PTS ON EMBEDDED ROTATED CRACKS AND PROJECTION RULES

摘要

The Pressurized Thermal Shock (PTS) is one of the transients of concern in a nuclear reactor. The phenomenon takes place when the down-comer and internal Reactor Pressure Vessel (RPV) surfaces are rapidly cooled down while the system is still under pressure. This event is considered life limiting for the safety case where cracks are postulated and the RPV material embrittled by neutron radiation damage. During this study, an elliptical embedded crack was postulated in a cylindrical geometry simulating the RPV. The system, initially at high temperature and under pressure load condition, was subject to a PTS transient. Thermal and structural analyses were carried out for various crack configurations. Particularly, besides the axial crack, skewed embedded axial cracks were modeled and analyzed (30°, 45° and 65°) for PTS phenomenon. Finite element analysis were carried out with ANSYS considering two variants: no-heat transmission and total heat transmission through the crack. Results showed that the highest stress intensity factor is obtained at an axial crack (0°). Moreover, it is shown that considering no-heat transmission through the crack is a conservative approach. The ASME code approach to the skewed axial cracks characterization by projection is considered. It is found that the ASME approach is conservative, with an excess conservatism for largely skewed axial cracks. The same conclusions were reached when considering the projection rules from the R6 code.