[en] Sixteen years after the accident of unit 4 of the Chernobyl NPP the Sarcophagus still remains one of the most dangerous nuclear facilities in the world. The ruin of the destroyed unit 4 and its surrounding Sarcophagus together are termed object Shelter, which still comprises about 96 % of the spent nuclear fuel. The big amount of irradiated nuclear fuel and radioactive waste may cause potential radiological hazards. Thus, a comprehensive and detailed description of all parameters having influence on the safety state of the Sarcophagus was needed. At the Vienna Chernobyl Conference in April 1996 Germany and France declared to support the international co-operation of institutions of the Ukraine, Belarus and Russia in view of a solution of the Chernobyl related issues. The first project identified within the French-German Initiative (FGI) was dedicated to the safety state of the Chernobyl Sarcophagus. This FGI project has been funded by the governments and by the electricity utilities of Germany and France, respectively, with 2 million Euro. The main aim of the project was to collect, analyse and verify all safety relevant data and to integrate these data in a comprehensive data base. The major fields of investigation were building constructions, systems and equipment, radiological situation, nuclear fuel, radioactive waste and environmental impact. In this paper in a first step the spent nuclear fuel and the correlating radiological hazards will be described briefly. In the following sections the FGI Sarcophagus project along with some results and practical applications to estimate the radiological risks as well as to support maintenance, waste management and stabilization measures will be presented