Boiling water reactor - Revision history

Jmdonev: 1 revision imported

2018-09-03T22:23:41Z

1 revision imported

← Older revision	Revision as of 22:23, 3 September 2018
(No difference)

energy>Jmdonev at 20:37, 26 August 2018

2018-08-26T20:37:20Z

← Older revision		Revision as of 20:37, 26 August 2018
Line 1:		Line 1:
	[[Category:Done 2018-07-20]]		[[Category:Done 2018-08-03]]
	*World unclear association source-now I am thinking even if may not be 'arms length', we are not using it for qualitative info. Just their data for pure numbers? Since we know it would be accurate. - Bethel'''
	[[File:Fermi_NPP.jpg\|300px\|thumb\|Figure 1. The Enrico Fermi Nuclear Generating Station in Newport, Michigan operates by use of a boiling water reactor.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/4/4d/Fermi_NPP.jpg</ref>]]		[[File:Fermi_NPP.jpg\|300px\|thumb\|Figure 1. The Enrico Fermi Nuclear Generating Station in Newport, Michigan operates by use of a boiling water reactor.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/4/4d/Fermi_NPP.jpg</ref>]]

	<onlyinclude>'''Boiling water reactors''' ('''BWR''') are a type of [[nuclear reactor]] that use [[light water]] (ordinary water, as opposed to [[heavy water]]) as their coolant and [[neutron moderator]]. They are the second most used reactor for [[nuclear power]] generation in the world, next to the [[pressurized water reactor]] (PWR)—with 80 in operation as of ~~2015~~.</onlyinclude><Ref name=~~wna~~>~~World Nuclear Association~~. ~~(June 29 2015). ''Nuclear Power Reactors'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Power-Reactors/Nuclear-Power-Reactors/</ref>~~		<onlyinclude>'''Boiling water reactors''' ('''BWR''') are a type of [[nuclear reactor]] that use [[light water]] (ordinary water, as opposed to [[heavy water]]) as their coolant and [[neutron moderator]]. They are the second most used reactor for [[nuclear power]] generation in the world, next to the [[pressurized water reactor]] (PWR)—with 75 in operation as of 2018.</onlyinclude><Ref name=PRIS/> Figure 2 graphs the percentage of various types of reactors worldwide and the chart details the number of each.

	With maximum operating [[temperature]]s of around [[celsius\|285<sup>o</sup>C]], the [[Carnot efficiency]] (maximum [[efficiency]]) of boiling water reactors in the production of power is 46%.<ref>Hyperphysics. (June 29 2015). ''Boiling water reactor'' [Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html</ref> However, the realistic efficiency of these reactors in power production is around 33-34%.<ref name=ine>J.R. Lamarsh and A.J. Baratta, "Power Reactors and Nuclear Steam Supply Systems" in ''Introduction to Nuclear Engineering'', 3rd ed., Upper Saddle River, NJ: Prentice Hall, 2001, ch.4, sec.5, pp. 136-185</ref>		With maximum operating [[temperature]]s of around [[celsius\|285<sup>o</sup>C]], the [[Carnot efficiency]] (maximum [[efficiency]]) of boiling water reactors in the production of power is 46%.<ref>Hyperphysics. (June 29 2015). ''Boiling water reactor'' [Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html</ref> However, the realistic efficiency of these reactors in power production is around 33-34%.<ref name=ine>J.R. Lamarsh and A.J. Baratta, "Power Reactors and Nuclear Steam Supply Systems" in ''Introduction to Nuclear Engineering'', 3rd ed., Upper Saddle River, NJ: Prentice Hall, 2001, ch.4, sec.5, pp. 136-185</ref>

	See the [[Boiling water reactor#Water flow\|section below]] to view a basic operating cycle of a boiling water power plant.		See the [[Boiling water reactor#Water flow\|section below]] to view a basic operating cycle of a boiling water power plant.

