Integrity analysis of a reactor pressure vessel subjected to pressurized thermal shocks by considering constraint effect

The integrity analysis of a reactor pressure vessel subjected to pressurized thermal shocks is performed. Linear elastic analysis leads to a more conservative result than the elastic– plastic analysis if the warm prestressing effect is not considered. The stress intensity factor for the deepest point of a surface crack front is not always larger than that for a surface point, indicating that both the deepest and surface points of the crack front should be considered. The safety margin of the reactor pressure vessel is larger based on the K–T approach than that only based on a K approach. Reactor pressure vessels (RPVs) of nuclear power plants are exposed to neutron irradiation, which causes embrittlement of the ferritic steel and makes the material susceptible to brittle fracture. This has negative consequences to the RPV integrity, especially in the case of unforeseen extreme loading conditions. One potential challenge to the integrity of a RPV in a pressurized water reactor is posed by a pressurized thermal shock (PTS), which is associated with severe cooling of the core together with or followed by repressurization of the RPV. PTS transients are arisen by a number of abnormal events and postulated accidents including a pipe break in the primary pressure circuit, a stuck-open valve in the primary pressure circuit that later re-closes, or a break of the main steamline. PTS transients lead to high tensile circumferential and axial stresses in the RPV wall. If the stress intensity factor (SIF) is too large this may result in crack initiation and in the worst case even to the failure of the RPV. Thus, the RPV has to be assessed against cleavage fracture [1–7]. The integrity analysis of RPV involves a comparison of KI with KIc for the whole PTS. Calculation of KI is generally based on linear elastic fracture mechanics (LEFM) for the simplification reasons. The material along the crack front will yield due to high tensile stresses in the vicinity of the crack front. Thus, elastic plastic fracture mechanics (EPFM) shall be used for the nonlinear fracture analysis. For the modeling of KIc, an important aspect is the constraint effect, which is arisen due to the different stresses and strains at the crack tip between components and the tested specimens under the same crack driving force (KI or J). Fracture toughness testing standards use highly constrained specimens with deep cracks to guarantee conservative fracture toughness data. The effective toughness for the deeper cracks (high constraint) is lower than that for shallow cracks (low constraint) due to the higher hydrostatic stress at the crack tip. If this data from deep cracks is directly used in a structure with low constraint, it may lead to over conservative results and a too early decommissioning of structures [8–10]. However, in the integrity analysis of RPV subjected to PTS transients the shallow cracks are of significant