AECOM were the designer for the Australian Nuclear Science and Technology Organisation’s (ANSTO) new molybdenum-99 (Mo-99) nuclear medicine processing facility at Lucas Heights in Sydney Australia. Together with Concrite, the premix supplier, Dr James Aldred developed of a high density concrete used to provide the necessary radiation shielding during the processing of the Mo-99, ensuring all adjacent habitable areas are safe for use. The target concrete density for the mix was 3,600 kg/m3. This provided significant reductions in thickness for the shielding elements compared with normal density concrete.
Figure 1 – Magnetite aggregate stockpiles at batching plant
James proposed the high density magnetite aggregate and the initial concrete mix design. Several finishing and pumping trials were undertaken in collaboration with Watpac (the Principal Contractor) and Concrite (the concrete supplier) to confirm the compatibility of the mix using conventional pumping and finishing methods as the mix was initially more cohesive than typical concrete.
Thermal modelling was conducted and subsequently verified by prototype testing and in-situ temperature monitoring to ensure satisfactory performance of elements up to 1.1 metres thick. The magnetite aggregate was found to significantly reduce temperature rise within the concrete.The high density concrete slabs were cured using water ponding to facilitate evaporative heat loss to reduce peak temperatures and subsequent thermal shrinkage.