			[[File:Number of reactor types.png\|400px\|thumb\|center\|Figure 2. Percentage of Reactor types worldwide.<ref name = PRIS>"PRIS - Reactor status reports - Operational & Long-Term Shutdown - By Type", Pris.iaea.org, 2018. [Online]. Available: https://pris.iaea.org/PRIS/WorldStatistics/OperationalReactorsByType.aspx. [Accessed: 13- Aug- 2018].</ref>]]

			{\| class="wikitable sortable"
			\|-
			! Type !! Number of Reactors
			\|-
			\| PWR \|\| 297
			\|-
			\| [[BWR]] (Boiling Light-Water Cooled and Moderated Reactor) \|\| 75
			\|-
			\| PHWR (Pressurized Heavy-Water Moderated and Cooled Reactor) \|\| 49
			\|-
			\| LWGR (Light-Water Cooled, Graphite Moderated Reactor) \|\| 15
			\|-
			\| GCR (Gas Cooled, Graphite Moderated Reactor) \|\| 14
			\|-
			\| [[FBR]] (Fast Breeder Reactor)\|\| 3
			\|-
			\|}

	==Characteristics==		==Characteristics==
Line 15:		Line 34:
	Boiling water reactors must use [[uranium enrichment\|enriched uranium]] as their [[nuclear fuel]], due to their use of light water. This is because light water absorbs too many [[neutron]]s to be used with natural [[uranium]], so the [[nuclear fuel\|fuel]] content of [[fissile]] Uranium-235 must be increased. This is done through [[uranium enrichment]]—which increases the concentration of Uranium-235 from 0.7% to around 4%.<ref name=ine/>		Boiling water reactors must use [[uranium enrichment\|enriched uranium]] as their [[nuclear fuel]], due to their use of light water. This is because light water absorbs too many [[neutron]]s to be used with natural [[uranium]], so the [[nuclear fuel\|fuel]] content of [[fissile]] Uranium-235 must be increased. This is done through [[uranium enrichment]]—which increases the concentration of Uranium-235 from 0.7% to around 4%.<ref name=ine/>

	The enriched uranium is packed into fuel rods, which are assembled into a fuel bundle, as seen in Figure 2. There are about 90-100 rods in each bundle, with up to 750 bundles in a reactor.<~~ref~~ name=wna/> This corresponds to nearly 140 [[tonne]]s of uranium!		The enriched uranium is packed into fuel rods, which are assembled into a fuel bundle, as seen in Figure 3. There are about 90-100 rods in each bundle, with up to 750 bundles in a reactor.<Ref name=wna>World Nuclear Association. (June 29 2015). ''Nuclear Power Reactors'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Power-Reactors/Nuclear-Power-Reactors/</ref> This corresponds to nearly 140 [[tonne]]s of uranium!

	[[File:Nuclear_fuel_element.jpg\|800px\|thumb\|center\|Figure 2. A nuclear fuel bundle for a BWR.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/2/2d/Nuclear_fuel_element.jpg</ref>]]		[[File:Nuclear_fuel_element.jpg\|800px\|thumb\|center\|Figure 3. A nuclear fuel bundle for a BWR.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/2/2d/Nuclear_fuel_element.jpg</ref>]]

	===Coolant and Moderator===		===Coolant and Moderator===
Line 23:		Line 42:
	As mentioned before, light water is used as the coolant and moderator for a boiling water reactor. Light water is ''much'' more abundant than heavy water, as it makes up 99.99% of natural water.<ref>Jefferson Lab. (June 29 2015). ''Isotopes of the Element Hydrogen'' [Online], Available: http://education.jlab.org/itselemental/iso001.html</ref>		As mentioned before, light water is used as the coolant and moderator for a boiling water reactor. Light water is ''much'' more abundant than heavy water, as it makes up 99.99% of natural water.<ref>Jefferson Lab. (June 29 2015). ''Isotopes of the Element Hydrogen'' [Online], Available: http://education.jlab.org/itselemental/iso001.html</ref>

	The use of light water as a coolant is beneficial as it can cool down the fuel at the same time as it heats up to [[steam]]. The steam moves through the [[turbine]]s which spin a [[generator]] to generate electricity. This simplifies the design of boiling water reactors, as there is ''only one primary loop'' (see Figure 3) needed which results in a lower cost of development.<Ref name=ine/>		The use of light water as a coolant is beneficial as it can cool down the fuel at the same time as it heats up to [[steam]]. The steam moves through the [[turbine]]s which spin a [[generator]] to generate electricity. This simplifies the design of boiling water reactors, as there is ''only one primary loop'' (see Figure 4) needed which results in a lower cost of development.<Ref name=ine/>

