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Topic: Void coefficient

	Void coefficient - Wikipedia, the free encyclopedia
		Voids may also form if coolant is lost from the reactor in some sort of accident (called a loss of coolant accident, which has other dangers).
		If the void coefficient is large enough and control systems do not respond quickly enough, this can form a positive feedback loop which can quickly boil all the coolant in the reactor.
		A negative void coefficient means that the thermal power output decreases as the void content inside the reactor increases - but it also means that the thermal power output increases if the void content inside the reactor is reduced.
	en.wikipedia.org /wiki/Void_coefficient (1006 words)

	Void effect
		The formation of steam or the ingress of gas bubbles in the moderator and/or the coolant influence the criticality of the reactor.
		The void effect can be decisively influenced by the design of the reactor core.
		in the case of a thermal reactor there is an optimum ratio of moderator to fuel volume, there is a void effect with positive coefficient in an excessively moderated reactor.
	www.euronuclear.org /info/encyclopedia/v/void-effect.htm (163 words)

	World Nuclear Association \| Information and Issue Briefs \| The RBMK reactor (Site not responding. Last check: 2007-10-13)
		Positive void coefficient is a term often associated with the RBMK reactors, the type involved in the Chernobyl disaster.
		The quantum of the coefficient is simply a measure of the speed of change of state of the reactor.
		When the void coefficient is strongly positive, the power can increase very rapidly because any power increment that occurs leads to increased steam generation, which in turn leads to a further increase in power.
	world-nuclear.org /info/inf31.htm (1860 words)

	Moderator
		The pressure coefficient of reactivity for the reactor is the result of the effect of pressure on the density of the moderator.
		The void coefficient is significant in water-moderated reactors that operate at or near saturated conditions.
		The void coefficient of reactivity becomes significant in a reactor in which the moderator is at or near saturated conditions.
	www.tpub.com /doenuclearphys/nuclearphysics64.htm (1137 words)

	RBMK
		In a water-moderated reactor, this effect is countered by the reduction in moderation, but in the RBMK the moderating effect of the water is small compared to that of the graphite, so the overall effect is positive.
		The RBMK as designed also had a "positive power coefficient", meaning that an increase in reactor power tends to further increase the rate of reaction.
		Large positive void and power coefficients can produce runaway conditions and have not been permitted in other reactor designs, but it was not possible to eliminate them from the RBMK if natural uranium fuel was to be used.
	www.ebroadcast.com.au /lookup/encyclopedia/rb/RBMK.html (452 words)

	Neutron Kinetics of the Chernobyl Accident
		The Chernobyl type of reactor has a positive void coefficient, which means that when a part of the water is replaced by steam the power will increase.
		To study the importance of the magnitude of the void coefficient, it is enough to plot the first colon of the x matrix.
		When the void coefficient is zero the power is not increasing at all.
	www.euronuclear.org /e-news/e-news-13/neutron-kinetics-print.htm (678 words)

	CBSNews.com (Site not responding. Last check: 2007-10-13)
		This peculiarity of the design is known as the positive void coefficient, which many other reactors also have but can be controlled by safety features that Chernobyl's RMBK reactor sadly lacked.
		The positive void coefficient happens when excess steam, which leads to an increase in power generation, collects to form pockets that are known as voids.
		The problem with the positive void coefficient is that an increase in power generation results in an increase in the level of steam, which thus leads to a further increase in the power generation.
	www.cbsnews.com /htdocs/nuclear_disasters/chernobyl_meltdown.html (361 words)

	C++ Programs - Cramer's Rule
		void allocate_floats(int and, float and, float and, float *and);
		void initialize(float andi_determinant_original, float i_variable, float i_constant, float *i_determinant_modified)
		void allocate_floats(int andaf_size, float andaf_variable, float andaf_constant, float *andaf_determinant_modified)
	members.tripod.com /gainsborough7/cPrograms/cramersRule.htm (535 words)

	The Canadian Nuclear FAQ - Section D: Safety and Liability
		It should also be noted that the void coefficient is but one contributor to total reactivity feedback, and the power coefficient, which is of more importance to operational stability, is actually quite small (see next FAQ for a discussion of the overall effect on safety).
		Finally, the void coefficient is highly dependent upon fuel composition, and it is practically possible to "tailor" the coefficient within a wide range, simply by altering the fuel design.
		For example, coolant voiding is known to cause a slight shift of thermal flux towards the centre of the fuel, simply because more thermal neutrons, diffusing in from the bulk moderator, are able to survive the journey.
	www.nuclearfaq.ca /cnf_sectionD.htm (7033 words)

