2. Nuclear Powerplant plant
•is a thermal power station in which the
heat source is a nuclear reactor. As is
typical in all conventional thermalpower
stations the heat is used to generate steam
which drives a steam turbine connected to
a generator which produces electricity. As
of 16 January 2013, the IAEA report there
are 439 nuclear power reactors in
operation operating in 31 countries.
•Nuclear power plants are usually
considered to be base load stations, since
fuel is a small part of the cost of production.
3. The Process
• In a nuclear-fueled power plant – much
like a fossil-fueled power plant – water
is turned into steam, which in turn
drives turbine generators to produce
electricity. The difference is the source
of heat. At nuclear power plants, the
heat to make the steam is created when
uranium atoms split – called fission.
There is no combustion in a nuclear
reactor. Here’s how the process works.
4. Pressurized Water Reactor
Pressurized Water Reactors (also known as PWRs) keep water
under pressure so that it heats, but does not boil. This heated
water is circulated through tubes in steam generators, allowing
the water in the steam generators to turn to steam, which then
turns the turbine generator. Water from the reactor and the water
that is turned into steam are in separate systems and do not mix.
5. Boiling Water Reactor
In Boiling Water Reactors (also known as BWRs),
the water heated by fission actually boils and turns
into steam to turn the turbine generator. In both
PWRs and BWRs, the steam is turned back into
water and can be used again in the process.
6. Energy source
• Nuclear power stations work in pretty much the same way as fossil fuelburning stations, except that a "chain reaction" inside a nuclear reactor
makes the heat instead.
• The reactor uses Uranium rods as fuel, and the heat is generated
by nuclear fission: neutrons smash into the nucleus of the uranium
atoms, which split roughly in half and release energy in the form of heat.
• Carbon dioxide gas or water is pumped through the reactor to take the
heat away, this then heats water to make steam.
• The steam drives turbines which drive generators.
• Modern nuclear power stations use the same type of turbines and
generators as conventional power stations.
• In Britain, nuclear power stations are often built on the coast, and use
sea water for cooling the steam ready to be pumped round again. This
means that they don't have the huge "cooling towers" seen at other
power stations.
• The reactor is controlled with "control rods", made of boron, which
absorb neutrons. When the rods are lowered into the reactor, they
absorb more neutrons and the fission process slows down. To generate
more power, the rods are raised and more neutrons can crash into
uranium atoms.
7. Efficiency
• One measure the efficiency of power plants that
convert a fuel into heat and into electricity is the heat
rate, which is the amount of energy used by an
electrical generator or powerplant to generate one
kilowatt-hour (kwh) of electricity. EIA expresses heat
rates in British thermal units (Btu) per net kwh
generated. Net generation is the amount of electricity a
power plant (or generator) supplies to the power
transmission line connected to the power plant. It
accounts for all the electricity that the plant itself
consumes to operate the generator and other
equipment, such as fuel, feeding systems, boiler water
pumps, cooling equipment, pollution control device
and others.
• To express the efficiency of a generator or powerplant
as a percentage, divide the equivalent Btu content of a
kwh of electricity (which is 3,412 Btu) by the heat rate.
8. Emergency power supply
• The emergency power supplies of a nuclear power plant are built up by several layers of redundancy,
such as diesel generators, gas turbine generators and battery buffers.
Feedwater pump
• The water level in the steam generator and nuclear reactor is controlled using the feedwater system. The
feedwater pump has the task of taking the water from the condensate system, increasing the pressure
and forcing it into either the Steam Generators (Pressurized Water Reactor) or directly into the reactor
vessel (Boiling Water Reactor).
Safety valves
• In the event of an emergency, two independent safety valves can be used to prevent pipes from
bursting or the reactor from exploding. The valves are designed so that they can derive all of the
supplied flow rates with little increase in pressure. In the case of the BWR, the steam is directed into the
condensate chamber and condenses there. The chambers on a heat exchanger are connected to the
intermediate cooling circuit.
Cooling system
• A cooling system removes heat from the reactor core and transports it to another area of the plant, where
the thermal energy can be harnessed to produce electricity or to do other useful work. Typically the hot
coolant is used as a heat source for a boiler, and the pressurized steam from that boiler powers one or
more steam turbine driven electrical generators.[10]
Nuclear reactors
• A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most
common use of nuclear reactors is for the generation of electric energy and for the propulsion of ships
Steam turbine
• The purpose of the steam turbine is to convert the heat contained in steam into mechanical energy.
Generator
• The generator converts kinetic energy supplied by the turbine into electrical energy.
9. Waste streams
• Nuclear power has at least four waste streams that
may harm the environment:
• spent nuclear fuel at the reactor site
(including fission products and plutonium waste)
• tailings and waste rock at uranium mines and mills
• releases of small amounts of radioactive
isotopes during reactor operation
• releases of large quantities of dangerous
radioactive materials during accidents
• The nuclear fuel cycle involves some of the most
dangerous elements and isotopes known to
humankind, including more than 100
dangerous radionuclides and carcinogens such
as strontium-90,iodine 131 and cesium -137, which
are the same toxins found in the fall out of nuclear
weapons".
10. Radioactive Waste
• The most long-lived radioactive wastes,
including spent nuclear fuel, must be
contained and isolated from humans and the
environment for a very long time. Disposal of
these wastes in engineered facilities, or
repositories, located deep underground in
suitable geologic formations is seen as the
reference solution
• Common elements of repositories include the
radioactive waste, the containers enclosing
the waste, other engineered barriers or seals
around the containers, the tunnels housing
the containers, and the geologic makeup of
the surrounding area.
11. Greenhouse gas emissions
• Nuclear power plant operation emits no or negligible
amounts of carbon dioxide. However, all other stages of
the nuclear fuel chain — mining, milling, transport, fuel
fabrication, enrichment, reactor
construction, decommissioning and waste management —
use fossil fuels and hence emit carbon dioxide.There was
a debate on the quantity of greenhouse gas
emissions from the complete nuclear fuel chain.
• Many commentators have argued that an expansion of
nuclear power would help combat climate change. Others
have pointed out that it is one way to reduce
emissions, but it comes with its own problems, such as
risks related to severe nuclear accidents the challenges of
more radioactive waste disposal. Other commentators
have argued that there are better ways of dealing with
climate change than investing in nuclear power, including
the improved energy efficiency and greater reliance on
decentralized and renewable energy sources.
