How does a RBMK reactor explode?


How does a RBMK reactor explode?

In: Chemistry

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.

Unlike other reactors this one gets hotter(more reactive) as it fills with steam. Oprators made too much steam for it to handle. It got hotter and made more steam witch made it even hotter untill the pressure is to high for the containment vessel.

In very simple terms – the reactor works because radioactive particles break apart and release radiation energy as they do so. This is used to heat water, to create steam, which then drives turbines (big fans) than generate electricity. The reaction also make lots of tiny particles called neutrons go bouncing around. These neutrons can bump into other radioactive particles making them break up.

Without anything to ‘put the breaks on’ this, it will lead get out of control, where more particles break up, sending more neutrons bouncing around, which makes even more particles break up.

In an RBMK reactor, one of the things that keeps the brakes on is the water that is being heated up by the reaction, as it absorbs the neutrons bouncing around. But if the water is boiling, the bubbles in the water make it less dense and so it absorbs fewer neutrons. That means the higher the rate of reaction, the more the water boils, the fewer neutrons get absorbed, so the reaction gets even stronger and so on. There are other ways to calm down the reaction, including rods made out of Boron that also absorb neutrons, these rods can be lowered into the reactor to slow it down, or raised up to increase reaction.

Essentially, an explosion happens if the various effects that are calming the reaction down are weaker than the effects that are ramping it up.