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NUCLEAR POWER PLANT

A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR


• Define and apply the concepts of Define and apply the concepts of mass numbermass number, , atomic numberatomic number, , and and isotopesisotopes..

• Define and apply concepts of Define and apply concepts of radioactive decayradioactive decay and and nuclear reactionsnuclear reactions..

• Calculate the Calculate the mass defectmass defect and the and the binding energy per nucleonbinding energy per nucleon for a for a particular isotope.particular isotope.

• State the various State the various conservation lawsconservation laws, and discuss their application for , and discuss their application for nuclear reactions.nuclear reactions.


All of matter is composed of at least three fundamental particles (approximations):

ParticleParticle Fig.Fig.SymSym MassMass ChargeCharge SizeSize

The mass of the proton and neutron are close, but they are about 1840 times the The mass of the proton and neutron are close, but they are about 1840 times the mass of an electron.mass of an electron.

Electron Electron ee-- 9.11 x 10 9.11 x 10-31-31 kg kg -1.6 x 10-1.6 x 10-19 -19 C C

Proton Proton pp 1.673 x 101.673 x 10-27-27 kg +1.6 x 10 kg +1.6 x 10-19 -19 C 3 fmC 3 fm

Neutron Neutron nn 1.675 x 101.675 x 10-31-31 kg kg 0 0 3 fm3 fm


Beryllium AtomBeryllium Atom

Compacted nucleus:Compacted nucleus:

4 protons4 protons

5 neutrons5 neutrons

Since atom is electri-cally Since atom is electri-cally neutral, there must be 4 neutral, there must be 4 electrons.electrons.

4 electrons4 electrons


A A nucleonnucleon is a general term to denote a nuclear particle - that is, either a is a general term to denote a nuclear particle - that is, either a proton or a neutron.proton or a neutron.

The The atomic number atomic number ZZ of an element is equal to the number of protons in the of an element is equal to the number of protons in the nucleus of that element.nucleus of that element.

The The mass number mass number AA of an element is equal to the total number of nucleons of an element is equal to the total number of nucleons (protons + neutrons).(protons + neutrons).

The mass number A of any element is equal to the sum of the atomic number Z and the number of neutrons N :

A = N + Z


A convenient way of describing an element is by giving its mass number and A convenient way of describing an element is by giving its mass number and its atomic number, along with the chemical symbol for that element.its atomic number, along with the chemical symbol for that element.

A Mass numberZ Atomic numberX Symbol

For example, consider beryllium (Be): 94Be


Lithium AtomLithium Atom

N = A – Z = N = A – Z = 7 - 3 7 - 3

A = A = 7; Z = 3; 7; Z = 3; NN = ? = ?

Protons: Z = 3Protons: Z = 3

neutrons: neutrons: NN = 4 = 4

Electrons: Electrons: Same as ZSame as Z

73 Li


IsotopesIsotopes are atoms that have the same number of protons ( are atoms that have the same number of protons (ZZ11= Z= Z22), but a ), but a different number of neutrons (N). (different number of neutrons (N). (AA11 A A22))

Helium - 4Helium - 4

42He

Helium - 3Helium - 3

32He Isotopes of Isotopes of

heliumhelium


Because of the existence of so many isotopes, the term Because of the existence of so many isotopes, the term elementelement is sometimes confusing. The term is sometimes confusing. The term nuclidenuclide is better. is better.

A nuclide is an atom that has a definite mass number A and Z-number. A list of nuclides will include isotopes.

The following are best described as nuclides:The following are best described as nuclides:

32He

42He 12

6C136C


One One atomic mass unitatomic mass unit (1 u)(1 u) is equal to one-twelfth of the mass of the is equal to one-twelfth of the mass of the most abundant form of the carbon atom--most abundant form of the carbon atom--carbon-12carbon-12..

Atomic mass unit: 1 u = 1.6606 x 10-27 kg

Common atomic masses:

Proton: 1.007276 u Neutron: 1.008665 u

Electron: 0.00055 u Hydrogen: 1.007825 u

2 8; 3 x 10 m/sE mc c


Recall Einstein’s equivalency formula for m and E:Recall Einstein’s equivalency formula for m and E:

The energy of a mass of 1 u can be found:The energy of a mass of 1 u can be found:

EE = (1 u) = (1 u)cc22 = = (1.66 x 10(1.66 x 10-27 -27 kg)(3 x 10kg)(3 x 1088 m/s) m/s)22

E = 1.49 x 10-10 J OrOr E = 931.5 MeV

When converting amu to When converting amu to energy:energy: 2 MeV

u931.5 c

NUCLEAR FUELNuclear fuel is any material that can be consumed to derive nuclear energy. The

most common type of nuclear fuel is fissile elements that can be made to undergo

nuclear fission chain reactions in a nuclear reactor

The most common nuclear fuels are 235U and 239Pu. Not all nuclear fuels are used in

fission chain reactionsA.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR

NUCLEAR FISSIONWhen a neutron strikes an atom of uranium, the

uranium splits ingto two lighter atoms and releases heat simultaneously.

Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as

electromagnetic radiation and as kinetic energy of the fragments


NUCLEAR CHAIN REACTIONS A chain reaction refers to a process in which neutrons released

in fission produce an additional fission in at least one further

nucleus. This nucleus in turn produces neutrons, and the process

repeats. If the process is controlled it is used for nuclear power

or if uncontrolled it is used for nuclear weapons


U235 + n → fission + 2 or 3 n + 200 MeV

If each neutron releases two more neutrons, then the number of fissions doubles each

generation. In that case, in 10 generations there are 1,024 fissions and in 80 generations about 6

x 10 23 (a mole) fissions.



Nuclear Fission

Nuclear FusionThe combining of atomic nuclei to form a larger atom is called fusion

Nuclear fusion occurs in the sun where hydrogen atoms fuse to form helium


4 H + 2 0 e- He + energy11

-1 24


Nuclear Fusion

A chain reaction can only occur if the starting material has enough mass to sustain a chain reaction. This amount is called the critical mass.

Nuclear Fission is what occurs in Nuclear Reactors and Atomic Bombs.

The Nuclear reactor is a controlled fission reaction, the bomb is not.


Review

Nuclear fission:

A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process

Nuclear fusion:

Several small nuclei fuse together and release energy.


Piecing Together a Reactor1. Fuel2. Moderator3. Control Rods4. Coolant5. Steam Generator6. Turbine/Generator7. Pumps8. Heat Exchanger



90U (2 ppm)4.5∙109 yr

90Th (6 ppm)14.05∙109 yr

238 23992 94U Pu

99.5% 235

92 U0.7%

Fuels

Natural Elements

233U7∙108 yr

Artificial Nuclides

239Pu24∙103 yr


Between thorium (Z=90) and bismuth (Z=83), the isotope with the longest half-life is 226Ra (T½=1600 years), and therefore there are no fuel candidates, quite apart from the issue of fissionability. Uranium and Thorium are the only natural elements available for use as reactor fuels. In addition, 233U and 239Pu can be produced from capture on 232Th and 238U in reactors. Of fissile materials, only U is both fissile and found in nature in useful amounts.


Fuels Few ”natural” nuclides that can be used as reactor fuels

Uranium (Z=92). This is the main fuel in actual use, especially 235U which is fissile. In addition, 238U is important in reactors, primarily as a fertile fuel for 239Pu production, and 233U could be used as a fissile fuel, formed by neutron capture in 232Th.

Protactinium (Z=91). The longest-lived isotope of Pa ( 231Pa) has a half-life of 3.3 x104 yr, and therefore there is essentially no Pa in nature. Further, there is no stable A =230 nuclide that could be used to produce 231Pa in a reactor.

Thorium (Z=90). Thorium is found entirely as 232Th, which is not fissile (for thermal neutrons). It can be used as a fertile fuel for production of fissile 233U.


Moderators

1H

Widely used

H2O or D2O

2He

Not used

Gas → Press.

3He absorbs

3Li

Not used6Li

absorbs

4Be

Was used

9Be toxic, expensiv

e

5B

Impossible10B

absorbs

6C

Widely used Must be

pure

No use to consider Z > 6

Only D2O and C can be used with Unat


Moderators

Hydrogen (Z=l). The isotopes 1H and 2H are widely used as moderators, in the form of light (ordinary) water and heavy water, respectively.

Helium (Z=2). The isotopes 3He and 4He are not used, because helium is a gas, and excessive pressures would be required to obtain adequate helium densities for a practical moderator. Moreover 3He absorbs neutrons very strongly (see lecture about detectors)

Lithium (Z=3). The isotope 6Li (7.5% abundant) has a large neutron-absorption cross section, making lithium impractical as a moderator.

Beryllium (Z=4). 9Be has been used to a limited extent as a moderator, especially in some early reactors. It can be used in the form of beryllium oxide, BeO. Beryllium is expensive and toxic.

CoolantsFunction – transfer heat

Objective: power density, temperatureLimitations: in PWR: below saturation T,

Tin=293, Tout = 315; in LMFBR, ΔT=140; in HTGR, ΔT=500.

