The possibility of LWR spent fuel rejuvenation in (D, T) (Deuterium and Tritium) driven hybrid reactors having 12.5 cm of the fissile zone thickness is investigated for various plasma chamber dimensions (DR = 18.7, 118.7, 218.7 and 418.7 cm) with a linear fusion neutron source (Plasma dimension is assumed as DR/2) under different first wall loads (P-w = 2, 4, 6, 8 and 10 MW m(-2)). The behavior of the spent fuel is observed over 36 months for discrete time intervals of Delta t = 15 days and by a plant factor of 75%. The fissile fuel zone is considered to be cooled with three different coolants, gas (helium or CO2), Flibe (Li2BeF4) and Natural lithium. As a result of the calculation, in the case of the first wall load and the plasma chamber, dimensions are selected to be high, although the first wall material was damaged considerably by the high neutron flux (DPA > 100 and He > 500 ppm for P-w > 2 MW m(-2) over 3 years of operation) and maximum temperature in centerline of the fuel rod (T-m) has reached the melting point (T-m > 2600 degrees C for P-w > 6 MW m(-2) and DR > 1 m), it was observed that the neutronic performance of hybrid reactor improved unnegligibly. For DR = 18.7 cm, at the beginning of rejuvenation, TBR (Tritium Breeding Ratio) values being about 1.35, 1.11 and 1.39 for gas, Flibe and Natural lithium, respectively, the end of the rejuvenation increased to 1.39, 1.17 and 1.43 for 2 MW m(-2) and to 1.55, 1.39 and 1.57 for 10 MW m(-2). In addition, the blanket energy multiplication (M) increase 5.10, 4.87 and 4.82 for 2 MW m(-2) and to 6.55, 7.04 and 6.04 for 10 MW m(-2) from 4.67, 4.24 and 4.46, respectively. For only Flibe, when the preferred DR value is about 1 m, M values increased to 5.70 and to 9.5 from 4.43 for 2 MW m(-2) 10 MW m(-2), respectively. At the same conditions, average CFFE values indicating the rejuvenation performance increased to 3.27%, 3.80% and 3.21% for 2 MW m(-2), to 6.71%, 8.74% and 6.52% for 10 MW m(-2) from 0.418%, respectively. For Flibe coolant, while the same CFFE value is 11.5% about DR = 1 m, it is 11.9% about DR = 4 m. The contribution of a large plasma chamber (DR > 1 m) to neutronic performance can be neglected. The best rejuvenation performance and neutron economy has been shown by Flibe. For all cases, the denatured character of the initial fuel charge remains denatured for all investigated cases over the whole plant operation period in a hybrid reactor, although the plutonium duality increases continuously during the rejuvenation process. In addition, our calculations have proved that the effects of the important fission products (Xe-135, Sm-149) and plasma densities up to 10(21) (D + T)/cm(3) can be neglected on the neutronic performance of hybrid reactor which is rejuvenating LWR spent fuel. (C) 1998 Elsevier Science S.A. All rights reserved.