NAME- KRITIKALPA SAHA

ENROLLMENT NO.- 16UEE020

SECTION – A
SEMESTER- 8TH
SUBJECT- POWER PLANT ENGINEERING
DATE OF SUBMISSION- 12/04/2020

ASSIGNMENT NO.-1
1. Various Generations of Nuclear Reactors-

 First Generation of reactors:

The first generation reactors were in the 1950s and 1960s the
precursors of today big commercial reactors producing electricity,
especially in the U.S., the former Soviet Union, France and the United
Kingdom. The powers of these precursors seem modest compared with
those of their faraway successors of today. In 1954 in the former Soviet
Union, the electric power of the world's first nuclear power plant
producing electricity in Obninsk, dubbed "Atom Mirny" did not exceed
5 Megawatts (MW). At the time, most of these reactors used natural
uranium as fuel, the use of enrichment being not available for civilian
purposes. Other first-generation reactors derived from the onboard
reactors of submarines were the precursors of the pressurized (PWR)
or boiling (BWR) water reactors. The 1950-1970 period was
characterized by an explosion of concepts. This period also saw the
first prototypes of fast breeder sodium-cooled reactors.

 Second Generation of reactors:

About 85% of electricity produced worldwide by nuclear power comes
from “second-generation” reactors, heirs to the 1950-1960s prototypes.
They make up the vast majority of some 439 units deployed today. In
2008 they supplied a total electric power of 372 GWe. These reactors
are located in 30 countries (93% of Generation II and 7% of Generation
I), accumulating altogether an experience of more than 13,600 reactor-
years. Second-generation reactors belong to main two families of light
water reactors (LWR): Pressurized Water Reactors or PWR and
Boiling Water Reactors or BWR. Both use enriched uranium as nuclear
fuel and neutrons moderated with water. Water is used also for cooling.
Through a heat exchanger, steam is generated, activating turbines and
producing electricity. In the late 1960s, uranium enrichment became
available for civilian purposes and was no longer reserved solely for
defence. This fact allowed the generalized use of light water for
reactors. The uranium fuel of second-generation reactors is enriched
from 3.5 to 5% in fissile uranium 235. The enrichment level offer the
advantage to allow the use of ordinary water to slow down the neutrons,
a slowing required for the operation of the reactors when the proportion
of fissionable material is low. The fuel in the form of pellets of uranium
oxide UO2 is encapsulated inside long rods of zirconium. This metal is
transparent to neutrons, and replaced stainless steel. In some reactors,
the nuclear fuel, includes up to 1/3 of MOX a mixed oxide of uranium
and plutonium containing around 6% of fissile plutonium. The United
Kingdom has developed its own AGR (advanced gas-cooled reactor)
reactors. AGR are graphite-moderated reactors operating with slightly
enriched uranium, following the original Magnox reactors. Canada has
improved their natural uranium CANDU reactors. The Soviet Union
developed the RBMK reactors, involved in the Chernobyl accident,
followed by the VVER pressurized water reactor, similar to the PWR.
In 2008, more than 550 plants have been built worldwide, including
more than 110 that have been shut down. Their average age was over
20 years while 50 reactors were over 30 years and 9 over 40 years, and
shut-downs are foreseen to peak after 2015.

 Third Generation of reactors:

