NUCLEAR FISSION

Dr. ANANT KUMAR SINHA ASSOCIATE PROFESSOR DEPTT. OF PHYSICS A.M. COLLEGE, GAYA CONTENTS

History Introduction Fission Chain Reaction Nuclear Reactor Applications HISTORY OF HISTORY:

 After James Chadwick discovered the neutron in 1932.  and his colleagues in Rome studied the results of bombarding with neutrons in 1934.

 Fermi concluded that his experiments had created new elements with 93 and 94 protons, which the group dubbed and respectively. However, not all were convinced by Fermi's analysis of his results. NUCLEAR FISSION OF HEAVY ELEMENTS WAS DISCOVERED ON DECEMBER 17, 1938 BY GERMAN OTTO HAHN AND HIS ASSISTANT FRITZ STRASSMANN.

Otto Hahn Fritz Strassmann CONT……

 Nuclear fission explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch.

 Frisch named the process by analogy with biological fission of living cells. It is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. INTRODUCTION TO FISSION REACTION INTRODUCTION:

 Nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei).  The fission process often produces free neutrons and gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.

 Fission is a form of nuclear transmutation because the resulting fragments are not same element as the original atom. WHEN NEUTRON STRIKES 92U235 CONVERTED TO 92U236 ; CONT……

 This process may be represented by the following nuclear equation:

235 1 141 92 1 92U + O n —› 56Ba + 36Kr + 3 0 n + Q

Where Q is the energy released in this reaction.  When this is done, the amount of energy typically released in the case of U-235 is around 200MeV (0.00,000,000,003,204 joules). FISSION REACTION OF 92U235 ; FISSION CHAIN REACTION INTRO:

 "Chain reactions" at that time were a known phenomenon in chemistry, but the analogous process in nuclear physics, using neutrons, had been foreseen as early as 1933 by Szilárd, although Szilárd at that time had no idea with what materials the process might be initiated. Szilárd considered that neutrons would be ideal for such a situation, since they lacked an electrostatic charge. CHAIN REACTION:

 A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place.

 An atom of uranium-235 to undergo fission by bombarding it with neutrons.

 Along with barium and , three neutrons are released during the fission process. These neutrons can hit further U-235 atoms and split them, releasing yet more neutrons. This is called a chain reaction. CHAIN REACTION; CONT……

 Although the half-life of U-235 is a very long time, if we get enough of the atoms together in one place the chances that any one of them will undergo spontaneous fission is very, very high.  Additional Neutrons create a chain reaction, which is controlled by the control rods.  Newly created fission neutrons move at about 7% of the speed of light, and even moderated neutrons move at about 8 times the speed of sound. NUCLEAR REACTOR NUCLEAR REACTOR:

 “The assembly which is used to convert heat generated in nuclear reaction into electrical energy is called Nuclear Reactor.”  In a reactor fission reaction produces heat.  When fission takes place in atom of uranium or any heavy atom, then energy at the rate of 200MeV per nucleus is produced in form of Kinetic energy of fission fragments.

 These fast moving fragments besides colliding with one another also collide to uranium atoms. CONT……

 Due to collisions kinetic energy gets transformed into heat energy.

 Heat produced is used to produce steam which in turn rotates the turbine.

 As a result, turbine rotates the generator which produces electricity. POWER GENERATION THROUGH NUCLEAR REACTOR; WORKING OF REACTOR;

 Reactor Core; cylindrical tubes in which fuel is kept. Uranium- 92U235 is used asfuel.  The quantity of 92U235 in the naturally occurring Uranium is 0.7%.  Fuel rods are placed in substances of small atomic weight, such as water, heavy water, carbon etc called moderators.  Moderator; is used to slow down the speed of neutrons produced during the fission process to direct them towards the fuel. CONT……

 Control rods; number of neutrons produced are controlled because only one neutron has to produce further fission reaction.  Control rods are made of cadmium or boron.  Chain reaction takes place in the core and produces heat. Temperature rise about 500°C.

 Steam is produced from this heat and is transported with the help of water or heavy water.  Temperature of steam coming out from turbine is about 300°C which is further cooled to produce water again. APPLICATIONS APPLICATIONS:

 December 20, 1951- Electricity was generated for the first time by a nuclear reactor – A the EBR-I experimental station near Arco, Idaho – initially produced about 100 kW

 1956 - world's first commercial nuclear power station in Sellafield, England – initial capacity of 50 MW (later 200 MW)  In July 1945, the first atomic explosive device, dubbed "Trinity", was detonated in the New Mexico desert. It was fueled by created at Hanford. IN AUGUST 1945, TWO MORE ATOMIC DEVICES – "LITTLE BOY", A URANIUM-235 BOMB, AND "FAT MAN", A PLUTONIUM BOMB – WERE USED AGAINST THE JAPANESE CITIES OF HIROSHIMA AND NAGASAKI. CONT……

 In August 1945, two more atomic devices – "Little Boy", a uranium-235 bomb, and "Fat Man", a plutonium bomb – were used against the Japanese cities of Hiroshima and Nagasaki.

 These fission reactions produce new nuclides or elements which are used in medical diagnose and treatments and biological experimentations.

 Nuclear fission reaction is used to produce energy for nuclear power.  It causes nuclear bomb to explode. ADVANTAGES & DISADVANTAGES

Advantages Disadvantages

 It produces  Difficult to dispose the tremendous energy radioactive waste from from small amount of nuclear fission nuclear fuel. reaction.  Once a fuel added a plant can work for  Risks of accidents in years. nuclear reactors.  Does not produce  High cost of installation greenhouse gases like of nuclear plants. CO2.