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Title: Experiments on liquid-metal fast breeder reactor aerosol source terms after severe accidents

Abstract

In the extremely unlikely event of a liquid-metal fast breeder reactor core disruptive accident, expanding core material or sodium vapor inside the sodium pool may cause leaks in the vessel head and transport of radioactive material, mostly aerosols, in one large bubble or several smaller bubbles under energetic conditions to the cover gas and through leaks to the inner containment (''instantaneous source term''). Out-of-pile experiments on bubble expansion from a pressurized source inside a liquid (water or sodium) and related phenomena like heat transfer, condensation, entrainment, rise, and aerosol transport were carried out in France and the United States and are continuing in the Federal Republic of Germany. Parameters and results of these experiments are described and discussed, mainly concerning the aerosol problem. It appears that several mechanisms exist for a very efficient removal of particles from the bubble. Retention factors larger than 10,000 were found in most cases. In addition, a short survey is given of French and German experiments on fuel and fission product release from evaporating or burning sodium pools (delayed source term).

Authors:
; ; ;
Publication Date:
Research Org.:
Commissariat a l'Energie Atomique, Centre d'Etudes Nucleaires, DGR-CEA/ERDI/CENG-85X, 38041 Grenoble, Cedex (FR)
OSTI Identifier:
5010746
Alternate Identifier(s):
OSTI ID: 5010746
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nucl. Technol.; (United States); Journal Volume: 81:2
Country of Publication:
United States
Language:
English
Subject:
22 GENERAL STUDIES OF NUCLEAR REACTORS; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; 42 ENGINEERING; 54 ENVIRONMENTAL SCIENCES; LMFBR TYPE REACTORS; HEAT TRANSFER; LOSS OF COOLANT; REACTOR ACCIDENTS; REACTOR SAFETY EXPERIMENTS; TEST FACILITIES; RADIOACTIVE AEROSOLS; ENVIRONMENTAL TRANSPORT; REACTOR CORES; FEDERAL REPUBLIC OF GERMANY; FRANCE; LEAK DETECTORS; SODIUM; USA; WATER; ACCIDENTS; AEROSOLS; ALKALI METALS; BREEDER REACTORS; COLLOIDS; DISPERSIONS; ELEMENTS; ENERGY TRANSFER; EPITHERMAL REACTORS; EUROPE; FAST REACTORS; FBR TYPE REACTORS; HYDROGEN COMPOUNDS; LIQUID METAL COOLED REACTORS; MASS TRANSFER; METALS; NORTH AMERICA; OXYGEN COMPOUNDS; REACTOR COMPONENTS; REACTORS; SOLS; WESTERN EUROPE 220900* -- Nuclear Reactor Technology-- Reactor Safety; 210500 -- Power Reactors, Breeding; 420400 -- Engineering-- Heat Transfer & Fluid Flow; 500300 -- Environment, Atmospheric-- Radioactive Materials Monitoring & Transport-- (-1989)

