An analysis of In-Vessel Melt Retention strategy for VVER-1000 considering the effect of torospherical lower head vessel

Abstract

In this paper, a Modified analytical In-Vessel melt Retention (MIVR) model is proposed to predict heat load on the VVER lower head vessel imposed by a steady state two-layer molten pool, with taking effect of the torospherical shape into consideration. The comparative calculation for the MIVR model was performed through a calculation of heat load from a quasi-steady state two-layer molten pool to the VVER-440 lower head wall. Then the MIVR model was adopted to analyze the IVR strategy for VVER-1000 reactor through a calculation of heat loads caused by four configurations of molten pools which were predicted by severe accident codes namely MELCOR v2.2, SOCRAT/B1, ASTEC v2.1 and ASTEC v2.0r3, respectively. The results clearly showed the effect of the torospherical shape of lower head on energy partition of oxidic pool with an increase of heat load from the oxidic pool to its vertical boundary. A parametric study on emissivity coefficients applied to the top of melt pool indicated that even without emissivity from the top (i.e. no radiation heat flow upwards), the peak heat flux from the vessel wall was still significantly below the maximum value of the Critical Heat Flux (CHF).