	Light water does not make as good of a moderator as heavy water or graphite due to its relatively high absorption of neutrons. However, its use as a moderator makes for an interesting and important safety feature; if there is a "loss of coolant accident: (LOCA), the moderator will also decline, causing the [[nuclear chain reaction]] to stop. In addition, if the moderating water overheats and turns to steam inside the bottom reactor core, there will be less moderator and therefore the chain reaction will stop.		Light water does not make as good of a moderator as heavy water or graphite due to its relatively high absorption of neutrons. However, its use as a moderator makes for an interesting and important safety feature; if there is a "loss of coolant accident: (LOCA), the moderator will also decline, causing the [[nuclear chain reaction]] to stop. In addition, if the moderating water overheats and turns to steam inside the bottom reactor core, there will be less moderator and therefore the chain reaction will stop.
Line 39:		Line 58:
	Less water needs to flow through a BWR than through a PWR, however, there are complications because the water becomes [[radioactivity\|radioactive]] in its circulation. This means that there must be extra shielding in the non-reactor parts of the power plant.<ref name=ine/>		Less water needs to flow through a BWR than through a PWR, however, there are complications because the water becomes [[radioactivity\|radioactive]] in its circulation. This means that there must be extra shielding in the non-reactor parts of the power plant.<ref name=ine/>

	[[Control rod]]s are placed in the bottom of the reactor, rather than the top as in PWRs. This is because in a boiling water reactor there is more steam at the top (visible in Figure 3 below), and placement of control rods in the steam portion would have a lesser effect than their placement in the water portion of the reactor.<ref name=ine/> There is higher reactivity of the fuel in the water portion due to its moderation, so the control rods are needed to change the reactivity as deemed fit by the operators.		[[Control rod]]s are placed in the bottom of the reactor, rather than the top as in PWRs. This is because in a boiling water reactor there is more steam at the top (visible in Figure 4 below), and placement of control rods in the steam portion would have a lesser effect than their placement in the water portion of the reactor.<ref name=ine/> There is higher reactivity of the fuel in the water portion due to its moderation, so the control rods are needed to change the reactivity as deemed fit by the operators.

	Seen below is the flow of water through a boiling water reactor power plant, and its production of electricity.		Seen below is the flow of water through a boiling water reactor power plant, and its production of electricity.

	[[File:BoilingWaterReactor.gif\|800px\|center\|thumb\|Figure 3. A boiling water nuclear reactor operates on a direct cycle, where the water from the core is also used as steam in the turbine section.<ref>NRC. (June 25 2015). ''Boiling Water Reactor'' [Online], Available: http://www.nrc.gov/reading-rm/basic-ref/students/animated-bwr.html</ref>]]		[[File:BoilingWaterReactor.gif\|800px\|center\|thumb\|Figure 4. A boiling water nuclear reactor operates on a direct cycle, where the water from the core is also used as steam in the turbine section.<ref>NRC. (June 25 2015). ''Boiling Water Reactor'' [Online], Available: http://www.nrc.gov/reading-rm/basic-ref/students/animated-bwr.html</ref>]]

	==For Further Reading==		==For Further Reading==

Jmdonev: 1 revision imported

2018-07-21T01:13:03Z

1 revision imported

← Older revision	Revision as of 01:13, 21 July 2018
(No difference)

Jmdonev at 15:24, 18 July 2018

2018-07-18T15:24:34Z

← Older revision		Revision as of 15:24, 18 July 2018
Line 1:		Line 1:
	[[Category:Done ~~2015~~-07-01]]		[[Category:Done 2018-07-20]]
			*World unclear association source-now I am thinking even if may not be 'arms length', we are not using it for qualitative info. Just their data for pure numbers? Since we know it would be accurate. - Bethel'''
	[[File:Fermi_NPP.jpg\|300px\|thumb\|Figure 1. The Enrico Fermi Nuclear Generating Station in Newport, Michigan operates by use of a boiling water reactor.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/4/4d/Fermi_NPP.jpg</ref>]]		[[File:Fermi_NPP.jpg\|300px\|thumb\|Figure 1. The Enrico Fermi Nuclear Generating Station in Newport, Michigan operates by use of a boiling water reactor.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/4/4d/Fermi_NPP.jpg</ref>]]