Citation Formats

Berthoud, G., Longest, A.W., Wright, A.L., and Schutz, W.P.. Experiments on liquid-metal fast breeder reactor aerosol source terms after severe accidents. United States: N. p., 1988. Web.
Berthoud, G., Longest, A.W., Wright, A.L., & Schutz, W.P.. Experiments on liquid-metal fast breeder reactor aerosol source terms after severe accidents. United States.
Berthoud, G., Longest, A.W., Wright, A.L., and Schutz, W.P.. Sun . "Experiments on liquid-metal fast breeder reactor aerosol source terms after severe accidents". United States. doi:.
@article{osti_5010746,
title = {Experiments on liquid-metal fast breeder reactor aerosol source terms after severe accidents},
author = {Berthoud, G. and Longest, A.W. and Wright, A.L. and Schutz, W.P.},
abstractNote = {In the extremely unlikely event of a liquid-metal fast breeder reactor core disruptive accident, expanding core material or sodium vapor inside the sodium pool may cause leaks in the vessel head and transport of radioactive material, mostly aerosols, in one large bubble or several smaller bubbles under energetic conditions to the cover gas and through leaks to the inner containment (''instantaneous source term''). Out-of-pile experiments on bubble expansion from a pressurized source inside a liquid (water or sodium) and related phenomena like heat transfer, condensation, entrainment, rise, and aerosol transport were carried out in France and the United States and are continuing in the Federal Republic of Germany. Parameters and results of these experiments are described and discussed, mainly concerning the aerosol problem. It appears that several mechanisms exist for a very efficient removal of particles from the bubble. Retention factors larger than 10,000 were found in most cases. In addition, a short survey is given of French and German experiments on fuel and fission product release from evaporating or burning sodium pools (delayed source term).},
doi = {},
journal = {Nucl. Technol.; (United States)},
number = ,
volume = 81:2,
place = {United States},
year = {Sun May 01 00:00:00 EDT 1988},
month = {Sun May 01 00:00:00 EDT 1988}
}
  • During a hypothetical core-disruptive accident (HCDA) in a liquid-metal fast breeder reactor (LMFBR), a considerable amount of radioactive material could be released in an aerosol form within the containment vessel. The role of condensation in influencing the source term in the cover-gas region of a liquid-metal fast breeder reactor was analyzed. A computer program was developed that considers both coagulation and condensation to solve the integro-differential equation governing the aerosol behavior in the cover-gas region. Results presented in this paper for a representative case show that condensation can have a very substantial effect on the particle size distribution in themore » cover gas and hence on the source term in the containment aerosol behavior computer programs. 14 refs.« less
  • This paper reports that analyses of unprotected loss-of-flow accidents for medium-size cores of current liquid-metal fast breeder reactors have shown that the accident proceeds into a transition phase where further meltdown is accompanied by recriticalities and secondary excursions. Assuming very pessimistic conditions concerning fuel discharge and blockage formation, a neutronically active whole-core pool of molten m material can form. Neutronic or thermohydraulic disturbances may initiate a special motion pattern in these pools, called centralized sloshing, which can lead to energetic power excursions. If such a whole-core pool is formed, its energetic potential must be adequately assessed. This requires sufficiently correctmore » theoretical tools (codes) and proper consideration of the fluid-dynamic and thermo-hydraulic conditions for these pools. A series of experiments has been performed that serves as a benchmark for the SIMMER-II and the AFDM codes in assessing their adequacy in modeling such sloshing motions. Additional phenomenologically oriented experiments provide deeper insight into general motion patterns of sloshing fluids while taking special notice of asymmetries and obstacles that exist in such pools.« less
  • Experimental and theoretical studies have been performed to characterize the behavior of airborne particulates (aerosols) expected to be produced by hypothetical core disruptive accidents (HCDAs) in liquid-metal fast breeder reactors (LMFBRs). These aerosol studies include work on aerosol transport in a 20-m-high, 850-m/sup 3/ closed vessel at moderate concentration; aerosol transport in a small vessel under conditions of high concentration (approx. 1 kg/m/sup 3/), high turbulence, and high temperature (approx. 2000/sup 0/C); and aerosol transport through various leak paths. These studies have shown that little, if any, airborne debris from LMFBR HCDAs would reach the atmosphere exterior to an intactmore » reactor containment building.« less
  • A proposed fuel freezing mechanism for molten UO2 fuel penetrating a steel channel was investigated in the course of liquid-metal-cooled fast breeder reactor hypothetical core disruptiv accident safety studies. The fuel crust deposited on an underlying melting steel wall was analyzed as being subjected to two stresses one due to the pressure difference between the flowing fuel and the stagnant molten steel layer, and the other resulting from the temperature variation through the crust thickness. Analyses based on the proposed freezing mechanism and comparisons with fuel freezing experiments confirmed that fuel freezing occurs in three modes. For initially low steelmore » wall temperatures, the fuel crust was stable and grew to occlude the channel. At high steel wall temperatures (above 1070 K), instantaneous wall melting leading to steel entrainment was calculated to occur with final penetration depending on the refreezing of the entrained steel. Between these two extremes, the stress developed within the crust at the steel melting front exceeds the critical buckling value, the crust ruptures, and steel is injected into the fuel flow. Freezing is dominated by the fuel/steel mixture. The theoretical penetration distances and freezing times were in good agreement with the experimental results with no more than 20% error involved.« less
  • A tripartite consortium DEBENE (Deutschland-Belgium-Netherlands), Japan, and France studied the sodium evaporation process of aerosols in a sodium fire. In an inert atmosphere, experimental and theoretical condensation rates were compared and indicated sodium hydride (NaH) to be the foreign nucleus for mist formation. In a normal atmosphere, the physicochemical characteristics of the aerosols produced by a sodium fire and their evolution in containment or in the environment were determined; models enabling the various countries to achieve harmonious results were derived. The proper functioning of the components, guaranteeing perfect operation during and after a sodium fire accident, was tested.