[en] Safety system for the prevention of LWR core severe damage have recently been studied, which are based on automatic primary system depressurization and on borated water injection by low pressure accumulators. These systems have been named Core Rescue Systems (SSN). Some concern might arise regarding the effects of a thermal shock on the pressure boundary, following a postulated spurious SSN actuation. Although this event is already included, as intermediate LOCA, in the plant design basis, a closer look to the pertinent phenomena is here given in order to more precisely access available safety margins. The conclusions of this study is that the spurious activation of SSN system, although entailing a significant (non pressurized) thermal shock, does not pose any threat to pressure boundary integrity provided pressure vessel mechanical properties are acceptably good. On the contrary, the availability of such a system at a plant may offer additional means to avoid pressurized overcooling transients of different origin