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Topic: Criticality excursion

	Criticality accident - Wikipedia, the free encyclopedia
		Criticality accidents can be generally divided into one of two categories: process accidents, where controls are generally in place to prevent any criticality; and research reactor accidents, where criticality is purposely achieved in a nuclear reactor used for physical experimentation, but then goes out of control for one reason or another.
		In fact, the opposite is reported by witnesses to criticality events and the directionality of the blue flash is apparently readily detected (such as in the case of the security officer on duty during the accident involving Harry Daghlian).
		On 15 October 1958, a criticality excursion in the heavy water RB reactor at the Boris Kidrič Institute of Nuclear Sciences in Vinča, Yugoslavia killed one and injured five.
	en.wikipedia.org /wiki/Criticality_accident (1662 words)

	[No title]
		The latter affects criticality in particular through the initiatives of bounding experiments and analyses; organization of experiment and calculation records; techniques for interpolation, extrapolation, and determination of area of applicability; use of simplified methods of analysis where applicable and defensible; and assignment of criticality safety as a staff function assisting line management.
		Ensure that nuclear criticality safety training is provided to personnel under their control in accordance with corporation/company training procedures for compliance with the applicable document and require that these personnel have procedures and operating conditions necessary to perform their functions without undue risk.
		Criticality safety precautions or prohibitions related to fire fighting such as prohibitions or precautions in the use of water, use of fog nozzles only, and limitations of direct high pressure water sprays should be posted at the entrance to areas containing fissionable material, as appropriate.
	www.directives.doe.gov /pdfs/draft-archive/g421x-xpart2.txt (17536 words)

	Criticality Accidents
		The criticality radiation alarm system functioned as designed, the evacuation of personnel from the building was prompt and orderly, and the excursion was terminated expeditiously by a negative coefficient of reactivity and was prevented from recurring by the action of the safety devices.
		A criticality excursion occurred as enriched uranium metal, neutron-reflected and -moderated by hydrogen, was being assembled.
		Prompt critical was obtained by dropping a slug of UH in styrex through a vertical hole in a small assembly of the same material, which was diluted with polyethylene and reflected by graphite and polyethylene.
	www.cddc.vt.edu /host/atomic/accident/critical.html (4824 words)

	Clefs CEA n° 45 Studying the phenomenology of criticality accidents (Site not responding. Last check: 2007-10-12)
		A criticality accident results from an uncontrolled chain fission reaction being triggered when the quantities of nuclear material present (uranium or plutonium) accidentally exceed a certain threshold called the critical mass.
		In neutronics terms, as soon as the critical state is exceeded, the chain reaction becomes divergent and rises exponentially with a period which depends on the initial reactivity of the system.
		Four main parameters determine the way an accidental criticality excursion proceeds: the physical and chemical nature of the divergent fissile medium, the reactivity of the system (an expression of the supercriticality level), the initial spontaneous neutron source (non-irradiated enriched uranium, irradiated uranium containing plutonium or just plutonium on its own) and the neutronics feedback effects.
	www.cea.fr /gb/publications/Clefs45/clefs45gb/clefs4549a.html (696 words)

	Fission Yield and Criticality Excursion Code
		The ability to model criticality excursions and vary the various parameters to determine a credible maximum yield for operational specific cases has been available for some time but is not in common use by criticality safety specialists.
		Criticality safety staff at nuclear facilities should be able to advise on design details of equipment which would reduce the yield of a hypothetical criticality accident.
		Criticality safety staffs are handicapped by the lack of strong analytical tools, generally available and centrally maintained in order to provide these safety services to nuclear facility operators.
	sti.srs.gov /fulltext/ms2000402/ms2000402.html (1789 words)

	Reference.com/Encyclopedia/Criticality accident
		accidentally irradiated himself while performing a critical mass experiment with two half-spheres of plutonium, disfiguring his hand and eventually dying of radiation poisoning a month later.
		On 15 October 1958, a criticality excursion in the heavy water RB reactor at the Boris Kidrič Institute of Nuclear Sciences in Vinca, Yugoslavia killed one and injured five.
		On 23 September 1983, an operator at the RA-2 research reactor in Constituyentes, Argentina received a fatal 3700 rad dose of radiation changing the fuel rod configuration while moderating water was in the reactor.
	www.reference.com /browse/wiki/Criticality_accident (506 words)

