Synchrotron radiation-induced total reflection x-ray fluorescence (TXRF) analysis was used for the trace element analysis of steels exploited in the construction of core components of existing fission plants and future fusion power plants. Detection of traces of niobium in reactor pressure vessel steel allows a retrospective determination of the fast neutron flux. For the construction of future fusion reactors, low activation steels are being investigated. Traces of Nb, Pd, Ag, Eu, Gd, Th, Dy, Ho, Er, Os and Bi cause a higher activity of the material than the steel itself. Synchrotron radiation allows the excitation of the heavier element K shells, avoiding the strong overlaps of their L lines. Moreover, the linear polarization of synchrotron radiation combined with side-looking detection manages to reduce the scattering due to the matrix contained in the analysed samples. Experiments were carried out at Hasylab Beamline L (bending magnet). The experimental set-up includes a double reflector collimator, a multilayer and a vacuum chamber. Chemical preparation of the sample included dissolution and separation by means of anion-exchange chromatography. Minimum detectable concentrations of 37 ng g(-1) for Nb and 400 ng g(-1) for Th in the steel were achieved. Copyright (C) 2001 John Wiley & Sons, Ltd.