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Topic: Subcritical reactor

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	Subcritical reactor - Wikipedia, the free encyclopedia
		subcritical reactor is a nuclear fission reactor that produces fission without achieving criticality.
		Subcritical reactors have been proposed both as a means of generating electric power and as a means of transmutation of nuclear waste, so the gain is twofold.
		However, the solution of a subcritical reactor might be favoured for a better public acceptance—it is considered more acceptable to burn the waste than to bury it for hundreds of thousands of years.
	en.wikipedia.org /wiki/Subcritical_reactor (747 words)

	Class Definition for Class 376 - INDUCED NUCLEAR REACTIONS: PROCESSES, SYSTEMS, AND ELEMENTS
		A nuclear reactor in which most of the fissions are caused by neutrons moving with substantially the high speeds they possess at the time of their birth in fission.
		A reactor in which the fuel in the form of particles is maintained in a fluidized state by a fluid medium.
		A reactor in which the fuel and moderator are intimately mixed or dispersed (e.g., the fuel may be a uranium salt dissolved in heavy water) as a solution or slurry.
	www.uspto.gov /go/classification/uspc376/defs376.htm (5079 words)

	Accelerator-driven reactors (B. Alan Guthrie)
		The proposed idea is take a subcritical reactor (which is probably more like 0.95 to 0.99 in its neutron multiplication) and use an accelerator to supply neutrons to sustain the reaction.
		Going back to my hypothetical reactor, let us suppose that the reactor has a multiplication factor of 0.95; that is, the neutrons resulting from 100 fissions will cause only 95 fissions in the next "generation." The accelerator would supply the additional five neutrons so that power level would be maintained at a constant level.
		The idea behind the accelerator-driven reactor is when the accelerator is turned off, the chain reaction would be subcritical and the reactor power would quickly die away.
	yarchive.net /nuke/accelerator_driven_reactors.html (1414 words)

	SUBCRITICAL (Site not responding. Last check: 2007-10-22)
		Subcritical multiplication is the phenomenon that accounts for the changes in neutron flux that takes place in a Subcritical reactor due to reactivity changes.
		The addition of source neutrons to the reactor containing fissionable material has the effect of maintaining a much higher stable neutron level due to the fissions occurring than the neutron level that would result from the source neutrons alone.
		In a subcritical reactor, the neutron level is related to the source strength by Equation (4-2).
	www.tpub.com /doenuclearphys/nuclearphysics77.htm (958 words)

	UWNR (Site not responding. Last check: 2007-10-22)
		Most nuclear reactors use the energy (heat) of the fission fragments to produce steam which is then used to spin a turbine and produce electricity.
		The UWNR is a research reactor primarily used to instruct students, train operators and perform scientific studies using the neutrons in the reactor core.
		Because of the large amount of water between the reactor core and the top of the pool and also because the water serves as a shield against radiation, personnel can go to the top of the pool during operation of the reactor.
	reactor.engr.wisc.edu /reactor.htm (829 words)

	Class 376: INDUCED NUCLEAR REACTIONS: PROCESSES, SYSTEMS, AND ELEMENTS / U.S. Patent Classification Definitions
		The fertile material may be (1) positioned in the fissile fuel assembly either (a) mixed with the fissile fuel material itself, or (b) as a separate distinct component of the fissile fuel assembly; or (2) positioned in a nonfissile fuel assembly, i.e., a fertile fuel assembly.
		Subject matter wherein (a) coolant is caused to traverse the reactor core through separate and independent routes, or (b) coolant is caused to traverse the reactor core a plurality of times prior to its being sent to a heat exchanger or other utilization means which would remove the heat from the coolant.
		Subject matter wherein the reactor structure is in an underground cavity or is caused to form the cavity and radioactive contamination resulting from operation of the reactor structure is removed or reduced.
	www.uspto.gov /go/taf/def/376.htm (9607 words)

	Nuclear reactor physics - Wikipedia, the free encyclopedia
		A reactor consists of an assembly of nuclear fuel (a reactor core), usually surrounded by a neutron moderator such as water, graphite, or zirconium hydride, and fitted with mechanisms such as control rods that control the rate of the reaction.
		Even in a subcritical assembly such as a shut-down reactor core, any stray neutron that happens to be present in the core (for example from spontaneous fission of the fuel, from radioactive decay of fission products, or from a neutron source) will trigger an exponentially decaying chain reaction.
		Nuclear reactors with heavy water moderation can operate with natural uranium, eliminating altogether the need for enrichment and preventing the fuel from being useful for nuclear weapons; the CANDU power reactors used in Canadian power plants are an example of this type.
	en.wikipedia.org /wiki/Nuclear_reactor_physics (2780 words)

