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CHAPTER 1
INTRODUCTION: ABOUT THE NUCLEAR SYSTEM
Considering the current Population growth, which has already crossed 100
crores in the 21st century and improvements in Standard of living of the
forthcoming generations, there will be a large increase in the use of
electrical energy particularly from clean green and safe energy sources.
The electricity will play a vital role in sustainable development of the
country.
Among all the available conventional and non-conventional energy
sources, the nuclear energy is the most efficient abundantly available,
sustainable and cost effective energy source. It does not emit obnoxious
gases that cause global warming, ozone depletion and acid rain.
The energy needs of a country cannot be met from a single source.
Hydroelectric stations produce cheap power but need a thermal backing to
increase the firm capacity. The coal reserves of the world are fast
depleting. The nuclear power is the only source, which can supply the
future energy demands of the world.
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We have an installed power generation capacity of about 3310MW. The
share of the nuclear energy is only 2.1% of total energy generated in India.
The main advantages which nuclear power plant possesses are:
The amount of fuel used is small therefore the fuel cost is low.
Since the amount of fuel needed is small, so there are no problems
of fuel transportation and storage.
Nuclear plants need less area than the conventional steam plants.
Greater nuclear power production leads to conservation of coal, oil
etc.
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CHAPTER 2
PRINCIPLE OF NUCLEAR POWER PRODUCTION
When a heavy nucleus breaks into smaller nuclei, a small amount of it is
converted into energy .The amount of energy produced is given by
Einstein’s mass energy relation E=MC2. This breaking up of nucleus is
called nuclear fission. Natural uranium has two types of isotopes U-238 and
U-235 found in the ratio of 139:1 in nature.
In a nuclear power station, U-235 is subjected to fission by
bombarding with thermal (slow moving) neutron. This nuclear fission takes
place in a nuclear reactor and produces a large amount of heat energy.
This heat energy is used to boil water to form steam. The hot pressurized
steam turns the steam turbine. When the turbine rotates, the electric
generator fixed on its shaft starts working and produces electricity. In a
nuclear reactor, heavy water (D2O) is used as a moderator to slow down
the speed of high-energy neutrons. Cadmium rods are used as “controlling
rods” to keep the fission reaction under control by absorbing the excess
neutrons. Heavy water is also used as coolant to transfer the heat
produced in the reactor to heat exchanger for converting water into steam.
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A complete chain reaction of nuclear fission is as shown in fig.
Fig-1:- Nuclear fission reaction.
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CHAPTER 3
NUCLEAR ENERGY
Mass defect is converted into energy through nuclear reaction. Two
processes produce this:
1. Nuclear fission.
2. Nuclear fusion.
A neutron splits a heavy nucleus like uranium-235 into two parts when it
strikes nucleus thereby releasing two more neutrons. However mass of the
two parts is slightly less than the original uranium nucleus. This mass
deficit is converted into energy (200Mev/fission). This process is called
nuclear fission.
In the reactor most of the neutrons are absorbed so that for every neutron
causing fission, only one is left. This neutron in turn collides with another U-
235 nucleus and causes fission. A chain reaction is thus set up. The fuel in
the nuclear reactor consists of uranium that may be natural or enriched.
Either light water (for enriched uranium) or heavy water (for natural
uranium) may be used as moderators for slowing down the neutrons. The
heat energy is absorbed by the coolant which transfers it to the light water
in heat exchanger. Ultimately water is turned into high pressure steam that
is used to drive turbine as in any conventional power plant.
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India has six Nuclear Power Plants:
At Tarapur in Maharashtra.
At Rawatbhata near Kota in Rajasthan.
At Kalpakkam near Madras in Tamil Nadu.
At Narora in Utter Pradesh.
At Kakrapar near Surat in Gujarat.
At Kaiga near Karwar in Karnataka.
The reactors at Tarapur use enriched uranium as fuel and light water as
coolant. All other power plants use natural uranium as fuel and heavy water
as coolant. Nuclear Power Plant under construction in Rawatbhata is two
units of 220 MWe each. Nuclear fission has become commercially viable
and is used in several countries.
3.1 SOME IMPORTANT NUCLEAR REACTIONS
92U238 + 0n1→ 92U239 + r → 93Np239 → 94Pu239 ………………………………..Eq 3.1.1
Typical fission reaction:
92U235 + 0n1 → 38Sr90 + 54Xe144 +2 0n1+ r + 200 MeV……………… Eq 3.1.2
Reactor poisoning reaction:
52Te135 → 53I135 → 54Xe144 → 55Cs135 → 56Ba135……………Eq 3.1.3
(Stable)
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We know that about 200 MeV of energy is released during per fission.
This energy is divided in the following way:
1. K.E. of the fission fragments: 167 MeV
2. K.E. of neutrons: 5 MeV
3. Energy of gamma rays released at fission: 5 MeV
4. Energy of gamma rays released on n-capture: 10 MeV
5. Gamma decay energy: 7 MeV
6. Beta decay energy: 5 MeV
________
199 MeV
________
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CHAPTER 4
POWER GENERATION SYSTEM
Turbine is a tandem compound machine directly coupled to an electric
generator. A turbine generally consists of high-pressure cylinder (Single
flow for 220 MW units and double flow for 500 MW Units) with External
Moisture separators and steam reheaters and double flow pressure
cylinders. Turbine is provided with necessary supervisory protection
instrumentation and devices.
Steam enters into the high pressure cylinder and subsequently passes
through the moisture separator and reheaters before entering the low
pressure cylinders. The steam then exhaust to a condenser under vacuum.
The condense steam is extracted form condenser by condensate extracting
pump and the condensate passes through feed water heaters to dearator.
Boiler feed pumps takes suction from dearator and pump feed water via
high pressure feed water heaters into steam generators.
Electrical generator is directly coupled to the turbine to produce
electricity and the generator transformer which intern is connected to switch
yard steps up the generated voltage. Generated power is thus transmitted
to the electrical power grid.
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Fig-2:- Power generation system.
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CHAPTER 5
NUCLEAR POWER PROGRAMME &
TECHNOLOGY IN INDIA
5.1 INTRODUCTION
India figured in the nuclear power map of the world in 1969, when two
boiling water reactors (BWRS) were commissioned at Tarapur (TAPS 1&2).
These reactors were built on the turnkey basis. The main objective of
setting these units was largely to prove the techno-economic viability of
nuclear power.
The nuclear power programme formulated embarked on the three-stage
nuclear power programme, linking the fuel cycle of pressurized heavy water
reactor (PHWR) & fast breeder reactors (FBR) for judicious utilization of our
reserves of uranium & thorium. The emphasis of the programme is self-
Reliance & thorium utilization as a long- term objective.
5.2 THE THREE STAGES OF OUR NUCLEAR POWER PROGRAMME ARE:
# STAGE 1 = This stage envisages construction of pressurized heavy
water reactor (PHWR) using natural uranium as fuel and
heavy water as moderator. Spent fuel from these reactors
is reprocessed to obtain plutonium.
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# STAGE 2 = This stage envisages on the construction of fast breeder
reactors (FBR) fuelled by plutonium & depleted U
produced in stage1. These reactors would also breed U233
from thorium.
# STAGE 3 = This stage would comprise power reactors using U233 –
thorium as fuel, which is used as a blanket in these types
of reactors.
