Structural assessment of fully flooded reactor cavity and penetration piping under steam explosion conditions

Steam explosion may occur in a nuclear power plant by molten core-coolant interactions when the external reactor vessel cooling strategy is failed. This phenomenon can threat the integrity of reactor cavity, penetration piping and support structures. Even though extensive researches have been performed to predict influences of the steam explosion, due to complexity of physical phenomena and environmental thermal-hydraulic conditions, it is remained as one of possible hazards. The present study is primarily to examine load carrying capacity of the reactor cavity under various steam explosion conditions through a series of numerical analyses; both hydro-dynamics and computational fluid-dynamics analyses were carried out in accordance with ten postulated conditions having different failure modes, explosion locations, corium conditions and turbulence models. Subsequent finite element analyses were conducted for the reactor cavity and penetration piping with support structures to calculate stresses and displacements. From the numerical analysis results, failure modes and corium conditions were identified as crucial parameters while the effect of explosion location was negligible. Moreover, structural assessment results showed that the reactor cavity had minor to medium potentials for localized damage but sustains the function of safety barrier to avoid release of radioactive substances under the steam explosion conditions.