الفهرس 
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Abstract
ABSTRACT : The present study aimed at the application of Monte Carlo methods to perform shielding calculations for CANDU spent fuel and estimate the radiobiological impact. The considered source of radiation was a single CANDU standard fuel bundle with 37 fuel elements. Two fuel compositions were selected for a comparative analysis of the spent fuel, namely natural uranium fuel (NU) and slightly enriched uranium (SEU) with 1.1 wt% enrichment in U235. The considered fuels were irradiated according to CANDU reactors specific conditions up to 8 MWd/kg HE for NU fuel, and up to 12 MWd/kg HE for SEU fuel, respectively. The inventory of the fissile isotopes (U235 and Pu239) and the inventory of isotopes interesting for proliferation resistance (Pu238, Pu240, and Pu241) were obtained after performing the simulation of fuel irradiation using ORIGEN-S burnup code. As the fuel irradiation increases, U235 consumption is higher than Pu239 accumulation leading to a reduction in the fissile inventory. At the end of irradiation, the total fissile inventory reduces by 50% for NU and 66% for SEU, respectively, in comparison with the initial fissile inventory (U235 only). The total fissile content in the SEU37 fuel bundle was 6% higher comparatively with the NU37 fuel bundle one. After the irradiation, the spent fuel was discharged from the reactor and kept inside the reactor’s pool for cooling for up to 5 years, to allow the fission products disintegration and reduction of the spent fuel radioactivity and heating. The photon dose rates were estimated using MORSE-SGC Monte Carlo code both to the shipping cask wall and in the air at different distances from the cask external surface to assure safe transport and manipulation of the spent fuel. As the cooling time increases, the estimated photon dose rates became lower and were significantly reduced as the distance to the shipping cask wall increased. SEU37 spent fuel is characterized by radiation dose rates ” ” " ~ " ” ” 30% higher than those estimated for the NU37 spent fuel. However, the photon dose rates characterizing both considered fuel compositions have values lower than the internationally agreed limits for safe transport of radioactive material using the shipping cask type B. According to internationally agreed transport regulations for radioactive material establish that the radiation level under routine conditions of transport shall not exceed 2 mSv/h to the cask wall, and 0.1 mSv/h at 2 m from the external surface of the conveyance, the results are under the permissible dose rate, using the cask wall after 6 months cooling time for NU37 and SEU37. The equivalent organs dose of the stomach, colon, lung, red bone marrow, gonads, urinary bladder, esophagus, liver, thyroid gland, breast surface, and skin depending on exposure to each NU37 and SEU37 is under the permissible dose rate, using the cask wall after 6 months cooling time for NU3237 and SEU37, passing by shielding using cask at distance 3 m at which the equivalent dose approximately zero. According to the international mission on radiological production for radioactive material establish that the excess lifetime cancer risks (ELCR) were also estimated, and the average values were recorded as (3.65±1.85×10−3), the results confirm that The excess probability of Lifetime Cancer Risk ELCR depending on effective dose equivalent of each NU37 and SEU37 is under the permissible dose rate, using the cask wall after 6 months cooling time for NU3237 and SEU37, passing by shielding using cask at distance 3 m at which the equivalent dose approximately zero.