Regelstab für einen Kernreaktor

A control rod for a nuclear reactor, having a cruciform shape with four flat planar members (S4) is provided with a membrane (70) for safeguarding against crevice cracking corrosion. Each of the four flat planar members (S4) of the control rod is fabricated from welded together side-by-side tubular members (or from longitudinally drilled flat plates) containing sealed neutron absorbing poisons. The protective membrane (70) is wrapped over each structural flat planar member. The protective membrane surrounds the member and is not under tension, being preferably maintained to the planar member under compression by ambient reactor pressure. The membrane provides an additional margin against crevice corrosion cracking by preventing the water of the reactor from coming into contact with the welded side-by-side tubular members (or drilled plates). Because the membrane is not under tension, it is not subject to either irradiation assisted stress corrosion cracking nor conventional stress corrosion cracking.