Station Blackout transient analysis for a PWR like design by using the MELCOR code

After the Fukushima accident the interest of each Country, that uses the Nuclear Power Plants (NPP) in its national energy mix, is more focused on the severe accident mitigation strategies. Several severe accident management analyses have been performed, to analyze the accident progression, the core damage, the grace period and the fission product release demonstrating the management strategy adequacy. Though the nuclear energy is not part of the Italian energy mix strategy, a deployment of NPPs is present in the Italian border, therefore the analyses of possible severe accident sequences are of interest for our national emergency preparedness strategy. The reference reactor, chosen for this analysis, is a generic PWR three loops design like. The state of the art severe accident code, chosen for this analysis, is the MELCOR code. A simplified preliminary, but exhaustive, MELCOR nodalization of the reference NPP has been developed. The aim of this work is to analyze, by using the MELCOR code, a Station Blackout (SBO) accident leading to a loss of the ultimate heat sink, and the possible thermal induced Steam Generator Tube Rupture (SGTR) due to this postulated event; several severe accident phenomena have been individuated and analyzed in the transient sequence, as the reactor core meltdown, the corium leaking into the reactor cavity and consequent reaction with the concrete. The results of the calculated data are in a general qualitative agreement with the other similar analyses. Different sensitivity analyses, and a review of the MELCOR nodalization, are in progress to assess the quantitative prediction of the code.