvial accretions ( sand, gravel, pebble, sandy soil), 3 - limno-glacial accretions (clay, alevrit, sand), 4 - fluvi-glacial accretions (sand, gravel, pebble), 5 - water - glacial accretions of local formations (sand, gravel, pebble, sandy soil), 6 - glucagon accretions of local formations (sandy soil, sandy loam) of late (a) and early (b) stage of last glacier