The work concerns the purification of saline solutions and concentration of low-level liquid radioactive wastes (LLLRW) produced from nuclear research reactor (WWR-K) by membrane distillation in direct contact configuration (DCMD) using track-etched membranes (TeMs). Poly(ethylene terephthalate (PET) TeMs were hydrophobized by UV-induced grafting of styrene. Modification of PET TeMs (pore sizes from 135 to 268 rim) at optimal conditions led to increasing of contact angle to 104 degrees. Hydrophobic PET TeMs were investigated by XPS, FTIR, SEM, liquid entry pressure (LEP) and goniometric. Prepared membranes were tested in DCMD of saline solutions and LLLRW. The effect of membrane pore diameter, temperature, concentration on fluxes and rejection degree was studied. Salt rejection was evaluated by conductimetry and atomic emission method (for Cs, Mo, Sr, Sb, Al, Ca, Fe, K, Mg and Na). Decontamination factors of radioisotopes (for Co-60, Cs-132, and Am-241) were evaluated by gamma-ray spectroscopy. Salt rejection and decontamination factors were found to depend on pore diameter and conditions of DCMD. In most cases the degree of rejection was between 90 and 100%. Decontamination factor of Cs-137 reached to 1727.