	Nuclear Regulatory Commission Letter
		The stable reactor period given by equation (1) strictly applies to the situation where power is constant, a step change in positive reactivity is inserted, and the power increases on a constant period, all other effects (such as temperature changes) being neglected.
		Without delayed neutrons in the core, the reactor period would be determined by prompt neutrons alone, resulting in an uncontrollably short reactor period for even a small addition of positive reactivity--this is what happens in a prompt critical reactor.
		The reactor period response from point 2 to 3 is due to combination of increasing prompt neutrons and increasing delayed neutrons.
	www.pipeline.com /~rstater/Nuknrc5f.html (2272 words)

	World Nuclear Association \| Information and Issue Briefs \| Accelerator-driven Nuclear Energy (Site not responding. Last check: 2007-10-22)
		In such a subcritical nuclear reactor the neutrons produced by spallation would be used to cause fission in the fuel, assisted by further neutrons arising from that fission.
		One then has a nuclear reactor which could be turned off simply by stopping the proton beam, rather than needing to insert control rods to absorb neutrons and make the fuel assembly subcritical.
		Therefore in principle, the subcritical nuclear reactor may be able to convert all transuranic elements into (generally) short-lived fission products and yield some energy in the process.
	www.world-nuclear.org /info/inf35.htm (1451 words)

	UWNR Quick Tour (Site not responding. Last check: 2007-10-22)
		The reactor core (fuel and control elements) resides at the bottom of a deep pool of water.
		It is a metal pipe that runs from the core to the outside of the reactor and it is used to carry a stream (or beam) of neutrons to the outside of the reactor.
		The reactor console is in the control room where reactor operators monitor the nuclear reactor.
	reactor.engr.wisc.edu /qtour.htm (3732 words)

	Fluidized Bed Nuclear Reactor
		The nuclear reactor based on the fluidized bed concept proposed by Dr. Farhang Sefidvash, professor of Nuclear Engineering at the Federal University of Rio Grande do Sul, is modular in design such that any size of the reactor can be constructed from the basic module.
		The reactor is surrounded by a graphite reflector and a biological shield.
		In the case for a probable accident, the motor of the pump is made to stop or rotate at a low velocity resulting in the precipitation of fuel elements from the reactor core into the fuel chamber where due to the geometric configuration stay in a highly subcritical condition.
	www.rcgg.ufrgs.br /fbnr_gc_ing.htm (1277 words)

	NUKEFACTS ... and fictions
		Answer: In a subcritical reactor, the fission process is not self-sustaining and would tend to cause the neutron population to decrease.
		Assume the reactor remains subcritical, and that the reactor reaches a stable condition before each reactivity insertion.
		Subcritical multiplication is a process that occurs whether a reactor startup is in progress or not.
	www.pipeline.com /~rstater/nuke1m3a.html (3732 words)

	US PATENT CLASS 376-- Class Notes
		reactor and some reactor structure is also recited (other than in a mere broad reference to the reactor), or where (b) the control element or portion thereof is defined as being absorbing material or neutron absorbing material - patents to such elements are classified in this class (376).
		53+, for patents to aircraft using a nuclear reactor as a power-generating source in which no structural elements of the nuclear reactor is claimed.
		All particles of less than atomic mass, i.e., the elementary particles (proton, neutron, electron, positron, neutrino, meson, etc.) as well as the alpha particles and deutrons, the charge and mass of which indicates them to be composite particles.
	www.patentec.com /data/class/defs/376/0.html (2873 words)

	Comments on Accelerator Driven
		For a critical reactor any random increase in power generation must be controlled by a rapid feedback mechanism through mechanical control of neutron absorbing rods (it is an energy amplifier with infinite gain).
		For Petrov, living in a country that designed the RBMK reactor which is very susceptible to accidents where the reactor can go prompt critical (as happened at Chernobyl) there is both a strong technical and a strong psychological advantage to avoid criticality.
		The reason is that the costs of a nuclear reactor are NOT connected with the reactivity control, but with the heat removal - and the heat removal problems are almost the same for a reactor and a subcritical assembly.
	phys4.harvard.edu /~wilson/publications/ppaper703.html (8130 words)

	Russia
		The State Specialized Design Institute designed the reactor.[1] The reactor is used for loop testing of fuel elements and assemblies for power and research reactors, and the production of transuranium elements.[2] The reactor core is about 1m in diameter, and it is submerged in a pool under 9m of water.
		This thermal/fast neutron research reactor was commissioned in 1961.[1,2] It is used for irradiating samples of reactor materials, studying their properties, producing transuranic elements, and a number of other studies in nuclear physics.[2] In 1991-1992 it underwent reconstruction.
		A safety precaution valve was activated, reducing pressure in the reactor, causing an emergency shutdown which resulted in the leakage of 100 tons of a steam and gas mixture which measured at 100 millicuries, contaminating some 200 sq.
	www.nti.org /db/nisprofs/russia/reactor/research/with/sriar.htm (5389 words)

	IEER: Science for Democratic Action Vol. 5 No. 4: Reactor Control (Site not responding. Last check: 2007-10-22)
		Control of a nuclear reactor is accomplished through control of the rate of fission reactions in the reactor.
		When the reactor is supercritical, the power output is increasing, and when it is subcritical, power decreases until the reactor shuts down.
		The rate of fission in a reactor is controlled through the insertion and withdrawal of neutron-absorbing material, such as boron, in the form of control rods which are interspersed with the fuel rods.
	www.ieer.org /sdafiles/vol_5/5-4/reactor.html (414 words)

