The water acts as a coolant. In order for the reactor to work, the bundle, submerged in water, must be able to sustain a chain reaction in such a manner that the rate of reaction increases. This means that if not regulated, the uranium would eventually overheat and melt. To prevent overheating, control rods are made from a material that can absorb neutrons, usually graphite. The control rods can then be raised or lowered by operators to control the rate of nuclear reaction. To produce more heat, the operator raises the control rods; to decrease heat production the operator lowers the control rods. The rods can be lowered all the way to shut down the system. As the uranium heats, it heats the water and turns it to steam. The steam drives a steam turbine, which spins a generator to produce power (How Nuclear Power Works 3). To put it simply, heat is generated from the uranium inside a reactor. As the reactor gets hot, cool water is then released and cools the reactor down. The reactor in turn boils the water and steam is produced, the steam spins a turbine. The turbine generates electricity and the water condenses, the water enters the cooling tower, and as the name implies the water is cooled down. This process is then repeated.
The test had already been conducted previously at the plant, and gone off without any problems. So what was different between the previous tests and the one that happened on April 25, 1986? In previous tests the reactor was in a stable controlled state, with all the safety systems working normally. The program's safety instructions were poorly designed. All operations carried out during the experiments were supposed to be cleared by the plant shift foreman. In an emergency, the staff would follow the instructions of the foreman. The program said that the emergency core cooling system should be switched off. This reduced the safety of the reactor greatly.
