A second explosion has occurred at the Fukushima Daiichi reactor complex this time at the Unit 3 nuclear power plant. Unit 3 lost control of cooling water and exposed the top of its nuclear fuel in the reactor core sometime early March 13, 2011 initiating the first stage of fuel melting. The hydrogen gas is generated during this stage of a partial core melt.  The explosive gas is being venting from the reactor vessel and then vented from the Mark I containment system to a roof top compartment. The large pocket of gas then found an ignition source and dramatically detonated with tremendous force.  The detonation has occurred outside of the vital containment system. Many questions remain about the integrity of the containment system and the condition of approximately 50 tons of irradiated used nuclear fuel being stored in approximately 40 feet of water in the rooftop storage pond.