5.3 THE PHWR WAS CHOSEN DUE TO THE FOLLOWING
# It uses natural uranium as fuel. Use of natural uranium available in India
helps to cut heavy investments on enrichment that are capital intensive.
# Uranium requirement is the lowest & plutonium production is the highest.
# The infrastructure available in the country is suitable for undertaking
manufacture of the equipment.
The short- term goal of the programme was to complement the generation
of electricity at locations away from coalmines. The long-term policy is
based on recycling nuclear fuel & harnessing the available thorium
resources to meet country’s long- term energy demand and security.
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5.4 INDIAN NUCLEAR POWER PROGRAMME
Indian nuclear power programme is essentially based on PHWRs
using natural uranium as fuel and heavy water as moderator and coolant.
India has six atomic power plants in which electricity is produced by using
the nuclear reaction.
NPCIL UNITS SYNCHRONISATION TO GRID &
COMMENCEMENT OF COMMERCIAL OPERATION.
Present installed nuclear power capacity is 3310Mwe. With the projects under construction at TAPP-3 (540Mwe), KAIGA-3&4 (440Mwe), KUDANKULAM (2000Mwe), RAPP-5&6 (440Mwe) & by re-rating of MAPS-1 to 220Mwe, a total nuclear power capacity of 6780Mwe is planned to be achieved by December 2008 progressively.
The list of proposed sites in India is:-
UNIT DATE OF FIRSTSYNCHRONIZATION
DATE OF COMMERCIAL OPERATION
TAPS-1 01.04.1969 28.10.1969TAPS-2 05.05.1969 28.10.1969RAPS-1 30.11.1972 16.12.1973RAPS-2 01.11.1980 01.04.1981MAPS-1 23.07.1983 27.01.1984MAPS-2 14.09.1985 21.03.1986NAPS-1 29.07.1989 01.01.1991NAPS-2 05.01.1992 01.07.1992KAPS-1 24.11.1992 06.05.1993KAPS-2 04.03.1995 01.09.1995KAIGA-2 02.12.1999 16.03.2000RAPS-3 10.03.2000 01.06.2000KAIGA-1 12.10.2000 16.11.2000RAPS-4 17.11.2000 23.12.2000TAPS-4 04.06.2005 12.09.2005
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KAPP-3&4 740X2 Pressurized Heavy Water Reactor
RAPP-7&8 740X2 Pressurized Heavy Water Reactor
Jaitapur(Maharashtra) 740X4 Pressurized Heavy Water Reactor
CHAPTER 6
DESCRIPTION OF STANDARD INDIAN PHWR
6.1 LAYOUT :
The nuclear power stations in India are generally planned as two units
modules, sharing common facilities Such as service building, spent fuel
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storage bay& other auxiliaries like heavy water upgrading, waste
management facilities etc. Separate safety related systems & component
are however provided for each unit. Such an arrangement retains
independence for safe operation of each unit & simultaneously permits
optimum use of space, finance & construction time. The layout for a typical
220MW station consists of two reactor building, active service building
including spent fuel bay, safety related electrical, control buildings and the
two turbine buildings. Orienting turbine building radial to the reactor building
provides protection from the effect of turbine missiles. Other safety related
building & structures are also located has not to fall in the trajectory of
missiles generated from the turbine. The building and structures have also
been physically separated on the basis of their seismic classification.
Sectional views of the reactor building are depicting general layout inside
the reactor building.
6.2- PLANT LAYOUT (RAPP-5&6)
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Fig-3:- Plant layout (RAPP – 5&6).
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The over all plant layouts are for a twin unit complex. The principal
features of the layout are: -
The layout is based on the concept of independent operation of each
unit.
Mirror image is avoided to the maximum extent possible to retain
uniformity in layout.
All safety related systems and components are grouped together.
Reactor auxiliary building is located near to the reactor building to avoid
long piping lengths.
Control room & control equipment room in this building are so laid out so
as to cater for unitized operation.
Emergency power system such as DG & batteries are provided
separately in safety related structures.
Physical protection scheme to protect against industrial sabotage &
external or internal malevolent ad ions.
6.3 MAIN PARTS OF N.P.P
The main and auxiliary equipment of layout in nuclear power plant are
described below:-
1. Nuclear Reactor
2. Turbine
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3. Steam generator
4. Calandria
5. Coolant assembly
6. End shield
7. Cooling Tower
8. Moderator pump & auxiliaries
9. PHT pumps
10. Fuel
11. Fuel design
12. Fuel handling
13. Moderator system
14. PHT system
15. Reactivity control mechanism
6.3.1. NUCLEAR REACTOR
A reactor plays an important role in nuclear power plant. In NPP, heat
energy is produced by the fission of nuclear fuel such as uranium, in a
reactor thus, the source of heat energy is the reactor, which is equipment to
the furnace in a coal fired plant. It is necessary to transport this energy to
the turbine where it is changed into Mechanical energy of rotation.
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In concept, the Indian Pressurised Heavy Water Reactor is a
pressure tube type reactor using heavy water moderator, heavy water
coolant and natural uranium dioxide fuel. The reactor consists primarily of
Calandria, a horizontal cylindrical vessel. It is penetrated by a large number
of Zircaloy pressure tubes (306 for 235 MWe reactor), arranged in a square
lattice. These pressure tubes, also referred as coolant channels, contain
the fuel and hot high-pressure heavy water coolant. The pressure tubes are
attached to the alloy steel and fitting assemblies at either end by special roll
expanded joints. A typical pressure tube assembly is present in a reactor.
End-shields are the integral parts of the calandria and are provided at each
end of the calandria to attenuate the radiation emerging from the reactor,
permitting access to the fuelling machine vaults when the reactor is
shutdown.
The end fittings are supported in the end shield lattice tubes through
bearings, which permit their sliding. The Clandria is housed in a concrete
vault, which is lined with zinc metallised carbon steel and filled with
chemically treated demineralized light water for shielding purposes. The
end shields are supported in opening in the vault wall, and form a part of
the vault enclosure at these opening. Removable shield plugs, fitted in the
end fittings, provide axial shielding to individual coolant channel. A
replaceable channel seal plug seals the end fitting. Each pressure tube is
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isolated from the cold heavy water moderator present in calandria by a
concentric zircaloy calandria tube. The pressure tubes are centered and
partially supported in the calandria tubes by garter spring spacers. The
annular space between the pressure tube and calandria tube has been
sealed by inconel bellows and is connected to the annulus gas system,
which circulated dry carbon dioxide gas. The moisture content of this gas is
monitored at inlet and outlet points to detect possible leaks in the pressure
tubes or the calandria tubes. Special care is taken in design of coolant
channels to ensure that they can be replaced easily when the situation
should warrant such a replacement. The en-mass coolant channel
replacement carried out successfully in RAPS#2 during 1997-98 by in-
house developed technology has demonstrated the capability of NPCIL to
take up this work in future reactors namely MAPS and NAPS. Coolant
channels of these stations are made of Zircaloy-2 which will need
replacement within 10 Effective Full Power Years (EFPY).
