UTILISATION OF THE MONTE-CARLO CODE ‘MCBEND’ AND THE DETERMINISTIC CODE ‘ATTILA’ TO ASSIST WITH THE SHIELDING AND DOSE ANALYSIS FOR THE LAND AND MARINE TRANSPORTATION OF AN INTERNATIONAL TRANSPORT FLASK

A shielding and dose uptake assessment is required for the transportation of nuclear fuel to overseas customers. The fuel is contained within transport packages that when transported individually meet the IAEA transport criteria. In addition to dose rate criteria around a transport flask, dose uptake to ship personnel must not exceed the criteria set by the International Atomic Energy Agency (IAEA) of 1milli-Sievert per year for the general public. Methods of driving down the dose were employed in accordance with the ‘As Low As Reasonably Achievable (ALARA) principle. Ship personnel living onboard the vessel are subject to radiation for the full duration of each day during the voyage. Consequently dose rates in occupied areas are required to be low in order to comply with the stipulated criteria. Methods to drive down dose are applied in line with the ALARA principle to restrict dose uptake. The Monte-Carlo computer code MCBEND has been used to optimise the shielding to be installed and to determine total neutron, primary and secondary gamma dose rates at key locations around the road vehicle. The use of Monte-Carlo methods in large models such as ships can present potential problems. With ship personnel able to occupy many locations around the ship, dose rates are required in various locations that may require individual acceleration methods in MCBEND. The three-dimensional deterministic code Attila solves the transport equation using a tetrahedral mesh system over all model space, assessing potential problem areas that could be overlooked when selecting dose rate regions. The post-processing tool TecPlot can be used to present twodimensional or three-dimensional dose rate contours. This can be useful for assessing potential weaknesses around the transport flask and as a visualisation tool for the project. It was demonstrated that calculated dose rates surrounding the vehicle and dose uptake on board the ship were within the criteria stipulated by the IAEA. With the aid of MCBEND and Attila, dose uptake estimates can be provided with a degree of confidence in addition to two-dimensional contour plots on the vessel.