nuclear power plant

Introduction to Nuclear Power

• It is the use of Nuclear Fission reactions to Generate Power

• Nuclear energy is the world's largest source of emission-free energy

• Most efficient Power Source per Unit Area• Used in 31 Countries (approx 441 reactors)1

• Accounts for about 16% of all electricity generated world wide (approx 351 Gigawatts)

1. 2003 Figures


The major benefits of Nuclear Power include:

• No Green House Gas emissions• No Air Pollutants such as CO,SO2,NO,Hg or

particulate matter, thus ensuring “Nil” contribution to Acid Rain, Global Warming etc.

• Relatively low risk of “Work Related Injury”• Efficiency per capita fuel unit is very high


Developed Countries are shifting to Nuclear Power


US 97

North America Region 109

France 63

Germany 21

U. K. 12

Western Europe Region 126

Japan 44

Asia Region 66

Eastern Europe Region 11

Former Soviet U. Region 34

World Nuclear Power Production in Gigawatts

Introduction to Nuclear PowerIndia Nuclear Power Production in MW

Plants under operation MWe

14 reactors at 6 sites viz., Tarapur, Rawatbhata, Kalpakkam Narora, Kakrapar and Kaiga

2720

Plants under construction 2x500 at Tarapur 1000

Plants likely to commence in the current financial year 2x220, 2x1000, 1x500 2940

Future Plans 2x220,4x500,10x500,6x1000 13440

Total 20100

NPP IN INDIA

Uranium mining- World (4,7)

Uranium mining- India(3)

Advantages over coal

• One gram of fissionable uranium can produce a

million times more heat than one gram of coal.

• For 400MW of electricity, only 20 kg of uranium

fuel is required per day. In comparison, a coal

burning thermal power station of the same

capacity would require about 4000 tonnes of

coal daily

Disadvantages• The problem of radioactive waste is still an unsolved one.

• High risks

• Nuclear power plants as well as nuclear waste could be

preferred targets for terrorist attacks.

• Radioactive waste is produced can be used for the

production of nuclear weapons.

• Uranium is a scarce resource

The Underlying Principle

“Nuclear Fission”• In Physics, “fission” is a nuclear process, i.e., it

occurs in the nucleus of an atom. Fission occurs when the Nucleus splits into two or more smaller nuclei plus some by-products. These by-products include free neutrons and photons (usually gamma rays). Fission releases substantial amounts of energy (the strong nuclear force binding energy).

• The use of this energy for generation of electricity is the essence of nuclear power generation.


• Radioactivity was discovered by Sir James Chadwick (1932) • Later Enrico Fermi experimented and Physicist Lise Meitner

and Otto Frish discovered Chain Reactions• Chicago Pile

– The first controlled chain reaction was conducted in December 1942, resulted in heat Generation of 2 kW using Uranium

• The Manhattan Project:

– Atomic bomb – Nagasaki & Hiroshima


• Fission can be induced by several methods, including bombarding the nucleus of a fissile atom with a free neutron moving at the right speed

• Neutron + U-235 --> fission products + more neutrons + energy

• The process releases a lot of energy compared to chemical reactions. • Energy released by a fission event is approximately 200 MeV.

Nuclear fission process

How does fission work

• A neutron hits a uranium nucleus.

• The nucleus becomes unstable and needs to release

energy.

• The nucleus breaks releasing energy, neutrons and 2

smaller atoms.

• The 2 smaller atoms formed are called fission fragments.

• When the neutrons are released during fission,

they go on to hit 2/3 other uranium nuclei.

• This continues and is called a chain reaction

• In a nuclear reactor the chain reaction is controlled.

• As the control rods are removed the chain reaction

increases, and if we want to slow the reaction

control rods are inserted.

Block Schematic for Nuclear Power Plant

A Nuclear Power Plant is basically a Thermal Power Plant in which steam is produced in a Nuclear Reactor rather than in a Conventional Boiler

Nuclear Power Plant - Working

Components of a Nuclear Power Plant

Basic Reactor Model

Pump

2. M

oder

ator

1. F

uel

3. C

ontr

ol r

od

5. S

team

gen

erat

or

4. Coolant

6.

8.

7.

Turbine

Generator

Major components of Nuclear ReactorTYPE DESCRIPTION

Fuel These are Fissile Elements like U235’ PU239 arranged in the form of Bundled rods

Control Rods /Nuclear Poison

A control rod is of chemical elements capable of absorbing many neutrons without fissioning themselves (E.g. silver, indium and cadmium)Control rods are usually inserted into guide tubes within a fuel element. A control rod is removed from or inserted into the central core of a nuclear reactor in order to control the neutron flux — increase or decrease the number of neutrons which will split further uranium atoms. This in turn affects the thermal power of the reactor, the amount of steam produced, and hence the electricity generated.

