Gavalek Michael TDD

7/30/2019 Gavalek Michael TDD

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Product Description of a PWR: Pressurized Water

ReactorBy: Michael Gavalek


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Purpose

This packet provides information about the components of a pressurized water reactor. The

packet will help the understanding of each of the components of the reactor core and supporting

components that harness the energy produced by fission.

Audience Analysis

This information introduces the reactor type to already employed nuclear engineers or reactor

operators. A general knowledge of nuclear reactor physics and atomic structure will benefit to the

understanding of the the PWR design. This information would be located in an information binder for

reference on the components and different processes or on a reference website.


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Science of Nuclear Power

Figure 2: A stable nucleus bombarded with a neutron then undergoing spontaneous decay

Fission simply means to break apart. In a fission reaction shown in figure 2, the unstable parent

nucleus undergoes decay by splitting apart into two daughter nuclei and releases neutrons. Theneutrons, released from the parent nucleus, interact with other stable nuclei and continue the decay

process. The chain reaction happens within seconds like dropping a ball into a container of set mouse

traps, setting off one mouse trap that sets off all the rest.

Power Generation (Power Loop)

The reactor coolant, typically water, is pressurized to 2200 psia or 150 bars and pumped into the

reactor vessel which contains the core. Reactor coolant flows through the reactor core via nozzle

systems to both cool the reactor and to transfer the heat energy out of the reactor vessel. Reactor

coolant pumps move the reactor coolant to a steam generator, where steam is produced and moved to

the turbine system. The steam then enters a condenser chamber and pumped back into the steam

generator.

Several companies such as Westinghouse and Babcock & Wilcox and various plant designs such

as combustion engineering for one example have various arrangements, however, they all have the

major components such a reactor vessel, reactor coolant pumps, steam generators, and a pressurizer.

Figures 3, 4, and 5 show several reactor containment systems from the companies mentioned.


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Figure 3: Two Loop Westinghouse Design

This design uses two reactor coolant pumps and two steam generators. The average power of this

arrangement ranges anywhere up to 500 MW.


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Figure 4: Babcock & Wilcox design

The Babcock & Wilcox design features two reactor coolant pumps with two Once-Through steam

generators. This arrangement ranges up to 850 MW.


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Figure 5: Combustion Engineering Design

The combustion engineering design features two reactor coolant pumps with combustion engine steam

generators. The power output ranges from less than 500 MW to more than 1200 MW.


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Reactor Vessel

The reactor vessel holds the reactor core and all supplemental support structures and alignment

devices. The four major components are the reactor vessel, the reactor core, the core barrel, and the

upper internals package.

The reactor vessel is a cylinder with two hemispherical ends, like a pill you take for medicine

with sticks coming out. The top part of the reactor is designed to be removed for refueling or any

maintenance that is needed to the reactor core or supporting equipment. Based on the amount of

reactor coolant loops, the number of inlet and outlet nozzles varies from one to four inlets and outlets.

The reactor vessel is constructed with manganese molybdenum steel, with all areas exposed to the

reactor coolant coated in stainless steel to increase corrosion resistance.

The core barrel slides down into the reactor vessel and houses the fuel like a spice rack. The fuel

assemblies will sit inside the core barrel on top of the core support plate. On the sides of the core

barrel, irradiated specimen holders are in place to test how radiation affects the fuel.

The upper internals package sits on top of the fuel as a guide for the control rods when they are

pulled out of the fuel for normal reactor operation.


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Figure 6: reactor vessel

The Reactor vessel cross section shows the core barrel, reactor core, and various other parts.

Reactor Coolant/Moderator

For PWRs, light water is used as the primary reactor coolant. Some reactor designs use heavy

water rather than light water where heavy water contains deuterium. The use for one or the other

depends on the reactor design specifications.


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Remember: for a PWR, there are two water cycles; one cycle is the primary reactor coolant

cycle which has direct contact with the reactor core, and the second cycle does not.

The important factor of a PWR is the primary reactor coolant is pressurized. By pressurizing the

reactor coolant (In most cases the reactor coolant is water. It does not have to be.) it prevents the water

from boiling when the temperature rises to 600 degrees Fahrenheit.

Primary reactor coolant pumps force reactor coolant into the reactor to cool the reactor down

and moderate the fission reaction. A moderator acts as sludge for neutrons to slow down to desirable

energies or speeds so uranium will accept the excited neutron and continue the fission chain reaction. If

the water temperature increases to undesirable levels, the density of water and the number of collisions

between the water molecules and neutrons decrease. It leads to an increase in fast neutron population.

That increase decreases the potential fission reactions with fuel which makes the PWR self-regulating.

Figure 7: Reactor coolant flow

The reactor coolant flows in from the inlet nozzle and travels through the reactor core, removing heat,

and out the outlet.


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The general flow path of the reactor coolant (Figure 7):

The reactor coolant enters the reactor vessel via the inlet nozzle system and hits the core barrel The core barrel forces the water to flow downward between the reactor vessel wall and the

core barrel

Once the reactor coolant reaches the bottom of the reactor vessel, the flow turns upwardthrough the fuel assemblies

The coolant flows through the fuel assembles removing the heat from the fission reaction The reactor coolant then leaves out the outlet nozzle to a steam generator.

