Scribd Technical Description

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Fission Reactors:

How is Energy

Generated?

Nick Caggiano

3/14/2012


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Fission Reactors: Powerful Energy Generation Nick Caggiano

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1.Audience and ScopeThe purpose of this technical description is to provide the common

student with a basic knowledge of the design and uses of nuclear fission

reactors. Many non-engineering students have no idea how these power

plants work and why they are not as dangerous as many people think. Mass

energy production is an important topic for everyone in the near future to

have a basic knowledge of. A lot of decisions about the future of our

nations energy production must be made in the coming years. I hope that

this description will provide some more helpful information on the subject

for those who read it.


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2.Introduction to ProcessA fission reactor produces power based on the reactions between

neutrons in a reactor core and the reactor fuel (normally uranium-235). If

the correct or desirable reaction occurs between a neutron and an atom of

fuel, a large amount of energy will be released in the form of kinetic energy.

This means that the atoms that come out of the reaction are moving very

fast in comparison with the speed of the neutron and fuel atom before the

reaction. The motion of these atoms produces a large amount of heat

because of many collisions that occur between the new faster atoms and

any atoms in their way.

The heat produced can be transferred into a coolant material. Most

of the time this coolant material is water, but there are other alternative

materials that we will discuss later in this technical description. No matter

what coolant material is used, the heat will eventually be transferred to a

system of fluid that will be used to generate gas that will turn turbines and

create electricity. Basically, through nuclear interactions we are able to

create a large amount of heat that is then converted into electricity that is

sent into the electrical grid and used to power homes across the country.


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3.Basics of Nuclear Fissiona. Neutron Nucleus Interaction

Nuclear fission is based on the interactions between a neutron and

an atom of nuclear fuel. It can be thought of in a very similar way as in

chemical reactions. We start with two atoms (a neutron and an atom of

fuel). Then, they interact in one of many ways. After this interaction

there is either a single resulting atom or many resulting atoms.

Depending on the outcome a change in energy can also be observed.

There are many possible outcomes, but for now we will focus on a few

of the more important and most likely outcomes.

b. Possible InteractionsThe interactions that we

are going to focus on right

now are radiative capture,

scattering, and nuclear

fission.

1.) Radiative capture- The

neutron is absorbed

into the fuel atomincreasing the total

energy of the fuel

atom by an amount

equal to the kinetic

energy of the neutron

before being absorbed.

2.) Neutron scattering- The neutron basically collides with the fuel

atom and bounces off of it. In this scattering collision it is possiblefor the neutron to transfer kinetic energy to the fuel atom leaving

it in an excited state.

Both radiative capture and scattering are important interactions

because in the overall process of a fission reactor they both affect the

amount of free neutrons and the energies of those neutrons in the


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reactor core. The use and control of fission reactors is almost completely

based on the study of neutron interactions.

3.) Fission- The neutron is first absorbed into the fuel atom. If the

neutron is able to overcome the activation energy then it is

possible for the fuel atom to fission.

In a few different isotopes of certain elements considered fissile

the activation energy is less than zero. That means that a neutron that is

moving very slow can still cause fission.

The most commonly used fissile fuel is uranium-235. A few types of

reactors are able to work with plain uranium that is found in nature. In

nature uranium-235 has an atomic abundance of 0.72%. The majority

(99.27%) of uranium found in nature is uranium-238 (Shultis).It is possible for uranium-238 to fission, however, uranium-235 is a

lot more likely to produce a fission reaction and in our fission reactors

the amount of uranium-235 is the more important number. For most

reactors the content of the uranium must be increased to a few percent

to have a critical amount of uranium-235 (Shultis).

c. Safety: Can a Fission Reactor Explode Like an Atomic Bomb?The simple answer to this question is no. The reactor core would

meltdown long before any catastrophic nuclear explosion occurred.When the term reactor meltdown is used it simply means that the

structure holding the fuel and moderator material inside of the core has

literally melted. Once it has melted down the integrity of the core is

gone. Not every meltdown occurs the same way, but radioactive

material can leak during a meltdown which is why it is so dangerous


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An important concept to consider in this discussion is the fission

chain reaction. In its most basic form this concept means that if we put

in one free neutron the reactor core will continue to produce fission

reactions because the products of a fission reaction are energy, 2 large

fission products and 2-3 neutrons.