Moderator Moderator is a medium which reduces the speed of fast neutrons, thereby turning theminto thermal neutrons capable of sustaining a nuclear chain reaction involving U235.Commonly used moderators include regular (light) water, used in roughly 75% of the world‘s reactors, solid graphite (20%) and heavy water (D2O) (5%). Beryllium has been used in some experimental reactor types, and hydrocarbons have been suggested as a possibility.

Coolant Coolant is a medium used to transfer heat generated in the Nuclear Reactor’s core to the heat exchanger to produce Steam for driving Steam Turbines. Light Water, Heavy Water, Carbon Dioxide, Nitrogen, Molten Sodium etc. are some commonly used coolants

Nuclear Power Reactor - Fuel

Uranium Fuel Cycle

Types of Nuclear Reactor

1. The Boiling Water Reactor (BWR): This is the simplest of all reactors. Water absorbs heat from the reactions in the core and is directly driven to the turbines. After condensing the water is pumped back to the reactor core

2. Pressurized water reactors, (PWR): In this type of reactor, the heat is dissipated from the core using highly pressurized water (about 160 bar) to achieve a high temperature and avoid boiling within the core. The cooling water transfers its heat to the secondary system in a steam generator

3. Pressurized Heavy Water Reactor (PHWR), : In this type of reactors, fuel bundles are inserted into the Heat Exchanger where a heavy water moderator is circulated to provide cooling in addition to moderating neutrons. This heavy water is then circulated to the steam generator to transfer its heat and then pumped back to the reactor. The steam is a secondary circuit as above and is used to drive a turbine assembly before condensing and re-use

4. The Gas Cooled Reactor (GCR) : It uses CO2 gas to remove heat from the core. This is then piped through the steam generator where heat is removed from the gas and it can then be re-circulated to the reactor. As usual steam generated is used to drive the turbine and generate electricity, condensed then recirculated. Graphite is used as a moderator to allow energy production by un-enriched uranium.

5. The Light Water Graphite Reactor (LWGR): Here Graphite replaces heavy water as moderator. Light water is used to remove heat from the core for transfer to steam drums. The steam evolved in these is used subsequently to power turbines.

6. The Fast Breeder Reactor (FBR): It uses a Plutonium fuel rather than Uranium. The Pu is surrounded by rods of U-238 which absorb neutrons and are transmitted into Pu-239 which undergoes fission to generate energy. As the plutonium in the core becomes depleted it creates or breeds more plutonium from the Uranium around it.

Nuclear Waste management• Radioactive wastes from the nuclear reactors

and reprocessing plants are treated and stored at each site

• High level waste is currently kept in storage facilities and will finally be put into specially engineered underground repositories.

• Research on final disposal of high-level and long-lived wastes in a geological repository is in progress .

Technology advancements in nuclear power reactors

Generation II reactor

• A generation II reactor is a design classification

for a nuclear reactor, and refers to the class of

commercial reactors built up to the end of the

1990s.

• Prototypical generation II reactors include the

PWR, CANDU, BWR, AGR, and VVER.

• Generation II reactor designs generally had an

original design life of 30 or 40 years.

(2,5)

Generation III reactors

• Advanced Boiling Water Reactor (ABWR) — A GE design that

first went online in Japan in 1996.

• Advanced Pressurized Water Reactor (APWR) — developed by

Mitsubishi Heavy Industries.

• Enhanced CANDU 6 (EC6) — developed by Atomic Energy of

Canada Limited.

• VVER-1000/392 (PWR) — in various modifications into AES-91

and AES-92.

(2,5)

Generation IV reactor• Generation I V reactors(Gen IV) are a set

of theoretical nuclear reactor designs currently being researched.

• commercial construction before 2030, with the exception of a version of the Very High Temperature Reactor (VHTR) called the Next Generation Nuclear Plant (NGNP).

• Research into these reactor types was officially started by the Generation IV International Forum (GIF)

(2,5)

Goals of Gen IV• Improve nuclear safety.

• Improve proliferation Resistance.

• Minimize waste and natural resource

utilization.

• Decrease the cost to build and run such

plants.

• Increase life time of nuclear reactors.

