The decommissioning of nuclear facilities demands an optimisation of analytical procedures to determine a variety of radionuclides in a variety of different materials on a wide activity scale ranging from very low to very high activities. Severe analytical problems arise from disadvantageous decay properties of a number of radionuclides. In the following the opportunities and limitations of recently developed analytical and nuclear detection methods are presented which has been applied successfully determining radionuclides like 55 Fe, 59 Ni, 63 Ni, 90 Sr, Th, U, Pu, Am, Cm. The applied analytical methods have to fulfil high quality standards including very low lower limits of detection, very high selectivity, sufficient precision and accuracy even in samples containing enhanced amounts of interfering elements. A new powerful tool is the application of collimated in-situ-γ-spectrometry. A recently developed calibration phantom named K-RISK is presented.