	<onlyinclude>'''Boiling water reactors''' ('''BWR''') are a type of [[nuclear reactor]] that use [[light water]] (ordinary water, as opposed to [[heavy water]]) as their coolant and [[neutron moderator]]. They are the second most used reactor for [[nuclear power]] generation in the world, next to the [[pressurized water reactor]] (PWR)~~, with~~ 80 in operation as of 2015.</onlyinclude><Ref name=wna>World Nuclear Association. (June 29 2015). ''Nuclear Power Reactors'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Power-Reactors/Nuclear-Power-Reactors/</ref>		<onlyinclude>'''Boiling water reactors''' ('''BWR''') are a type of [[nuclear reactor]] that use [[light water]] (ordinary water, as opposed to [[heavy water]]) as their coolant and [[neutron moderator]]. They are the second most used reactor for [[nuclear power]] generation in the world, next to the [[pressurized water reactor]] (PWR)—with 80 in operation as of 2015.</onlyinclude><Ref name=wna>World Nuclear Association. (June 29 2015). ''Nuclear Power Reactors'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Power-Reactors/Nuclear-Power-Reactors/</ref>

	With maximum operating [[temperature]]s of around [[celsius\|285<sup>o</sup>C]], the [[Carnot efficiency]] (maximum [[efficiency]]) of boiling water reactors in the production of power is 46%.<ref>Hyperphysics. (June 29 2015). ''Boiling water reactor'' [Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html</ref> ~~The~~ realistic efficiency of these reactors in power production ~~however~~ is around 33-34%.<ref name=ine>J.R. Lamarsh and A.J. Baratta, "Power Reactors and Nuclear Steam Supply Systems" in ''Introduction to Nuclear Engineering'', 3rd ed., Upper Saddle River, NJ: Prentice Hall, 2001, ch.4, sec.5, pp. 136-185</ref>		With maximum operating [[temperature]]s of around [[celsius\|285<sup>o</sup>C]], the [[Carnot efficiency]] (maximum [[efficiency]]) of boiling water reactors in the production of power is 46%.<ref>Hyperphysics. (June 29 2015). ''Boiling water reactor'' [Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html</ref> However, the realistic efficiency of these reactors in power production is around 33-34%.<ref name=ine>J.R. Lamarsh and A.J. Baratta, "Power Reactors and Nuclear Steam Supply Systems" in ''Introduction to Nuclear Engineering'', 3rd ed., Upper Saddle River, NJ: Prentice Hall, 2001, ch.4, sec.5, pp. 136-185</ref>

	See the [[Boiling water reactor#Water flow\|section below]] to view a basic operating cycle of a boiling water power plant.		See the [[Boiling water reactor#Water flow\|section below]] to view a basic operating cycle of a boiling water power plant.
Line 12:		Line 13:
	===Fuel===		===Fuel===

	Boiling water reactors must use [[uranium enrichment\|enriched uranium]] as their [[nuclear fuel]], due to their use of light water. This is because light water absorbs too many [[neutron]]s to be used with natural [[uranium]], so the [[nuclear fuel\|fuel]] content of [[fissile]] Uranium-235 must be increased. This is done through a [[uranium enrichment]] ~~processes, in which~~ the concentration of Uranium-235 ~~is increased~~ from 0.7% to around 4%.<ref~~>World Nuclear Association. (June 25 2015). ''Uranium Enrichment'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Conversion-Enrichment-and-Fabrication/Uranium-Enrichment/<~~/~~ref~~>		Boiling water reactors must use [[uranium enrichment\|enriched uranium]] as their [[nuclear fuel]], due to their use of light water. This is because light water absorbs too many [[neutron]]s to be used with natural [[uranium]], so the [[nuclear fuel\|fuel]] content of [[fissile]] Uranium-235 must be increased. This is done through [[uranium enrichment]]—which increases the concentration of Uranium-235 from 0.7% to around 4%.<ref name=ine/>

	The enriched uranium is packed into fuel rods, which are assembled into a fuel bundle, as seen in Figure 2. There are about 90-100 rods in each bundle, with up to 750 bundles in a reactor.<ref name=wna/> This corresponds to nearly 140 [[tonne]]s of uranium!		The enriched uranium is packed into fuel rods, which are assembled into a fuel bundle, as seen in Figure 2. There are about 90-100 rods in each bundle, with up to 750 bundles in a reactor.<ref name=wna/> This corresponds to nearly 140 [[tonne]]s of uranium!
Line 22:		Line 23:
	As mentioned before, light water is used as the coolant and moderator for a boiling water reactor. Light water is ''much'' more abundant than heavy water, as it makes up 99.99% of natural water.<ref>Jefferson Lab. (June 29 2015). ''Isotopes of the Element Hydrogen'' [Online], Available: http://education.jlab.org/itselemental/iso001.html</ref>		As mentioned before, light water is used as the coolant and moderator for a boiling water reactor. Light water is ''much'' more abundant than heavy water, as it makes up 99.99% of natural water.<ref>Jefferson Lab. (June 29 2015). ''Isotopes of the Element Hydrogen'' [Online], Available: http://education.jlab.org/itselemental/iso001.html</ref>