After shutdownCoolant is either gas or liquid: H2O, D2O,

He, CO2, Na, Na-K, Pb, Pb-Bi.Coolant is moderatorClassification: LWR, HWR, GR, LMR



Coolants

•The main function of the coolant in any generating plant is to transfer energy from the hot fuel to the electrical turbine, either directly or through intermediate steps

•. During normal reactor operation, cooling is an intrinsic aspect of energy transfer.

• In a nuclear reactor, cooling has a special importance, because radioactive decay causes continued heat production even after the reactor is shut down and electricity generation has stopped.

• It is still essential to maintain cooling to avoid melting the reactor core, and in some types of reactor accidents (e.g., the accident at Three Mile Island) cooling is the critical issue.

•The coolant can be either a liquid or a gas. For thermal reactors, the most common coolants are light water, heavy water, helium, and carbon dioxide.

•The type of coolant is commonly used to designate the type of reactor. Hence, the characterization of reactors as light water reactors (LWRs), heavy water reactors (HWRs), and gas-cooled reactors (GCRs).


• Control materials are materials with large thermal neutron-absorption cross sections, used as controllable poisons to adjust the level of reactivity.

• They serve a variety of purposes:

• To achieve intentional changes in reactor operating conditions, including turning the reactor on and off

• To compensate for changes in reactor operating conditions, including changes in the fissile and poison content of the fuel

• To provide a means for turning the reactor off rapidly, in case of emergency


PWR. The pressurized water reactor accounts for almost two-thirds of all capacity and is the only LWR used in some countries, for example, France, the former Soviet Union, and South Korea.

BWR. The boiling water reactor is a major alternative to the PWR, and both are used in, for example, Sweden, the United States and Japan.

PHWR. The pressurized heavy water reactor uses heavy water for both the coolant and moderator and operates with natural uranium fuel. It has been developed in Canada and is commonly referred to as the CANDU. CANDU units are also in operation in India and are being built in Romania and South Korea.

323232

Classification of reactorsClassification of reactorsClassification of reactors by purpose:

Power reactors

Research reactors

Material test reactors

Propulsion reactors

Production reactors

Space reactors

Radiation Protection Workshop-Cairo Univ.- NSPA - 15 Jan - 2 Feb, 201218 January 2012

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Classification of reactors (Cont)

Classification of reactors by neutron spectrum:

Thermal spectrumFast spectrum


343434

Classification of reactors (Cont)Classification of reactors by coolant

Light water

Heavy water

Gas

Liquid metal


353535

Classification of reactors (Cont)Classification of reactors by moderator:

Light water reactors

Heavy water reactors

Graphite moderated reactors


Basic Diagram of a PWR

A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR http://www.nrc.gov/

Boiling Water Reactor (BWR)Direct Boiling10% Coolant =

SteamSimilar Fuel to PWRLower Power

Density than PWRCorrosion Product

Activated in CoreHigher Radiation

Field

GE – ABWR1350 MWe

(3926 MWt)UO2 Fuel60 – yr Service LifeInternalized Safety

and Recirculation Systems


383838


Classification of reactors by fuel type


393939

Classification of reactors (Cont)Classification of reactors by fertile fuel type


404040


Classification of reactors by fissile fuel balance:

Converter reactors

Breeder reactors

Fuel self-sustained (sustaining) reactors


Basic Diagram of a BWR

A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR http://www.nrc.gov/


Classifications of Reactors

Thermal Reactors and Fast Reactors Reactors designed to operate with slow, thermalized neutrons (to take advantage of increase of cross-sections with neutron energy decrease) are termed thermal reactors. However, it is also possible to operate a reactor with ”fast” neutrons, at energies in the neighborhood of 1 MeV or higher. These reactors are called fast-neutron reactors or just fast reactors. The only prominent example of a fast reactor is the liquid-metal breeder reactor.

Homogeneous and Heterogeneous Reactors All reactors used today for power generation are HETEROGENEOUS, i.e. fuel, coolant and/or moderator are physically different entities with non-uniform and anisotropic composition.

STEAM GENERATORS Steam generators are heat exchangers used to

convert water into steam from heat produced in a nuclear reactor core.

Either ordinary water or heavy water is used as

the coolant.


STEAM TURBINE A steam turbine is a mechanical device that

extracts thermal energy from pressurized steam, and converts it into useful mechanical

Various high-performance alloys and superalloys have been used for steam generator

tubing.


COOLANT PUMPThe coolant pump pressurizes the coolant to

pressures of the orderof 155bar.

The pressue of the coolant loop is maintained almost constant with the help of the pump and a

pressurizer unit.


FEED PUMPSteam coming out of the turbine,

flows through the condenser for condensation and recirculated for the

next cycle of operation.

