HIGH PERFORMANCE UO$sub 2$ PROGRAM. Quarterly Progress Report No. 8, January-March 1963

Technical Report · Mon Apr 15 04:00:00 EST 1963

OSTI ID:4671939

Weidenbaum, B

The post-irradiation examination of two fuel rods is in progress from the group of five that were irradiated. Direct fission-gas pressure measurements are available for the two rods being examined to determine the relation between fission-gas release and fuel-control temperature or fraction of the fuel above the crystallization temperature. The second powder-filled fuel assembly, EPW 6/ 8A, for the GETR Pressurized Water Loop which contained two swaged rods and two vibratory compacted rods, each type to operate at 600,000 and 800,000 Btu/hr-ft/ sup 2/, experienced a rod failure while the reactor was coming to power during a programed start-up. The failure occurred in the swaged 800,000 rod (located furthest from the core center), whereas the vibratory compacted 800,000 rod operating at a higher heat flux at the time of failure did not show any increase in diameter. A cored pellet fuel rod assembly, EPT-12, with rods designed to operate in excess of 1.3 x 10/sup 6/ Btu/hr-ft/sup 2/ was irradiated without incident for the equivalent of nineteen days at full GETR power. The irradiation of EPT-12 was continued through this cycle without difficulty for approximately an additional twenty-six days at full power. Fuel assembly EPT-12 which contained UO/sub 2/ pellets with a 0.140 inch diameter central hole was irradiated with the highest power rated rod attaining a calculated peak surface heat flux of 1.4 x 10/sup 6/ Btu/hr-ft/sup 2/. The irradiation of fuel assembly EPT-12 was continued and reached an average burnup of over 5000 Mwd/Te at the end of the cycle. On the basis of high temperature, thermal conductivity data, over 70% of the UO/sub 2/ cross section is molten in the peak heat flux zone with only a 0.040 inch solid UO/sub 2/ band adjacent to the cladding during operation of the highest rated rod in ETP-12. A second powder fuel assembly, EPT 6/8A, containing both swaged and vibratory compacted UO/sub 2/ fuel rods designed to operate at 600,000 and 800,000 Btu/hr-ft/sup 2/ experienced a cladding failure in the swaged rod with the higher power rating before the reactor reached full power. Both swaged rods in EPT 6/8A had considerable clad swelling and could not be removed from the assembly; neither vibratory compacted rod showed any measurable clad swelling. Failure occurred in the swaged rod with apparent clad melting at the peak heat flux region with the rod operating at a heat flux of 750,000 Btu/hr- ft/sup 2/, the vibratory compacted rod at that time had a heat fiux of over 800,000. A mechanism for the clad melting, either molten UO/sub 2/ reaching the clad or a heat transfer burnout,'' is being looked for in the examination of the fuel rod. The cause of the failure in the swaged fuel rod in the first powder assembly at a point below the peak heat flux was apparently due to a localized weakness in the cladding. After irradiation of the EPTCOM assembly, for a full GETR cycle, the rod which operated at a peak heat fiux 1,000,000 Btu/ hr-ft/sub 2/ had clad swelling to the extent of 13 mils, while the 1,100,000 rod did not show any diameter increase. The reason for this anomalous result is not known. Post irradiation examination of rod 10D from the EPT-10 assembly indicated a

• Research Organization: General Electric Co. Atomic Power Equipment Dept., San Jose, Calif.
• NSA Number: NSA-17-025829
• OSTI ID: 4671939
• Report Number(s): GEAP-3771-8; EURAEC-642
• Country of Publication: United States
• Language: English

Related Subjects

BURNUP
CANNING
COMPACTING
CONTROL
CROSS SECTIONS
DEFECTS
DENSITY
DISTRIBUTION
ENRICHMENT
EXPANSION
FAILURES
FISSION PRODUCTS
FUEL CANS
FUEL ELEMENTS
GASES
GETR
GRAIN SIZE
HEAT TRANSFER
HEAT TREATMENTS
HEATING
HIGH TEMPERATURE
IRRADIATION
MEASURED VALUES
MELTING
MELTING POINTS
METALLOGRAPHY
METALS, CERAMICS, AND OTHER MATERIALS
NUCLEAR REACTIONS
PELLETS
PERFORMANCE
POROSITY
POWDERS
PRESSURE
RADIATION DOSES
RADIATION EFFECTS
REACTIVITY
REACTOR CORE
REACTORS
RECRYSTALLIZATION
RESEARCH REACTORS
SCATTERING
TEMPERATURE
THERMAL CONDUCTIVITY
URANIUM DIOXIDE
VAPORS
VARIATIONS
VIBRATIONS
VOIDS
WATER COOLANT