[en] Recently, the very rare process of nuclear ternary fission has been of great interest in nuclear dynamics. Based on the statistical theory of fission, we discuss here the ternary-fission mass distribution of _1_8_4"4"6"6","4"7"6X formed in low-energy U + U collisions for different heavy third fragments at T = 1 and 2 MeV. The expected ternary configurations "2"0"8Pb + "2"0"8Pb + "5"0Ca and "2"0"4Hg + "2"0"4Hg + "5"8Cr are obtained from the ternary fission of _1_8_4"4"6"6X at T = 2 MeV. In addition, for both the systems, various possible ternary modes are listed for different heavy third fragments. Our results clearly indicate that the favored ternary configurations have either proton and/or neutron shell closure nucleus as one of their partners. (orig.)