Author: Eng. Anas Elsayed Ahmed Omara
Human being is exposed to background radiation that originated from natural and man-made sources. Approximately, from 70 to 80% of the natural total radiation dose for a person comes from natural radionuclides of both terrestrial and cosmoginic origin. Building and operation of the proposed nuclear power plant (NPP) in El-Dabaa region in the North Western coastal desert of Egypt may affect the environment in the vicinity of the NPP and other territories adjacent to the plant. Therefore, the evaluation of the possible hazards that may occur due to the release of some radionuclides into the environment is necessary. The aim of the current work which is establishing baseline radioactivity levels in the environs around the proposed El-Dabaa nuclear power plant (NPP), besides assessing the human health risk due to the exposure to naturally occurring terrestrial radionuclides and predicting via some mathematical models the radiological consequence of accidental release of radionuclides from the planned NPP. A survey of natural radioactivity in different components in the environment is represented. Samples of soils, plants and water were involved as prime ecological indicators. Thymelea hirsuta )L.( Endl. (a dominant plant species in all locations) was selected to accomplish this study. As well as, a complete description of the study area, methods of sampling and preparation for gamma rays spectroscopic analysis using high resolution gamma spectrometer (Hyper Pure Germanium detector) (HPGe) were included. It also included the specifications of RESRAD model used to predict the radiation levels and its risk in different environmental compartments such as soil, plant and water. Finally, the results and discussion of the obtained baseline radioactivity for soil, plant and water samples were represented. The main results are given as the following: Soil Samples *Three different sites (El-Dabaa, Sidi Abdelrahman and El-Alamein) were selected to accomplish the present study. The texture of the collected soil samples from all the study sites was sandy loam. *The average activity concentrations of 226Ra (238U-series) in the three study sites were 45.67, 47.88 and 57.76 Bq/Kg, respectively. The value for 228Ra (232Th-series) in all the study sites were 14.99, 31.77, 28.67 Bq/Kg, respectively. For 40K, the concentrations were 203.4, 246.2, 264.8 Bq/Kg in the study sites, respectively. For 7Be, the values were 2.69, 7.33, 7.32 Bq/Kg in the study sites, respectively. Finally, 137Cs attained concentrations of about 1.28, 0.64, 1.55 Bq/Kg in all sites, respectively. *Concerning radiological hazard assessment, the average values of the radium equivalent (Raeq) in the three sites were 92.25, 112.26 and 119.14 Bq/Kg which lowers than recommended value 370 Bq/Kg. The average values of the absorbed dose (D) rate in air calculated for natural radionuclides concentrations in all sites were 42.45, 52.33, 55.40 nGyh–1, respectively. Values of about 52.06, 64.13, 67.95 µsvy-1 were attained for the annual effective dose (E) in the three sites, respectively. The external and internal hazard indices are lower than guidance level which is one. The fatal cancer risk attained values of about 1.82 x 10-4, 2.25 x 10-4 and 2.38 x 10-4, for the three sites, respectively. Notably, the highest value of risk parameters was recorded in El-Alamein site. Plant Samples *The average activity concentrations of 226Ra (238U-series) in the three study sites were 5.25, 6.83 and 6.93 Bq/Kg, respectively. The value for 228Ra (232Th-series) in all the study sites were 8.47, 8.63, 6.78 Bq/Kg, respectively. For 40K, the concentrations were 317.1, 329.7, 321.2 Bq/Kg in the study sites, respectively. For 7Be, the values were 143.8, 146.8, 167.1 Bq/Kg in the study sites, respectively. Finally, 137Cs attained concentrations of about 0.88, 1.34, 1.24 Bq/Kg in all sites, respectively. *Concerning radiological hazard assessment, values of about 16.71, 17.85, 15.51 µsvy-1 were attained for the annual effective dose (E) in the three sites, respectively. The fatal cancer risk attained values of about 5.85 x 10-5, 6.24 x 10-5 and 5.42 x 10-5, for the three sites, respectively. Notably, the highest value of risk parameters was recorded in Sidi Abdelrahman site. Water Samples Water samples were only collected from El-Dabaa and Sidi Abdelrahman sites. *The average activity concentrations of 226Ra (238U-series) in the two study sites were 0.26 and 0.41 Bq/L, respectively. The value for 228Ra (232Th-series) were 0.44 and 0.63 Bq/L, respectively. For 40K, the concentrations were 2.13 and 3.17 Bq/L, respectively. *Concerning radiological hazard assessment, the average values of about 269.5 and 419.2 µsvy-1 were attained for the annual effective dose (E) in the two sites, respectively. The fatal cancer risk attained values of about 9.43 x 10-4 and 1.47 x 10-3, for the two sites, respectively. Notably, the highest value of risk parameters was recorded in Sidi Abdelrahman site. Summary for the application of RESRAD model The RESRAD model developed under the U.S. Department of Energy (DOE) and the U.S. Nuclear Regulatory Commission (NRC) was applied offsite to predict the radiological consequences of a nuclear accident. Chernobyl (1984) accident consequence released radioactive materials amounted to 70000 Bq/Kg from134Cs, 1250000 Bq/Kg from 137Cs and 420000 Bq/Kg from 90Sr. The scenario was taken as a guide to apply the RESRAD model in the present study. As well as, the local environmental conditions were added and taken in the consideration. The obtained results from the model were: *The maximum total annual dose from direct exposure pathway was 4 x 103 µsvy-1 at the beginning the accident and decreased to be 5 x 102 µsvy-1 after 100 years. *The contribution from manmade residual radioactive material will be reduced from 99% at the time of the accident to 9% after 100 years. *The maximum total annual dose from soil ingestion pathway was 4 x 10-3 µsvy-1 after 30 years from the accident and decreased to be 2 x 10-3 µsvy-1 after 100 years. *The maximum total annual dose from plant ingestion pathway was 1.0 µsvy-1 during the first 20 years from the accident and decreased to be 0.3µsvy-1 after 100 years. *The contribution of dose from residual radioactive material (man-made) to the maximum total dose was 65% after 100 years. *The total annual dose from water ingestion pathway was minimum compared with other pathways. *The maximum fatal cancer risk from direct exposure pathway was 6 x 10-3 at the initiation time of the accident and decreased to be 1 x 10-3 after 100 years. *The maximum fatal cancer risk from soil ingestion pathway was 9 x 10-9 after 20 years from the accident and decreased to be 4.5 x 10-9 after 100 years. *The maximum fatal cancer risk from plant ingestion pathway was 2 x 10-6 after 10 years from the accident and decreased to be 6 x 10-7 after 100 years. *The fatal cancer risk from water ingestion pathway was minimum compared with other pathways due to the lowest annual effective dose.