A steam-generator-tube rupture (SGTR) in a pressurized-water reactor is a design-basis accident with which plants have been designed to cope. Its specific significance is in its potential to bypass the containment thereby providing a pathway for radioactivity release to the environment. In combination with significant core damage, uncontrolled SGTR may lead to accidental release of radioactivity in the form of aerosol particles and gas-phase iodine compounds.

In this paper, we describe the phenomena identification and ranking tables (PIRT) prepared as an international collaboration for uncontrolled SGTR in connection with core damage. This PIRT is limited to fission-product transport and retention in the steam generator and release to the auxiliary building, i.e., the source term. The phenomena affecting the fission-product retention in the steam generator and release to the environment were divided into those relevant to a dry steam-generator secondary side, and those relevant to a flooded secondary side. Rankings were given to 17 phenomena in the dry and 16 phenomena in the flooded secondary side regarding their: i) impact on the source term, ii) the availability of experimental data applicable to SGTR severe-accident conditions, and iii) the availability of codes / models to describe the phenomenon under the conditions of SGTR severe accidents.

Based on this work, two phenomena in the dry and two in the flooded secondary side were considered to be of medium-to-high significance and low-to-medium level of knowledge. These phenomena and their interactions with other fission product retention mechanisms are discussed. In addition, several issues were identified that are considered to need further attention.