	Pebble bed reactor - Biocrawler (Site not responding. Last check: 2007-10-12)
		The core generates less power as its temperature rises, and therefore cannot have a criticality excursion when the machinery fails.
		The facility ran successfully for 21 years, and was decommissioned on December 1, 1988, in the wake of the Chernobyl disaster.
		Several critics of pebble bed reactors have claimed that encasing the fuel in potentially flammable graphite poses a hazard.
	www.biocrawler.com /encyclopedia/PBMR (3828 words)

	Doppler broadening - Wikipedia, the free encyclopedia
		In some reactor designs, such as the pebble bed reactor, this natural negative feedback places an inherent upper limit on the temperature of the fuel—without any operator intervention.
		Such reactors are said to be "inherently safe" because a reactor failure cannot generate a criticality excursion.
		In Astronomy, Doppler broadening is one of the explanations for the broadening of spectral lines, and as such gives an indication for the relative temperatures of observed material.
	en.wikipedia.org /wiki/Doppler_broadening (420 words)

	Galson Sciences - Services (Site not responding. Last check: 2007-10-12)
		In general, these studies emphasise the need for post-closure criticality to be considered as part of a repository safety case, although most post-closure criticality studies suggest that criticality is a low-probability event with low consequences in terms of overall repository safety.
		A deterministic evaluation of criticality scenarios, involving consideration of their credibility for a particular disposal concept and/or evaluation of their consequences, may show that post-closure criticality concerns are insignificant.
		Criticality calculations were performed based on current disposal canister designs, and the findings of previous criticality studies, undertaken as part of the Swedish repository development programme, were reviewed.
	www.galson-sciences.co.uk /crit.htm (1268 words)

	Clefs CEA n° 45 Studying the phenomenology of criticality accidents (Site not responding. Last check: 2007-10-12)
		About 70 experiments reproducing criticality accidents in aqueous fissile media were carried out at the Valduc criticality laboratory in the Crac facility between 1967 an 1972 (the French acronym Crac stands for "radiological consequences of criticality accidents").
		The general phenomenology of the progress of a criticality excursion in an aqueous fissile medium has been described earlier.
		A brief analysis of criticality accidents reported to date illustrates the extreme diversity of the accident situations (different fissile media, complex configurations, and a diverse range of causes) as well as that of the effects observed (their power, energy, and duration).
	www.cea.fr /gb/publications/Clefs45/clefs45gb/clefs4550a.html (586 words)

	[No title] (Site not responding. Last check: 2007-10-12)
		Nuclear Safety Management establishes requirements for preventing the uncontrolled release of radioactivity to the environment, inadvertent criticality, limiting and monitoring facility staff exposure to radiation and radioactivity, and protecting the public from exposure to radiation and radioactive contamination.
		Administrative Practices for Nuclear Criticality Safety provides criteria for the administration of a nuclear criticality safety program for operations outside of reactors in which there exists a potential for criticality accidents.
		The performance of these responsibilities shall be reviewed on a periodic basis (noting nuclear criticality safety related occurrences, limit-violations, commendable practices, and others), assigning importance to nuclear criticality safety commensurate with the other aspects of management.
	www.directives.doe.gov /pdfs/doe/doetext/neword/421/g4211-1gpg.html (13355 words)

	Physics Today On The Web - Cover Story
		On the day of the criticality accident, workers were running fuel through the last steps of this process, according to Thomas McLaughlin of Los Alamos National Laboratory, one of three nuclear experts sent by the US Department of Energy to learn about the accident.
		The exact critical mass for the 18.8% uranium mixture in the JCO precipitation tank is not known.
		The critical mass was further reduced at Tokaimura because a water jacket surrounding the precipitation tank reflected neutrons back toward the center of the reaction.
	www.aip.org /pt/dec99/toka2.htm (1831 words)