However in KAPS#2 coolant tubes having Zirconium-2.5% Niobium alloy
has been used. This alloy has superior mechanical properties, low
deuterium pick-up rate and low irradiation assisted creep. Adequate creep
allowances are given for the full 30 years design life of the station. Zr-2.5%
Nb is being used as pressure tube material, which has improved creep
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properties, higher strength (hence neutron economy) and above all
improved properties with regard to in pile corrosion and hydrogen pick-up.
It has been the experience that garter spring spacers between the
calandria tubes and pressure tubes of the earlier design were prone to
displacement during operation and hence a modified design of garter
spring capable of ensuring their freedom from displacement is used from
KAPS, Unit#2 onward reactors. The garter spring used in standardized
PHWRs are tight fit on the coolant tubes. In-situ measurements/studies in
KAPS, Kaiga and RAPP-3&4 subsequent to hot conditioning have
indicated this design to be effective in preventing displacement of garter
springs.
6.3.2. TURBINE
Turbine is tandem compound machine directly coupled to electrical
generator. A turbine generally consists of low- pressure cylinder (double
flow for 500 MW units).
Turbine has a maximum continuous & economic rating of 229MW. Turbine
is the horizontal tandem compound re-heating impulse type running at
3000RPM with special provision for the extraction of moisture. A steam
turbine converts heat energy of steam into mechanical energy and drives
the generator. It uses the principle that the steam when issuing from a
small opening attains a high velocity. This velocity attained during
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expansion depends on the initial and final heat content of steam. The
difference between initial & final heat content represents that the heat
energy is converted into mechanical energy. They are of two types:
1. Impulse turbine: - In this, steam is expanded in turbine nozzle and
attains a high velocity, also complete expansion of steam takes
place in the nozzle & steam pressure during the flow of steam
over turbine blades remains constant. The blades have
symmetrical profile.
2. Reaction turbine:- In this, only partial expansion takes place in nozzle
and further expansion takes place as the steam flows over the rotor blades.
6.3.3. STEAM GENERATORS
The boiler assemblies contain 10-u shaped shell & tube heat exchangers,
connected in parallel. The hot coolant inlet channel and returning cold-
water channel are welded, the shell material is carbon steel & tube material
is Monel. Each heat exchanger has 195 tubes approximately 42 ft.long,
4.5” dia, and 0.049 thou thick. The design pressure on the heavy water side
of the boiler is 1350 psig at 5700 f.
6.3.4. CALANDRIA
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It is the heart of reactor and contains fuel and moderator; it is made of
Austenitic Stainless Steel. It contains 306 horizontal calandria tubes made
form Nickel- free- Zicaloy-2. It also contains a special tube, which has 12
fuel bundles making a total of 3672 fuel bundles. It also has 6 openings at
the top through which pass the reactivity control mechanism assemblies. In
the middle it has piping connection for moderator outlet & inlet. The entire
assembly is supported from calandria vault roof.
6.3.5. COOLANT ASSEMBLY
The primary function of coolant assembly is to house the reactor fuel & to
direct the flow of primary coolant part to remove the nuclear heat. At the
end of 306 tubes low neutron capture containment’s structure is provided,
while the end fitting provides entry and end connections both to the primary
coolant system.
6.3.6. END SHIELD
Two circular water coolant end shields of diameter about 5.12m &
thickness about 1.11m are located in the north and south calandria vault.
They are penetrated by 306 passages form reactor coolant tube
assemblies.
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These end shields provides shielding to reduce the radiation in the fuelling
machine vaults, the heat due to a closed water circulation removes
radiation from the calandria into shields.
6.3.7. COOLING TOWERS
Mainly there are two types of cooling towers:-
§ IDCT: Induct Draft Cooling Towers
§ NDCT: Natural Draft Cooling Towers
The main purpose of these cooling towers is to bring down the temperature
of circulating water. This is light water which circulates through the heat
exchanger and carry away the heat generated by the DM water. This DM
water condenses the steam. Hence by the application of cooling towers the
efficiency of the plant gets enhanced.
Following is the description of these types of cooling towers:-
IDCT:
As the name indicates it requires induced draft for cooling the active
process water. Big fans are used to produce the draft. The active water is
used in reactor building to cool various equipments.
NDCT:
The inductive water, which is used to condense water, is further cooled by
natural draft. They are 150m high with hyperbolic shape atomizing action.
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6.3.8. MODERATOR PUMP AND AUXILIARIES
The main moderator circulating systems consists of 5 pumps, 2 heat
exchangers, and necessary valves and piping. The pumps circulate
moderator form cal. through the two shells & tube heat exchangers to keep
the temp. Between 700f &1450. The cooled heavy water is again fed to the
cal. cooling necessities to reduce capture of thermal neutral and the
thermal stresses. The moderator receives about 37Mwe fission heat. The
system contains about 140,000kg heavy water.
6.3.9. PHT PUMPS
The PHT pump circulates the coolant (HW) in reactor core to steam
generator to generate steam. The complete system contains 8-circulating
pumps, 8-sets of boiler isolating valve of special design, 2 pressurizing
pump, a stand by cooling system, a relief control valve and feed & bleed
system.
6.3.10. FUEL
The use of natural uranium dioxide fuel with its low content of fissile
material (0.72% u-235) precludes the Possibility of a reactivity accident
during fuel handling or storage. Also, in the core there would no significant
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increase in the reactivity, in the ever of any mishaps causing redistribution
of the fuel by lattice distortion.
The thermal characteristics namely the low thermal conductivity and high
specific heat of UO2, permit almost all the heat generated in a fast power
transient to be initially absorbed in the fuel. Furthermore, high melting point
of UO2 permits several full power seconds of heat to be safely absorbed
that contained at normal power.
Most of the fission products remain bound in the UO2 matrix and may get
released slowly only at temperatures considerably higher than the normal
operating temperatures. Also on the account of the uranium dioxide being
chemically inert to the water coolant medium, the defected fuel releases
limited amount of radioactivity to the primary coolant system.
The use of 12 short length fuel bundles per channels in a PHWR,
rather than full- length elements covering the whole length of the core,
subdivides the escapable radioactive facility in PHWR has also the singular
advantage of allowing the defected fuel to be replaced by fresh fuel at any
time.
The thin zircaloy-2/4 cladding used in fuel elements is designed to
collapse under coolant pressure on to the pellets. This feature permits high
pellet- clad gap conductance resulting in lower fuel temperature and
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consequently lower fission gas release from the UO2 matrix into pellet- clad
gap.
6.3.11. FUEL DESIGN
Fuel assemblies in the reactor are short length (half meter long) fuel
bundles. Twelve of such bundles are located in each fuel channel. The
basic fuel material is in the form of natural uranium dioxide a pellet,
sheathed & sealed in thin Zircaloy tubes. Welding them to end plates to
form fuel bundles assembles these tubes. A 19-element fuel bundle is used
in 220Mwe PHWRs. A fuel bundle is shown below.
Fig-4:- Fuel bundle.
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6.3.12. FUEL HANDLING
On – power fuelling is a feature of all PHWRs, which have very low excess
reactivity. In this type of reactor, refueling to compensate for fuel depletion
& for over all flux shaping to give optimum power distribution is carried out
with help of 2 fueling machines, which work in conjunction with each other
on the opposite ends of a channel. One mounted on a bridge & column
assembly. Various mechanisms provided along tri-directional movement (X,
Y&Z Direction) of fueling machine head and make it mechanisms have
been provided which enables clamping of fueling machine head to the end
fitting, opening & closing of the respective seal plugs, shield plugs &
perform various fuelling operations i.e. receiving new fuel in the magazine
from fuel transfer system, sending spent fuel from magazine to shuttle
transfer station, from shuttle transfer station to inspection bay & from
inspection bay to Spent fuel storage bay.
