POWER PLANT ENGINEERING

1. Types of Reactor
Prof. Swapnil Gadgune

2. TYPES OF REACTORS
• Nuclear Reactors are of two types-
1. Heterogeneous- It has a large number of fuel rods with the coolant
circulating around them and carrying away the heat released by
nuclear fission.
2. Homogeneous- the fuel and moderator are mixed, e.g. a fissionable
salt of uranium like uranium sulphate (or nitrate) dissolved in the
moderator like H2O or D2O. The solution is critical in the core. Due
to difficulties in component maintenance, induced radioactivity,
erosion and corrosion, homogeneous reactors are not common.

3. Reactor Classification
• Present day nuclear reactors are of the heterogeneous class. These
reactors are again classified according to the type of fuel used, the
neutron flux spectrum, the coolant, and the moderator, if used.
Neutron flux
spectrum
Moderator Coolant Fuel material
Thermal Light water Light water Enriched uranium
Heavy water Heavy water Natural uranium
Graphite Gas (CO2) Natural or enriched uranium
Fast Nil Liquid metal (Na, K) Plutonium, Thorium

4. Reactor Classification
• Light water-cooled and moderated reactors (LWR) using slightly enriched
uranium fuel are the type most commonly used for power production.
• Fast reactors which use high energy neutrons for fission and require no
moderator utilize a liquid metal as a coolant with either plutonium or a
plutonium–uranium mixture for fuel.
• These reactors are further divided into:
1. Pressurized water reactor (PWR)
2. Boiling water reactor (BWR)
3. High temperature gas-cooled reactors (HTGCR) are used in countries like
the UK, France and Germany.
4. Liquid metal fast breeder reactors (LMFBR) are likely to be the source of
electrical power for the future. A breeder reactor produces more
fissionable isotope then what it consumes.

5. PRESSURIZED WATER REACTOR (PWR)
• A PWR power plant is composed
of two loops in series, the
coolant loop, called the primary
loop, and the water–steam or
working fluid loop. The coolant
picks up heat in the reactor and
transfers it to the working fluid in
the steam generator. The steam
is then used in a Rankine type
cycle to produce electricity.

6. BOILING WATER REACTOR (BWR)
• A BWR differs from the PWR in that the
steam flowing to the turbine is produced
directly in the reactor core.
• Steam is separated and dried by
mechanical devices located in the upper
part of the pressure vessel assembly.
• The dried steam is sent directly to the
high pressure turbine thus eliminating the
need for steam generators.
• The coolant thus serves the triple
function of coolant, moderator and
working fluid.

7. GAS-COOLED REACTORS
• The first gas-cooled reactors with CO2
gas (at a pressure of 16 bar) as
coolant and graphite as moderator
were developed in Britain during
1956–69. The fuel was a natural
uranium, clad with an alloy of
magnesium called Magnox.
• Advanced Gas-cooled Reactor (AGR)
system- uses UO2 as the fuel clad in
stainless steel tubes with CO2 gas as
coolant and graphite as moderator.
• helium-cooled, graphite-moderated
systems (HTGR-high-temperature gas-
cooled reactor)- designed to use U-
233 as the fissile material and
thorium as fertile material

8. LIQUID METAL FAST BREEDER REACTOR
• Fast breeder reactors are designed to
create or breed new fissile material, while
producing useful electric power. Most
produce fissile plutonium from fertile
uranium 238.
• The high concentration of fissile fuel and
the absence of moderator makes the core
of a fast reactor smaller than a thermal
reactor of the same power.
• Sodium is the most common coolant for
fast reactors.
• Because of induced radioactivity of liquid
sodium, an inter mediate loop using Na or
NaK as coolant is used between the
primary radioactive coolant and the
steam cycle.

9. HEAVY WATER REACTORS
• The very low neutron capture cross
section of heavy water makes it an
excellent moderator and coolant.
• CANDU-PHW (Canadian Deuterium
Uranium Pressurized Heavy Water)
• The moderator is contained in a
cylindrical steel vessel, called the
calandria, with a large number of
zircaloy tubes through it parallel to its
axis, which is horizontal.
• The heavy water coolant pressure in the
reactor is 88.3 bar, and the inlet and
outlet temperatures are 250 °C and 290
°C, respectively.
• In heat exchangers, steam is generated
at 41 bar, 251 °C.

10. INDIA’S NUCLEAR POWER PROGRAMME
• http://www.barc.gov.in/about
/anushakti.html
• https://www.world-
nuclear.org/information-
library/country-
profiles/countries-g-
n/india.aspx
Photo Credit: civilsdaily.com/indias-nuclear-
energy-program/

11. References
• P K Nag, "POWER PLANT ENGINEERING", Fourth Edition (Book),
McGraw Hill Education (India) Private Limited, NEW DELHI