Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGAs stated previously, naturally radioactiveisotopes decay bythe emission of alpha particles,beta particles, gamma rays, or a combinationthereof. In the case of induced nuclear reactionsthere are many other phenomena which mayoccur, including fission and the emission ofneutrons, positrons, nutrions, and other formsof energy.^CONSERVATION OF MASS-AND ENERGYThe conservation of energy is discussed inchapter 8 of this text. It now becomes necessaryto consider mass and energy as two phases of thesame principle. In so doing, the law of conservationbecomes:(mass + energy) before =(mass + energy) after.Fundamental to the above and to the entiresubject of nuclear power is Einstein's massenergyequation where the following relationholds:wheremCE = energy in ergs,M = mass in grams,C = velocity of light (3 X 10^° cm/sec)Mass and energy are not conserved separatelybut can be converted into each other.Several units and conversion factors whichhave become conventional to the field of nuclearengineering are listed below.1 ev (electron-volt = the energy acquired byan electron as it movesthrough a potential differenceof 1 volt1 Mev (million electronvolts)= lO^ev= 1.52 X 10-l6BtuFor detailed information on nuclear particles, referto Samuel Glasstone, Sourcebook on Atomic Energy(2d ed.; Princeton: D. Van Nostrand Company, Inc.,1958).1 amu 1.49 X 10 erg1.66 X 10 24gm931 Mev1.415 X 1013 BtuNUCLEAR ENERGY SOURCE1 amu (atomic mass unit = 1/16 of an oxygenatom (by definition)It was previously stated that the atomicmass number is the total number of nucleonswithin the nucleus. It can also be said thatthe atomic mass number is the nearest integer(as found by experiment) to the actual mass ofan isotope. In nuclear equations, the entiremass must be accounted for; therefore the actualmass must be considered.The atomic mass of any isotope is somewhatless than indicated by the sum of the individualmasses of the protons, neutrons, and orbitalelectrons which are the components of thatisotope. This difference is termed mass defect:it is equivalent to the binding energy of thenucleus. Binding energy may be defined as theamount of energy which was released when anucleus was formed from its component parts.The binding energy of any isotope may befound, as in the following example of copper(ggCu"^) which contains 34 neutrons, 29 protons,and 29 electrons. Using the values givenin figure 24-2 we find:34 X 1.00894 = 34.30496 amu29 X 1.00785 = 29.21982 amu29 X 0.00055 = 0.01595 amuTotal of component massesLess actual mass of atomMass defectConverting to energy, we find:931 Mev/amu x 0.61093Mev, or 560.8 + 63 == 63.54073 amu= 62.9298 amu= 0.61093 amuamu = 568.775838.9 Mev/nucleonThe relationship between mass number andthe average binding energy per nucleon isshown in figure 24-5.Since binding energy was released when anucleus was formed from its component parts,it is necessary to add energy to separate anucleus. In the fissioning of uranium 235, theadditional energy is supplied by bombarding thefissionable fuel with neutrons. The fissionablematerial absorbs a neutron and is converted618