Dose assessment of a contaminated land containing radioactive materials

Abstract

An attempt has been made in the work to assess the radiological consequences due to the deposition of lJ7es and Illr on ground, planl, milk and meat Emphasis on the determination oflhe migration parameters oflhesc radionuclides has been given in the present work. The migration parameters e.g., mainly the transfer factors (TFs) and distribution coefficients (1<.0)of 1J1eshave been investigated using the soil of the AERE campus. The IF values of ])'1 have been taken from the literatures. TFs of 1l1es have been measured both in pot and field experiments and compared with the calculated results using Absalom model. In the pol experiment, TF values were measured for the main foodstuffs in Bangladesh such as leafy vegetables (LaIshak, Palangshak), Ladyfinger, Radish, Potato, Potato Plant, Paddy, Paddy plant, Grass, Ginger, Ginger plant, Turmeric, and Tunneric plant by pot experiments grown in the AERE soil. IF values of the leafy parts and products of the corresponding plants were found to lie within the range of2.02 x 10-1 to 1.8 x 10'2, whieh compares well with literature values. 11has been observed that the TF values in the leafy part of the plants are higher than the products. II' values of 137CS measured by field experiment for the leafy plants grown in the contaminated land within the AERE campus were found to lie within the range of 2, 7 x 10.2 to 4.7 x 10-2,which are again in agreement with the literature and also with the measured values by pot experiment. Soil characteristics have also been investigated to assist the measured values of the corresponding radionuelide with the prediction of Absalom model which considered pH, organic maller content, exchangeable K" and clay content as input model parameter. The calculated values compares well with the measured values for pot and field experiments. Ko defined as the ratio of concentration of a radionuclide absorbed in solid phase to the concentration of that radionuclide left in liquid phase were found to be 2327, 591, 209, 78, and 84 mVgm at depths 0-5, 20-25, 45-60, 90-115, and 150-175 It respectively using batch method. vii The source term and release rate for the above mentioned radionuc1ides as well as Gaussian diffusion factor and diffusion ,coefficients as a function of downwind distance have also been investigated. The maximum air concentratIOn has been estimated to identify downwind distance that was found to be 100 m from the core of the reactor. Then the ground concentration, concentration in vegetation, milk and meat as well as probable doses to human population through ground deposition, ingestion of vegetation, milk and meat for the above-mentioned radionuc1ides have' also been estimated. The maximum dose due to 1l11,'J7Cs and both (1J1r+IJ)CS) for all pathway summed were found to be 26.379, 0.0280 and 26.407 I-lSvfhr respectively. The maximum dose due to IJ7CSwas within the background limit (0.30 flSvihr) but the maximum dose due to tJlr was higher. However, the dose due to Ill! (t'l2 = 8.04 days) will be reduced to background level within ten half-lives (;=.80days). Vegetation was found to be the dominant contributor both for "'I and IJ7Cs (- 90%) compared to other pathways. Contribution of Ill1 in milk is higher (7%) than the contribution of mCs (3%) while the contribution of l)7Cs in meat is higher (5%) than that of "lr (2%). For both tJlr and 1l7CSthe contribution from ground deposition is almost negligible (1%) compared to vegetation. The measured site characterization data can be used as a reference database while predicting the migration behavior of radionuc1ides through various media around AERE campus. Radionuclidc concentration and probable dose assessment of the human population living in the vicinity of the 3 MW reactor site could be utilized to comply with the regulatory requirements. This study can ultimately be used to determine the radiological protective measures, which might be required to ensure the safety of the human population living in the vicinity ofthe reactor site .