Conceptual Design of a Medical Reactor for Neutron Capture Therapy

A conceptual design of a passively safe reactor facility for boron neutron capture therapy is presented. The facility configuration and its neutronic, thermalhydraulic, and safety issues are addressed in order to demonstrate the deployability of reactor technology for routine patient treatments and advanced research and dosimetry. The reactor has a power level of <10 MW(thermal) and is based on low-enriched UZrH fuel. The reactor facility generates a clean epithermal neutron beam capable of treating deep-seated brain tumors (∼70 mm) in <10 min. The incident fast neutron and gamma-ray contaminants in the beam are 1.8 and 0.4 Gy, respectively, for a 20-Gy therapeutic dose to a deep-seated tumor. With an expected operation schedule of ∼2000 treatment periods per year, the reactor core lifetime is equal to the 30-yr facility lifetime and no refueling is necessary. Five beam ports are available for simultaneous patient treatments allowing between 2000 and 10000 treatments per year with expansion capabilities of at least threefold for 24 h/day operation. The cost per patient treatment is small, about $1000, making the therapy very affordable. The reactor system design includes several passive safety features that allow the reactor to respond in a safe and benign manner in the event of off-normal transients. The response for various instantaneous reactivity insertions is assessed. Results show the reactor can passively respond to a reactivity insertion of 2 $ such that the maximum temperature limits of the fuel are not exceeded.