Designed in the 1990s, third-generation reactors are expected to
gradually replace the second-generation reactors currently in service.
France has chosen the EPR (European Pressurized water Reactor), of
which a protype is being built on the Flamanville site. By early 2018,
the Flamanville EPR was entering its final stage, with fuel loading. On
the same date, the Chinese Nuclear Safety Authority was preparing to
give the go-ahead for fuel loading in its first Taishan EPR. They are
often very large reactors, whose power reaches 1600 MWe in the case
of the EPR. The main players are competing for the future market:
advanced pressurized water reactors with AREVA for the EPR and
Westinghouse-Toshiba for the AP-1000; advanced boiling water
reactors with ABWR and US-Japan ESBWR from General-Electric-
Hitachi; or Russian reactors (VVER-1200) from Rosatom or Canadian
heavy water CANDU (ACR-1000). although second generation light
water reactors have an excellent record of safety, great efforts have
been made to further improve this safety and reduce the already very
low levels of radioactivity released into the environment. EPR reactors
have very advanced safety systems. A double thick concrete wall
ensures the containment of radioactive materials in case of accidental
fusion of the core. A hydrogen recombination system allows to avoid
hydrogen accumulation and therefore detonation. The protection
against earthquakes is improved. A significant novelty is a "corium
recuperator", a device that would reduce limit as much as possible the
consequences of a core fusion that would occur, despite the multiple
preventive measures. Safety is finally increased by the presence of
more than redundant security and control systems.
 Fourth Generation of reactors:
In 2001, ten countries-US, UK, Canada and others agreed to cooperate
on developing a new 'generation' of nuclear energy producing systems,
collectively known as 'Generation IV'. The European Commission
joined in 2003 and was followed by Russia and China in 2006. The
objective of this research is to design nuclear 'Generation IV' reactors
compatible with a sustainable development and acceptable to society.
These specifications require calls for much more efficient fuels,
improved safety, minimal production of radioactive waste and do not
lend to the diversion of fissile material. Within this initiative, six
designs of reactors have been selected - four of which are 'breeder'
reactors which can regenerate the fissile isotopes they burn. Some of
these will even be able to burn plutonium and other actinides left
behind, leading to the reduction of the stockpiles of these controversial
materials. One of these four breeder reactors would use thorium instead
of uranium 238, thereby producing very little plutonium and very few
actinides. A version of this reactor powered by fast neutrons would also
be able to burn up quantities of actinides produced by today water
reactors. Three of the four breeding reactors involve fast neutrons -
cooled down by gas, lead, or liquid sodium. The fourth uses thorium-
based fuel, and is remarkable in that the fuel is dissolved into the
soluble cooling liquid. In this case there are no more the problems of
the resistance to radiation of fuel rods. The materials may in principle
remain indefinitely in the reactor core. All heavy nuclei of thorium,
uranium, plutonium, … entering the reactor will come out "feet first"
because they would be ultimately destroyed by fission, whatever the
route taken. Another potentially interesting area of research is that of
high-temperature reactors – which are not 'breeders' but have a much
better thermal efficiency than conventional reactors.
2. Various turbines used in hydro power plants-
There are a number of different hydropower turbine types available that
are suited to different heads and flows. We are often asked which the
best turbine type is, but the answer is always that there isn’t a ‘best’ but
there is a ‘most appropriate’ for your particular site.
For each hydropower turbine type there will be a number of
manufacturers who provide turbines of differing performance and
quality. In our experience it is always worth buying a good quality
turbine with a proven track record, because these will perform day-in,
day-out reliably. Also most hydropower turbines have the concrete
structures designed around them and in many cases the main casing is
cast into the structure.
The table below summarises the main hydropower turbines that are
available and where you would use them. For the common turbines
types we have a lot more detail on the relevant page in the Hydro
Learning Centre, so click the link for more information.
Hydropower Typical Site Characteristics
Turbine Type

Archimedean Low heads (1.5 – 5 metres)Medium to high flows

Screw (1 to 20 m3/s).For higher flows multiple screws
are used.

Crossflow Low to medium heads (2 – 40 metres)

turbine Low to medium flows (0.1 – 5 m3/s)

Kaplan turbine Low to medium heads (1.5 – 20 metres)

Medium to high flows (3 m3/s – 30 m3/s)
For higher flows multiple turbines can be used.

Pelton/Turgo High heads (greater than 25 metres)

turbine Lower flows (0.01 m3/s – 0.5 m3/s)

Waterwheels Low heads (1 – 5 metres) – though turbines

often
more appropriate for higher heads
Medium flows (0.3 – 1.5 m3/s)

Francis No longer commonly used except in very large

turbines storage hydropower systems, though lots of
older, smaller turbines are in existence and can
be restored.
For older turbines : Low to medium heads (1.5 –
20 metres)
Medium flows (0.5 – 4 m3/s)
There are two main types of hydro turbines: impulse and reaction. The
type of hydropower turbine selected for a project is based on the height
of standing water—referred to as "head"—and the flow, or volume of
water, at the site. Other deciding factors include how deep the turbine
must be set, efficiency, and cost. Turbines convert the energy of
rushing water, steam or wind into mechanical energy to drive a
generator. The generator then converts the mechanical energy into
electrical energy. In hydroelectric facilities, this combination is called
a generating unit.

