Radioisotope production needs in Japan seek to look for feasible paths to obtain radionuclides being used in industry and medicine. In the latter area, \(\alpha\) -emitter nuclides are becoming a feasible option as its high linear energy transfer (LET) allows them to eventually destroy undesirable tissues inside the human body. With more ligands being developed and current clinical trials being executed, the necessity of establishing a secure route for procuring these elements emerges as an opportunity for the scientific community. The current configuration of the reactor core of Joyo has established four irradiation locations where probes can be placed to undergo an irradiation routine. At those places, we are intending on obtaining a description in terms of physical quantities. The quantities we are looking for are the neutron energy and flux spectrum and the gamma-rays energy and flux spectrum. Those values and distributions will allow us to eventually design and test main targets and target containers that can produce the desirable radioisotopes at that facility. We employ two different computational codes, namely OpenMC and Serpent, to estimate the searched physical parameters. One motivation is that there is no current evidence on the literature that the two previous software have been used on the latest upgrade of the reactor core (MK-IV). The three-dimensional replica of Joyo on OpenMC yielded a neutron flux of 2.9047 \(\frac{neutrons}{{\text{m}}^{2}*\text{s}}\) in the center of the core—which was compared with the values reported by the operator of the reactor.