In an atomic bomb the rate of fissions per second increases

exponentially. This means that an enormous amount of energy is

released in a short amount of time creating the huge explosion

associated with a bomb. In a fission reactor the moderator material

limits the increase in the fissions per second. The moderator material

absorbs neutrons, hence making fewer neutrons available to cause

fission. Almost any explosion associated with a fission reactor is most

likely due to a steam explosion caused by a buildup of pressure.

d. PollutionOne key fact about nuclear fission that makes it far more efficient

than other types of energy generation (coal, natural gas, etc) is that it

takes a very small amount of fuel to produce huge amounts of energy.

One kilogram of pure uranium-235 can produce the same amount of

energy as 2.7 million kilograms of coal. Uranium also only produces a

small amount of nuclear waste in comparison with the pollution thatcoal causes. The nuclear waste that is produced is also capable of being

reused. New techniques are being developed to use the nuclear waste

as fuel in certain reactors.


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4.Energy Production Process

a. Water CondenserThe water condenser cools the hot water vapor and returns it to a

low temperature to be sent back though the cycle. It is important to

always keep a certain level of cold water flowing through the reactor

because if it cannot be cooled effectively the reactor may overheat

and meltdown. This system can be connected to a giant cooling

tower or a large body of water to maintain a low temperature.

b. PumpsThe pumps are very important to all of the fluid cycles in the

reactor. The water that is in the reactor core needs to be cycled

through the system so that it can transfer heat to the secondary

water cycle. This secondary water cycle, as seen above in the picture,

is heated to create steam and turn the turbines.

c. Reactor CoreThe reactor core contains the nuclear fuel and the moderator

material. This is where the fission reactions take place and the heat is

generated. The reactor core must be completely sealed and


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contained so that no radioactive material can escape. It must also be

kept below a certain temperature to avoid meltdown.

d. Steam Turbine GeneratorThe steam turbine

generator is where the

heat generated from the

reactor core is converted

into useful energy. The

hot steam produced by

the heat of the reactor

pushes and turns the

turbines before it is

cooled and cycled back

through the system. The

rotational energy of the spinning turbines can be converted into

electrical energy.

e. Electrical GridThe electrical grid

consists of a largenetworking of high

voltage power lines,

transformers and

power plants. The

electrical energy

produced by the

steam turbine

generators can be sent into the electrical grid and transported usingtransmission lines across the country. Using transformers the high

voltage electricity in the transmission lines can be reduced to a lower

voltage that is usable and comes out of the wall sockets in individual

homes. The whole point of all of this is to deliver usable energy into

the homes of Americans across the country.


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5.Different Models of a Fission Reactora. Light Water Reactor

Light water reactors are the most commonly used reactors around

the world. There are many different designs for light water reactors, but

any reactor that uses light water as the moderator falls into this broad

category. To clarify, light water is H2O where the hydrogen atom is only

of the isotope1H (protium). The hydrogen atom is composed of only one

proton and an electron.

b. Heavy Water ReactorHeavy water reactors, in contrast to light water reactors, use heavy

water as the moderator. Heavy water is H2O where the hydrogen atom

is the isotope2H (deuterium). This atom consists of one neutron, one

proton and one electron. Deuterium is far scarcer than protium making

up only 0.015% of all hydrogen in the earths natural abundance. This

makes heavy water more expensive than light water because of the

processing that must occur to produce enough heavy water for a

reactor.


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c. Pressurized Water ReactorIn a pressurized water reactor the moderator fluid is pumped

through a cycle from the reactor core around to a thermal couple where

the heat of the fluid is transferred to another cycle of water. The water

in the first cycle that goes through the reactor must be kept under high

pressure at all times so that air bubbles are not produced. Air bubbles

can mess up the heat transfer coefficient of the fluid and endanger the

whole process.

With the water under high pressure the fluid remains in a liquid state

at a higher temperature than it would otherwise. With a higher

temperature the efficiency of the conversion of heat energy over to

electrical energy is increased. An example of this reactor is pictured

above in section 4 on page 7.

d. Boiling Water ReactorIn a boiling water reactor the cooling water is allowed to boil inside

of the reactor. The steam produced is then directly passed directly into

the turbine compartment. This removes one of the cycles of water

which can improve the efficiency of the system. Since the water in this

cycle is radioactive it must be contained and controlled at all times. Also,

since the water is now in direct contact with the turbine system all ofthis system must now be contained and monitored so that no

radioactive material is leaked.