 Impulse Turbine:
The impulse turbine generally uses the velocity of the water to move
the runner and discharges to atmospheric pressure. The water stream
hits each bucket on the runner. There is no suction on the down side of
the turbine, and the water flows out the bottom of the turbine housing
after hitting the runner. An impulse turbine is generally suitable for
high head, low flow applications.

o Pelton:
A pelton wheel has one or more free jets discharging water into
an aerated space and impinging on the buckets of a runner. Draft
tubes are not required for impulse turbine since the runner must
be located above the maximum tailwater to permit operation at
atmospheric pressure.

A Turgo Wheel is a variation on the Pelton and is made

exclusively by Gilkes in England. The Turgo runner is a cast
wheel whose shape generally resembles a fan blade that is closed
 on the outer edges. The water stream is applied on one side, goes
across the blades and exits on the other side.

o Cross-flow:
A cross-flow turbine is drum-shaped and uses an elongated,
rectangular-section nozzle directed against curved vanes on a
cylindrically shaped runner. It resembles a "squirrel cage"
blower. The cross-flow turbine allows the water to flow through
the blades twice. The first pass is when the water flows from the
outside of the blades to the inside; the second pass is from the
inside back out. A guide vane at the entrance to the turbine directs
the flow to a limited portion of the runner. The cross-flow was
developed to accommodate larger water flows and lower heads
than the Pelton.

 Reaction Turbine:
A reaction turbine develops power from the combined action of
pressure and moving water. The runner is placed directly in the water
stream flowing over the blades rather than striking each individually.
Reaction turbines are generally used for sites with lower head and
higher flows than compared with the impulse turbines.

o Propeller:
A propeller turbine generally has a runner with three to six blades
in which the water contacts all of the blades constantly. Picture a
boat propeller running in a pipe. Through the pipe, the pressure
is constant; if it isn't, the runner would be out of balance. The
 pitch of the blades may be fixed or adjustable. The major
components besides the runner are a scroll case, wicket gates, and
a draft tube. There are several different types of propeller
turbines:

 Bulb Turbine:
The turbine and generator are a sealed unit placed directly in
the water stream.

 Straflo:
The generator is attached directly to the perimeter of the
turbine.

 Tube turbine:
The penstock bends just before or after the runner, allowing a
straight line connection to the generator.

 Kaplan:
Both the blades and the wicket gates are adjustable, allowing for a
wider range of operation. Austrian engineer Viktor Kaplan (1876-
1934) invented this turbine. It's similar to the propeller turbine, except
that its blades are adjustable; their position can be set according to the
available flow. This turbine is therefore suitable for certain run-of-river
generating stations where the river flow varies considerably.

Each Kaplan turbine at Brisay generating station weighs 300 tonnes...

That's the weight of 50 African elephants.
  Francis:
A Francis turbine has a runner with fixed buckets (vanes), usually nine
or more. Water is introduced just above the runner and all around it and
then falls through, causing it to spin. Besides the runner, the other
major components are the scroll case, wicket gates, and draft tube.
Water strikes the edge of the runner, pushes the blades and then flows
toward the axis of the turbine. It escapes through the draft tube located
under the turbine. It was named after James Bicheno Francis (1815-
1892), the American engineer who invented the apparatus in 1849.

 Kinetic:
Kinetic energy turbines, also called free-flow turbines, generate
electricity from the kinetic energy present in flowing water rather than
the potential energy from the head. The systems may operate in rivers,
man-made channels, tidal waters, or ocean currents. Kinetic systems
utilize the water stream's natural pathway. They do not require the
diversion of water through manmade channels, riverbeds, or pipes,
although they might have applications in such conduits.

4. Site selection parameter for Nuclear Power:

The purpose of characterisation of any particular area during the site

selection stage is to determine the suitability of particular site for setting
up a Nuclear Power Project (NPP). The site evaluation typically involves
the following stages-
 Selection stage:
One or more preferred candidate sites are selected after investigation of
a large region, rejection of unsuitable sites, and screening and comparison
of the remaining sites.
 Characterization stage:
This stage is further subdivided into:
o Verification, in which the suitability of the site to host a nuclear
power plant is verified mainly according to predefined site exclusion
criteria;
o Confirmation, in which the characteristics of the site necessary for
the purposes of analysis and detailed design are determined.
 Pre-operational stage:
Studies and investigations from the previous stages are continued to
refine the assessment of site characteristics. Data obtained from site allow
a final assessment of simulation models used in the ultimate design of
foundation and superstructure as well.

 Operational stage:
Selected investigations are pursued over the lifetime of the plant, to
ensure that the variation of engineering properties are not varying
significantly during the operating life of the plant.