	11co997
		Most of the fundamental parameters in the nuclear reactor along with the measurement techniques for neutron detection are explored in this course.
		Discussion of reactor physics concepts, solutions to the wave equation in cylindrical and flux perturbations due to fuel void regions and void regions containing poison (such as control rods).
		Measurement of Radial and Vertical Buckling in a Subcritical Reactor.
	www.eng.uc.edu /~abehbaha/htmfiles/rl/11co198.html (1943 words)

	Instinct Training Ltd. - Nuclear Plant Theory - Neutron Kinetics at Low Power
		Define the subcritical multiplication factor and explain how it is used to calculate the equilibrium neutron level.
		Sketch the curve of neutron flux against time showing the effect of inserting and removing a source from a subcritical reactor.
		Sketch the curve of neutron flux against time showing the approach to criticality by raising control rods in a subcritical reactor with a source.
	www.instinct-training.co.uk /nuclear/nb.htm (166 words)

	Thorium
		Also, all of the mined thorium is potentially useable in a reactor, compared with the 0.7% of natural uranium, so some 40 times the amount of energy per unit mass might theoretically be available (withouit recourse to fast breeder reactors).
		Kakrapar-1 was the first reactor in the world to use thorium, rather than depleted uranium, to achieve power flattening across the reactor core.
		Molten salt reactors - This is an advanced breeder concept, in which the fuel is circulated in molten salt, without any external coolant in the core.
	www.uic.com.au /nip67.htm (2703 words)

	ANS : Store : Electronic Articles
		It is found that subcritical operation provides features that are favorable from a point kinetics view of application.
		If a subcritical reactor is subject to a change in the strength of the external source, or a change in reactivity within the subcritical range, the neutron population will adjust to a new stationary level.
		However, the effect is characteristically lowered in subcritical versus critical or near-critical reactor operation.
	www.ans.org /store/index.cgi?i=E110000-nse-149-3-298-311 (290 words)

	IAC - AFCI RACE Project
		The purpose of the AFCI RACE Project is to conduct subcritical nuclear experiments to contribute to the understanding of neutron coupling in Accelerator-driven Subcritical Systems (ADS).
		This knowledge of coupling between particle accelerators (electron or proton), heavy metal targets, and subcritical systems is necessary for the development of accelerator-driven transmutation of nuclear waste from used nuclear fuel.
		The subcritical assembly consists of an aluminum tank, 150 water-moderated uranium-aluminum fuel plates, and a graphite reflector inside the tank.
	iac.isu.edu /research/RACE.html (356 words)

	ANS : Publications : Journals : Nuclear Science and Engineering : Volume 131 : Design of a Subcritical Assembly for ...
		Although less powerful than using a research reactor as the source of neutrons, these assemblies will provide an adequate source of neutrons for detecting gold concentrations in rock or soil samples down to the limits of economic importance.
		Using a field-portable source of neutrons eliminates the need for shipping samples back to the reactor for analysis, which may be important for reasons of sample security and measurement turnaround time.
		It was found that the optimal location for the irradiation facility (a 4.0-cm-high, 2.0-cm-diam right cylinder) in the subcritical assemblies is the grid location as close to the neutron emitter location as possible.
	www.ans.org /pubs/journals/nse/va-131-2-275-281 (369 words)

	Nuclear Engineering Laboratories
		Otherwise known as the RSEC Beam Laboratory, this facility passes a well-collimated beam of neutrons from the reactor, thermalized by a D2O thermal column, into the Center for use in nondestructive testing and evaluation.
		Perturbed angular correlations spectroscopy is a type of a hyperfine measurement used to determine a change of state in a variety of materials, such as superconductors, ceramics and metals, as a function of experimental parameters.
		The apparatus in this laboratory is instrumented to detect hyperfine interactions that occur in the electric field in the region of the nucleus.
	www.mne.psu.edu /undergrad/NELabs.htm (628 words)

	Method and apparatus for preventing inadvertent criticality in a nuclear fueled electric powering generating unit ...
		At the end of each incremental time period, the microcomputer compares the latest average flux count rate signal with the oldest, and preferably each of the intervening stored values, and if it exceeds any of them by at least a preselected multiplication factor, an alarm is generated.
		The interval and multiplication factor are chosen such that an alarm is generated early enough in the event to provide adequate time for an automatic system or the operator to take action which prevents the reactor from going critical yet minimizes the likelihood of a spurious response.
		As applied to a pressurized water reactor system, boron dilution events are detected in time that the chemical and volume control system can be isolated and the valves for the refueling water storage tank can be opened to inject highly borated water into the reactor coolant system to keep the reactor subcritical.
	www.delphion.com /details?pn=US04582672__ (437 words)

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