6.3.13. MODERATOR SYSTEM
The heavy water moderator is circulated through the calandria by aid of a
low temperature & low- pressure moderator system. This system circulates
the moderator through two heat exchangers, which remove heat dissipated
by high- energy neutrons during the process of moderation. The cooled
moderator is returned to the calandria via moderator inlet nozzles. The high
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chemical purity and low radioactivity level of the moderators are maintained
through moderator purification system. The purification systems consists of
stainless steel ion – exchange hoppers, eight numbers in 220MW contains
nuclear grade, mixed ion- exchange Resin (80% anion & 20% cation
resins). The purification is also utilized for removable of chemical shim;
boron to affect start- up of reactor. Helium is used as a cover- gas over the
heavy water in calandria. The concentration deuterium in this cover –gas is
control led by circulating it using a sealed blower and passing through the
recombination containing catalyst alumina- coated with 0.3% palladium.
The purpose of heavy water moderator is to maintain criticality in
the reactor core by slowing down the high energy fast neutrons to low
energy thermal neutrons where their probability of fission capture is
greater.
Heavy water, used as moderator inside the calandria, gets heated up due
to neutron moderation and capture attenuation of gamma radiation as well
as due to the transfer of heat from reactor components in contact. The heat
in the moderator is transported to the moderator heat exchangers outside
the core where it is removed by process water. Circulation of moderator
through moderator heat exchangers is accomplished by moderator pumps.
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In Units 5&6 moderator is filled up to 100% as the shutdown mechanism is
entirely different. It has got primary shut off rods which gets inserted into
calandria and absorbs neutrons, thus causing a breakage of chain reaction.
For this there are 14 shut off rods made up of cadmium sandwiched in SS.
The other components of the moderator system consists of calandria,
coolant channels, over pressure rupture disc, expansion joints, moderator
pumps, heat exchangers and control valves.
6.3.14. PRIMARY HEAT TRANSPORT (PHT) SYSTEM
The system, which circulates pressurized coolant through the fuel channels
to remove the heat generated in fuel, referred as Primary Heat Transport
System. The major components of this system are the reactor fuel
channels, feeders, two inlet headers, two reactor outlet headers, four
pumps & interconnecting pipe & valves. The headers steam generators &
pumps are located above the reactor and are arranged in two symmetrical
banks at either end of the reactor. The headers are connected to fuel
channels through individual feeder pipes. The coolant circulation is
mentioned at all times during reactor operation, shutdown & maintenance.
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6.3.15. REACTIVITY CONTROL MECHANISMS
Due to the use of natural uranium fuel & on-load refueling, the PHWR’s do
not need a large excess reactivity. Standard reactor designs are provided
with four systems for reactivity control, viz.
1. Regulating rods.
2. Shim rods.
3. Adjuster rods for xenon override
4. Natural boron addition in the moderator to compensate for the
excess reactivity in a fresh core & for absence of xenon after a long
shutdown.
The reactivity control devices are installed in the low-pressure
moderator region & so they are not subjected to potentially severe
hydraulic & thermal forces in the event of postulated accidents.
Furthermore, the relatively spacious core lattice of PHWR allows sufficient
locations to obtain complete separation between control & protective
functions. The regulating systems are thus fully independent with its own
power supplies, instrumentations & triplicate controls channels. Cobalt &
stainless steel absorber elements have been utilized in the reactivity control
mechanisms. For 220MW standardized design, two diverse, fast acting &
provides a high degree of assurance that plant transients requiring prompt
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shutdown of the reactor will be terminated safety. The primary shutdown
system consists of 14 mechanical shut off rods of cadmium sandwiched in
stainless steel & makes the reactor sub critical in less than 2 sec. Fail-safe
features like gravity fall & spring assistance has been incorporated in
design if mechanical shut off rods. The second shutdown system, which is
also fast acting, Comprise 12 liquid poison tubes, which are filled with
lithium pent borate solution under helium pressure. The trip signal actuates
a combination of fast acting valves and causes poison to be injected
simultaneously in 12 interstitial liquid poison tubes of calandria of the
machines is used to fuel the channel while the other one accepts the fuel
bundles. In, Addition, the fueling machines facilitate removal of failed fuel
bundles. Each fueling machine is mount thin zircaloy tubes. Welding them
to end plates to form fuel bundles assembles these tubes.
6.4 STATUS OF NUCLEAR POWER GENERATION & FUTURE PLANS
The nuclear power programme in India up to year 2020 is based on
installation of a series of 235 MWe & 500MWe pressurized heavy water
reactor (PHWR) units, 1000 MWe light water reactors (LWR) units & fast
breeder reactors (FBR) units. NPCIL plans to contribute about 10% of the
total additional needs of power of about 20000MWe per year i.e.
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10000MWe per year in the coming two 5 year plans. The total installed
capacity of nuclear generation would increase.
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CHAPTER 7
CRITERIA FOR SELECTION OF SITES FOR
NUCLEAR POWER PLANT
7.1 OBJECTIVE:
The main objective in siting of Nuclear Power Plants from the point of view
of nuclear safety is to be able to construct and operate Nuclear Power
Plants safely & to provide protection to the public against radiological
impact resulting from accidental releases of radioactive material as well as
release of such materials during normal operation of the plant. Hence the
basic criteria for selection of a site for the location of a nuclear power plant
shall be to ensure that the site plant interaction will not introduce any
radiological risk or others of an unacceptable magnitude.
This can be achieved by:
A. The radiological risk to the Nuclear Power Plant due to the
external events should not exceed the range of radiological
risk associated with accidents of internal origin.
B. The possible radiological impact of a Nuclear Power Plant on
the environment should be acceptably low for normal
operation, an accident conditions and with in the stipulated
criteria for radiological safety.
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In evaluating the suitability of a site for locating a Nuclear Power Plant, the
following are the major aspects that need to be considered:
Effect of external events (nature & man – induced) on the
plant.
Effect of plant on environment & population
Implementation of emergency procedures particularly
counter measures in the public domain.
7.2 DESIGN BASIS FOR INTERNAL NATURAL EVENTS:
Natural phenomenon, which may exist or can occur in the region of a
proposed side, shall be identified and these should be classified as per
their importance. Design basis shall be derived for each important event by
adopting appropriate methodologies. These should be justified as being
compatible with the characteristics of the region & also with the current
state of art of the extent possible.
7.3 DESIGN BASIS FOR EXTERNAL MAN - INDUCED
EVENTS:
Proposed sites shall be adequately investigated with respect to all the
design basis man- induced events that could affect the plant safety.
The region shall be examined for facilities and human activates that may
affect the safety of the proposed Nuclear Power Plant. These facilities &
activates shall be identified and the conditions under which the safety of
P a g e | 35
the plant is likely to be affected shall be considered in fixing the design
basis for man-induced events. Information concerning the frequency &
severity of those important, man-induced events shall be collected &
analyzed for reliability, accuracy & completeness.
