Simplify the following text for a Grade 15 native English-speaking person.
Original: Evidence arose of partial core meltdown in reactors 1 , 2 , and 3 ; hydrogen explosions destroyed the upper cladding of the buildings housing reactors 1 , 3 , and 4 ; an explosion damaged the containment inside reactor 2 ; and multiple fires broke out at reactor 4 .
Simplified: There was a partial core meltdown in reactors 1 , 2 , and 3 ; hydrogen explosions destroyed the upper part of the buildings housing reactors 1 , 3 , and 4 ; an explosion damaged the containment inside reactor 2 ; fires broke out at reactor 4 .