Nuclear Energy

The Fuel: Uranium Present nuclear power plants consume U- 235 as fuel Uranium has 92 protons Two isotopes are important. U-235 has an atomic mass of 235 and U-238 has an atomic mass of 238.

Usable Fuel: 5% U-235 Separating isotopes is expensive Plants exist for separating U-235 from the U-238 in natural uranium For nuclear reactors, enriched uranium (4 to 5% U-235) is used instead of the 0.7% U-235 of natural uranium Bombs need over 90 percent U-235.

Fission When an atom of U-235 absorbs a neutron it fissions: breaks apart into two atoms of smaller elements and some neutrons When a reactor is operating, fission of an atom of U-235 generates on the average a bit more than two neutrons per fission d.html d.html

Meltdown If each of two neutrons produced by a fission was absorbed by an atom of U-235 the number of fissions would double again and again generating enough power to melt the reactor

Chain Reaction-simplified One U splits yielding 2 n which can go on to hit 2 U which will split to yield 4 n

Controlling Fission When the reactor is turned on, the multiplication of fissions is allowed to continue until the reactor is generating power at the desired rate Control rods are inserted to absorb neutrons until exactly one neutron from each fission causes another fission.

Types of Nuclear Plants moderator: control rods/ coolant: heat absorber

Safety Precautions Some of the neutrons caused by a fission are emitted only after a delay of a minute It is not difficult to control the power level of the reactor Redundant safety systems are in place that will stop the reactor if the power level gets too high or if the cooling water stops flowing

Power Generation The power to produce electricity comes from high speed products of fission They quickly hit something and kinetic energy is changed to heat energy If the heat weren't removed, the reactor would meltdown

Power Generation The heat from fission is taken up by water or steam pumped through the reactor The hot steam goes through turbines connected to electric generators About 2/3 of the heat energy is lost, and is emitted to the atmosphere or to a body of water

Post Power Production U-235 fuel rods last for about 2 years leaving mainly fission products which still produce heat and are radioactive Fuel rods cool in large pools of water and become less radioactive with time and can be chemically reprocessed to remove and then reuse remaining U and newly produced plutonium as reactor fuel