Comparative study of a boron dilution scenario in VVER reactors

ubsequent studies have identified many scenarios, which can lead to reactivity excursions due to boron dilution. The comparative study, presented in this paper, deals with the so-called ``restart of the first reactor coolant pumpʹʹ scenario and its reactor-dynamic consequences for both Russian designed VVER reactor types, VVER-440 and VVER-1000. The transient simulations were performed using the three-dimensional core dynamics code DYN3D. The DYN3D modeling features, including recent developments, as well as the cross-section meth- odology involved in these calculations, are described. The analyzed accident scenario is out- lined together with the assumptions made. The results of core response in this boron dilution accident for both VVER reactors are compared within the ranges, determined by the two reactivity values of interest: the criticality limit and the reactivity initiated accident (RIA) limit.