What is the function of control rods in a nucleus reactor?

Answer 1

A control rod in a nuclear reactor absorbs neutrons and limits the chain reaction. It is used as a "setpoint" for operation in that it is pulled out a certain amount to allow the chain reaction to heat the reactor. The control rod can also be inserted to absorb neutrons and shut the reactor down.

Answer 2

To prevent overheating, control rods made of a material that absorbs neutrons are inserted into the uranium bundle using a mechanism that can raise or lower the control rods. Raising and lowering the control rods allow operators to control the rate of the nuclear reaction. When an operator wants the uranium core to produce more heat, the control rods are raised out of the uranium bundle (thus absorbing fewer neutrons). To create less heat, they are lowered into the uranium bundle. The rods can also be lowered completely into the uranium bundle to shut the reactor down in the case of an accident or to change the fuel.

Answer 3

They absorb excess neutrons, to control the rate of reaction. Neutrons collide with the nucleus of the radioactive materials to start off the nuclear fission reaction. If there are too many neutrons around to do this, then there will be an uncontrolled reaction, which will cause a meltdown.

The radioactive material should be kept below the critical mass or an uncontrolled reaction may lead to it exploding (like a nuclear bomb)

Answer 4

The control rods include some material that strongly absorbs neutrons-boron is the most common though others like cadmium are also effective. The safety function of the rods is to quickly shut the reactor down should conditions require it. This would most likely be a loss of coolant flow, whether water flow or gas flow, which would cause a rapid rise in fuel temperature, so the best way to kill this quickly is to insert the rods (in a few seconds) so that the reactor power is immediately shut off (except for the decay heat which requires some emergency cooling flow). During steady operation or power changes the rods are used to maintain the reactor just critical, so that the chain reaction is maintained steady or changed at a slow controlled rate. Changes in the reactors reactivity state are caused by variations in neutron absorption by some fission products, notably Xenon 135, which varies in concentration with power level, and by fuel burn up during the period between refuelling outages, so that control rod adjustments are needed to accommodate these changes. If the reactor maintains a steady power level for several days, the xenon reaches an equilibrium level and the rods will move very little from then on, just gradually coming out to offset the fuel burn up.

Answer 5

They don't affect what happens in the nucleus directly, what they do is absorb some of the neutrons which are continually moving around in the active core. Every fission releases neutrons, with U-235 on average 2.5 neutrons per fission (not all fissions have the same result), of these 2.5 per fission some are absorbed in the reactor or coolant material, some are lost at the core boundaries, but the continued steady chain reaction depends on just one neutron per fission being captured by another nucleus and repeating the process. The control rods provide in effect a variable amount of absorber so that reactor power can be raised or lowered by either reducing or increasing the number of neutrons absorbed.

Answer 6

The control rod would have a tendency to absorb neutron which is the key for nuclear fission. So by inserting control rods such as Cadmium or Boron rods the reaction rate can be reduced. If we take off the rods the rate of reaction would increase.

Answer 7

They control nuclear reactions by absorbing neutron.