RRFM 2009 Transactions - European Nuclear Society

4. In-pool plate thickness measurements
The plate thickness measurements were collected plate by plate, at each intercycle, on five
axial and one transverse (at the MFP) profiles 3 (fig. 3a and 3b). Note that the measurements
after the 2 nd cycle F230 are not available due to technical problems encountered on the inpool
measurement device at that moment. The precision of these measurements is about 15
µm.
As can be seen in Fig. 3a, the plate 8044 testing oxidised UMo in Al+2.1%Si did not show
abnormal swelling after the fourth cycle (peak BU estimated to ~38%). The thickness of both
plates containing oxide coated UMo + Si increased normally as irradiation proceeded. The
maximal thickness increase for the hottest plate (8044) was between 40 and 50 µm at the
end of cycle F232, taking into account thickness measurement differences between axial and
transverse profiles performed at MFP (see Fig. 3a).
By comparison, Fig. 3b shows the thickness evolution of plate 8053 containing oxidised UMo
particles dispersed in pure Al. Fig.3b indicates a more heterogeneous swelling, particularly
during the 4 th cycle. Local thickness increases up to 70 µm have been measured. Same
results are evidenced for the plate 8054. IRIS4 plates without silicon added to the Al matrix
show a slightly higher swelling than those with 2.1%Si.
Plate 8044 (UMo ox - 2.1 wt% Si)
Plate 8053 (UMo ox - 0% Si)
before
axial points - before
F229
F231
F232
axial points - F232
1370
1360
before
F229
F231
F232
1390
1380
1370
1350
1360
Plate thickness (μm)
1340
1330
1320
Plate thickness (μm)
1350
1340
1330
1310
1320
1300
1310
1290
1300
-30 -20 -10 0 10 20 30
transverse position (mm)
Fig. 3a: In-pile evolution of the transverse
thickness profiles of plate 8044 at MFP
-30 -20 -10 0 10 20 30
transverse position (mm)
Fig. 3b: In-pile evolution of the transverse
thickness profiles of plate 8053 at MFP
5. Discussion
IRIS4 experiment is currently testing for the first time the behaviour of oxidised UMo fuel
dispersed in pure Al or in Al+2.1%Si alloy matrix using full-size plates.
In order to discriminate both effects of oxide layer and silicon addition on the UMo irradiation
behaviour, the average plate thickness versus the fission density is represented on Fig. 5,
comparing results of IRIS2 (pure Al), IRIS3 (2.1%Si and 0.3%Al) and IRIS4. Fig. 4 reminds
the heat flux history for these three IRIS experiments.
At the current status of IRIS4 experiment, if we compare the behaviour of UMo fuel without
Si, one can notice that no pillowing has occurred in IRIS4 plates whereas, at similar fission
density and even lower temperature, large pillowing was already observed on IRIS2 plates
(whose irradiation conditions were higher than IRIS3 ones). However, local thickness results
from Fig. 3b could indicate a beginning of degradation of the oxidised UMo plates.
3 These measurements are done in the OSIRIS reactor pool with a dedicated device, originally
developed for the qualification of the U 3 Si 2 fuel.
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