Nuclear Fuel

Nuclear fuel is the fissionable material used in nuclear reactor. Generally, U-233, U- 235 and Pu- 239 is taken as nuclear fuel in form of cylindrical rods arranged in regular pattern in the active reactor core. However, the volume of core is filled with material of light nuclei called moderator. The geometry of core is such that on average out every three neutrons produced per fission. one neutron is used to trigger next fission. However, other neutrons are lost without undergoing any fission.

Moderator

Slow moving neutron have more tendency to facilitate fission reaction rather than the fast moving neutrons. Average energy of neutron produced in fission of U-235 is 2 MeV. these are the fast neutrons and have low tendency to cause fission. In order to facilitate fission reaction there is need to slow down the neutrons. The job is done by moderator in nuclear reactor, by transferring the energy with elastic collision to lighter nuclei. In nuclear reactors water, solid graphite or heavy water are used as moderators.

Control Rods

Nuclear reaction if not controlled can cause massive explosion. Multiplication factor K helps us to determine if reaction is in control or not. K=1 is required for sustained energy production. If K exceeds unity control rods made of boron or cadmium are inserted in the reactor core upto desirable length. The rods have the ability to absorb neutrons. Therefore, the nuclear reaction can be controlled thereby bringing down the multiplication factor down unity.

Safety Rod

In addition to control rods, the reactors are provided with safety rods. These rods can be inserted into reactor in order to bring value of K below unity. Hence, it keeps power generation safe.

Coolant

Heat produced in the core is absorbed by coolant. Later this energy is passed to water in heat exchanger. Thus, it produces steam. The steam is used to drive turbine coupled with electric generator and thus, electric energy is produced. In general water or heavy water is used as coolant. In case of high temperature, liquid sodium is used as coolant.

Shielding

Nuclear fission produces hazardous radiations, therefore, nuclear reactor is kept in concrete walls of 2 m to 2.5 m thick. This prevents radiations from reaching outside environment.

Nuclear Reactor

Working

The cadmium rods are slowly removed so that slow moving neutrons can cause fission of U-235 nuclei generating energy . In the primary-loop, coolant absorb energy . The energy is transported at high temperature and pressure to the steam generator in secondary loop where evaporation of water takes place. Evaporation provides high-pressure steam to operate the turbine and in turn, drives the electric generator. The low-pressure steam from the turbine is cooled and condensed to water and forced back into the steam generator.

Advantages and disadvantages of nuclear reactor

It is advantageous because in very small quantity of fuel it produce large energy . However, the disadvantage is that there is problem of disposal of radioactive nuclear waste and maintenance of equipment.

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Keywords: Nuclear Fission, Electricity, Heavy water, Sodium