Following are the important desirable aspects for a favourable

NPP site:
 Ground water table should be low to minimize uplift pressures on
buildings.
 Future development plan around the area is minimal.
  Industries handling toxic chemicals and waste are beyond 10km
from the site.
 Railway sidings, and major road transport depots are beyond 10km
from the site.
 Availability of construction materials, are well identified.
 Basic infrastructural facilities are available to start pre-project
activities
 Easier availability of construction materials and access to fetch them
to site
 Access to site with respect to movement of persons and ODCs.
 Identified nearest highway, rail, sea and air links
 Rocky and leak tight founding media for solid waste management
facilities.

In evaluating the suitability of a site, following are the major

aspects that need to be considered, and discussed in detail-
 Effect of external events (natural and man-induced) on the plant.
 Effect of plant on environment and population

External Natural Induced Events:

Earthquake being one of the governing criteria for acceptance or rejection
of a candidate site, the same is dealt in details, in the later part of
discussion.

Flooding is one of the important natural phenomenon for the selection of

site. Hence, past history of the flooding at site is collected. The site should
not have experienced any submergence.
External Man-Induced Events:
In order to safeguard the NPP from man-induced event, the sites are
located away from the zone of human activity at a minimum distance,
designated as Screening Distance Value (SDV). Accepting or rejecting a
site is decided based on this evaluation.
 Any information concerning the frequency and severity of those
important man-induced events are collected and analyzed for
reliability, accuracy and completeness.
 In addition, industries handling toxic chemicals and waste, railway
sidings, or road transport depots within 10km from the site are not
allowed, to rule out of the possibility and severe events due to any
unforeseen circumstances. Out of the listed man-induced events,
such as, Aircraft Crash, Chemical Explosions and Toxic Gas
Releases, Oil Slick, blasting Operation, Mining, Drilling and Water
Extraction form important man-induced events.

Cooling water requirements:

NPP need adequate quantities of assured supply of cooling water of
acceptable quality, for condenser cooling and process water cooling, and
other safety related requirements. The available quantity of cooling water
on long term basis, for the design life of the plant governs the cooling
water system of the plant.
 For a coastal site, large volume of sea water can be utilized for once-
through condenser cooling water systems. However, for an inland
site, closed loop cooling water system is be suitable, considering the
 minimum requirement of water and least damage to ecological
system and environment.
 Loss of heat sink is one of the safety concern for the plant. Any
breach / failure of downstream dam (due to an earthquakes or floods)
may result in this condition and hence evaluated during initial stage
itself. If the probability and consequences of this event cannot be
reduced to acceptable levels, then such events shall be included in
the design basis for the plant, and suitable alternate heat sink is
established.

Effect of plant on environment and population:

The general principle in the siting of nuclear power plants is to have the
facilities in a sparsely populated area and far away from large population
centres.
Lower population density in the region will help in achieving reduced
population dose, and help in ensuring effective implementation of
emergency measures and planning in case of an accident and easier to
implement to a smaller population group.
Population characteristics, its distribution in the region, including data on
permanent residents, transient and seasonal population, present and future
uses of land and water resources, cattle and livestock, agricultural
produce, fish catches on annual basis, and other relevant particulars
including any special characteristics which may influence the potential
consequences of radiological releases to the environment are studied.
A nuclear power plant site extends to 1.5km all around from the centre of
the facility where only power plant related activities are allowed as an
administrative rule.
The nuclear facility is to be surrounded by an emergency planning zone,
about 30 kms from the facility covered by detailed rescue plans for public
protection. Special attention shall be paid to the characteristics of the site's
surroundings, such as recreational settlements.
Availability of transportation network, means of communication, etc. are
of significance during any emergency condition, hence these aspects are
reviewed.

Implementation of emergency procedures:

In order to plan and implement emergency measures under accident
conditions the characterisation of land use is carried out, considering the
following,
 Extent of agriculture land, principal food products and their yields.
 Extent of dairy farming and yield.
 Extent of drinking water demand and its sources in the near vicinity
of the plant.
 Extent of easy access for food supply from outside.
 Studies on all water bodies in the vicinity of the site and their
outflow characteristics.
 Use of water for drinking, irrigation, fishing, agriculture, and
industrial use.
 Information on groundwater (the groundwater regime, locations and
characteristics of the hydrological units, physical chemistry of the
water).
Hence, proposed site is thoroughly investigated and characterised to
arrive at geo-technical parameters for design of structures. These
investigations are normally carried out in two phases.