Design Studies of an Epithermal Neutron Beam for Neutron Capture Therapy at the Musashi Reactor

摘要

Studies were carried out to design an epithermal neutron beam for neutron capture therapy at the Musashi reactor, a TRIGA-II of 100kW. The idea in this design is to use spent fuel elements as a converter assembly to convert thermal neutrons from the core to fission neutrons which would then be moderated to epithermal neutrons. In the design, 43 elements were placed outside of the graphite reflector but inside the tank. These elements could be cooled by water in the reactor tank and also be easily removed for inspection. Monte Carlo computations indi- cated that by using a 63cm-thick Al2O3 moderator, an epithermal neutron beam with an intensity of 0.34×109n?cm-2?s-1 and fast neutron and γ-doses per epithermal neutron of 4.3×10-11 cGy?cm2?n-1 and 0.3×10-11cGy?cm2?n-1, respectively, could be produced. The multiplication factor of the 43 spent fuel elements was <0.95 and negligible reactivity coupling to the core by the spent fuel was calculated. Such an epithermal neutron beam, if built into the Musashi reactor, would significantly increase the chance of success of Boron Neutron Capture Therapy (BNCT) in Japan.