Analysis of Design Extension Conditions in a heavy water research reactor

In this study, the core behavior following the reactor vessel lower head rupture together with the moderator system failure in a tank type heavy water research reactor, IHWRR, is analyzed through the MELCOR code. The focus is on the safety assessment of the reactor core for Design Extension Conditions and overall assessment of safety features of the reactor for any residual risk posed by severe accidents. The inherent features of IHWRR provide a broad spectrum of scenarios where the fuel does not melt, even if primary and moderator cooling are lost. Accordingly, coincident with vessel rupture, three different scenarios are considered for moderator failure: i) loss of moderator forced circulation, calandria tube rupture in ii) the upper and iii) the lower parts of the core. The obtained results showed that the vessel rupture that coincides with the tube rupture in the lower part of the core leads to the oxidation of entire Zr cladding and failure of the calandria tubes without core melt or hydrogen explosion in the containment.