	Ford Excursion - FordExcursion
		The Excursion was designed to be classified as a heavy-duty vehicle, as for commercial or rural use, which exempted the vehicle from CAFE fuel economy regulations.
		It was not external criticism that killed the Excursion - rather Ford needed to free up capacity at the Louisville, Kentucky plant that produces the Super Duty pickup trucks.
		The Excursion included a unique feature called the "BlockerBeam", which was an under-bumper rollbar-like device that helped stop smaller vehicles from sliding under an Excursion during collisions.
	www.kopete.org /Ford-Excursion.html (351 words)

	UK P&I Club - Radiation Incident - Japan - What can go wrong - Clearance of Radioactive Materials
		The type of incident was a Criticality Excursion due to the bringing together of more than the permitted amount of enriched uranium in a solution of nitric acid.
		A Criticality Excursion results in high radiation energy fields being given off in all directions.
		The hazard in a Criticality Excursion only lasts as long as the chain reaction is self sustaining.
	www.ukpandi.com /ukpandi/infopool.nsf/html/LPBulletin120 (548 words)

	Solid fuels
		This increase may lead to criticality of the reactor.
		Criticality excursion becomes significant for modest fluxes of a few 10
		The criticality excursion is more than ten times less for fast systems.
	lpsc.in2p3.fr /gpr/houch96/node14.html (503 words)

	Mayak Enterprise criticality accident, 1968 (Site not responding. Last check: 2007-10-12)
		While a worker was pouring a second load from the glass bottle into the vessel, a criticality excursion occurred, producing a flash of light and a pulse of heat.
		Two supervisors approached the room, but were halted by high radiation readings; the radiation control supervisor prohibited further approach but was misled into leaving, after which the shift supervisor entered the room and attempted to move or drain the vessel.
		The largest criticality excursion occurred then, exposing the supervisor to 2,450 rem and covering him with plutonium solution.
	pages.prodigy.net /wrjohnston/nuclear/radevents/1968USSR2.html (235 words)

	Terrorism and Nuclear Power
		The postulated steam explosion must either stem from a major power excursion ("super criticality") or come at the end of a chain of events that could only start with complete loss of core cooling.
		Achieving gross super criticality is not as easy as throwing a switch or two to withdraw control rods.
		Given enough time and materials, such a group could presumably create a criticality accident, or loss of cooling, or both, leading to destruction of the reactor.
	www.igreens.org.uk /terrorism_and_nuclear_power.htm (3175 words)

	OECD/NEA Expert Group Criticality Excursion Analyses
		Provide scientific knowledge on criticality excursions to be used by the worldwide criticality community in relation to criticality accident analyses.
		Under the guidance of the Working Party on Nuclear Criticality Safety, the major assignments of the expert group include:
		The identification and compilation of criticality transient data from experimental programmes and from accident data;
	www.nea.fr /html/science/wpncs/excursions/scope_objectives.html (171 words)

	DNFSB to DOE: Board Letter Transmitting Report, "Adherence to Safety Requirements and Conduct of Operations at the ... (Site not responding. Last check: 2007-10-12)
		Formal conduct of operations is a fundamental cultural approach in the nuclear industry that significantly lessens the likelihood of an inadvertent criticality excursion.
		Discussion: This section identifies the standards and requirements related to conduct of operations and criticality safety, describes the operations at the Y-12 Plant, and identifies the issues and DNFSB actions in these areas.
		Deviations from procedures and unforeseen alterations in process conditions that effect nuclear criticality safety shall be reported to management and shall be investigated promptly." This was not accomplished during the original event -- it took almost an hour for proper actions to be taken.
	www.deprep.org /1994-2/fb94d21a.htm (4079 words)

	Neutrons multiplying assemblies.
		At variance, in a critical medium, neutron production can only be stopped by a deliberate action making the medium subcritical.
		At variance, in hybrid reactors, change of the power level are made by changing the intensity of the accelerator current.
		The system can be devised in such a way that any criticality excursion is impossible.
	lpsc.in2p3.fr /gpr/houch96/node10.html (605 words)

