Test was being performed on reactor to improve safety
Reactor power fell too low, leading to reactor poisoning - control rods had to be removed
Alarms were tripped, but thermal-hydraulic parameters were ignored
Testing conditions caused controlled positive feedback loop
Shortly thereafter, emergency shutdown initiated
EPS-5 button was pressed for unknown reason, inserting all control rods

Possibilities include malfunctioning of the emergency system, or crews continuing test despite alarms
Due to flawed design, control rods displaced coolant, initially increasing reaction rate
Core overheated, blocking control rod column
Power level rose to ten times normal operating parameters, triggering explosions