	Nuclear is Our Future: Energy Policy in the Shadow of Chernobyl
		PWRs have a negative temperature coefficient as well, since they slow down on the expansion of the fuel, and a negative void coefficient, since they slow down when they lose the neutron-moderating effect of their cooling water if it boils.
		The net effect of the positive void coefficient and the badly-designed geometry was a positive temperature coefficient (i.e., if the temperature goes up, the reactor speeds up, raising the temperature, making it speed up more, until power is manually reduced or it melts down).
		The positive void coefficient then performed its only good function and lowered the power of the reactor, since higher coolant flow would result in fewer voids, and more control rods were removed to make up for this.
	blog.niof.org /2006/04/energy-policy-in-shadow-of-chernobyl.html (4524 words)

	Nuclear Safety Parameters of TRIGA Reactor
		Negative void effect of the core is prevailing considering water density changes due to heating or cooling.
		Power reactivity coefficient, which is a "superposition" of fuel temperature reactivity and water temperature reactivity coefficient is also negative.
		Power peaking factors and temperature reactivity coefficients are the most important reactor parameters for normal operation and transient safety analysis in research as well as in power reactors.
	www-rcp.ijs.si /ric/safety_parameters-a.html (943 words)

	Time Line
		This new core subcooling increases the poisoning of the core and a greater void collapse.
		The steam pressure increases due to the removal of the relief of steam associated with the turbine and the reduction of the feedwater flow.
		These factors combine to increase the void coefficient of the coolant and at the same time the increase the power of the reactor.
	users.owt.com /smsrpm/Chernobyl/tlinedt.html (2418 words)

	Pressure Coefficient
		coefficient of reactivity for the reactor is the result of the effect of pressure on the density of the
		coefficient is caused by the formation of steam voids in the moderator.
		The void coefficient is significant in water-moderated reactors that operate
	www.tpub.com /content/doe/h1019v2/css/h1019v2_51.htm (268 words)

	Light water graphite reactor (RBMK) - Encyclopedia of Earth
		After the accident in unit 4 at the Chernobyl, Ukraine nuclear facility, the primary concern became reducing the positive void coefficient.
		Positive void coefficient is a term often associated with the RBMK reactors—the type involved in the Chernobyl, Ukraine disaster.
		Either the nuclear reactor characteristics can be altered to reduce the positive void coefficient, or systems can be provided that will shut the reactor down very quickly if an increase in power is detected.
	www.eoearth.org /article/Light_water_graphite_reactor_(RBMK) (1958 words)

	Chernobyl sequence
		The most important characteristic of the RBMK reactor is that it possesses a "positive void coefficient".
		However, at a lower power output of less than 20% the maximum, the positive void coefficient effect is dominant and the reactor becomes unstable and prone to sudden power surges.
		The loss of cooling water exaggerated the unstable condition of the reactor by increasing steam production in the cooling channels (positive void coefficient), and the operators could not prevent an overwhelming power surge, estimated to be 100 times the nominal power output.
	www.uic.com.au /Chernosequence.htm (2512 words)

	Products
		The principal difference between the two models is that instead of voids, core flow control, a P-F Map, and IR scram, the PWR Trainer includes B-10 poison control and control by steam demand.
		Without steam flow there are no voids in the core, the moderator temperature can increase with reactor power, and the moderator temperature coefficient is in effect.
		There are no voids in the core for this condition, the moderator temperature can change depending on the mismatch between reactor power and steam flow, and the moderator temperature coefficient is in effect.
	www.echoscaninc.com /product.cgi?code=U1VSLTAwMQ== (1813 words)

	INSC: Soviet Designed Reactors
		The relative magnitudes of the reactivity change due to changes, on voiding, in neutron absorption and in neutron moderation are compared for several lattice configurations that include either absorber rods or followers of various materials.
		This has led to the identificaiton of the mechanism that makes the void coefficient dependent on the number of absorber rods in the core.
		In line with these results, it is shown that replacing the graphite in the follower with nonmoderating materials reduces the void coefficient dependence on the number of absorber rods and is an economic method that may have potential in the void coefficient reduction program.
	www.insc.anl.gov /sov_des/chernbib.php (1600 words)

	Chernobyl shut down
		Because of the pressure-tube design using water as coolant within channels in the graphite moderator, RBMK reactors have a significant positive void coefficient of reactivity in which a reduction in the coolant density results in an increase in the system reactivity due to a reduction in neutron absorption by the coolant.
		This reactor also has a positive moderator coefficient of reactivity in which the reactivity increases as the temperature of the moderator increases.
		Both of these operating characteristics are compensated by the negative temperature coefficient of the fuel which loses reactivity as the fuel temperature increases.
	hps.org /publicinformation/ate/q1743.html (847 words)

