system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a RBMK reactor explode?
gpt
Reactors use really hot water that’s maintained at a constant pressure as a coolant. 

The pressure prevents the water from boiling at its normal temperature.

If there is change in this balance and the water turns to steam in the “primary coolant loop” the water becomes ineffective as a coolant.

The reactor gets hotter and so does the water. More heat, more steam. This causes a feedback loop and eventually something in the system will break down.