These and other features of the blowoff were satisfactorily explained in terms of nucleation and growth of polymeric species. However, mass spectrometric analysis of the emitted vapor showed large deviations in the quantity and waveform shape of the monomer species. Neutron activation analysis of the collected vapor indicated that the total quantity of liquid UO/sub 2/ evaporated in the pulse followed more » the Hertz-Langmuir formula. More energetic transients produced gasdynamic blowoffs accompanied by significant supersaturation in the expanding plume. At temperatures below approx.2400 K for UO/sub 2/, the vapor pulse followed the Hertz-Langmiur vacuum vaporization theory. Maximum surface temperatures measured by optical pyrometry ranged from 1900 to 4200 K. The nature of the vapor produced by pulse surface heating of UO/sub 2/ and several other materials was investigated using normal-mode laser pulses with peak power densities between 10/sup 4/ and 10/sup 6/ W/cm/sup 2/. This was attributed to oxidation of the surface. Below the melting point much more uranium was collected than was expected theoretically. There was good agreement between theory and experiment above the melting point of 3120/sup 0/K. The Hertz-Langmuir formula, in conjunction with the measured surface temperature transient, was used to calculate the theoretical amount of uranium deposited. more » The maximum surface temperature ranged from 2400 to 3700/sup 0/K. The surface temperature was measured by a fast-response automatic optical pyrometer. Neutron activation analysis was used to measure the amount of uranium deposited. Scanning electron microscopy and X-ray analysis showed very little droplet ejection directly from the laser target surface. The uranium bearing species condensed on a graphite disk placed in the pathway of the expanding uranium vapor. The uranium surface was vaporized into a vacuum. In this study, the surface of a uranium dioxide target was heated rapidly by a laser. Safety analyses of nuclear reactors require information about the loss of fuel which may occur at high temperatures. ![]() The possibility of the mass spectrometer malfunction was also investigated. The experimental set-up was improved to eliminate possible sources of errors in the temperature measurement and in the transmission and collection of transient signals. Purpose of the present work was to investigate this discrepancy in the vapor pressure measurement of UO/sub 2/. The measured vapor pressures were found to be two orders of magnitude lower than more » the predictions based on thermochemical models and were also lower than other reported investigations. This experimental technique was used in past to measure high temperature vapor pressures of nuclear fuel materials UO/sub 2/ and UC. The pulse of vapor species from the laser-heated target is detected in-flight by a quadrupole mass spectrometer. ![]() The target of solid is held in vacuum and can be rapidly heated to peak temperatures of 4500 K, as measured by a fast response automatic optical pyrometer. The vaporization of UO/sub 2/ is studied in an experiment utilizing a Nd-glass laser as a millisecond pulsed heat source.
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