Lining for Nuclear Power Station Units

Cubic zirconia–based ceramics were first posited by the Russian Academy of Science’s Institute of High Temperatures jointly with the Kurchatov Institute in the mid 1990-ies as the most reliable existing lining material for active zone melt traps in nuclear reactors – which are essential in the event of severe accidents.

As the recent accident at the Fukushima nuclear station demonstrated, in order to prevent leaks of radiation into the surrounding environment, a station should have a nuclear reactor active zone melt (corium) trap that functions at temperatures of up to 2800 K. This kind of trap is the last barrier stopping uranium fission leaks. That trap was missing at the Japanese power station built in the 1970s, - the reason behind the severe radiation and environmental consequences. The trap must accommodate and cover the whole mass of the reactor melt, ensure a decrease in temperature and the efficient removal of residual energy released by uranium fission products so as to stop the base of reactor shaft melting and destroying the containment core inside, - as actually happened at Fukushima as a result of earthquake.

Active Russian nuclear stations VVER-1000 are also missing this melt trap. A passive trap for reactor active zone melting (melt trap) has been installed at the nuclear power stations currently under construction including the Baltiyskaya, Leningradskaya 2, Novovoronezhskaya 2 stations. That device has a body located under the reactor filled with non-metallic materials that keep solid and liquid pieces of the reactor’s active zone and structural materials from leaking when mixed with active zone melt. A crucible type dry trap is another modern design. This is an active trap for distributing the melt over a large area as a thin (0,2 – 0,3 m) and smooth layer out of the reactor shaft. This technology cannot be applied to stations that have already been built.

There is a particular need for introducing zirconium dioxide –based passive traps at stations with nuclear reactors of the VVER-1000 type that have no technological solutions for trapping melt and preventing explosive hydrogen generation. The melt trap is located in the bottom of the reactor shaft and can be designed as a container with a spherical bottom that includes a cubic zirconia concrete thermal protection layer (see picture). The high thermo-mechanical properties of cubic zirconia ceramics make this lining able to keep corium for a long time.