7.4 RADIOLOGICAL IMPACT ON THE ENVIRONMENT :
The radiological consequences due to Nuclear Power Plant on environment
should be as low as is reasonably achievable taking into account. Social
and economical factors, both for normal & accidental conditions are within
the stipulated criteria for radiological safety.
In evaluating a site for the radiological impact by the Nuclear Power Plant
on the region for operational states & accidental conditions, appropriate
estimates shall be made of expected or potential releases of radioactive
material taking into account the design of the plant including its safety
features.
The direct & indirect pathways, by which radioactive materials released
from the Nuclear Power Plant could reach & affect the people, shall be
identified for use in the estimation of the radiological impact. Thus, the main
points to be considered for sitting Nuclear Power Plants are as follows:
A. Land requirements.
B. Accessibility.
P a g e | 36
C. Construction facility.
D. Cooling water.
E. Electrical system and energy resources.
F. Geology.
G. Seismology.
H. Flooding.
I. Natural events.
J. Man-induced events.
K. Population.
L. Radiological impact.
M. Meteorological & air releases.
N. Hydrology & liquid waste.
O. Geo hydrology & solid waste.
P. Land use & Environment impact.
7.5 SAFETY DESIGN PRINCIPALS
It has been ensured that systems, components & structures having a
bearing on reactor safety are designed to meet stringent performance &
reliability requirements. These requirements are met by adopting the
following design principles:
P a g e | 37
a) The quality requirements for deign, fabrication, construction, &
inspection for these systems are of the high order,
commensurate with their importance to safety.
b) The safety related equipment inside the containment building is
designed to perform its function even under the elevated
pressure & temperature & steam environment conditions
expected in the event of postulated loss of coolant accidents
(LOCA).
c) Physical & functional separation is assured between process
systems & safety systems.
d) Adequate redundancy is provided in systems such that the
minimum safety functions can be performed even in the event
of single active components in the system.
e) To minimize the probability of unsafe failures.
f) Provisions are incorporated to ensure that active components in
the safety systems are testable periodically.
g) All the supplies/services (electric, compressed air or water) to
these systems, necessary for the performance of their safety
functions are assured & ‘safety grade’ sources.
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CHAPTER 8
SWITCH YARD
8.1 SYSTEM DESCRIPTION
The 220KV switchyard consists of double bus bar scheme, each bus being
designed for evacuation of full power of the station taking into consideration
of the failure of the one line with another line under maintenance. The
switchyard is provided with breakers and isolators for feeding load through
either of the buses. A by-pass isolator is also provided for each feeder to
facilitate taking breaker maintenance. All the feeders are provided with
lightning arrestors, on each phase. CVTs are provided on each phase of
out going feeders to facilitate carrier communication and line protection.
Current transformers and EMPTs of adequate rating are provided as per
requirement of the protection scheme. Adequate provision has been made
to provide off site power supply to station auxiliaries through start-up
transformers.
8.2 220KV SWITCH YARD
220KV switchyard of RAPP-5&6 consists of 2 start–up transformer bays,
one bus coupler bay and 2 line bays. There are total 5 bays in 220KV
switchyard of RAPP-5&6.
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Double main bus bar with by-pass switching scheme is provided for the
switchyard. This arrangement provides for maintenance of one main bus or
one circuit breaker at any time without interruption of power supply to any
feeder.
Details of the design parameters adopted for 220KV switchyard are as
below:
Type of switchyard - Out door
Normal voltage - 220KV
Rated voltage - 245KV
Basic one-minute power frequency level - 460KV RMS
Rated current for main bus bars - 2000 Amp
Rated current for feeder bus bars - 1600Amp
Phase to phase minimum clearances - 2.7 Meters
Ground minimum clearances - 5.5 Meters
8.3 DESIGN DETAILS:
Main aspects that are considered in the design of 220KV switchyard are as
follows:
I. It shall be possible to take out any circuit without interrupting the
corresponding circuit from service.
II. It shall be possible to isolate main bus for maintenance without loss
of any circuit.
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III. A bus fault shall not result into shut down of complete station.
IV. Further expansion should be easily possible without any lengthy
shut downs.
V. Crossing of outlets shall be avoided.
All switchyard equipment shall be suitable for outdoor installation in hot,
humid and tropical atmosphere. All equipment shall be capable of
withstanding the dynamic and thermal stresses due to short circuit current
without any damage or deterioration. The equipments shall be designed as
per codal design for meeting seismic requirement. The string bus bars of
outdoor switchyard are of ACSR conductor. Conductor sizes are selected
which is based on the current rating and other site conditions. The circuit
breakers are of sulphur hexafluoride (SF6) type & can carry rated current
continuously and short time current for 3 seconds. The isolators are three-
pole double end breaker in Air. Center post rotating type with contact
blades moving through horizontal plane.
The current transformers are oil immersed, self-cooled and hermetically
sealed type. The current transformers are single pole unit, suitable for
upright mounting on steel structure. Voltage transformers are of Electro-
magnetic/capacity type. Capacitive voltage transformer used with power
line carrier communication (PLCC) system are suitable for a PLCC system
having frequency range of 40 to 500 Hz. Design of other switchyard
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equipment (wave trap, lighting arresters, earth switch etc.) shall govern by
respective data and environmental conditions.
8.4 SWITCHING SCHEME:
Double bus with bypass isolator system for 220 KV switching scheme has
been adopted for RAPP-5&6.
Advantages of this scheme are as follows:
Circuit breaker of any feeder can be taken out without interruption of
that circuit.
Maintenance of any bus can be carried out by transferring all the
circuit on one bus, without loss of any circuit.
Fault on any of the buses will result in the shutdown of the circuits
connected to that particular bus at that time. However, after isolating
faulty bus, these circuits can be connected to healthy bus.
Expansion of switchyard for RAPP-3&4 is possible at one side.
Crossing of lines can be avoided by proper arrangement of bays.
An independent control room is provided inside the switchyard. This
houses all control required for lines and bus coupler bay. Independent
battery banks and battery charges are provided in switchyard control room
feeding 250 volts D.C. control and protections. These battery chargers are
fed from class-III MCCs (P2 &Q2) to ensure reliability.
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8.5 400KV SWITCH YARD
400KV switchyard of RAPP-5&6 consists of 3 bays, 2 for GT-5 & GT-6 and
one bay for Kota feeder. In future there will be total 5 bays including GT-7
and GT-8. Power evacuation from the generating units of RAPP-5&6 would
be done at 400KV, whereas 220KV voltage level shall be used for drawing
start-up power.
400 KV System:
Following feeders will be operated at 400KV:
a) Two nos. 400KV feeders from Generator
Transformer of unit-5&6.
b) Two (2) nos. 400KV line feeders to Kankroli.
c) One (1) no. 400KV line feeder to Kota.
8.6 TRANSMISSION LINES
Five transmission lines 514-L-1 to 514-L-5 interconnecting the station to
RSEB grid are given below:
A. RAPP-5&6-Anta single circuit line is long 80 Km route length.
B. RAPP-5&6-To RAPS-3&4 single circuit line.
C. RAPP-5&6-To Kankroli-I double circuit line.
D. RAPP-5&6- To Kankroli-II double circuit line.
E. RAPP-5&6- Kota double circuit line is long 50Km route length.
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RAPP-5&6 is connected to Anta gas power plant and RAPS-3&4 Nuclear
Power Plant for taking start-up power. Thus RAPP-5&6 is connected to two
sources of power generators for off-site power.
