Population is constantly exposed to naturally occurring ionizing radiation types. The sources of natural radiation are the cosmos, radiation from the surface layers of the Sun, the Earth’s crust radiation and those radionuclides that the crust emits. Thus, the radionuclides can easily occur in water and air. Besides the natural background radiation, the population is exposed to artificial radiation as well. One of the main artificial radiation sources in Lithuania at the moment is the decommissioning process of the State Enterprise Ignalina NPP. On December 31st 2009, the INPP moved from the stage of energy production into the plant decommissioning stage, but secured the status of being a nuclear facility. Ignalina NPP remains an enterprise that works with nuclear fuel and radioactive waste, because of this fact an enterprise’s activity is regulated by the law on nuclear energy, radiation safety and radioactive waste control, etc.
Undertaking all possible efforts on protection of the population and environment, the activity of radionuclides emission from the INPP into the air and Drūkšiai lake is strictly limited by certain rules and requirements of the Lithuanian law.
In order to make sure, that the activity of radionuclides emission from the Ignalina NPP is really not exceeding the environmental protection regulations a rigorous monitoring is constantly being made. Measurements of different samples have been investigated such as air, precipitations, ground, flora, water (from Drūkšiai lake, drinking water, etc.), dregs from the bottom of the lake and foodstuffs (for example: different fish spices from Drūkšiai lake, meat, milk, cereal crops, cabbage, potato and mushrooms). Such type of monitoring is carried out only by the qualified personnel with a current license at the INPP up-to-date equipped laboratories (radiological measurements laboratory and environment monitoring laboratory). During the investigations, no excess of radionuclides emission into the INPP surroundings was found. Nevertheless, level of the radionuclides emission is identified under the regulation norm and is considered to be at a minimum level. (Figures 1, 2)
Fig. 1 Emission of IRG, radioaerosol and iodine-131 into the air and Drūkšiai lake from INPP, with sewage water between 2001-2009
Fig. 2 Emission of IRG, radioaerosol and iodine-131 into the air and Drūkšiai lake from INPP, with sewage water between 2010-2015
Survey results of 2015 showed that a radiation dose received by “the critical group of people”, as a result of the INPP activity, was only 0, 0000812 mSv that represents 0.04% of general background. Hypothetically, “the critical group” are the people who live in the vicinity of nuclear facility, close to radioactive waste storage facility site and use water from closely located wells or water reservoirs.
The radiation doses received by population are measured by thermoluminescent dosimeters, which are located in different places of sanitary protection area (3 km around INPP) and radiation control area (30 km around INPP). Furthermore, the dose rate is measured by 22 stationary sensors of “Skylink” system.
There are 10 measurement sensors located in radiation control area and 12 sensors in sanitary protection area, which enable to control dose rates on a real time basis. Moreover, the institutions of the Republic of Lithuania have the possibility to monitor the results of measurement data continuously.
The dose rate measurement data are shown below:
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By analyzing the monitoring data, it can be seen that the radiation dose rate around INPP site fluctuates between 8 and 13 µR/h. Current data match the data of the researches by the Radiation Protection Center. The data received from the Radiation Protection Center researches shows that the dose rate at the INPP site in 2015 was changing from 5.1 µR/h up to 10.5 µR/h.
Besides the INPP, the Radiation Protection Center also realizes the researches of possible radiation doses that environment can get. The measurements of external radiation doses that were taken in the 50 km area around INPP, compared with such a region as Kupiškis and other big cities of Lithuania are presented in Figures 3 and 4.
Fig. 3 Possible exposure dose received by INPP and other regions population in 2015
Fig. 4 Annual average dose of radiation received in various places of Lithuania in 2015 (data collected by RPC)
Considering the data received by Radiation Protection Center in 2015, the annual average radiation dose measured in INPP region was 0.64±0.05 mSv, and in Kupiškis region was 0.63±0.05 mSv. The measurements are more or less the same comparing with the researches of the previous years and the data collected by the INPP. (Fig. 5)
Fig. 5 The change of annual average radiation dose in INPP region, Kupiškis district and Vilnius city from 2005 until 2015
As it was previously mentioned, measurements of different samples have been investigated in INPP region such as air, precipitations, ground, flora, water (from Drūkšiai lake, drinking water, etc.), dregs from the bottom of the lake and foodstuffs (for example: different fish spices from Drūkšiai lake, meat, milk, cereal crops, cabbage, potato).
During the monitoring process, mushrooms are considered to be the best indicator of environmental contamination. The natural activity of 137Cs element in mushrooms is the biggest than in any other foodstuff types. The mushrooms average contamination by chemical element 137Cs in Lithuania (RPC data) and inside the INPP region (INPP data) is shown in figures number 6.
Based on collected data presented by INPP and RPC, the annual effective dose of radiation received by Lithuanian population due to detection of 137Cs element in mushrooms was about 5×10-3 mSv (RPC data) and for INPP region about 1.9×10-3 mSv (INPP data) on conditions that up to 10 kg of mushrooms are consumed annually.
It might be a conservative assessment, as the amount of element 137Cs that vaporizes during cooking is not included into the shown data.
During the investigations of water reservoirs, fish is considered to be a good indicator of environmental contamination. The data of fish contamination by elements 137Cs and 90Sr collected in different places of Lithuania (RPC data) and in Drūkšiai lake (INPP data) are presented in Figures 7 and 8.
As of INPP data, the annual effective dose of radiation received by the Lithuanian population due to detection of elements 137Cs and 90Sr inside the fish of Drūkšiai lake was 1.81×10-4 mSv on conditions that up to 18 kg of fish is consumed annually.
Fig. 6 Assessment of natural activity Cs-137 in edible mushrooms (600 Bq/kg allowed level)
Fig. 7 Assessment of natural activity Cs-137 inside the fish samples, 2001-2015
Fig. 8 Assessment of natural activity Cs-137 inside the fish samples, 2001-2015
On the basis of all the data received by monitoring processes realized by RPC and Ignalina NPP, it is possible to conclude that there was no additional radiation received by the Lithuanian population during the INPP commissioning and decommissioning periods.