[en] The quality of the fast neutron fluence estimates to be used at the prediction of pressure vessel (PV) steel embrittlement may be significantly improved by the combined use of PV cladding dosimetry (Fe,Ni,Nb), by applying relative standardized measurements and by utilizing the low energy threshold reaction ⁹³Nb(n,n')⁹³sup(m)Nb. In this way the influence of the relatively large systematic (correlated) errors in the reaction cross sections (and possibly other nuclear data) and in the spectrum shapes at the surveillance chain (SC) and at the PV may be significantly suppressed. The influence and need of nuclear data at these types of measurements is discussed and is exemplified by the use of the ⁵⁴Fe(n,p)⁵⁴Mn and ⁹³Nb(n,n')⁹³sup(m)Nb reactions. Iron is a common reactor structural material, which also may be used for dosimetric purposes by the sampling or scraping technique. The Nb-reaction is of special importance due to its low threshold energy (approx. 1 MeV) and long half-life (16.1 y) and due to practical problems with the low threshold energy fission reactions. The quality of the dose estimates, especially the absolute ones, may be further improved if the uncertainties in some Nb data (cross section and γ to X conversion probability), and the relatively large discrepancies between the measured and calculated (Nb) cross sections could be reduced. (author)