[en] V.S.O.P. (Very Superior Old Programs) is a system of codes linked together for the simulation of reactor life histories and temporary in-depth research. It comprises neutron cross section libraries and processing routines, repeated neutron spectrum evaluation, 2-D diffusion calculation with depletion and shut-down features, in-core and out-of-pile fuel management, fuel cycle cost analysis, and thermal hydraulics (at present restricted to HTR's). Various techniques have been employed to accelerate the iterative processes and to optimize the internal data transfer. The storage requirement is confined to 17 M-Bytes. The code system has extensively been used for comparison studies of reactors, their fuel cycles, simulation of safety features, developmental research, and reactor assessments. Beside its use in research and development work for the gas cooled High Temperature Reactor the code has succesfully been applied to Light Water Reactors, Heavy Water Reactors, and hybride systems with different moderators. (orig.)