Shielding Calculations for a Tank-In-Pool Reactor

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2000-07

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University of Ghana

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The effectiveness of the water shield above the core and in the pool for shielding gamma rays and neutrons was investigated by measurements and calculations for a tank-in-pool type reactor, Ghana Research Reactor-1, GHARR-1. Experimental determination of y - dose rates were made using Radiation Alert Monitor-4 and halogen counter type J613 y probe with readout on y -radiation monitoring system of the control console and the microcomputer control system. The PC version of the one-dimensional transport code ANISN was used to estimate the gamma and the neutron dose-rates at various positions of the reactor. All computations were carried out using the Sg angular quadrature in a cylindrical geometry pertaining to the reactor GHARR-1. The P3 scattering order was assumed. The microscopic cross-sections of materials for various regions were extracted from VITAMIN C master library consisting of 171 neutron and 36 photon energies. Concentrations in various regions were computed based on procedures outlined in WIMS-D/4. The calculational result of gamma dose rate was 25.8 fiSv / hr at the edge of the pool for nominal power of 30kW which agreed with the experimental one of 25 juSv / h r . The maximum and minimum percentage variation of the calculational and the experimental results were 8.21 and 0.27 respectively with corresponding standard deviations of0.42 and 0.04. Based on this satisfactory result, the dose profile along the slant tubes used to commission the reactor was studied using the code and an assessment was also performed for the radiological consequences of postulated accidents due to loss-of-coolant accidents. With the available information on the variation of the neutron and the gamma doses along the slant tubes, high dose theimolumniscent (TLD) badges could be used to confirm the calculated values in the future. The tubes could then be mapped for studies on the effect of neutron and gamma irradiation on mutation breeding of seeds in the field of agriculture. The effectiveness of the shielding in the case of loss-of-coolant due to a break in the pipe of the reactor vessel or crack in the pool caused by an earthquake was investigated. The results of the study indicate that the dose rates around the reactor vessel and pool would be abnormally high. However, core melt-down is not expected because the design features of the reactor are such that the core will remain covered with coolant in the event of a break in a pipe line to the purification plant.

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Thesis (MSc) - University of Ghana,2000

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