Control rods are used in nuclear reactors to moderate the chain reaction and prevent explosions. They absorb neutrons without undergoing fission and are made of metal or metal alloy. They are lowered or raised to control the temperature and can shut down the reactor in an emergency. They are part of failsafe systems and can function without human intervention.
Control rods are tools used to control the chain reaction that occurs inside a nuclear reactor. Left unchecked, the chain reaction can quickly spiral out of control, causing the reactor to explode. Control rods moderate the rate of the reaction, ensuring it occurs safely and sustainably. These rods are also later part of the safety systems used to prevent reactor disasters.
As the name suggests, a checker rod is a rod made from a metal or metal alloy. It is usually integrated into a housing with other rods designed to be raised and lowered together by the reactor. The composition of the metal or metals in a control rod varies, depending on the type of reactor in which it is used. In all cases, metals share the property of being able to absorb neutrons without undergoing fission.
Fission, of course, is the reaction that drives nuclear reactors. In fission, a nucleus absorbs a neutron and then splits, releasing heat, energy, and more neutrons. In a controlled nuclear reaction, reactor personnel want to keep neutron production equal to neutron consumption, with each fission reaction generating a single neutron to replace the one lost. In reality, neutrons are produced two to three times faster than they are consumed, which can quickly cause a runaway reaction.
This is where control bars come into play. Control rods are lowered into the reactor to absorb some of the neutrons produced during the fission reactions to keep the ratio in check. As the temperature rises, the rods are lowered, and as the temperature drops, the rods are raised to allow more fission reactions to occur. In an emergency where the reactor appears to run out of control, rods are lowered all the way into the reactor to shut it down entirely.
Also known as absorption rods, nuclear reactor control rods are designed to function even during a crisis situation where a human is unavailable. With many reactors, the rods are placed on top of the reactor in a system designed to drop the rods if the reactor temperature gets too high. In other cases, failsafe systems can be activated both inside the reactor hall and outside via remote systems. Staff also keep a close eye on what’s happening inside the reactor, monitoring fuel and control rods for replacement as needed.
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