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e. Gas Cooled ReactorsIn a gas cooled

reactor CO2 or He gas is

used as the coolant

instead of water. Also,

graphite is used as the

moderator instead of

water. This can eliminate

the need for a high

pressure container

vessel around the core.

f. Breeder ReactorsA breeder reactor works using a different concept. A breeder reactor

uses fertile nuclei such as thorium-232 and uranium-238. These

materials themselves are not fissionable, but they can produce fissile

materials. Breeder reactors can be considered superior because of their

fuel economy, but they are

not widely used because it isstill cheaper to mine

uranium than use a breeder

reactor.

In the figure at the right

it shows how uranium-238

can be used to produce the

fissile material plutonium-

239. Bombarding uranium-

235 with neutrons will

trigger two beta decays that

will result in the production

of plutonium-239.


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6.ConclusionNuclear energy is one of the most powerful and useful sources of

energy for the U.S. in the future. While there are dangers associated

with the use of radioactive material the positives far outweigh thenegatives. Through the controlled and contained burn-up of a critical

reactor core huge amounts of heat can be converted into electrical

energy. The system in general will need to include a water condenser,

many pumps, a reactor core, one or many steam turbines, and a

connection to the electrical grid to make the energy usable.

There are many types of reactors used today, but all of them are very

effective at creating safe energy. New safer and more effective models

of reactors are being built and designed now. The first approvals for

reactor construction in over thirty years were made in February this

year. These reactors are both being built in Georgia and plan to start

operating by 2016 and 2017 (Hargreaves). In the figure below the

locations of every nuclear power plant in the world as of 2005 can be

seen.


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Works Cited

Hargreaves, Steve. "New Nuclear Reactors Set to Be OK'd for Georgia." CNNMoney. Cable

News Network, 08 Feb. 2012. Web. 12 Mar. 2012.

.

Shultis, J. Kenneth., and Richard E. Faw. Fundamentals of Nuclear Science and Engineering.

2nd ed. Boca Raton: CRC, 2008. Print.

Pictures Used (In Order of Appearance)

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0/ST1kK8c48YI/AAAAAAAAAO8/ZogUHoELJ1U/s400/nu1.jpg

Figure 2 - https://reader009.{domain}/reader009/html5/0502/5ae9ada616446/5ae9adae7cf08.jpg

Figure 3 - https://reader009.{domain}/reader009/html5/0502/5ae9ada616446/5ae9adb039815.jpg

Figure 4 - http://www.petrolog.net/webhelp/Logging_Tools/cnl/cnl01.gif

Figure 5 - https://reader009.{domain}/reader009/html5/0502/5ae9ada616446/5ae9adb125ea7.jpg

Figure 6 - "Energy for the World - Why Uranium?" : Education. Web. 14 Mar. 2012.

.

Figure 7 - https://reader009.{domain}/reader009/html5/0502/5ae9ada616446/5ae9adb1e61f6.jpg

Figure 8 - http://www.engineeringexpert.net/Engineering-Expert-Witness-Blog/http://www.engineeringexpert.net/web/Engineering-Expert-Witness-Blog/wp-

content/uploads//2011/02/turbine_wheel.jpg

Figure 9 - http://static.ddmcdn.com/gif/power-transmission.gif

Figure 10 - http://www.humanresonance.org/protium_deuterium_tritium.jpg

Figure 11 - https://reader009.{domain}/reader009/html5/0502/5ae9ada616446/5ae9adb28cbc9.jpg

Figure 12 - https://inlportal.inl.gov/portal/server.pt/gateway/PTARGS_0_2_2629_277_2253_43

/http%3B/exps3.inl.gov%3B7087/publishedcontent/publish/communities/inl_gov/research_programs/nuclear_energy/gfr_introduction/gfr_sm.jpg

Figure 13 - http://www.3rd1000.com/nuclear/fbre.gif

Figure 14 - "The Incontiguous Brick." The Incontiguous Brick. 21 Aug. 2007. Web. 14 Mar.

2012. .

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