	NUKEFACTS ... and fictions
		The moderator temperature coefficient of reactivity is ____________ negative at end of core life because, over core life, the utilization of thermal neutrons ____________.
		MTC becomes less negative because as control rods are withdrawn from the core, the increase in the number of neutrons leaking from the core for a 1 F increase in moderator temperature is smaller.
		The void coefficient is adding more negative reactivity in the upper half of the core.
	www.pipeline.com /~rstater/nrccoeff.html (2198 words)

	CRACK DEVELOPMENT IN SULFATE (Site not responding. Last check: 2007-10-13)
		where D is the generalized diffusion coefficient which accounts for ion motion in the material cavity space and void shape and number per unit section, while k is a constant of chemical reaction rate and c is the ion concentration per unit volume.
		is a coefficient of sulfate ion diffusion in water, regarding cement stone porosity and grain size, b is a constant and c
		Regarding the diffusion of electrolytes, the diffusion coefficient D depends on the solution ion concentration –[8], [9], and ion motion hampers under comparatively high concentration close to that of the saturation concentration.
	jan.ucc.nau.edu /nms35/Congress_mech.htm (1262 words)

	Step-by-Step
		Although the error estimator (and its implementation in the deal.II library) is capable of handling variable coefficients in the equation, we will not use this feature since we are only interested in a quick and simple way to generate locally refined grids.
		After setting up all the degrees of freedoms, here are now the differences compared to step-5, all of which are related to constraints associated with the hanging nodes.
		The region outside is refined rather randomly, since the second derivative is constant there and refinement is therefore mostly based on the size of the cells and their deviation from the optimal square.
	www.dealii.org /developer/tutorial/chapter-2.step-by-step/step-6.html (4729 words)

	How was the Nuclear Reator Designed? (Site not responding. Last check: 2007-10-13)
		Another thing, the positive void coefficient, prepared the Chernobyl power plant for the explosion.
		The void coefficient is the change of the state in a reactor.
		In the positive void coefficient, more energy is produced, yet it is hard to control this sudden increase of energy.
	www.upd.edu.ph /HomePages/ismed/public_html/agham/archive/6th/extras/lawrence/design2.htm (259 words)

	Effects of variation of soil properties in pore pressure dissipation
		The coefficient of hydraulic conductivity k is constant and the soil is an isotropic material.
		One of these parameters is the coefficient of hydraulic conductivity, which has been related to the void ratio by several researchers using different functions.
		K (coefficient of hydraulic conductivity) was assumed to be constant during the experiment for a certain applied load.
	www.ce.gatech.edu /~geosys/guillermo (1937 words)

	INSP: RBMK Description
		In tech nical terms, this characteristic is called a "positive void coefficient." Soviet engineers sought to mitigate this tendency by backfitting RBMKs with faster-acting control rods and other improvements.
		U.S.- style light water moderated plants, however, are designed with just the opposite characteristic--a "negative void coefficient"--so that the nuclear chain reaction automatically stops when coolant is lost.
		The design of the Kursk-5 RBMK has reportedly been modified, resulting in a negative void coefficient.
	insp.pnl.gov /-profiles-reactors-rbmk.htm (336 words)

	Hazards
		In plain English, the positive void coefficient means that whenever there is a loss of coolant in one or more channels of the reactor core, there is an immediate power surge.
		The pressure-tube design of the ill-fated Chernobyl reactor was an important factor contributing to the sudden surge in power and heat -- brought on by the positive void coefficient -- that led to the melting of the core and the explosive penetration of containment in the accident of 1986.
		The positive void coefficient of reactivity is a generic design flaw of all pressure tube reactors; it is one of the worrisome characteristics of the Cernavoda 2 reactor.
	www.protectia-mediului.ro /en/nuclear/cernavoda2npp/hazards.html (7484 words)

	Sequence Of Events Leading To The Accident (Site not responding. Last check: 2007-10-13)
		For the test the reactor was to be stabilised at 1,000MW prior to shutdown, however, due to operational error the power fell to about 30MW where the positive void coefficient became a problem.
		This created additional steam in the cooling channels (positive void coefficient) and the operators could not control a power surge estimated to 100 time the nominal power.
		The sudden increase in temperature caused part of the fuel to rupture, fuel particles then reacted with the water creating a steam explosion which destroyed the reactor core.
	www.chernobyl.co.uk /sequence.html (316 words)

	Nuclear Engineering International
		Although the influence on the breeding ratio is of the same order, however, the effect on the void coefficient is not identical.
		It follows from this that the state of the reactor at the end of the transition phase, when all additional absorbers are removed, is more hazardous than its state when reload fuel is installed, although this fuel is comparable in terms of mean burnup”.
		INSAG-7 (para 2.1): “Thus, although the void coefficient of reactivity varied over a wide range from negative to positive values as a function of the composition of the core and the operating regime of the reactor, the fast power coefficient remained negative under normal operating conditions.
	www.neimagazine.com /storyprint.asp?sc=2035398 (4607 words)

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