	The use of light water as a coolant is beneficial as it can cool down the fuel at the same time as it heats up to [[steam]]. The steam ~~then directly flows to~~ [[turbine]]s which spin a [[generator]] to generate electricity. This simplifies the design of boiling water reactors, as there is only one primary loop needed which results in a lower cost of development.<Ref name=ine/>		The use of light water as a coolant is beneficial as it can cool down the fuel at the same time as it heats up to [[steam]]. The steam moves through the [[turbine]]s which spin a [[generator]] to generate electricity. This simplifies the design of boiling water reactors, as there is ''only one primary loop'' (see Figure 3) needed which results in a lower cost of development.<Ref name=ine/>

	Light water does not make as good of a moderator as heavy water or graphite ~~as a result of~~ its relatively high absorption of neutrons. However its use as a moderator makes for an interesting and important safety feature; if there is a loss of coolant accident (LOCA), ~~there~~ will also ~~be a loss of moderator~~ causing the [[nuclear chain reaction]] to stop. ~~Also~~ if the moderating water overheats and turns to steam inside the bottom reactor core, there will be less moderator and therefore the chain reaction will stop.		Light water does not make as good of a moderator as heavy water or graphite due to its relatively high absorption of neutrons. However, its use as a moderator makes for an interesting and important safety feature; if there is a "loss of coolant accident: (LOCA), the moderator will also decline, causing the [[nuclear chain reaction]] to stop. In addition, if the moderating water overheats and turns to steam inside the bottom reactor core, there will be less moderator and therefore the chain reaction will stop.

	===Pressures===		===Pressures===

	Boiling water reactors must operate at fairly high [[pressure]]s in order for the water to perform adequately; at high pressures the water can remain in liquid form at temperatures much higher than its normal 100<sup>o</sup>C [[boiling point]]. Therefore boiling water reactors operate at around 7 [[pascal\|MPa]]~~, around~~ 70 times higher than [[atmospheric pressure]].<ref name=ine/>		Boiling water reactors must operate at fairly high [[pressure]]s in order for the water to perform adequately; at high pressures the water can remain in liquid form at temperatures much higher than its normal 100<sup>o</sup>C [[boiling point]]. Therefore, boiling water reactors operate at around 7 [[pascal\|MPa]]—around 70 times higher than [[atmospheric pressure]].<ref name=ine/>

	Although very high, these pressures are still less than half of the pressures needed for [[pressurized water reactor]]s. Since the pressures in boiling water reactors are less than those of pressurized ones, the [[specific power]] is less. This means that the boiling water reactor needs to be larger in order to provide the same power as a pressurized reactor, which results in higher costs. However the walls do not need to be as thick as in PWRs, so the costs are essentially the same.<ref name=ine/>		Although very high, these pressures are still less than half of the pressures needed for [[pressurized water reactor]]s. Since the pressures in boiling water reactors are less than those of pressurized ones, the [[specific power]] is less. This means that the boiling water reactor needs to be larger in order to provide the same power as a pressurized reactor, which results in higher costs. However, the walls do not need to be as thick as in PWRs, so the costs are essentially the same.<ref name=ine/>

	===Water flow===		===Water flow===

	Since the BWR has only one primary loop, as mentioned earlier, the very ~~same~~ water that flows through the reactor core is ~~what is~~ used ~~for the spinning of~~ the turbines. ~~This is in~~ contrast to pressurized water reactors~~, where~~ the hot water in the core ~~is not converted~~ to steam, ~~and~~ therefore two loops are necessary. This is the main difference between BWRs and PWRs.<ref name=wna/>		Since the BWR has only one primary loop, as mentioned earlier, the very ''water that flows through the reactor core is the same one used to spin the turbines''. In contrast, pressurized water reactors do not convert the hot water in the core to steam, therefore, two loops are necessary. This is the main difference between BWRs and PWRs.<ref name=wna/>

