A probabilistic approach to the evaluation of the PTS (pressurized thermal shock) issue

The pressurized-thermal-shock (PTS) issue is concerned with the possibility of failure of pressurized-water-reactor (PWR) pressure vessels under a very specific set of conditions. These conditions include: (1) the occurrence of reactor transients that subject the vessel to severe thermal shock as well as the normal pressure loading, (2) the existence of sharp, crack-like defects (flaws) at the inner surface of the vessel wall, and (3) high enough fast neutron fluence and concentrations of copper and nickel in the vessel wall to result in a extensive radiation-included reduction in the fracture toughness of the vessel material. Under these conditions, the mechanism for vessel failure involves propagation of the flaws through the vessel wall, in which case adequate containment of coolant for the core might not be possible. The portion of the vessel of concern is the so-called beltline region because, it is directly opposite the core (high influence rate), it is adjacent to the coolant downcomer (potential for thermal shock), and coolant leakage in this area would tend to uncover the core. This document discusses the behavior of flaws in reactor pressure vessels under pressure and thermal-shock loading conditions.