Reactor Core and Fuel

Figure 8: Fuel Assembly

A reactor core shown in figure 6 has a

diameter of approx. 12 feet. Inside, it consists of200 fuel assemblies with a square cross section

of approximately eight and a half inches on its

side. A fuel assembly is shown in figure 8.

Fuel assemblies are arranged in a 17 by

17 or a 16 by 16 square array. In the fuel

assemblies, about one third of the fuel

assembly contains control rods which are

strategically placed by control rod guides. The

rest of the space is used for core

instrumentation and extension of core life.The fuel rods consist of uranium oxide

pellets with an enrichment ranging from 2.1 to

3.1 percent of uranium 235. The pellets shown

in figure 6 are 0.32 inches in diameter and 0.6

inches in length. The fabrication process leaves

a radial clearance between the cladding of the

fuel pellets of about 0.003 inches. The pellets

are enclosed in cylindrical Zircalloy-4 sheathes

four meters long and a diameter of one

centimeter. Zircalloy is a zirconium alloy that

has low neutron absorption and helps the

neutron economy in the PWR.


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Pressurizer

Figure 9: Pressurizer

The Pressurizer monitors pressure levels by heating up or releasing primary reactor coolant.

Shown in figure 9, the pressurizer maintains the reactor coolant system by controlling the

pressure of the reactor coolant. The pressure is controlled by the use of electrical heaters, relief valves,

and a pressurizer system.


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The pressurizer consists of a cylindrical vessel with electrical heaters at the base. Towards the

top of the vessel, relief and safety valves help decrease pressure inside the vessel. During normal

operation, the pressurizer contains liquid and vapor reactor coolant in equilibrium. Depending on the

level of liquid reactor coolant, the pressurizer will adjust by either spraying in more liquid reactor

coolant or increasing the temperature via the electric heaters.

Remember: The primary reactor coolant cycle needs to remain pressurized to prevent the reactor

coolant from boiling. The pressurizer needs attention so the reactor does not fall into a meltdown.

Steam Generator

Figure 10: Once-Through Steam Generator


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Steam generators house the primary interface between the primary reactor coolant and the

secondary water loop. As other parts of the primary reactor coolant, the general shape is a cylindrical

vessel with hemispherical ends. Inside the steam generator, the primary reactor coolant flows into tiny

tubes. The secondary coolant then flows around the outside of the tubes and picks up the heat through

heat conduction. The secondary coolant converts from liquid to steam and then flows out of the steam

generator to the turbine system where electricity is generated. The remaining primary coolant gets

pumped back into the reactor core after being heated to a desired temperature.

Babcock & Wilcox designed a steam generator called a Once-Through Steam Generator as

shown in figure 10. The primary reactor coolant flows in from the primary inlet into the large cavity in

the center of the steam generator. The secondary coolant loop flows into small channels along the sides

of the steam generator and turns into steam via superheating. The steam gets directed out through the

feed water outlets into the turbine chamber.

There are other designs of steam generators such as the combustion engineering steam

generator and the Westinghouse designs. If you would like to look into more about the designs, check

out:

http://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdf

There are excellent descriptions of each of the steam generator types that not mentioned.

Conclusion

Nuclear power has become the new kid on the energy street; in comparison to coal usage, anywherefrom the early 1900s, the first commercial nuclear reactor came on line in the 1960s. Since the early

reactor designs, nuclear reactor designs have become more complex to better harness the energy in the

fission reaction. The PWR design uses pressurized light water to extract the heat energy of the fission

reaction inside the reactor vessel to transfer the heat to a steam generator where steam produces and

gets channeled through turbines that generate electricity.
http://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdfhttp://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdfhttp://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdf


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Work CitedInformation sources:

netfiles.uiuc.edu

mitnse.files.wordpress.comGraphics sources:

Figure 1:http://en.wikipedia.org/wiki/Pressurized_water_reactor

Figure 2:http://www.mining-journal.com/supplements/mj-uranium-supplement-0411/on-a-fission-mission

Figure 3, 4, 5, 6, 9, 10:http://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdf

Figure 7:https://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engine

ering/Pressurized%20Water%20Reactors.pdf

Figure 8:http://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_71.html
http://en.wikipedia.org/wiki/Pressurized_water_reactorhttp://en.wikipedia.org/wiki/Pressurized_water_reactorhttp://www.mining-journal.com/supplements/mj-uranium-supplement-0411/on-a-fission-missionhttp://www.mining-journal.com/supplements/mj-uranium-supplement-0411/on-a-fission-missionhttp://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdfhttp://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdfhttps://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Pressurized%20Water%20Reactors.pdfhttps://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Pressurized%20Water%20Reactors.pdfhttps://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Pressurized%20Water%20Reactors.pdfhttp://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_71.htmlhttp://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_71.htmlhttp://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_71.htmlhttps://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Pressurized%20Water%20Reactors.pdfhttps://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Pressurized%20Water%20Reactors.pdfhttp://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdfhttp://www.mining-journal.com/supplements/mj-uranium-supplement-0411/on-a-fission-missionhttp://en.wikipedia.org/wiki/Pressurized_water_reactor

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