Recently, Paul Scherrer Institut (PSI) commenced a project on "Feasibility and plausibility of innovative reactor concepts in an European electricity supply environment". The investigation in the project will be done on two reactor types: the pebble bed High-Temperature Gas-Cooled Reactor (HTGR) and Molten Salt Reactor (MSR) with the main focus being on the HTGR. Firstly, the project consists of an extensive literature study on the current status of the technology and research on the HTGR and MSR. Secondly, based on the findings from the literature survey, several topics of particular interest have been chosen for more thorough investigations. On the pebble bed HTGRs, the areas of investigation include risk assessment study, preliminary economic assessment, investigation of accident scenarios, and preliminary study on reduction of waste volumes. For both HTGR and MSR an analysis and optimization of the fuel cycle is foreseen. At the initial stage the equilibrium closed Th-U and U-Pu cycle performance will be evaluated and compared with 16 other reactor types. Later the knowledge from equilibrium study will be applied to optimize especially the MSR but also HTGR fuel cycle. At the end of the project, based on the literature survey and the results from the scoping studies, future research needs and areas of special interest will be identified for successive projects related to HTGR and MSR in PSI.