Reactor types

Thermal reactors

• 1. Very-high-

temperature reactor

(VHTR)

• 2. Supercritical-water-

cooled reactor

(SCWR)

• 3. Molten-salt reactor

(MSR)

Fast reactors

• 1. Gas-cooled fast

reactor (GFR)

• 2. Sodium-cooled fast

reactor (SFR)

• 3. Lead-cooled fast

reactor (LFR)

• VHTR:- Concept uses a graphite-moderated core with a once-

through uranium fuel cycle, using helium or molten salt as the

coolant.

• SCWR:- Concept that uses supercritical water as the working fluid.

It could operate at much higher temperatures than both current

PWRs and BWRs.

• MSR:- Nuclear reactor where the coolant is a molten salt. Nuclear

fuel dissolved in the molten fluoride salt as UF4 or ThF4.

• FR:- Fast-neutron spectrum and closed fuel cycle. The reactor is helium-cooled. Based on Brayton cycle gas turbine.

• SFR:- Builds on two closely related existing projects, the liquid metal fast breeder reactor and the Integral Fast Reactor.

• LFR:-fast-neutron-spectrum lead or lead/bismuth eutectic (LBE) liquid-metal-cooled reactor with a closed fuel cycle.

Advantages

• Nuclear waste that lasts a few centuries

instead of millennia.

• 100-300 times more energy yield from

the same amount of nuclear fuel.

• The ability to consume existing nuclear

waste in the production of electricity.

• Improved operating safety.

Facts of disaster• 6-7 % heat still decay out from core even in shutdown

condition which is must to remove.

• In emergency shutdown back up gens ets take 60-75 seconds

to achieve full load.

• Test was conducted with night shift workers instead of trained

day shift workers.

• Production of xenon reduced the stable power level required

for test causing withrawal of more control rods.

• Human error by Er. Toptunov who inserted control rods in the

core.

• To increase power output control rods were removed

instantly in large number causing rise in temperature and

hence massive power spike occurred which damaged the

fuel rods also .

• As power was around 700 mw actual test begins and

turbine generator went off and ext. gensets resumed the

working of ECCS.

• Due to some alarm triggering 4 of 8 main circulation

pumps went off air causing serious steam voids in coolant

process thus increasing the temperature of core.

• To reduce the increased power output control rods

are allowed to get in the core which was already

damaged. So only1/3 part of rods was in the core.

• Consequently power output rose up to 33GW(10

times of peak output).

• Hydrogen blast took place first blowing off the

secondary containment and then flammable

graphite blasted with huge impact involving

radioactive core also.

Fukushima Daiichi Event

Unit 1 439 MW

11 March 2011

(2,5)

Fukushima Event The Fukushima nuclear facilities were damaged in a

magnitude 8.9 earthquake on March 11 (Japan time), centered offshore of the Sendai region, which contains the capital Tokyo. Plant designed for magnitude 8.2 earthquake. An

8.9 magnitude quake is 7 times in greater in magnitude.

Serious secondary effects followed including a significant tsunami, significant aftershocks and a major fire at a fossil fuel installation.

The Fukushima nuclear facilities were damaged in a magnitude 8.9 earthquake on March 11 (Japan time), centered offshore of the Sendai region, which contains the capital Tokyo. Plant designed for magnitude 8.2 earthquake. An

8.9 magnitude quake is 7 times in greater in magnitude.

Serious secondary effects followed including a significant tsunami, significant aftershocks and a major fire at a fossil fuel installation.

Waste ManagementDisposal of waste of nuclear power plant

Nuclear power plant wastes can be classified

• Low level radioactive waste• High level radioactive waste

Waste Management

• It includes cooling water pipes,radiation suits,discarded fuel elements cans and gloves

• Low level radioactive waste are easy to dispose off

• Low level radioactive wastes are stored under sea bed and large stable geologic formations on land

Low level radioactive waste

Waste ManagementHigh level radioactive waste

• It includes materials from the core of the nuclear reactor.• Plutonium, Uranium, Control rods and other radioactive

elements made during fission• Difficult to dispose

Waste Management

• These radioactive materials are stored in shielded storage vaults

• Shielded vaults are stored in deep salt mines• Sometimes high level nuclear waste can be sunk to the

bottom of the sea & oceans• Fired into the sun or into a long term stable orbit.• Transmutation

High level radioactive waste disposal

• Necessary to guard personnel and delicate instruments• Materials used are lead, Concrete, Steel and cadmium• Water is used to slow down fast neutrons• Boron and steel are employed for absorption of thermal

neutrons• Heavy metals like lead is required to act as thermal shield and

to absorb gama rays

Waste ManagementShielding of Nuclear reactor

nuclear power plant

Engineering