Power Plant Engineering

336 POWER PLANT ENGINEERING

Ion

source

Accelerating

H.V. Power electrodes

supply

Magnetic

field

region

Collectors U^235

U^235

Filament

Light molecule

Heavy moelcule

Fig. 10.10 Fig. 10.11

4. Centrifugation Method, This method is based on the fact that when a mixture of two gases
   with different molecular weight is made to move at a high speed in a centrifuge, the heavier gas is
   obtained near the periphery. UF^6 vapour may be filled in the centrifuge and rotated to separate uranium
   isotopes.

10.21 Reactor Power Control

The power released in a nuclear reactor is proportional to the number of mole fissioned per unit
time this number being in turn proportional to density of the neutron flux in the reactor. The power of a
nuclear reactor can be controlled by shifting control rods which may be either actuated manually or
automatically.

Power control of a nuclear reactor is simpler than that of conventional thermal power plant
because power of a nuclear reactor is a function of only one variable whereas power of a thermal power
plant depends on number of factors such as amount of fuel, its moisture content, air supply etc. This
shows that power control of thermal plant requires measuring and regulating several quantities which is
of course considerably more complicated.

10.22 Nuclear Power Plant Economics

Major factors governing the role of nuclear power are its economic development and availability
of sufficient amount of nuclear fuel.

It is important to extract as much energy from a given amount of fuel as possible. The electrical
energy extracted per unit of amount of fuel or expensive moderator might be called the “material effi-
ciency”. In a chain reactor the high material efficiency as well as high thermal efficiency leads to low
over all energy cost.

Since the most attractive aspect of nuclear energy is the possibility of achieving fuel costs con-
siderably below that for coal, all nuclear power system being considered for large scale power produc-
tion involve breeding or regenerative systems. This program includes the development of the technol-
ogy of low neutron absorbing structural materials such as zirconium, the use of special moderating
materials such a D20 and the consideration of special problems associated with fast reactors. In so far as
economic factors are concerned it is necessary to consider neutron economy in a general way such as
that measured by the conversion ratio of the system. The conversion ratio is defined as the atoms of new