Design Considerations for the Proposed Hifar Thermal and Epithermal Neutron Capture Therapy Facilities

At the Australian Nuclear Science and Technology Organisation (Ansto) the 100kW reactor Moata has been used successfully for Boron Neutron Capture Therapy (BNCT) of murine melanoma xenografts.1 Envisaged large animal and human irradiations would require a beam from the High Flux Australian Reactor (HIFAR). Attaining a therapeutic beam for BNCT at HIFAR presents a challenge in physical design and engineering, as there is restricted access to core neutrons. Major modifications to the HIFAR shielding are precluded as this action would require a long shutdown and a significant and costly safety analysis. The only feasible existing beam tube that may provide a BNCT beam is the 28 cm diameter 10H re-entrant hole, located at the core mid-plane. The 10H end-plate is located approximately 9 cm from two outer core fuel elements, separated from them by D2O. The 10H facility is currently used for neutron diffraction studies, and has a collimator installed which reduces the beam to a 5 cm square hole. Figure 1 shows a vertical section of the reactor and the relative position of the 10H facility.