Sensitivity Analysis of Tube and Pipe Rupture Time during Thermally-Induced Steam Generator Tube Rupture (TI-SGTR)

Thermally-induced steam generator tube rupture (TISGTR) or consequential SGTR (C-SGTR) is the event that the initiating event such as station blackout (SBO) causes the heat-up of the core and then causes a creep rupture of steam generator (SG) tube. The TI-SGTR causes the fission products from the core to be released to the environment via the secondary side of SG, therefore is one of the containment-bypass accidents. Although the probability of occurrence is very low, the TI-SGTR has a high radiological influence to the public, collecting interests in terms of public health risk. The typical TI-SGTR is initiated by a complete loss of cooling such as station blackout (SBO). When the reactor cooling pumps (RCPs) are stopped operating and the additional cooling measures are lost, the reactor core is cooled by the natural convection via the SG tubes. Absent of external cooling for a long time, the core and the entire primary system is heated up, and then a piping of primary system such as the SG tube, the hot leg and the surge line ruptures by creep failure. Among the potential location, the rupture at the hot leg and the surge line has relatively less important because the containment-bypass of fission products does not occur when the rupture occurs at these locations. However, the initial location of the creep rupture among those positions are highly uncertain and are believed to be the function of the natural convection behavior via the SG tubes. In this article, the sensitivity analysis of the creep rupture at primary side of APR1400 was performed with respect to the variables including the parameters related to the natural convection via the SG tubes. The order of rupture between the SG tubes and the hot leg/surge line was statistically shown along with the variables.