	Less water needs to flow through a BWR than through a PWR, however there are complications because the water becomes [[radioactivity\|radioactive]] in its circulation. This means that there must be extra shielding in the non-reactor parts of the power plant.<ref name=ine/>		Less water needs to flow through a BWR than through a PWR, however, there are complications because the water becomes [[radioactivity\|radioactive]] in its circulation. This means that there must be extra shielding in the non-reactor parts of the power plant.<ref name=ine/>

	[[Control rod]]s are placed in the bottom of the reactor, rather than the top as in PWRs. This is because in a boiling water reactor there is more steam at the top (visible in Figure 3 below), and placement of control rods in the steam portion would have a lesser effect than their placement in the water portion of the reactor.<ref name=ine/> There is higher reactivity of the fuel in the water portion due to its moderation, so the control rods are needed to change the reactivity as deemed fit by the operators.		[[Control rod]]s are placed in the bottom of the reactor, rather than the top as in PWRs. This is because in a boiling water reactor there is more steam at the top (visible in Figure 3 below), and placement of control rods in the steam portion would have a lesser effect than their placement in the water portion of the reactor.<ref name=ine/> There is higher reactivity of the fuel in the water portion due to its moderation, so the control rods are needed to change the reactivity as deemed fit by the operators.
Line 43:		Line 44:

	[[File:BoilingWaterReactor.gif\|800px\|center\|thumb\|Figure 3. A boiling water nuclear reactor operates on a direct cycle, where the water from the core is also used as steam in the turbine section.<ref>NRC. (June 25 2015). ''Boiling Water Reactor'' [Online], Available: http://www.nrc.gov/reading-rm/basic-ref/students/animated-bwr.html</ref>]]		[[File:BoilingWaterReactor.gif\|800px\|center\|thumb\|Figure 3. A boiling water nuclear reactor operates on a direct cycle, where the water from the core is also used as steam in the turbine section.<ref>NRC. (June 25 2015). ''Boiling Water Reactor'' [Online], Available: http://www.nrc.gov/reading-rm/basic-ref/students/animated-bwr.html</ref>]]

			==For Further Reading==
			*[[Pressurized water reactor]]
			*[[Nuclear reactor]]
			*[[Light water]]
			*[[Radioactive]]
			*[[Control rod]]
			*Or explore a [[Special:Random\|random page]]


	==References==		==References==
	{{reflist}}		{{reflist}}
	[[Category:Uploaded]]		[[Category:Uploaded]]

J.williams: 1 revision imported

2015-08-26T21:30:52Z

1 revision imported

← Older revision	Revision as of 21:30, 26 August 2015
(No difference)

J.williams at 16:51, 12 August 2015

2015-08-12T16:51:33Z

New page

[[Category:Done 2015-07-01]]
[[File:Fermi_NPP.jpg|300px|thumb|Figure 1. The Enrico Fermi Nuclear Generating Station in Newport, Michigan operates by use of a boiling water reactor.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/4/4d/Fermi_NPP.jpg</ref>]]

<onlyinclude>'''Boiling water reactors''' ('''BWR''') are a type of [[nuclear reactor]] that use [[light water]] (ordinary water, as opposed to [[heavy water]]) as their coolant and [[neutron moderator]]. They are the second most used reactor for [[nuclear power]] generation in the world, next to the [[pressurized water reactor]] (PWR), with 80 in operation as of 2015.</onlyinclude><Ref name=wna>World Nuclear Association. (June 29 2015). ''Nuclear Power Reactors'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Power-Reactors/Nuclear-Power-Reactors/</ref>

With maximum operating [[temperature]]s of around [[celsius|285<sup>o</sup>C]], the [[Carnot efficiency]] (maximum [[efficiency]]) of boiling water reactors in the production of power is 46%.<ref>Hyperphysics. (June 29 2015). ''Boiling water reactor'' [Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html</ref> The realistic efficiency of these reactors in power production however is around 33-34%.<ref name=ine>J.R. Lamarsh and A.J. Baratta, "Power Reactors and Nuclear Steam Supply Systems" in ''Introduction to Nuclear Engineering'', 3rd ed., Upper Saddle River, NJ: Prentice Hall, 2001, ch.4, sec.5, pp. 136-185</ref>

See the [[Boiling water reactor#Water flow|section below]] to view a basic operating cycle of a boiling water power plant.

