Prestressing technology for increased integrity of embrittled reactor vessels

Abstract

Prestressing has the potential to improve safety margins in pressure vessel failure assessments for reactor vessels that have been subjected to neutron embrittlement. The technology is a mechanical alternative to annealing. Prestressing a reactor pressure vessel reduces the resultant stress in the vessel wall. This includes stresses due to normal operating pressure, possible residual stresses and pressurized thermal shock transients (PTS). The reduced stress intensity factor affects crack growth rates and conditions for crack arrest. Prestress can be accomplished by applying a mechanical tool on the outside diameter of the vessel in the region of concern. A technique to permanently apply a compressive load based on wire winding technology, utilizing shape-memory alloy wire, is currently under development. © 1994.