The EBR-1 Meltdown: Physical and Metallurgical Changes in the CoreAs a result of the partial meltdown which occurred in EBR-1 on November 29, 1955, it was necessary to remove the core assembly from the reactor and to separate the enriched fuel section from upper and lower un-enriched blanket sections. A temporary cave was constructed on top of the reactor in order to remove the core assembly, and at this time about one-fourth of the fuel elements were removed. In order to perform further disassembly operations under less hazardous conditions, the core assembly was shipped from the Idaho Division of Argonne National Laboratory, at the National Reactor Testing Station, to the Lemont, Illinois, site of the Laboratory, where disassembly was completed in a protective atmosphere. It was found that approximately 40 to 50% of the core had melted and reached temperatures ranging between approximately 850 and 1400 deg C, and that the molten portion had separated into three clearly defined zones characterized by different porosities. Densities of the zones ranged from 2.5 to 15.4 gm/cm3, depending upon the degree of porosity. It was also found that molten fuel alloy had traveled upward 5 inches and downward 3 inches between the blanket rods. Chemical and mass spectrographic analyses indicated that relatively little mixing occurred in the core during the period in which it was molten, that the fuel alloy which penetrated the blanket sections originated primarily from outer part of the molten zone, and that the blanket did not enter the molten phase. Observations during disassembly of the core and subsequent simulated meltdown experiments indicated that the porous structure which formed in the molten core could have resulted from the vaporization of contained NaK. |
Common terms and phrases
2X Figure 500X Figure analogous to U6Fe analogous to UFe2 Argonne National Laboratory blanket material blanket slugs Bottom of Fuel cage casting shown cave atmosphere Centrifugally Cast chemical samples coarse sponge zone contained core after removal damaged by melting damaged EBR-I core dark phase analogous deliquescence density disassembly operations dissolved fuel slugs EBR-I core assembly eutectic Experimental Breeder Reactor Figure 17 Figure 55 Figures 42 final disassembly fuel and blanket fuel section hexagonal separator interdiffusion J. H. Kittel Lemont light phase lower blanket rods mass spectrographic analyses meltdown Metallurgy Microstructure in sample molten fuel alloy molten phase November 29 outer row Partially dissolved fuel phase is believed plutonium porosity in sample pyrophoric reactor tank Remotely operated samples were taken shown in Figure solidified material stainless steel jacket steel outer jacket temperature temporary cave thermocouple thimble Typical fuel element Typical porosity unenriched blanket uranium vertical cross section zirconium