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Fission-Product Release During Transient Heating of Irradiated CANDU Fuel

Zhendong Liu, Raymond S. Dickson, Lawrence W. Dickson, Zoran Bilanovic, David S. Cox

Nuclear Technology

Volume 131 / Number 1 / July 2000 / Pages 22-35


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A direct-electric-heating (DEH) apparatus was developed to heat Zircaloy-sheathed irradiated fuel samples. The apparatus was used in the temperature gradient 1 (TG1) experiment to measure fission product releases from Zircaloy-sheathed irradiated Canada deuterium uranium (CANDU) UO2 fuel samples during fast temperature ramps in the presence of a radial temperature gradient in the fuel. The ohmic heating of the UO2, combined with surface heat removal by the surrounding helium coolant flow, produced a radial temperature profile that approximates the profile for fission- or decay-heated fuel.

The 11 tests conducted in the TG1 experiment simulated various transient heating rates and high-temperature annealing conditions. The results indicate that the DEH technique can produce large radial temperature gradients and rapid heating rates. Ceramographic examinations showed columnar grain growth and evidence of UO2 melting. Chemical interactions between the tungsten electrodes and the UO2 were also observed. Releases of krypton, and release and redistribution of cesium were measured. Fission product release and redistribution results from some of the tests are also reported.

The Kr measurements indicated that the amount of Kr released was highly dependent upon the peak dwell power: The higher the dwell power, the higher the cumulative release. The redistribution of cesium was mapped using emission gamma radiography of the fuel specimen after the test. Cesium was released from the center of the fuel sample where temperatures were the highest. A well-defined area was confirmed near the center where the Cs activity was depleted. The measured Kr releases were in good agreement with the Cs migration and release.

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