Prospects for Improved Zr-2.5 Nb Pressure Tubes

Abstract

The service life of pressure tubes is a function of their changes in dimensions relative to design allowances and their mechanical properties continuing to exceed minimum requirements. In the newer reactors with four garter springs, their service life will probably be limited by hcanges in mechanical properties, particularly their reduction in fracture toughness and the consequent reduction in their ability to leak-before-break. Leak-before-break is a function of hydrogen concentration, susceptibility to delayed hydride cracking and fracture toughness. Pressure tubes are beig developed that should have lower rates of hydrogen ingress, yttrium sinks to collection the hydrogen and a different texture to reduce susceptibility to delayed hydride cracking. These tubes will be less likely to crack and should have a longer service life than current tubes.