Certain aspects of the RBMK reactor design, such as the active removal of decay heat, the positive void coefficient properties, the 4 meters graphite displacer ends of the control rods and instability at low power levels, contributed to the 1986 Chernobyl disaster, in which an RBMK experienced a very large reactivity excursion, leading to a steam and hydrogen explosion, a large fire and subsequent meltdown.