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CHAPTER 9
ELECTRICAL EQUIPMENT USED IN NPP
9.1 220KV CIRCUIT BREAKER
Circuit breakers are the switching and current interrupting devices.
Basically a circuit breaker comprises a set of fixed and movable contacts. It
switches during normal and abnormal conditions and interrupts the fault
circuit.
9.1.1 INTRODUCTION
The 220Kv breakers form part of the main power output system which
consists of 21Kv isolated face bus duct, two main transformer with 220Kv
lightning arrestor disconnect switches, 220Kv bus and start-up transformer,
line and bus transformer.
9.1.2 DESCRIPTION
Type SF6 gas Circuit BreakersRated voltage 245KVRated current 2000AmpRated making capacity 100KA peakRated short time current 40 KA for 3secRated line charging breaking 125AmpArching time 30MillisecondClosing time 100Millisecond SF6 gas pressure 7kg/cm2 Air pressure 15.5Kg/cm2
P a g e | 45
The circuit breakers are of SF6 puffer type design. The circuit breakers are
of single pole type. The control scheme of line circuit breakers has
provision for single or three phase auto reclosing and tripping. The
reclosing scheme has also provision for reclosure on dead line or reclosing
with synchronizing check features. There are unities compressed air
systems for feeding air to the circuit breakers. The compressors are located
inside the central pole cubicle of respective breakers. The air piping
between the poles of each circuit breaker is provided with copper tubes and
are run inside the cable trenches.
The 220 KV SF6 circuit breakers are provided with compressed air for
holding contact in position when closed. The opening & closing of breaker
is by compressed air & closing spring respectively. Air reservoirs are
provided on each pole and are inter connected by copper tubing. One
single air compressor of adequate capacity is provided in the central pole
control cubicle. The pole column provided on each phase consists of
breaker chamber, two support insulators, on each phase consists of
breaker chamber, two support insulators, driving rod, pneumatic drive,
control valves & closing spring, All components such as contractor, relays
etc, are accommodated in the central inside the central pole cubicle of
control cubicle.
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The control system comprises equipments for SF6 density monitoring,
functional lockouts, signaling, compressed air monitoring etc. A wafer type
auxiliary switch is coupled directly mechanically to the pneumatic drive. An
antipumping device provided, prevents repeated closing and tripping of the
breaker when there is a sustained close and trip signal. A temperature
compensated dens meter is provided on each pole. The current rating of all
outdoor 220 KV circuit breaker is 2000A. This current rating of circuit is
selected on the load (current) requirement and symmetrical short circuit
level of 40 kA at 220 kV system.
All circuit breakers have short time withstand capacity of 40 KA for 3 sec.
with symmetrical breaking capacity of 15000 MVA and a making capacity of
102KA (peak). The circuit breaker is operational even under ‘phase
opposition’ arising out of faulty synchronization. Each outgoing line feeder
circuit breaker compromise three identical poles complete with individual
operating mechanism and shall have provision for both single and three
phase auto reclosing. Three (3) poles of the breaker are linked together
electrically/pneumatically for SF6 breakers. Breakers have been tested for
one- minute power frequency test voltage of 460 KV (rms) and impulse test
voltage of 1050 KV (peak) with 1.2/50 micro sec. impulse.
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9.2 ISOLATING SWITCHES:
The isolators are motor operated center post rotating type and are capable
of remote operation from control room in switchyard. In the event of
necessity they can also be operated by manual operation with operating
handle.
Necessary electrical and mechanical interlocks to meet the logic as per IE
rules standards have been incorporated. The isolators are also tested for
all interlocks and for 1000 cycle ‘on’ and ‘off’ operations in the factory.
Grounding switches are provided on the line & bus EMPT isolators. These
are mechanically and electrically interlocked with the main isolators so that
they are not closed to earth when the system is charged. All operating
mechanisms are sufficiently earthed as required by standards to prevent
any electrical shock for operators during local operation. The bus bar-II
selector isolators are of tandem type. The isolators are type tested as
relevant standards in approved testing institutions.
All isolating switches are rated to carry current of 1600A continuously
except for bus coupler bay where it will be 2000A. All isolators will carry
short circuit current of 40KA for 3 sec. The isolating switches are AC motor
operated, horizontal center post rotating double break type. Isolators have
been type tested at CPRI, Bhopal for its short circuit with stand capacity.
The isolating switches are capable of making and breaking:
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a) Magnetizing current of the voltage transformer.
b) Capacitive current of the buses and short connections.
The air break 3- pole isolating switches are gang operated type so that all
the poles make and break simultaneously. The isolating switches are
suitable for sequential interlocking with associated equipment, for closing
and opening.
9.3 CURRENT TRANSFORMER
Five core CTs are provided for each of the feeder of the switchyard.
The general allocations of the five cores are as follows:
A Bus differential - 2 Cores
B Main protection - 1 Cores
C Metering - 1 Core
The CTs for bus couplers are of live tank design. These CTs are supplied
by M/S Crompton Greaves Ltd Nasik. All other CTs are of dead tank type
and are supplied by M/S TELK Angamally. While type-1 CTs used for lines
& GT bays are rated for the short circuit of 40KA-3 Sec. The type II CTs
used for SUT bays are rated for 40KA for 1 sec due to manufacturing
limitations.
9.4 VOLTAGE TRANSFORMER
In line with the requirement of Rajasthan state electricity board for
communication purposes 4400 pf capacitance CVTs have been procured
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for RAPP-5&6.These CVTs serve dual function Viz. as PTs for under/over
voltage protection and as coupling capacitors for carrier communication.
The CVTs are provided on all the three phase. The CVTs are supplied by
M/S ABB Baroda. Electromagnetic Voltage Transformer (EMPTs) is
supplied by M/S Telk Anagamally.
There is one (1) set voltage transformer (VT) for each 220kv bus bar.
Each set consists of three single phase VTs.
Each outing line from switchyard has its own voltage transformer. Line
voltage transformer is of capacitor type. It is used for communication
system.
These line CVTs are of single-phase type. Each CVTs has three
secondary winding and winding connection will be of star/star, star, open
delta.
9.5 GENERATOR TRANSFORMER
The generator transformer is required to step up the generating voltage to
the transmission line voltage (16.5kV to the transmission line voltage of
400KV). Two power transformer 512T3and 512T4 rated.
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9.6 CONTROL UPS
U.P.S. or uninterrupted power supply is used to maintain continuity of
power supply in case of power failures. The control U.P.S. used in RAPP-
5&6 consists of mainly 4 blocks:
a) Rectifier
b) Battery
c) Inverter
d) Static switch and manual bypass switch
RECTIFIER:Rectifier feeds the inverter & battery or the U.P.S. The main
functions of the rectifier are:
Rating 260 MVA
Low voltage winding 16.5KV
High voltage winding 400KV
Type of cooling Air cooled
Type of tap changer OLTC
Temp. Rise oil 450C
Temp. Rise winding 550C
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i.) Produce control output voltage ranging from 226V to 286V with
accuracy of 1% of the set value.
ii.) Supply trickle charge to 220V DC battery bank.
iii.) Following the loss of AC supply and its subsequent restoration
to the rectifier provides full load and boost charging current to
battery.
