why is graphite used in nuclear reactors?

Answer 1

It is used as a moderator. Natural uranium will not undergo nuclear fission by itself because neutrons emitted by fissioning U-235 tend to be absorbed by U-238. However, if the neutrons can be slowed down, it turns out that U-238 is less likely to eat them, and enough are available to fission U-235 and keep the reaction going. Graphite has the useful property that it can slow neutrons down without eating them, so if you imbed uranium lumps in a graphite matrix with appropriate spacing, the neutrons which get into the graphite will be slowed down, and when they finally hit a lump of uranium they are likely to be taken up by U-235 and cause fission.

Any light element with a sufficient distaste for neutrons can be used as a moderator. Heavy water (deuterium oxide) works nicely. Natural water has slightly too high an appetite for neutrons to work well, but if the concentration of U-235 is raised a bit, you can make a reactor with natural water moderator. That is how power reactors work in the USA and most other countries.

Note that previous answers to this question are not correct. Absorption of neutrons is NOT what you want. Graphite moderators were used in the three plutonium production reactors at Hanford to produce the plutonium that destroyed Nagasaki, and were extensively used in the Soviet Union to produce power and to create plutonium for weapons. The Chernobyl reactor was of this type.

Answer 2

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RE:
why is graphite used in nuclear reactors?

Answer 3

Graphite is used to absorb neutrons. Most reactors in the USA use heavy water(deuterium), graphite is used in some military reactors and was used in the reactors in Chernobyl.

Answer 4

In its pure glassy (isotropic) synthetic forms, paralytic graphite and carbon fiber graphite is an extremely strong, heat-resistant (to 3000 °C) material, used in reentry shields for missile nosecones, solid rocket engines, high temperature reactors, brake shoes, electric motor brushes and as electrodes in EDM electrical discharge machines. Graphite melts at 3652 - 3697 Degrees Celsius and boils at 4200 degrees Celsius. in a nuclear reactor its used in the core because its so heat resistant.

Answer 5

The graphite is used as a moderator, to slow down the neutrons so they can interact with the nuclear fuel. They are not used as control rods, as some have previously answered. Other elements are employed in the construction of control rods, like cadmium and cobalt.

Answer 6

The core, surrounding neutron reflector, and thermal and radiation shielding of a modular HTGR is constructed of ceramic materials capable of withstanding very high temperatures. This capability is an essential property for the passive heat removal feature of the modular HTGR designs. Graphite, the predominant ceramic material, serves as an effective neutron moderator with low neutron absorption properties. The long-term behaviour of graphite under the temperature and irradiation conditions representative of the designs is a complex function of the initial material properties and service conditions.

Answer 7

To slow neutrons down. Fission works by using neutrons from the fisson of one nucleus to trigger another fission. Neutrons emitted by fission are fast moving and inefficient at triggering fresh fission. Bouncing these neutrons of carbon atoms (graphite) slows them down and keeps the reaction going.
Another material often used for this is heavy water.
Substances used to slow neutrons are known as moderators.

Answer 8

They are what is known as a moderator. To control the reaction, graphite rods are inserted. Depending on the position of the rods, they can change the neutron flux and thus the production of power.

Answer 9

graphite is use to absorb the some of the Norton's that are realised in the fission process to keep a chain reaction in controlled so k = 1 if you sre interest in this subject read the source below

Answer 10

graphite rods help to absorb excess neutrons and maintain the reaction rate. To slow down the reaction the rods are inserted deeper and to speed up the reaction the rods are take out.
Barium rods can also be used.