The Double Closure Plate Sub-Plate (DCPSP) was introduced in the Electron Cyclotron Upper Launcher (EC UL) design in order to minimize the openings exposing the interior of the Port Plug (PP) to the port cell; avoiding thus the near environment activation in case of maintenance or intervention on the In-Vessel (IV) components. The load combination Vacuum Vessel (VV) baking + Seismic level 2 is considered as one of the most relevant accidental events in terms of structural conformity affecting the DCPSP. The modal analysis of the DCPSP shows that the natural frequencies are far from the peaks of the ITER reference spectra at the PP flange. Therefore, the feasibility of analyzing the seismic event by using a static method, as a replacement of the Response Spectrum approach, is also investigated. Next, the results due to the seismic event are combined with those produced by loads on the DCPSP that occur during the VV baking scenario. The comparison of the categorized stresses and the allowable design limits showed that the mechanical integrity of the DCPSP is preserved during this load combination.