BATTERY:
Battery back up is provided through Lead Acid batteries.
INVERTER:
It takes DC supply as input from the rectifier / battery and inverters to 240V
AC, 50Hz for supplying 1-phase (2 Wire), control loads such as computers,
recorders and controllers etc. Inverters for 20kVA UPS are transistorized
and for 60kVA inverters are thrusters based.
9.7 STATIC SWITCH AND MANUAL BYPASS:
The main U.P.S. and the standby UPS are isolated by this static switch. It
consists of 2 SCR connected back to back (Antiparallel). Normally both the
SCR’s will be in blocking mode. When the inverter trips on fault the static
switch get firing pulses and the stand by supply is connected to load. Static
switch has only short time rating, hence once the parallel contactor closes,
SCR’s will be commutated.
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CHAPTER 10
ELECTRICAL POWER SYSTEM
10.1 INTRODUCTION
Nuclear power stations require electrical power supply to perform their
functions when the reactor is under normal operation, anticipated
operational occurrences and emergency situations and accident conditions.
In order to meet the requirement at various stages of operation, electrical
power supply system is provided with adequate redundancy. It consists of
main power evacuation system, off site supplies and associated
transformers & distribution boards.
This project report is prepared to educate, and familiarize on the
electrical equipments in general and RAPP-5&6 electrical system in
specific. Attempts have been made to elaborate the equipment selection
criteria advantages of them whenever it is felt important.
10.2 ELECTRICAL SYSTEM (OBJECTIVES)
The electrical power system for RAPP-5&6 is designed to provide for the
following objectives:
a) To evacuate the power generated from the turbo generators to
the off site grid connected to the station at 400KV switchyard.
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b) To provide required quality of power to the station auxiliaries
through start-up transformer (SUT), unit auxiliary transformers
(UAT), on site diesel generator sets and uninterruptible power
supply systems.
c) To provide emergency electric power supply to safety system of
the station during simultaneous occurrence of postulated
initiating events and single failure of any active/passive electric
component/system.
d) To provide station emergency electric power system with
reliable off site power from at least two transmission lines
preferably connected to two generating stations.
e) To provide fast transfer systems, emergency transfer systems
and load shedding schemes so that electrical power supply is
restored within the interruption time permitted by the connected
loads.
f) To provide operational flexibility.
g) To provide necessary isolations, alarms and indications for safe
operation and maintenance of electrical equipment.
h) To provide fire protection and safety.
i) To provide earthing of electrical systems and equipment for
personnel and system safety and isolation of defective system.
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j) To provide surge suppression, lighting protection.
k) To provide adequate lighting during plant operation and during
emergency.
GENERAL
The major objective in the design of an electrical power distribution system
in a power distribution system in a power plant is to obtain the best possible
reliability compatible with economic considerations. A further factor which
has influenced the design of distribution system for this system is the fact
that there is very high ratio of capital costs to running costs which makes
downtime due to failure of equipment very costly and higher degree of
reliability must be built into system than the conventional generating
stations or industrial plants.
10.3 CLASSES OF POWER
CLASS I POWER: The class I power supplies low loads that require a
220 volt DC voltage, which is un- interruptible.
CLASS II POWER: The class II power system supplies all loads that must
be fed from an AC source which is un- interruptible.
CLASS III POWER: The class III power system covers all loads which may
be interrupted for a short period (1-2 minute) during
an outage or disturbance on the system.
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CLASS IV POWER: The class IV station service system covers all other
loads which may be interrupted during outage or
disturbance on the system without endangering the
plant.
Various auxiliaries (i.e. electrical loads) of the power station are provided
with power supply from off-site and on-site sources. The station power
supply system is connected to transmission network with the help of at
least 2 independent transmission connected to the 220kV switchyard.
The system is designed to have adequate standby power sources so that in
the event of loss of normal supplies, the essential equipment required for
reactor safety can be kept running. Essentially, the power sources for
station requirement are:
• Normal supplies provided from two redundant sources, viz, from the
grid (off-site power) or from the unit generator.
• Standby diesel generator.
• Storage batteries.
The station auxiliary power system is classified into four classes as
mentioned above.
Class I system (based on batteries) is the most reliable system and is used
for the supply of control power for the circuit breakers and control such as
diesel engine control schematics, turbine control schematics, static
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excitation for turbine generators, control schemes for diesel driven fire
fighting pumps etc.
Class II power supply is derived from uninterrupted power supply system
consisting of rectifiers, inverters and a dedicated battery bank. The battery
bank is capable of feeding inverter loads for a period of at least 30 minutes
after the failure of ac power supply to the rectifier. Major loads on class II
include FM supply pumps, emergency lights, seal oil pumps, flushing oil
pump etc.
Class III power supply is connected to emergency diesel generator to
provide power supply in the event of class IV power has failed. Diesel
generator sets are designed to provide power automatically to the class III
bus whenever class IV bus has failed. Loads connected to the class III
supply can tolerate short interruptions in power supply.
The class III power can be resorted within two minutes
from the loss of class IV. The capacity of each on-site emergency diesel
generator is 2250 kW. Three DGs, each of 2250 kW capacity, are provided
for each unit.
Major loads connected to class III supply are primary feed pumps, power
and control uninterrupted power supply, moderator circulating pumps,
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ECCS pumps air compressors, ABFPs, shutdown cooling pumps and
process water pumps.
Class IV power supply is derived from 220kV grid through start up
transformer and from turbo generator through unit transformer. The
capacity of each transformer is 35 MVA and adequate to supply all start up
and operating loads of the unit. The load connected to this system can
withstand prolonged power supply interruption.
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CHAPTER-11
SWITCHGEAR
Switchgear is a general term covering a wide range of equipment
concerned with switching and protection. Switchgear includes switches,
fuses circuit breakers, isolators, relays, control panels, lightning arresters,
current transformer.
KV Metal Clad Switch Gear is combining of circuit breakers, instrument
transformer relays, meters with there interconnections and enclosures
arrange in such a way to open and close that circuit with full safety to the
operator whenever required.
The most important component of metal clad switchgear is a air magnetic
power circuit breaker in which the circuit interruption takes place in a
intense magnetic field.
The metal clad switchgear assemblies are used to provide power
distribution, power switching and relaying facilities for the 6.6KV or 3.3KV,
50Hz, 3-phase power to station service equipment.
11.1 6.6KV switchgear (Class-III & Class-IV)
Type - 8BK 20
Rated voltage - 7.2KV
Rated insulation
(a) One minute power frequency withstand - 27KV
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(b) Impulse - 60KV peak
Rated bus bar currents
(a) Class-IV - 2000Amp.
(b) Class-III - 630Amp.
11.2 415 Volt switchgear (Class-III & Class-IV)
Type - M-PACT
Rated voltage - 415 V
Rated insulation level - 2.5 KV for 1 min
Rated bus bar currents - 2500Amp
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CHAPTER 12---------PROTECTIVE RELAYING AND METERING
12.1 INTRODUCTION
Protective relaying is necessary with almost every electrical plant, and no
part of the system is left unprotected. The choice of protection depends
upon several aspects such as type and rating of the protected equipment,
its importance, location probable abnormal conditions, cost etc between
generators and final load points, there are several electrical equipment and
machines of various ratings. Each needs certain adequate protection.
