Reflood Investigation of Fuel Assemblies Based on Analysis of High-Temperature Integral Experiments

A series of high-temperature experiments with an electrically heated fuel assembly in a steam–argon mixture followed by rapid cooling of the assembly with water or saturated steam is analyzed. The possibility of efficiently cooling a water-heated and water-moderated reactor core, heated to high temperature during a serious accident, by flooding the core with water from the bottom is studied. The oxidation of fuel-element cladding, hydrogen release upon heating and reflooding and heat-transfer processes, characteristic for a serious accident in a reactor and determining the effectiveness of flooding as a measure to control the accident, are analyzed in detail for a single experiment. The analysis is performed using the SOKRAT/V2 software code developed for modeling measures taken to control serious accidents in VVER. Analysis of experiments shows that reflooding the core, heated in a steam medium to temperature not exceeding 2100–2200 K, can be an effective measure to stop catastrophic development of a serious accident at NPP with VVER.