FUKUSHIMA LESSONS LEARNED: MITIGATION AND CONTAINMENT OF SEVERE ACCIDENT CONDITIONS BY MEANS OF GLASS-TO-METAL SEALED ELECTRICAL PENETRATION ASSEMBLIES

摘要

Analysis of the Fukushima accident showed that, following the earthquake and tsunami which caused a power failure at the plant, degraded organic seals under high temperature and pressure led to an explosive release of hydrogen. These seals are necessary at points where electrical conduits penetrate the reactor vessel, as well as around key doors and hatches, and are therefore important points in the reactor containment. Standards for critical safety components, such as electrical penetration assemblies (EPAs) and other seals in the reactor containment, are to be revised to raise them to severe accident standards. SCHOTT's glass-to-metal sealed EPAs are constructed of glass set under compression by metal. They are robust and can withstand various conditions, including high temperatures, pressures, radiation as well as submergence. The EPAs have performed well in tests representing severe accident scenarios. Sweden's Forsmark 3 upgrades in 2014 incorporated severe accident standards into the safety evaluation of the nuclear plant, and included installation of SCHOTT EPAs. Cables and seals that form the severe accident equipment chain should be made of inorganic materials. SCHOTT is developing technology made of crystalizing glass ceramic combined with superalloys. This technology provides constant compression on the glass seal over the entire operational temperature range, ensuring full pressure resistance and a hermeticity at elevated temperatures. This paper reports on safety margin improvements that are achieved by using enhanced, proven technology of glass-to-metal sealed EPAs, and outlines the future for even more robust EPAs, as well as enhanced cable connectors for severe accident equipment.