Trefoil Bundles of NPD 7-Element Size Fuel Irradiated to 9100 MWd/tonne U

Technical Report · Wed Jan 01 04:00:00 EST 1964

OSTI ID:4001653

Bain, A S; Christie, J; Daniel, A R

NPD prototype elements (1 in. OD, 19 in. long) were assembled into trefoil bundles and irradiated in the X-5 pressurized-water loop of NRX. The first tests were for only a few weeks but showed that elements made by sheathing UO{sub 2} pellets in Zircaloy-2 behaved well under irradiation; later similar elements were irradiated for 1800 hours to a burn-up of 9100 MWd/tonne U at {integral}kd{theta} = 40 W/cm. The dimensional stability of all the elements was good. Only those subjected to long irradiation showed progressive diametral increases, and these were attributed to relocation of the UO{sub 2} during interim inspections. Length measurements demonstrated that pellet end-dishing is effective in controlling axial expansion, but that for a given depth of dishing the amount of expansion depends on the shoulder width. The extent of grain growth in the UO{sub 2} was compatible with previously reported results when the duration of irradiation, density of the fuel, and variations in growth characteristics of the different batches of UO{sub 2} are considered. The elements taken to high irradiation released up to 135 ml of fission-product gases, which is 27% of the amount formed. The transverse tensile strength of ring samples from the Zircaloy-2 sheaths increased from 75000 to 95000 lb/in{sup 2} at room temperature, but the ductility dropped. The completely brittle fracture of some rings was due to ZrH{sub 2} precipitation. The failure of one element was caused by increased stress due to a higher heat rating, combined with low ductility of the Zircaloy-2 resulting from radiation damage and with precipitation of ZrH{sub 2} because of a lower coolant temperature. The fission-product release from the split was not excessive, and the element was easily withdrawn from the loop after operating at full power for four days from the time of the failure. (auth)

• Research Organization: Atomic Energy of Canada Ltd., Chalk River, Ontario (Canada)
• NSA Number: NSA-18-022523
• OSTI ID: 4001653
• Report Number(s): CRFD-1179; AECL-1895
• Country of Publication: Canada
• Language: English

Related Subjects

BEARINGS
BRITTLENESS
BURNUP
CONFIGURATION
CONTROL
COOLANTS
DEGASSING
DENSITY
DUCTILITY
EXPANSION
FAILURES
FISSION PRODUCTS
FUEL CANS
FUEL ELEMENTS
GRAIN SIZE
IN PILE LOOPS
INSPECTION
IRRADIATION
MATERIALS TESTING
MEASURED VALUES
METALS, CERAMICS, AND OTHER MATERIALS
NESDPS Office of Nuclear Energy Space and Defense Power Systems
NRX
PELLETS
PRECIPITATION
PRESSURE
RADIATION EFFECTS
RESEARCH REACTORS
SAMPLING
STABILITY
STRESSES
TEMPERATURE
TENSILE PROPERTIES
THICKNESS
URANIUM
URANIUM DIOXIDE
VARIATIONS
WATER
ZIRCALOY
ZIRCONIUM HYDRIDES