Monte carlo analysis of various geometrical blankets in a fusion-fission hybrid reactor

•A dense plasma focus device design as a fusion neutron source.•Investigate the neutron diffusion equation in the cylindrical layer, the spherical layer and the frustum cone layer geometries.•Investigate the lowest probability of a neutron returning from the second blanket to the first blanket in the cylindrical layer, the spherical layer and the frustum cone layer geometries.•Investigate the neutron parameters in the One-Blanket Reactor and Two-Blanket Reactorand the ultimate energy of the hybrid reactor by MCNPX code.•To check the safety of staff and reactor facilities, the dose rate of neutrons and photons in the concrete shield is calculated by MCNPX code. Fusion - fission hybrid reactor consists of two main parts. The first part is the Dense Plasma Focus (DPF) where the fusion process is performed and the second part is the blankets which surround the DPF and the fission process is done in the blankets. The most of the fusion neutrons, near the fusion source, are directed upward, so the blanket over the DPF is designed in forms cylindrical, spherical and frustum cone of volumes 183,347 cm3, 136,378 cm3 and 58,223.2 cm3 respectively at the same effective multiplication factor. Then the thermal neutron diffusion equation, buckling and neutron parameters are studied. After selecting the first blanket, the second blanket is designed in forms cylindrical, spherical and frustum cone of volumes 4.500 × 106 cm3, 3.689 × 106 cm3 and 6.441 × 105 cm3 respectively. So the frustum cone is chosen for the first and second blanket. The neutron return probability in the frustum cone from the second blanket to the first blanket is low, so the first blanket's effective multiplication factor does not change and the reactor's total effective multiplication factor is stable. Also, MCNPX code has been used to checkout and select neutron multiplier and reflector cells for the most neutron yield.