The feed pump circulates the condensed water in the working fluid

loop.A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR

CONDENSERCondenser is a device or unit which is used to

condense vapor into liquid.

The objective of the condenser are to reduce the turbine exhaust pressure to increase the

efficiency and to recover high qyuality feed water in the form of condensate & feed back it to the

steam generator without any further treatment.


COOLING TOWERCooling towers are heat removal devices used

to transfer process waste heat to the atmosphere.

Water cirulating throughthe codeser is taken to the cooling tower for cooling and reuse


ADVANTAGES Nuclear power generation does emit relatively low amounts of carbon dioxide (CO2). The emissions of

green house gases and therefore the contribution of nuclear power plants to global warming is therefore

relatively little.

This technology is readily available, it does not have to be developed first.

It is possible to generate a high amount of electrical energy in one single plant


DISADVANTAGES The problem of radioactive waste is still an unsolved

one.

High risks: It is technically impossible to build a plant with 100% security.

The energy source for nuclear energy is Uranium. Uranium is a scarce resource, its supply is estimated to last only for the next 30 to 60 years depending on

the actual demand.


DISADVANTAGESNuclear power plants as well as nuclear waste could be preferred targets for terrorist attacks..

During the operation of nuclear power plants, radioactive waste is produced, which in turn can

be used for the production of nuclear weapons.


What is a CANDU reactor?

CANDU stands for Canada Deuterium Uranium. Deuterium is another name for heavy water, which occurs naturally in all bodies of water. In Lake Huron, it occurs one part in every 7,000. Once extracted, heavy water is 10 per cent heavier than ordinary water due to an extra neutron in its nucleus giving it added weight.

Developed in Canada, the first CANDU reactor came on line in 1962. There are now 22 CANDU reactors in Canada and 17 abroad.


CANDU Reactor

Heavy-water moderatorNatural-uranium dioxide

fuelPressure-tube reactorCANDU is a PHWR


CANDU Natural-uranium fuel Heavy-water moderator & coolantCoolant physically separated from moderator Small/Simple fuel bundle

PWR Enriched-uranium fuel Light-water moderator/coolant No separation of coolant from moderator Large, more complex fuel assembly

Where were the first nuclear power stations sited and when?Issues:Issues:

distance from urban centresaccess to national gridgood water supply for coolingabsence of natural hazardstransport linksproximity to both civil airports and military

installations


Distance from urban centres and access to the national gridEarly on, everyone knew that radiation was dangerous.

Most of those alive could remember what happened to Japan when the H-bombs were dropped and the devastating after effects.

So long as there were concerns about the safety of nuclear power plants, it was felt that it was essential that they were as remote as possible from the big cities.

However, in terms of cost and efficiency this had a downside.

Remote areas would not have the heavy duty transmission lines necessary to take all the electricity generated by the power station to the grid.

The only feasible way to get it there was by carrying it in huge ugly pylons that stretch far over the country in a visually intrusive way.

These remote areas were often near National Parks. The National parks did not appreciate their presence.


Distance from urban centres and access to the national grid

But generally the overhead power transmission is very reliable, although overhead power lines are vulnerable to: lightning strikes; high winds; heavy snowfall.

But the cost of burying and the difficulty in repairing underground cables if things did go wrong meant that this means of transmitting electricity almost impossible.

Another problem is that electricity does loose power over distance. So the electricity from these remote sites did not provide as much energy to the public as electricity from a power station nearer to centres of population.

So once a design was tested and deemed to be safe, the inclination was to build the ones that came after closer to centres of population. This cut down on the number and cost of transmission lines and was a more efficient use of the electricity.

But when any new technology was developed, the tendency was again to go for the remoter sites.


Good water supply for cooling

Because of the heat generated by the process, often more than by coal or gas fired stations, there was a need for vast quantities of water to carry out the cooling process.

Cooling towers had been used for coal fired power stations.

Bigger, tall more intrusive versions would have required for nuclear power, provide the site was near enough to a good water supply, like a large river for example.

The other solution was to put the power station near the sea, where no cooler tower would be needed. The sea would always bring in more water to cool the steam down.


Transport links

For both the building and maintenance of nuclear power stations, good transport links were a priority.

All nuclear power stations have a rail link, often a side line from a main line not too far away and very often the roads have had to be reinforced to take the heavy loads that enter and leave the power station.

These are massive structures to build, which need very heavy machinery and vast quantities of raw materials to build them.

Once on-line, the fuel rods which are radioactive have to be changed regularly. This was the main use of the railway. It was not acceptable to take these in and out by road as there could accidents or even terrorism attacks were considered.


