## 7 Discussion  
The use as irradiation port of one of the 16 equatorial ports of the DEMO tokamak was considered. This port should include at least two essential parts: the space for the isotope production, i.e., the irradiation unit, and the associated port cell hosting robots, drive mechanisms, and special equipment. The modeling of the irradiation unit is the subject of this work. The layout of the port cell is out of the scope of this paper. Starting from the CAD model of the DEMO baseline 2017, the MCNP geometry model with the integrated irradiation unit and adjacent breeding blanket volumes modeled according to the HCPB concept was used for the comprehensive analyses.  
The numerical simulations were conducted with MCNP code for the assessment of the neutron spectra in the irradiation rods, and FISPACT II was used for the inventory calculations to obtain the material compositions after the specified neutron irradiation. The irradiation campaigns were chosen on the basis of the available information for the commercial isotopes' production in fission reactors and were customized to the foreseen operation of EU DEMO.  
The assessment of the radioisotopes' production was carried out for 12 different nuclides with half-lives ranging from tens of hours to several years. Several nuclear responses were obtained to figure out the possible outcome of the neutron irradiations in the DEMO port: radial distributions of the accumulated activity of the isotopes along the radial depth of the rods, the maximum achievable specific activity of the isotopes (Bq/g), and the eventual yields of the isotopes (commercial and total in Bq).  
The efficiency of the generation in the DEMO irradiation unit is different for various isotopes. The highest efficiency was found in the production of the short-lived \({}^{192}\)Ir, \({}^{103}\)Pd, and \({}^{169}\)Yb isotopes (T\({}_{1/2}\) = 17-73 days). Also, technically feasible but with a lower predicted efficiency, was the production of the \({}^{99}\)Mo, \({}^{125}\)I, \({}^{131}\)I, \({}^{90}\)Y, \({}^{153}\)Sm, \({}^{177}\)Lu, and \({}^{204}\)Tl (T\({}_{1/2}\) = 46 h-3.8 years). The production of \({}^{60}\)Co and \({}^{186}\)Re isotopes was found to be less attractive because the specific activity level of these isotopes typically produced in the reactors was not reached in EU DEMO. The layout of the irradiation port allows theoretically simultaneous, parallel production of several isotopes even with different half-lives. This flexibility of the irradiation unit operation also opens the possibility for research activities to pursue the generation of promising and rare radioactive isotopes for future medical and industrial applications.  
The scope of this research work was also to estimate the possible financial potential of the irradiation unit in the case of industrial utilization of the generated isotopes. The eventual profit coming from the radioactive isotopes' production could make the DEMO project economically more attractive. To this end, the approximate market price of the final raw product for each isotope was assessed, making use of the available open sources. The estimate of the actual financial gain is complex and it is out of the scope of this work.  
The use of the irradiation unit of \(\sim\)6 m\({}^{3}\) volume integrated in the DEMO equatorial port for the production of radioactive isotopes could theoretically provide a significant financial outcome up to several hundred million USD per year. The DEMO operation in such dual mode (energy and isotope productions) could make the project more attractive also because the end use of the isotopes in medicine could highlight another socially well-appreciated aspect of the fusion energy. Therefore, with the new design option, the DEMO project could become more complex, which, nevertheless, could finally increase the attraction of the fusion energy.