PREVENTION OF EARLY CONTAINMENT MELT-THROUGH DURING SEVERE ACCIDENT OF LIGHT WATER REACTOR VVER-1000

摘要

An analysis had been performed within an earlier PHARE project in Bulgaria that has discovered a vulnerability of VVER-1000, V-320 design consisting in early (up to one hour) containment melt-through via ionization chambers channels situated around the reactor pit. Based on this analysis, an original technical solution containing know-how has been developed by the authors for prevention of early melt penetration outside the containment potentially leading to massive radioactive releases. Additional thermo-mechanical analyses have been performed proving the high temperature resistance and tightness of the ceramic plugs designed to be used for plugging the bottom of ionization chambers. Two types of experiments have been done to validate the analyses - a cold one and a hot one. The cold experiment aimed to prove the operability in normal conditions of the system for lifting the ionization chambers together with the new plugs that will be installed. The hot experiment consisted in preparation of suitable melt stimulant and pouring it in a tube with plug at M=l:l to prove the reliability of the plug. This way the Design of VVER-1000 can be enhanced against early containment failure during severe accident and decrease the value of Large Early Release Frequency (LERF) calculated in PSA Level 2.