[en] This paper presents a modification of the response spectrum method intended to be used for seismic analysis of systems and components in Nuclear Power Plants. It combines the response from the first few modes, together with residual terms to account for the higher modes. The conventional response spectrum method has the limitation that it produces responses lower than the actual at mode points close to the support. The proposed procedure rectifies this information and produces realistic responses at all points. The seismic response of an example tank is worked out using the proposed method. The results are compared with that obtained from the time-history method and found to have reasonable agreement. 5 refs