The Nuclear Fuel Cycle Simulation System (VISTA) is a simulation system which estimates long term nuclear fuel cycle material and service requirements as well as the material arising from the operation of nuclear fuel cycle facilities and nuclear power reactors. It is a scenario based simulation tool which can model several nuclear fuel cycle options including existing nuclear power reactor types and future possible reactor types. The past operations of the power reactors and fuel cycle facilities can be modelled in the system, in order to estimate the current amount of spent fuel stored or total Pu in stored spent fuel. It can also accept future projections for nuclear power and other scenario parameters in order to predict future fuel cycle material requirements.The model has been designed to be an optimum mixture of simplicity, speed and accuracy. It does not require too many input parameters if the purpose is just to compare the requirements for selected scenarios. Furthermore, the accuracy of the system can be improved by introducing more detailed and correct sets of input parameters.