Proximity to both civil airports and military installationsWhilst the buildings that house the nuclear

power stations are extremely strong, aircraft crashing into them or stray shells falling nearby was not something the authorities wished to happen.

So military training grounds nearby was a definite NO.

As 75% of all accidents to planes happen close to take-off or landing, nuclear power plants could not be sited under the landing or take-off paths of major airports.


Absence of natural hazardsRelease of radio active materials was the main

worry, so the buildings containing the process could not be allowed to be damaged by natural hazards, such as earthquakes, fault lines, floods.

In addition places which liable to high winds, extremes of temperature or drought, all of which in excess cause land movements also had to be watched out for.

However, now that sea levels are rising due to global warming, this could be problems for those power stations built near the sea.



•Recently nuclear power has entered many discussions as world energy needs rise and oil reserves diminish. •Most opponents of nuclear power point to two main arguments: meltdowns and nuclear waste.•Nuclear waste is any form of byproduct or end product that releases radioactivity.•How to safely dispose of nuclear waste is pivotal for the continued operation of nuclear power plants, safety of people living around dump sites, and prevention of proliferation of nuclear materials to non-nuclear states.

ClassificationsNuclear waste is segregated into several

classifications.Low level waste is not dangerous but

sometimes requires shielding during handling.Intermediate level waste typically is chemical

sludge and other products from reactors.High level waste consists of fissionable

elements from reactor cores and transuranic wastes.

Transuranic waste is any waste with transuranic alpha emitting radionuclides that have half-lives longer than 20 years.


Low Level WasteLLW

Low level waste is any waste that could be from a high activity area.

90% volume of wasteIt does not necessarily carry any

radioactivity.Split into four catagories: A, B, C, and

GTCC.


Intermediate Level WasteILW

Intermediate level waste requires shielding when being handled.

7% volume of wasteDependent on the amount of activity it can be

buried in shallow repositories. Not recognized in the United States.


High Level WasteHLW

High level waste has a large amount of radioactive activity and is thermally hot.

3% volume of waste95% of radioactivityCurrent levels of HLW are increasing about

12,000 metric tons per year.Most HLW consists of Pu-238, 239, 240, 241,

242, Np-237, U-236


Transuranic Waste TRUW

Transuranic waste consists of all waste that has radionuclides above uranium.

TRUWs typically have longer half-lives than other forms of waste.

Typically a byproduct of weapons manufacturing.

Only recognized in the United States.


Waste Management (LLW)There are several

options available for the disposal of LLW due to its lack of radioactivity.

Waste Isolation Pilot Plant

On-site disposal


Map of WIPP Facility

Treatment (LLW)FiltrationIon ExchangeEvaporationIncinerationCompactionSolidification


Typical LLW treatment facility.

Treatment

Most common initial treatment of waste is vitrification.Waste is first mixed with sugar and then

passed through a heated tube to de-nitrite the material.

This material is then fed into a furnace and mixed with glass.

The molten glass mixture is poured into steel cylinders and welded shut.


Treatment (Cont.)Mid level active waste is commonly treated

with ion exchangeProcess reduces the bulk volume of

radioactive material.Typically, mixed with concrete for a solid

storage form.


Treatment (Cont.)Synroc is a new method for storing nuclear

waste developed in 1978 by Ted Ringwood.Attempts to hold radioactive material in a

crystalline matrix.Currently in use for military waste

management at Savannah River Site.Can hold 50%-70% volume of waste.


Deep Geological RepositoryMost common method

for handling nuclear waste.

Typically kept separate from actual plants and buried far below ground.

First used in 1999 in the US.

Current research is focusing on Yucca Mountain.


Yucca Mountain Site

Reuse of Nuclear WasteResearch is being performed to find uses for

nuclear waste.Caesium-137 and strontium-90 already used

in industrial applications.Some waste can be used for radioisotope

thermoelectric generators (RTGs). Overall can reduce total HLW but not

eliminate it.


Nuclear Plant FutureThe countries of the world are each planning

their own course of nuclear plant development or decline

Nuclear power is competitive with natural gas It is non-pollutingIt does not contribute to global warmingObtaining the fuel only takes 5% of the energy

outputPlant licenses have been extended from 20 years

to an additional 20 years


Nuclear Plant FutureNewer designs are being sought to make them more

economical and saferPreapproval of a few designs will hasten developmentDisposal of high level radioactive waste still being

studied, but scientists believe deep burial would workBecause they are have large electrical output, their

cost at $2 billion is hard to obtain and guarantee with banks

Replacing plants may be cheaper using the same sites and containment vessels


78A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR

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