==Characteristics==

===Fuel===

Boiling water reactors must use [[uranium enrichment|enriched uranium]] as their [[nuclear fuel]], due to their use of light water. This is because light water absorbs too many [[neutron]]s to be used with natural [[uranium]], so the [[nuclear fuel|fuel]] content of [[fissile]] Uranium-235 must be increased. This is done through a [[uranium enrichment]] processes, in which the concentration of Uranium-235 is increased from 0.7% to around 4%.<ref>World Nuclear Association. (June 25 2015). ''Uranium Enrichment'' [Online], Available: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Conversion-Enrichment-and-Fabrication/Uranium-Enrichment/</ref>

The enriched uranium is packed into fuel rods, which are assembled into a fuel bundle, as seen in Figure 2. There are about 90-100 rods in each bundle, with up to 750 bundles in a reactor.<ref name=wna/> This corresponds to nearly 140 [[tonne]]s of uranium!

[[File:Nuclear_fuel_element.jpg|800px|thumb|center|Figure 2. A nuclear fuel bundle for a BWR.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/2/2d/Nuclear_fuel_element.jpg</ref>]]

===Coolant and Moderator===

As mentioned before, light water is used as the coolant and moderator for a boiling water reactor. Light water is ''much'' more abundant than heavy water, as it makes up 99.99% of natural water.<ref>Jefferson Lab. (June 29 2015). ''Isotopes of the Element Hydrogen'' [Online], Available: http://education.jlab.org/itselemental/iso001.html</ref>

The use of light water as a coolant is beneficial as it can cool down the fuel at the same time as it heats up to [[steam]]. The steam then directly flows to [[turbine]]s which spin a [[generator]] to generate electricity. This simplifies the design of boiling water reactors, as there is only one primary loop needed which results in a lower cost of development.<Ref name=ine/>

Light water does not make as good of a moderator as heavy water or graphite as a result of its relatively high absorption of neutrons. However its use as a moderator makes for an interesting and important safety feature; if there is a loss of coolant accident (LOCA), there will also be a loss of moderator causing the [[nuclear chain reaction]] to stop. Also if the moderating water overheats and turns to steam inside the bottom reactor core, there will be less moderator and therefore the chain reaction will stop.

===Pressures===

Boiling water reactors must operate at fairly high [[pressure]]s in order for the water to perform adequately; at high pressures the water can remain in liquid form at temperatures much higher than its normal 100<sup>o</sup>C [[boiling point]]. Therefore boiling water reactors operate at around 7 [[pascal|MPa]], around 70 times higher than [[atmospheric pressure]].<ref name=ine/>

Although very high, these pressures are still less than half of the pressures needed for [[pressurized water reactor]]s. Since the pressures in boiling water reactors are less than those of pressurized ones, the [[specific power]] is less. This means that the boiling water reactor needs to be larger in order to provide the same power as a pressurized reactor, which results in higher costs. However the walls do not need to be as thick as in PWRs, so the costs are essentially the same.<ref name=ine/>

===Water flow===

Since the BWR has only one primary loop, as mentioned earlier, the very same water that flows through the reactor core is what is used for the spinning of the turbines. This is in contrast to pressurized water reactors, where the hot water in the core is not converted to steam, and therefore two loops are necessary. This is the main difference between BWRs and PWRs.<ref name=wna/>

Less water needs to flow through a BWR than through a PWR, however there are complications because the water becomes [[radioactivity|radioactive]] in its circulation. This means that there must be extra shielding in the non-reactor parts of the power plant.<ref name=ine/>

[[Control rod]]s are placed in the bottom of the reactor, rather than the top as in PWRs. This is because in a boiling water reactor there is more steam at the top (visible in Figure 3 below), and placement of control rods in the steam portion would have a lesser effect than their placement in the water portion of the reactor.<ref name=ine/> There is higher reactivity of the fuel in the water portion due to its moderation, so the control rods are needed to change the reactivity as deemed fit by the operators.

Seen below is the flow of water through a boiling water reactor power plant, and its production of electricity.

[[File:BoilingWaterReactor.gif|800px|center|thumb|Figure 3. A boiling water nuclear reactor operates on a direct cycle, where the water from the core is also used as steam in the turbine section.<ref>NRC. (June 25 2015). ''Boiling Water Reactor'' [Online], Available: http://www.nrc.gov/reading-rm/basic-ref/students/animated-bwr.html</ref>]]

==References==
{{reflist}}
[[Category:Uploaded]]