physics : fission and fusion 7(c)

how much energy does a nucleus of an atom have

it has a huge amount of energy roughly one million times greater than the amount of energy involved in chemical reactions

why is nuclear energy good

if used safely, they can reduce or replace our dependency on fossil fuels for energy, which reduces pollution and the emission of greenhouse gases

how can nuclear energy be released

fusion, fission, radioactive decay

what is nuclear fission

the splitting of a large atomic nucleus into smaller less massive daughter nuclei

how does nuclear fission work in a U-235

a neutron hits a uranium-235, 92 nucleus, which causes it to become uranium-236, which is very unstable, the nucleus splits into two daughter nuclei and a small number of neutrons (2 or 3) which causes a chain reaction as they strike other uranium 235 nuclei

energy release in nuclear fission on U-235

fast moving neutrons carry most of the energy from the reaction with them - 99% is their kinetic energy.

nuclear fission U-235 equation

1/0n + 235/92 U → 141/56Ba + 92/36Kr + 3 1/0n

how does nuclear fission generate power

lots of heat energy is produced by fission, which is harnessed and used to generate electricity in nuclear power stations

what do control rods and moderators do during fission

the water acts as a moderator as it slows down the fission neutrons to allow them to be absorbed by uranium nuclei and sustain the chain reaction. it also acts as a coolant. the control rods made of boron or cadmium can be inserted into the reactor to absorb surplus neutrons to prevent uncontrolled fission

what does a fission reactor always contain

fuel rods made of uranium isotope which will start the fission process when hit by a neutron. graphite core to slow neutrons so they will be absorbed. control rods to stop uncontrolled fission. coolant which is heated by energy released in fission and used to boil water to drive turbines to generate electricity. concrete shield

what does the concrete shield do

it is a thick concrete shield which can withstand very high temperatures and stops radioactive daughter products and alpha, beta particles and gamma rays from escaping into the environment.

nuclear fusion

when two smaller, less massive nuclei join together to make a larger, more massive nucleus however some mass is not accounted for and released as energy. It is the energy source in stars.

how does nuclear fission work

positively charged nuclei repel each other, however as the nuclei are heated they move faster and collide, which creates a larger heavier nucleus, however it loses mass which is converted to energy.

what temperature needs to be reached for nuclear fusion and why

150 million degrees, as high temperatures need to be reached to overcome the electrostatic repulsion of protons. High pressure also needs to be reached.

fusion equation e.g.

2/1H + 3/1H → 4/2He + 1/0 n + energy