The laser-Compton scattering (LCS) phenomenon is one known method for producing energetic and high intensity gamma rays with variable photon spectrums. Availability of high-intensity gamma rays has made probing the (gamma,n)-based photonuclear transmutation possible and worth consideration. Parametric studies of LCS have shown that the gamma ray's spectrum is tunable and dependent upon various facility-related parameters. In this paper, a systematic optimization study of the LCS spectrum has been performed in view of the incident laser energy, electron beam energy and collimation angle. This optimization has been done with the aim to maximize the transmutation reaction rates of long-living fission products (LLFPs) such as I-129,Cs-135, and Cs-137 that have an isotopic composition of typical LWR spent fuel. In addition, the (gamma,n) and (gamma,2n)-reaction rates have been simultaneously calculated in order to evaluate the feasibility of photonuclear transmutation using the (gamma,n)-reaction. It has been shown that careful optimization of the LCS spectrum noticeably enhances the (gamma,n)-reaction rate without requiring any isotopic separation of the iodine and cesium targets. Furthermore, in order to enhance the energy efficiency of the LCS-based photo-transmutation system, a novel multiple laser-Compton scattering extraction (MULEX) concept has been introduced in this work, and it has been shown that the total production of the LCS photons can easily be increased by a factor of 10 or 20 in a single accelerator system. (C) 2017 Elsevier Ltd. All rights reserved.