Nuclear Fission Reactions [+ MCQs]

Conditions for Nuclear Reactions

Following conditions are necessary for the nuclear reactions to take place.

Conservation of mass:     The number of protons and neutrons in the nucleus remains the same because these are not produced neither destroyed.

In this reaction,

Number of protons: 7+2= 8+1

Number of neutrons: 7+2= 9+0

Conservation of Energy: The net energy including the rest of mass-energy remains constant before and after the nuclear reaction. In the above reaction;

Difference in mass= 18. 0069 – 18. 0057 = 0.0012

This energy should be supplied to reactants to start this reaction.

Nuclear Fission Reactions

The reaction in which heavy nucleus such as Uranium ²³⁵₉₂ U is split down into two nuclei of nearly equal size as a result of bombardment of particles along with the release of energy. Such a reaction is called nuclear fission.

Discovery

Two German scientists named Otto Hahn and Fritz Strassmann, in 1939 made a very important discovery. They bombarded a sample of Uranium with slow neutrons. A nuclear reaction was initiated.

As a result of the reaction, barium and krypton were formed, 3 neutrons were released along with the emission of 200 Me V energy.

Fission reaction is possible for Uranium and other heavy elements. Uranium and Plutonium are the most commonly used elements for fission purposes as they are very easy to control and initiate. The energy produced by the fission reaction is used to heat water, which converts it into steam. The steam is used to run turbines and generators for the production of electricity.

Fission Chain Reactions

A chain reaction refers to a process in which by efficiently using emitted (2 or 3) neutrons can further produce more Uranium atoms such that, the reaction can continuously maintain itself. Following are the two types of fission chain reactions.

Controlled Chain Reaction

The conditions are produced in which out of all neutrons produced, only one can further initiate a fission reaction. The other neutrons are absorbed by some medium or escape out of reaction. The fission reaction with the constant initial speed in a controlled environment is called a controlled chain reaction.

Critical mass: The minimum mass of Uranium capable of a sustained fission reaction is called the critical mass.

Uncontrolled Chain Reaction

The three neutrons emitted along with the barium and krypton, initiate further three fission reactions. As a result, ²³⁵₉₂ U and 9 neutrons are produced. These 9 neutrons will initiate additional fission.

In this way, multiple fission reactions will occur and the chain goes on. This process is called an uncontrolled chain reaction. Multiple fission can cause an atomic explosion and a huge amount of energy is released.

Amount of energy in Fission reaction

Nuclear reactions liberate a large amount of energy compared to chemical reactions. One fission reaction results in the emission of about 200 MeV of energy, or about 3.2 x 10^-11 watt-seconds. Therefore, 3.1 x 10¹⁰ fissions per second produce1 W of thermal power.

The fission of 1 g of uranium or plutonium per day liberates about 1 MW. This is the energy equivalent of 3 tons of coal or about 600 gallons of fuel oil each day, which when burned produces around 1/4 tons of carbon dioxide.

Atomic power plants make their own fuel, given that they produce 239Pu from 238U. With the overall around the world installed nuclear capacity of 3.4 x 10⁵ MWe (megawatt electrical), one can estimate that more than 100 tons of 239Pu are produced each year in reactors whose primary energy source is the fission of 235U. This 239Pu can be reprocessed from used fuel rods and utilized to power other reactors.

MCQs About Fission Reaction