An electrical penetration assembly for a nuclear reactor vessel, mountable in an aperture of a nuclear reactor vessel, includes a penetration body including first and second ends to be positioned, respectively, inside and outside the vessel; a sealed electrical connector providing a first seal for the electrical penetration assembly, the sealed connector insulating the penetration body at the first end; a feed-through carrier flange having a plurality of unitary electrical feed-throughs, each unitary feed-through allowing a single electrical conductor to pass therethrough, thereby ensuring continuity of the electrical connections, each unitary feed-through being individually insulated by an individual insulator providing a second seal, the unitary feed-throughs insulating the penetration body at the second end; and an anti-ejection device formed by the engagement between a narrowed portion provided at each unitary feed-through and a shoulder that is larger than the narrowed portion and provided on each of the electrical conductors.