The force of the second explosion and the ratio of xenon radioisotopes released after the accident led Yuri V. Dubasov in 2009 to theorise that the second explosion could have been an extremely fast nuclear power transient resulting from core material melting in the absence of its water coolant and moderator. Dubasov argued that there was no delayed supercritical increase in power but a runaway prompt criticality which would have developed much faster. He felt the physics of this would be more similar to the explosion of a fizzled nuclear weapon, and it produced the second explosion.