The protective relaying senses the abnormal conditions in a part of
the power system and gives an alarm or isolates that part from the healthy
system.
The relays are compact, self-contained devices, which respond to
abnormal condition. Whenever an abnormal condition develops the relays
close its contacts. Thereby the trip circuit of the circuit breaker is closed.
Current from the battery flows in the trip coil of the circuit breaker and the
circuit breaker opens and the faulty part is disconnected form the system, is
automatic and fast.
In RAPP-5&6 “Numerical Relay” has been used to provide protection
to various electrical equipments. Numerical relay has its own memory. It
can store time and various parameters during faulty conditions.
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CHAPTER 13--------------------IMPORTANT SECTIONS OF RAPP
13.1 ENVIRONMENT SURVEY LAB (ESL):
Environment survey laboratory located in each nuclear site is continuously
monitoring the radioactive release from the plant at various points upto 30
kms. radius. Any radiological release requiring for off-site emergency is
notified through the local authority. Proper procedures for off-site
emergency have been chalked out and necessary plans are checked
periodically. However public will not be able to come to know about the
releases because of the inherent nature of radioactivity which cannot be felt
by sensory organs. Proper instruments are necessary for any one to find
out about the presence of radioactivity. Also newer reactors have double
containment making any significant release of radioactivity in public domain
highly impossible.
13.2 INDUSTRIAL SAFETY SECTION:
Safety organization in the plant is the agency employed by management to
assign responsibility for accident preservation and to ensure performance
under that responsibility.
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According to the factories act, it is the duty of the management to provide a
safe working place and instructions on the hazards involved in operations
and indicate the safety way of performing the job.
Accidents are caused, they do not just happen. All accidents are
preventable because they happen due to the human failure in unsafe act /
unsafe conditions. The basic functions of safety committee are:-
(i). To discuss and formulate safety policies and recommend their adoption
by management.
(ii). To discover unsafe conditions and practices and determine their
remedies.
(iii). To work to obtain results by having its management approved
recommendations put into practice.
13.3 WASTE MANAGEMENT FACILITY:
A waste management site for the storage / disposal of low intermediate
level solid / solidified waste generated in the exclusion zone of 1.6 km
radius of the reactor which is exclusively under the control of the power
plant. This is a small area of the exclusion zone and it is isolated from the
public use after retiring of the station until the radioactivity decays down to
acceptable levels.
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Radioactive wastes can be categorized in three types, they are:-
1. SOLID WASTE:
This type of waste is disposed deep inside the earth (1000-1500m).
The least radioactive waste i.e. 0-2 mSv/year is disposed into earth
trenches. The radioactive waste from 2 mSv – 50 mSv/year is
disposed in RCC trenches and the rest from 50 mSv/year radioactive
waste is disposed in the tie holes.
2. LIQUID WASTE:
This type of waste is treated separately in a different plant where
after applying ion exchange method we release this water into the
lake.
3. GASEOUS WASTE:
Gaseous radio nuclides are generated during the operation of NPPs
fission in fuel and activation product in vault air cooling. These
gaseous nuclides are passed through filters and absorbers before
releasing them to atmosphere.
13.4 WATER TREATMENT PLANT:
The water treatment plant supplies domestic water and demineralised
water to fulfill the RAPS station requirement. The water after filtration,
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decomposition and chlorination is sent to domestic water tank to supply
within the station.
Water is taken from LP process water supply and feed to the up flow
sedimentation tank where it enters from bottom and flow upwards. Before
the up flow to the sedimentation tank, we add alum dose to coagulate the
fine dust. After doing all these processes, clear water is obtained. Then the
part of this clear water after chlorination is sent for domestic purposes and
from the rest of the clear water, DM water is obtained by ion exchange
method.
13.5 ESTATE MANAGEMENT (EM):
This department is placed within the colony to rectify all the civil, electrical
or any other problems taking place in the houses. And one of the main
work is to step – down the 11KV high voltage into 220V or 415V for the
domestic purposes. The water treatment plant is also coming under this
department.
13.6 FIRE STATION:
Here in the fire station, we came to know about the classification of fire,
how these types of fires can be extinguished and how the whole safety
purposes of the huge power plant are solved.
13.6.1 WHAT IS FIRE?
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The combination of HEAT, FUEL, and OXYGEN give rise to FIRE.
For fire to arise, the presence of all three components is necessary.
Now as the type of fuel varies the classification of fire also differs and since
there are different types of fires, so the methods to extinguish these fires
are also different as studied below:
13.6.2 CLASSIFICATION OF FIRE:
There are four types of fire:-
1. A CLASS FIRE:-
When grass, paper, cloth, jute, etc. act as fuel then the fire which
arises is of A class type. To extinguish this A class fire water is used.
2. B CLASS FIRE:-
When the liquid fuels like petrol, diesel, oil, and other hydrocarbons are
the reason for fire, then foam is used to extinguish it.
Here the foam generated is of two types:-
(i). Chemical foam
(ii). Mechanical foam
Chemical foam is formed by mixing Al2SO4 + NaHCO3; whereas
mechanical foam is obtained by using foam generator.
3. C CLASS FIRE:-
When gaseous fuels like LPG, Br2, H2S, etc. are the reason for fire,
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then carbon dioxide {CO2} is used to extinguish it. Actually CO2
extinguishers are used for fire fighting purposes, in which pressurized
CO2 is filled.
4. D CLASS FIRE:-
When fire arises due to metals like Al, Fe, Cu, etc, then the dry chemical
powder [DCP] is used to extinguish the corresponding D class fire. DCP
is formed by adding Na + K + Ba + steroid.
Also there are some other fire fighting systems which are used in RAPP.
These can be classified as:-
1. ACTIVE FIRE FIGHTING SYSTEMS:
These systems are used externally to extinguish fire. Different active
fire fighting systems are:
CO2 spreading system
Fire hidden system
Fire brigades
Dilute system
Water tender
Emergency tender
2. PASSIVE FIRE FIGHTING SYSTEMS:
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These systems are placed internally i.e. inside the building, so as to
restrict the spreading of fire from one room to other. Different passive
fire fighting systems are:
Fire dampers
Fire doors
Fire sensor cabins
Fire resistor paint
Fire barriers
Smoke detectors
13.7 RAPP COBALT OPERATING FACILITY (RAPPCOF):
RAPP cobalt operating facility has been set up at RAPS site to handle and
process large quantities of Co-60 produced in adjuster rods and fuel
channels of power reactors. The facility is designed to handle about 2
mega curies of Co-60.
USES:
Cobalt - 60 is used in many fields. These are:-
1. Food irradiation
2. Treatment of cancer through radiation
3. Sterilization of medical products
4. Vulcanization of rubber latex
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CONCLUSION
An engineer needs to have not just theoretical knowledge but practical
knowledge also. So every student is supposed to undergo a practical
training session after III year. I have taken my summer training from
NUCLEAR TRAINING CENTRE (RAPP) where I practically saw that how
electric power is generated. I have also got a chance to saw different
electrical equipments which helps me to enlarge my knowledge.
During our 45 days training session we were acquainted with the
working of the power plant.
At last I would like to say that practical training taken at NTC (RAPP) has
broadened my knowledge and has widened my thinking as a professional.