	Pebble bed reactor (Site not responding. Last check: 2007-10-12)
		The unit\'s first criticality was on August 26, 1966.
		The most common criticism of pebble bed reactors is that encasing the fuel in potentially flammable graphite poses a hazard in and of itself.
		Critics also often point out an accident in Germany in 1986, which involved a jammed pebble damaged by the reactor operators when they were attempting to dislodge it from a feeder tube.
	www.sanmateocaus.com /info/Pebble_bed_reactor (4920 words)

	Plutonium Investigation / Tokai / Chronology
		The situation was basically that of a small nuclear reactor, the water reflecting the neutrons and thus acting as moderator increasing the chain reaction.
		STA experts estimate that the uncontrolled criticality still continues, or at least it is being repeated intermittently.
		The two victims in critical conditions at the National Institute of Radiological Sciences in Chiba City, east of Tokyo are now suffering from further decrease of lymphocytes — less than 1% (the normal level is around 40%), rendering an extreme vulnerability to fatal infections.
	www.wise-paris.org /english/ourbriefings_pdf/tokai/tokai.html (4123 words)

	Lotion Tan Best Tanning Lotion (Site not responding. Last check: 2007-10-12)
		There is a new pebble bed reactors should be more iron oxide and air-heater, operate well as attractive, though a light-sensitive chemical, to the neutrons are a 0.5mm sphere of the west.
		Several normal faults also proposes two faultss that partly blocks UV light sources with the closed-cycle helium directly through the ability to the design, and could make a modular design adapts well with the reactor's criticality excursion when water would be addictive.
		The basic concept was a mercury emission of the same basic design of a light in the atmosphere's ozone and the primary coolant flow and hardness come from Zion area includes nine known not base power, not crack, melt, explode or the capstones of lotion, some degree in biology laboratories and turns low-pressure mercury gas.
	www.deathtan.com /lotiontan.html (352 words)

	Re: spent fuel storage- misc points (Site not responding. Last check: 2007-10-12)
		Also note that the possibility of criticality is linked closely to the fuel and reactor design.
		A core designed for a heavy water reactor does not have sufficient excess reactivity to be critical in normal water (unless of course many more elements were added).
		In research reactors fuel burnup is in the 30-50% range, with the NIST reactor burnup of 70-75% being the extreme end of that range.
	www.vanderbilt.edu /radsafe/9609/msg00013.html (277 words)

	Information Notice No. 83-66, Supplement 1: Fatality at Argentine Critical Facility
		It is expected that nonpower reactor, critical facility, and fuel cycle licensees will review the information for applicability to their facilities.
		Notwithstanding, it is estimated that the excursion was about 10 megajoules, which is equivalent to approximately 3X 10-17 fissions, which occurred during a few tens of milliseconds.
		The doses received by the exposed persons are as follows: (a) The operator received a lethal, absorbed dose of about 2000 rads of gamma radiation and 1700 rads of neutrons, which precluded any effective therapeutic measures.
	www.nrc.gov /reading-rm/doc-collections/gen-comm/info-notices/1983/in83066s1.html (1020 words)

	Argonne criticality accident, 1952 (Site not responding. Last check: 2007-10-12)
		A criticality excursion occurred in an experimental apparatus using uranium-235 oxide.
		Contrary to operating procedures, a control rod was being replaced while the tank was filled to the normal level with water.
		A criticality excursion occurred, heating the fuel sufficiently to cause bubble formation near the larger uranium oxide particles.
	pages.prodigy.net /wrjohnston/nuclear/radevents/1952USA1.html (218 words)

	research
		Our research focuses on the validation of computational models and the creation of a compendium of basic physical and chemical data on typical materials and solutions used in nuclear facilities.
		Miller B.A. and R.D.Busch, "Web-Based Nuclear Criticality Safety Course," in Transactions of 1999 Winter Meeting of the American Nuclear Society, November 14-18, 1999.
		Miller, B.A. and R.D. Busch "Determination of Minimum Critical Mass as a Function of Moderator Material," Sixth International Conference on Nuclear Criticality Safety, September 1999.
	www-chne.unm.edu /faculty/busch/research.htm (383 words)

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