INTRODUCTION
Nuclear Power Corporation of
India (NPCIL) is a Government of India organization, under which the Kudankulam
Nuclear Power Project (KKNPP) is being constructed. India is one of the largest
producer of electricity. Two units each of 1000 MWe capacity are constructed in
Kudankulam, Tamilnadu. This project is in collaboration with Russia. Design and
equipments are supplied by Russia. Indian scope is the construction and
commissioning of entire plant with Russian technical support. This is a Light
Water Reactor (LWR).
A Nuclear power plant operates
basically the same way as a fossil fuel plant, with one difference: the source
of heat. The process that produces the heat in a nuclear power plant is
the fission or splitting of nucleus of any fissile material in the Nuclear
Reactor. The part of the plant where the heat is produced is called the reactor
core.
The heat generated by Nuclear
fission is carried by a medium which in turns transfer it’s heat energy to
water in steam generator thus generating steam.
This steam drives the
turbine-generator, just as in a fossil fuel plant. Generator produces the
electricity.
Nuclear fuel used in this
reactor is slightly enriched Uranium-235. Inside the reactor self sustained
chain reaction goes on thus generating heat energy continuously. In this
process a fraction of fissile material is consumed. Control rods are used to
regulate the rate of chain reaction. Water is used as a heat transfer medium.
ABOUT
THE SITE
Kudankulam is a small village in
Radhapuram taluk, Tirunelveli district, located about 30 km north east from
kanyakumari in the Gulf of Mannar. Kudankulam site area is rock type with high
mineral content in an otherwise plain region. Plant area is about 2 km2.
2/3rd of the area covered by the sea. This place before occupation was barren land.
We
were accompanied to take familiarization about the equipments housed in the
Reactor building, Turbine building, Pump house etc.,
Some
of the points given during our in-plant training, site visit are listed below:
REACTOR
SYSTEM
VVER is the acronym for the
Russian designed “water cooled, water moderated energy reactor”. The VVER reactors belong to the family of Pressurized
Water Reactors (PWRs).
Reactor plant consists of a
Reactor Pressure Vessel, four circulating loops each containing a Horizontal Steam
Generator and a main Reactor Circulating Pump. All the primary circuit
pipelines are made up of SS material.
Pressurising system
(Pressuriser) and Emergency Core Cooling System (Safety system – pumps,
Hydro-accumulators etc.,) are also connected to the Reactor.
The Reactor plant also consists
of Reactor Protection system, Auxiliary systems etc.
Salient features of the KKNPP
are presented below:
Reactor rated thermal power,
MWth 3000
Output (gross power), MWe
1000
Fuel enriched UO2 (average.2.5%)
Average fuel burn up, MWD/Ton
of U 43,000
No. of fuel Assemblies in core 163
Refueling is done once a year.
It is a three-circuit system:
·
Primary
circuit (closed loop) contains Borated water radioactive coolant.
·
Secondary
circuit (closed loop) is a DM (DeMineralised) water non-radioactive circuit
steam.
·
Third
circuit (once through) is non-radioactive circuit sea water.
Absorber Rod (Control Rod):
Control and Protection System
Absorber Rods (Control Rods) move within the guide tubes in each of the Fuel Assembly.
The absorbing material is Boron carbide (B4C).
To arrest quickly the nuclear chain
reaction all the electromagnets are de-energized, the latches are unlocked and
the Absorber Rods falls in to the reactor by gravity within 2 to 4 sec and
makes Reactor sub critical (Stops the chain reaction).
Reactor Circulating Pump:
The reactor coolant pumps serve
to circulate the reactor coolant in the closed loops through the Reactor
Pressure Vessel, the Reactor coolant piping and the Steam Generators. It is centrifugal pump.
Pressuriser:
The Pressuriser serves to build
up and maintain the necessary pressure in the Reactor Coolant System. Pressure
is controlled by electrical heaters and water sprays.
Steam Generator:
The Steam Generators serve to
produce steam required for the operation of turbine by transferring heat from
primary coolant (tube side) to secondary side feed water (shell side). It is shell & tube type.
Safety System (Emergency Core
Cooling System):
Borated cooling water is
injected into the Reactor core to remove the decay heat by High pressure and
low pressure Safety system pumps (active system which requires power
supply) and Borated water filled stage-I and stage-II Hydro-accumulators
(passive system which do not require power supply).
They are provided to do safety
function incase-of abnormal conditions by quick shutting down the reactor and
making it sub-critical, fast cooling down, and continuous decay heat removal
from core, confining radioactivity release from the core and safeguarding
integrity of various systems.
The Containment Spray System through
the spray headers provided in the top condenses the steam and quickly reduces
the pressure buildup inside the containment during pipeline break and
containment integrity is assured.
The Passive Heat Removal system
(PHRS) removes the core residual heat in the event of complete loss of normal
(grid power) and Diesel Generator power supply.
Hot primary coolant is cooled by atmospheric air in this PHRS heat
exchanger.
Core catcher has
been provided to confine the molten core if melting of the reactor core happens
and prevents radiation release to the outside environment.
Hydrogen recombining system provided
inside the primary containment. They
recombine Hydrogen and Oxygen molecules and change to water. By this it prevents Hydrogen explosion and
integrity of the containment structure is assured.
