Basic Reactor Principles
The principle of the nuclear reactor is based on the transport of neutrons and their interaction with matter within a reactor. Various terminologies involved in the design of nuclear reactors, based on the fission process, have been included in this chapter.
In nuclear physics, the nuclear masses are determined by using the mass spectroscopes (Ghoshal 2010). The actual mass is always less than the sum of the masses of the constituent nucleons. The difference is called the mass defect. The mass defect is related to the energy binding the particles in the nucleus. In other words, if we want to break up a nucleus of Z protons and N neutrons completely so that they are all separated from each other, a certain minimum amount of energy is to be supplied to the nucleus. This energy is known as the binding energy.
Let us consider the mass of protons, nucleus and electrons as mp, mn and me, respectively. The mass defect is defined as (Stacey 2007)
Z(mp + me) + (A - Z)mn is the masses of the constituents of the atom M is the observed mass of the atom
Using the Einstein equation, the binding energy can be calculated as follows: where
Am is the mass defect c is the velocity of light («3 x 108 m/s)
In other words, binding energy = Am x 931.5 MeV, where 1 u = 931.5 MeV.
Calculation of 1 u
It is well known that 1 mole of 12C has the mass of 12 g or 12 x 10-3 kg. Since 1 mole contains 6.02205 x 1023 atoms (Avogadro number), the mass of each 12C atom is
Hence, the unit of atomic mass is
The energy equivalent of this amount of mass is
If Am is in gram, then E will be in MeV per gram atom.
The binding energy of a nucleus, when divided by the number of nucleons, gives the mean binding energy per nucleon.
The binding energy per nucleon is a measure of the stability of the nucleus. The greater the binding energy per nucleon, the more stable the nucleus.
It is noted that if the value of binding energy is negative then the product of the nucleus or nuclei will be less stable than the reactant nucleus or nuclei. If the binding energy is positive, then the product nucleus is more stable than the reactant nucleus.