As an alternative, coal miners were deployed to excavate a tunnel below the reactor to make room for a cooling system. The final makeshift design for the cooling system was to incorporate a coiled formation of pipes cooled with water and covered on top with a thin thermally conductive graphite layer. The graphite layer as a natural refractory material would rapidly cool the suspected molten uranium oxide without burn through. This graphite cooling plate layer was to be encapsulated between two concrete layers, each one meter thick for stabilisation. This system was designed by Leonid Bolshov, the director of the Institute for Nuclear Safety and Development formed in 1988. Bolshov's graphite-concrete "sandwich" would be similar in concept to later core catchers that are now part of many nuclear reactor designs.