## 2 Methods and Materials  
FISPACT-II is a nuclide inventory code that models radiation damage, time-dependent inventory, and activation-transmutation processes using nuclear data library databases. The Culham Center of Fusion Energy (CCFE) is where the FISPACT code was conceived and created. The code algorithm was created for computations of material activation produced by neutrons, deuterons, and protons in nuclear devices. The FISPACT-2 code computational framework encompasses a few key stages aimed at resolving a given problem. Firstly, nuclear data libraries serve as the primary sources of information. In this study, computations were performed employing the EAF-2010 and TENDL-2021 nuclear data libraries. EAF-2010 is an original FISPACT data library based on the JEF-1 [15] and JEFF3.1.1 [16] nuclear libraries. TENDL-2021 is a third-party universal nuclear library encompassing reaction energy data caused by various particles, including neutrons, protons, photons, alpha particles, and others, up to an energy of 200 MeV. The TENDL nuclear data libraries are regarded as some of the most comprehensive available and are routinely updated every few years. Both nuclear databases use evaluated experimental data to describe the reaction cross-sections (the data are weighted by the relevance and reliability of the experiments performed). Outside of the novelty of experimental data, the main difference between EAF-2010 and TENDL-2021 is that the latter, besides the experimental data, also uses mathematical modeling to account for the missing isotopes and energy ranges [14]. After the selection of libraries, a number of input files are prepared that describe the irradiation scenario and material composition. An irradiation scenario is divided into irradiation history and particle spectra. Our original neutron spectra obtained with neutron transport calculations correspond to a 175-energy-group structure [17], which is a standard for EAF-2010 deuterium-tritium nuclear fusion applications. The FISPACT-II code converts this spectrum into its own standard of 709 energy groups [18], interpolating values in between. TENDL-2021, on the other hand, only uses 1102 energy groups, so another conversion is required. After the input deck is set, deterministic methods are employed to obtain activation results through the solution of a set of differential rate equations. By solving Bateman differential equations, the yield of various radionuclides in materials following irradiation and cooling steps is derived. In FISPACT-II calculations, a slab of homogeneous material extending infinitely and diluted to an infinite degree is exposed to a time-varying flux of neutron projectiles, corresponding to the operational sequences of a fusion device [19]. Finally, radiological quantities are computed and generated. Additionally, the code provides information about uncertainty, and a pathway analysis of nuclear reactions is carried out. Presently, the FISPACT code is widely adopted by multiple research teams across Europe, playing a pivotal role in computing neutron activation products in the JET experimental fusion reactor. In our case, we used an elaborate irradiation scenario representing two JET campaigns consisting of three parts: a tritium experiment (C40) and Deuterium-Tritium Experiment 2 (C41). We have used daily DD (2.45 MeV) and DT (14 MeV) neutron budgets from irradiation sessions. As for tritium-tritium (TT) reactions, a neutron conservative assumption was applied: that the neutron yield for this reaction is two times larger than for DD neutrons. Tritium can be injected into the plasma mixture, or it can be created from DD reactions. There is also a possibility of having traces of tritium in a system from previous operations. The neutron budgets for DD and DT reactions are seen in Figures 1 and 2. Also note that the tritium campaign was split into two parts and was conducted before and after the DTE2 experiment.