Kinetics of fission-vaporized UO/sub 2/ fuel determined from sampled fuel debris. [LMFBR] Page: 2 of 9
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could be viewed from either the n*id or the side, -jas backlighted with a 3u0 w
lamp and photographed at a distance of 10 m using a Questar telescope and Fast ax
camera. Two front surface minois and a quartz window in the experiment canister
and two front surface mirrors in the reactor offset tube helped bnckligut and
provided a viewing path to the fuel . Hiotoj* raph ic resolution was about 10 line-
pa irs/inm.
The fuel was heated to vapor by a single 5 ras FWHM neutron pulse of
2380 KJ/kg. A view of fuel disruption is shown in the film strip (Figure 2)
taken at^ 3000 frair.es/sec. Timing marks on the film are every millisecond.
(The bands shown on the fuel pin were used to measure fuel resistance during
heating and also to secure a thermocouple to the pin for monitoring fuel tem-
per rture prior to tim shot.) During a ppriod of several milliseconds the fuel
is seen to hr at vitn an increasing brightness, melt and eject particles. Tm-
smallest particles that can be resolved on the film are about 0.1 mm in size
with initial velocities of several m/$. Within a fraction of a millisecond after
the particles appear, a vapor front is seen to move outward at a velocity of
50 m/s. Vapor fills the field of view, condenses on the optics and eventually
obscures the action.
Fuel Temperature
Fuel surface temperatures were obtained from a measurement of fuel radi-
ance, an emissivity value of 0.87' for the temperature range of interest and
the assumption that radiation from the fuel is distributed according to Planck’s
Law. (A spectrogram from U0? heated resistively showed the radiant energy was
distributed in a continuous spectrum over the visible range.) Radiance was
determined from microdensitometer measurements of rhe density of exposed and
processed photographic film and the relation between film density and radi-
ance. Known radiance values were obtained using a standard spectral radiance
lamp and a neutral density step wedge. *ihis relation was determined in the
optical geometry of the experiment at a wave length of 530 ntn with a band width
of 100 nm. Uncertainty of fuel temperatures was stated at 3 percent although
when the standard lamp was used as an unknown source, the calculated and actual
temperatures of the lamp agreed within 2 percent. Sensitivity of calculated
temperature to the emissivity value is slight. Changing the emissivity from t'.;-;
to 0,90 changes temperature by 30K at 3000K. Fuel temperatures were measured
photometrically from 2100K to 3340K (melt temperature). Temperature profiles
across the diamete*- of the pin were estimated from measurements of surface tem-
perature and of centerline temperature made on successive but similar shots.
Centerline temperature was esc floated oy viewing the fuel pin from the end in
which a deep hole had been drilled along the. center of the pin. Average pin
temperatures were calculated from these temperature profiles.
Energy vs. Temperature
The total thermal energy absorbed in the UO^ fuel due to fission of the
isotope was estimated from fission product inventories on a series of
dosimetry shots. The uncertainty in total fission energy was about 5 percent.
Time variation of this energy was determined from the integral of the measured
pulse of neutrons delivered by che reactor.
The experimentally measujed relation between the energy state of the fuel
and the corresponding average fuel temperature in the temperature range from
2JCOK. to melt lies less chan 3 0 percent above the oritualpy-temperature relation
given in Ref, 2. After the. experimental data was corrected for heat losses, the
two sets of data effectively agreed to within experimental uncertainty. The
j*i"
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Elrick, R.M. Kinetics of fission-vaporized UO/sub 2/ fuel determined from sampled fuel debris. [LMFBR], article, January 1, 1979; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1097462/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.