[en] Results are given for the application of the unfolding code FERRET and two versions of SAND-II to the Light Water Reactor Pressure Vessel surveillance damage function unfolding problem. FERRET is preferred when detailed knowledge of off-diagonal covariance matrix elements is available. One of the versions of the SAND-II code allows weighting of a priori estimates of the damage function and is equivalent to a log-normal least squares procedure. For intuitive and qualitative analytical understanding, the problem of sensitivity analysis of LWR PV surveillance extrapolation is most easily understood by application of a method whereby the spectrum in which the damage is to be calculated is expressed as a linear sum of the spectra used to derive the damage function. FERRET and the two SAND-II codes have been found to give consistent results. FERRET has the advantage of providing output covariance matrices as a standard feature