Boron and/or Cadmium control rods. They are inserted into the core to slow the reaction and withdrawn from the core to speed up the reaction. Both elements have a very high neutron capture crosssection, the more in the core the more excess neutrons they remove from the chain reaction.
No, the function of the control rods is to absorb surplus neutrons so that the chain reaction proceeds at a steady rate, and to compensate for the reducing reactivity of the reactor as the fuel is burned up over the refuelling cycle. They also have a very important safety function in shutting down the reactor fully when required, by inserting them fully, thus preventing any chain reaction from starting.
I found this: " The control rods, another important part of the reactor, regulate or control the speed of the nuclear chain reaction, by sliding up and down between the fuel rods or fuel assemblies in the reactor core. The control rods contain material such as cadmium and boron. Because of their atomic structure cadmium and boron absorb neutrons, but do not fission or split. Therefore, the control rods act like sponges that absorb extra neutrons." Here (you may have to copy and paste in two parts): http://www.aboutnuclear.org/view.cgi?fC=Electricity,Operation,Reactor,Control_Rods
You did not provide the list of "the following". However, the answer to the question is moderation. Moderation is the process whereby the neutron is slowed down in order to facilitate its subsequent capture by the nuclei of the fuel.
It is related to the specific nuclear reactor design including the nuclear fuel amount and the reactor control system and the energy extracting medium (coolant) capacity.
Heavy water can be used in a nuclear reactor to moderate the speed of neutrons, making it easier for uranium-238 to absorb a neutron and become plutonium-239. This process is known as breeding plutonium in a reactor and is one method of producing plutonium for nuclear weapons or fuel.
Control rods are devices that absorb neutrons and are used to control the speed of a fission reactor. By adjusting the position of the control rods within the reactor core, operators can regulate the rate of the nuclear chain reaction and manage the reactor's power output.
No, the function of the control rods is to absorb surplus neutrons so that the chain reaction proceeds at a steady rate, and to compensate for the reducing reactivity of the reactor as the fuel is burned up over the refuelling cycle. They also have a very important safety function in shutting down the reactor fully when required, by inserting them fully, thus preventing any chain reaction from starting.
Control rod act as brakes to reduce the reaction rate. However as nuclear reactors have so much excess reactivity, its like a car rolling downhill: remove the control rods a bit (release the brakes some) and the reaction rate increases.
True. Brakes control the speed of a car by reducing its kinetic energy, while control rods in a nuclear reactor control the rate of fission reactions by absorbing neutrons and reducing the chain reaction. Both mechanisms are essential for safely managing the system.
speed
I found this: " The control rods, another important part of the reactor, regulate or control the speed of the nuclear chain reaction, by sliding up and down between the fuel rods or fuel assemblies in the reactor core. The control rods contain material such as cadmium and boron. Because of their atomic structure cadmium and boron absorb neutrons, but do not fission or split. Therefore, the control rods act like sponges that absorb extra neutrons." Here (you may have to copy and paste in two parts): http://www.aboutnuclear.org/view.cgi?fC=Electricity,Operation,Reactor,Control_Rods
A moderator in a nuclear reactor slows down fast-moving neutrons to increase the likelihood of fission reactions. By reducing the speed of neutrons, the moderator helps maintain a chain reaction within the reactor core. This process helps control the nuclear reaction and sustain the reactor's power output.
Control rods absorb excess neutrons. By withdrawing them the power level of the reactor goes up. By inserting them the power level of the reactor goes down. They act similar to the throttle control on airplane engines.
Moderator such as graphite or heavy water would reduce the speed of neutron there by making them as thermal neutrons. Such slow speed neutrons are needed to bring Uranium-235 into fission. Control rods such as Boron carbide or Cadmium are there to abosorb neutrons. So chain reaction of fission is ketp under control.
Control rods need to contain material that is a strong absorber of neutrons, so that rapid shutdown can be achieved when necessary. Two such materials are Cadmium and Boron. Both have been used in different types of reactor. The elements may be used as alloys or as chemical compounds, and will be encased in stainless steel to avoid corrosion in the reactor.
I think you are talking about nuclear reactors. PWR is a Pressurized Water Reactor, and is the basis for most power generators. BWR is a Boiling Water Reactor. As the water is a major moderating component, controlling the speed and intensity of the nuclear reaction, the steam bubbles in a BWR can present a problem.
moderator, slows fast fission neutrons to thermal (near room temperature) energies rapidly enough to prevent their capture by uranium-238 before they can participate in the chain reaction and fission uranium-235control, remove excess neutrons so as to hold the reactor at exactly critical at all times, permit control of increases and decreases of operating power level