Both fusion and fission are examples of NUCLEAR reactions, which are accompanied by a net release of energy.   The energy comes from the difference in MASS between the starting materials known as the REACTANTS and the final PRODUCTS.  Einstein’s equation, E = mc2 explains the mass – energy relationship.  Most of the energy release is in the form of heat.  This resultant hat can be captured, in principle, and converted to electricity or directly to mechanical energy.




Fission reactions are inducted by the collision of a NEUTRON with a target nucleus; if the neutron provides sufficient activation energy, the target nucleus will fragment into two parts of unequal mass and release additional neutrons plus an excess of energy.  In principle, most of the atomic nuclei toward the heavy mass side of the periodic table undergo fission.  Uranium 233, Uranium 235, and Plutonium 239 are relatively unstable and undergo fission upon colliding with low energy or thermal, neutrons.  The role of the neutron in fission reactions resembles that of a catalyst.


N + U 235                    fission fragments (Nd 144 + Y 89)  + 3 n + E




U 235  = 235.04394                                    Nd 144  =  143.91013

        n  =     1.00866                                      Y   89  =   88.90587

               ________                              3n         =      3.02600


               236.05260                                             235.84200


mass difference = .21060

E = mc2      931.1  MeV = 1 amu/c2

                   c2 = 931.1 MeV/amu

.21060 x 931.1 MeV = 196.08 MeV


amu = atomic mass unit

MeV = million electron volts




By contrast, fusion reactions require collisions between two nuclei, which subsequently undergo rearrangements to produce two new nuclei and release an excess of energy.  Most of the nuclei on the light mass side of the periodic table undergo fusion or nuclear rearrangement reactions.  The sun derives its energy from a chain of fusion reactions by which ordinary hydrogen is converted to helium.


564 million tons of H ions collide/sec.                     560 million tons of Helium

4 million tons lost as radiation


Nuclear Fuels


Fissile or Fissionable Isotopes

          U 235 (0.7% of natural uranium)

          U 233 (bred from Th 232)

          Pu 239 (bred from U 238)       


Fertile Isotopes

          U 238 (99.3% of natural uranium)

          Th 232 (naturally occurring)




Roentgen    unit of exposure dose (exposure/unit volume) for x-rays or gamma rays


REM  -  roentgen Equivalent Man (unit of biological dose or dose equivalence)


RAD  -  relative biological effectiveness; RBE factor is used to compare the biological  effectiveness of absorbed radiation dose (i.e. RAD) due to different types of ionizing radiation


RAD & REM are roughly equivalent for x-rays and gamma rays since the RBE is 1 for both, thus REM = RAD x RBE


A does of 100 to 200 rems at one time over the entire body would cause nausea, fatigue, and blood changes.




In 1984, there were 76 reactors on line in the United States.


There are at least seven obstacles hindering the development of nuclear power as a major energy source.

          1.       supplies and cost of uranium fuel

          2.       concern over plant accidents and sabotage

          3.       highjacking of nuclear fuel shipments

          4.       waste storage problems

          5.       nuclear weapons proliferation

          6.       soaring costs

          7.       net useful energy for the entire system


*major public considerations


Benefits of nuclear energy


1.       minimal air pollution

2.       less radiation than coal-fired plants

3.       smaller amounts of fuel used – a conventional nuclear reactor using 130 tons of uranium/year will produce the same amount of energy as a coal-fired plant using 2 million tons of coal/year.

Detriments of nuclear energy


1.       high and low level radioactive wastes

2.       large volumes of cooling water required

3.       heat loss from plant leading to thermal pollution 1000 cubic feet/second is the flow needed through the condensor; the temperature of a lake cannot be raised more than 3 degrees Fahrenheit; a river must have a flow of at least 5x that needed to condense

4.       siting constraints – geological considerations and water flow

5.       useful operating life – about 30 years


The environment is exposed at three points in the nuclear fuel cycle:

          at the reactor

          at the fuel processing and reprocessing plants, and

          at the waste disposal site




Light Water Reactors

BWR           boiling water reactors; water is used as the coolant and moderator and  converted to steam


PWR            pressurized water reactor; water is used as a coolant and moderator but kept under pressure to prevent conversion to steam; water in a second circuit is converted to steam by means of heat exchanger


HTGR          high temperature gas cooled reactor; heat from the reactor core is removed by a closed loop of circulating helium gas; the heated gas is pumped through heat exchangers and the heat is used to convert water into steam in a secondary system which drives the turbine-generator producing electricity; the HTGR converts Thorium into U 233 which is a fissionable fuel and thus uses less uranium than water-cooled reactor systems