This study presents design of a Beam Shaping Assembly (BSA) optimized for accelerator-based Boron Neutron Capture Therapy (AB-BNCT), emphasizing high neutron flux generation and enhanced safety. Achieving optimal neutron beam parameters, as recommended by the International Atomic Energy Agency (IAEA), is critical for effective treatment but remains a significant challenge for AB-BNCT systems. These challenges include difficulties in achieving sufficient neutron flux, minimizing fast neutron and gamma doses, and mitigating the production of undesired radioisotopes. To address these limitations, this work proposes a novel BSA design to produce high-flux neutrons, moderated by zirconium tetrafluoride (ZrF4). The use of ZrF4 eliminates the need for a separate fast neutron filter, as this material has a high inelastic scattering cross-section and low absorption cross-section, reducing the induced radioisotope production and minimizing residual radioactivity. The BSA design, simulated using Geant4, assumes a 9Be target bombarded with a proton beam of 10-MeV energy and an 8-mA current. A key novel feature of the design is the incorporation of adjustable energy spectrum control via sliced ZrF4 discs. These removable discs enable neutron energy spectrum adjustment, providing clinical flexibility for cases requiring higher or lower energy spectra. This work shows the potential of the proposed BSA design to advance AB-BNCT technologies by delivering an adjustable, high-flux epithermal neutron beam while enhancing safety through reduced fast neutron and gamma doses and minimized residual radioactivity.