Note:
- In
case of normal power supply fails, Diesel Generator will start and power
supply will be restored back.
- In
case of DG fails, supply will be through Battery bank.
Reactor containment System:
The Reactor building has a
double containment structure.
The primary containment is a
cylindrical structure made of pre-stressed reinforced concrete, with 8 mm
carbon steel inner lining and a dome top. Pre-stressed by Steel wires horizontally and
vertically which gives additional compressive and tensile strength to the
Primary containment structure.
This sealed enclosure houses
main equipments of the primary system
Acts as
shielding and protects personnel against radiation under normal and accidental
conditions. Protects equipments located
inside against external hazards.
Inside
the containments, slightly negative pressure is maintained by separate
ventilation systems. Hence contaminated air
(radiation) will not release from the containment to outside atmosphere.
Primary
containment is 1200mm thickness and Secondary containment is 600mm thickness.
Airlock
(entrance) provided in the Reactor building with two doors. Only one door can be opened at a time. By this inside and outside environment are
not communicated directly.
REACTOR
AUXILIARY BUILDING
This building houses various mechanical equipments, pumps,
tanks etc for operational purposes and for maintaining the chemistry of the Reactor
system. Main control room is located in this building annexure. The parameters
of Reactor system, Turbine system and other functions are monitored from this
building. This building contains lot of rooms, tunnels and shafts for pipelines
and electrical cables which come from the Reactor. Fire proof doors,
ventilation system and all mechanical equipments are located.
TURBINE
BUILDING
Secondary
circuit Convert the thermal energy (steam)(3000 MWth) produced in
the Reactor to electricity (1000 MWe) by using the Turbo – generator.
The
Turbine Systems consists of:
- A single, High Pressure
turbine with dual flow design.
- A single stage
combined Moisture Separator and Re-heater which removes the moisture from
the stream after used in High pressure turbine.
- Three Low Pressure
turbines with dual flow design.
- Three Condensers to
condense the steam after used in the Low pressure turbine.
- Regenerative Feed
Heating System contains Heaters heated by steam bled from the
turbine. The set of heaters heat
the condensed water collected in the condenser and goes to the de-aerator.
Here required chemistry of the Feed water is maintained before supplying
to the Steam generator to produce steam.
The turbine rotates with a
speed of about 3000 rpm. The turbine is impulse-reaction type. The Turbine and
Generator connected in the same shaft.
Electrical power is produced in the Generator is 1000 MW.
The generated output power is
transmitted through 400 kV switchyard building to Tirunelveli and thereby to
southern grid.
The bearings used in the
turbine is Journal bearing. They are lubricated by oil system. The water used
to produce steam is de-mineralized (DM) to avoid any corrosion or erosion to
the components.
The turbine is mounted on the
vibro isolator provided in the turbine building.
SALIENT FEATURES OF VIBRO
ISOLATORS
- Elimination,
transmission of forces, motion resonance effects.
- Can
compensate for misalignment of foundation or equipment.
- Ability
to take shock.
- Reduces
mass of foundation.
- Ability
to take up seismic load.
PUMP
HOUSE BUILDING
It
houses Condenser cooling water circulating pumps (6 nos.). These pumps circulate sea water which comes
from forebay structure and through condensers (3 nos.) go back to the sea.
In
Fish catching facility Screens & meshes are provided through this large
size fishes cannot enter. And compressed air is given in the entrance. It tends
the small size fishes to swim in the upper surface only. Three stages of curved structures do not
allow the fishes through them. Upper
portion of the water is discharged back to the sea. But sea water for the plant
purpose is collected from the bottom of this structure through underground
tunnels and connected to the fore-bay structure where pump house is connected.
COMMON BUILDINGS
Both Unit-1 and Unit-2 share
common buildings for reasons of safety and economy. Orientation and location of
these buildings are optimized from topographical consideration.
Common building houses;
·
Chiller
building: Chillers for supplying chilled (cold) water for maintaining
ventilation.
·
Compressor
building: Compressors for giving compressed air for the requirement of the
operation of pneumatic valves.
·
Health
physics building: For monitoring and controlling the radiation field and
radiation workers.
·
Centralised
mechanical workshop: Maintenance of mechanical equipments are being done here.
·
Engineering
utility building: All maintenance and
operation personnel office is located here.
Desalination
plant:
It comprises of triple stage process with mechanical vapour compression. Almost 2/3rd of the sea water is
rejected as brine to the sea and the remaining water is qualified as usable
water. It is free from minerals and
salts.
After
this, water is sent to De-mineralising (DM) plant where the ionic impurities
are removed through Ion-exchangers and qualified for the use in Reactor and
Turbine system.
Water
after desalination process is added with calcium dosing to make as domestic
(drinking) water. This is the only water
serves for plant usage and township usage.
CONCLUSION
The complete training period
has allowed us to learn new things and concepts on how ideas are transferred from
paper to the field. Instead of looking concepts from books, observing them
first hand at the site is self explanatory.
We have also learnt that safety
and quality are to be given prime Importance. We are sure that this training
will be of great help to us in the Engineering future.
During this training period,
the concepts of nuclear plant and its safety are understood thoroughly. Safety
systems provided in the KKNPP makes this plant more safer than other nuclear
plants in this world.
