RRFM 2009 Transactions - European Nuclear Society

Four various experiments IRIS1 [5], IRIS2 [1], IRIS3 [6] and IRIS-TUM (in collaboration with
German FRMII and TUM) [7] were carried out with ground or atomised powder, dispersed in
pure or silicon enriched aluminium matrix. Ground fuel particles showed a good in-pile
behaviour in IRIS1 experiment confirmed by IRIS-TUM one, performed at higher heat flux
and reaching higher equivalent burn-up. Benefit of silicon addition into the Al matrix was
particularly evidenced in the IRIS3 (2.1%Si) fuel plates involving atomised UMo particles. For
the plates made of ground UMo powders (case of IRIS-TUM), the positive effect of Si is less
discernable and certainly covered by the intrinsic characteristics of the ground fuel (shape
microstructure, defects, oxidized powder surface, induced porosity…) supposed to be at the
origin of the good in-pile behaviour as discussed in previous papers [4, 8].
Based on these European irradiation results, on recent Russian in-pile experiments with UO 2
coated UMo particles [9] and on CEA out-of-pile studies attesting that an oxide layer
deposited on atomised UMo particles appear to be a promising protective barrier as regard to
UMo/Al interdiffusion [8, 10, 11], a new IRIS4 experiment was designed to further evaluate
the oxide layer effect. Atomised UMo particles were selected because of manufacturing
aspects and particularly the difficulties to industrialize a grinding process.
IRIS4 experiment has been defined by CEA, within a specific collaboration with AREVA-
CERCA. The irradiation has begun in October 2008 in OSIRIS Reactor.
The first objective of IRIS4 experiment is to discriminate the role of the oxide layer on the
irradiation behaviour of the UMo fuel independently of the contribution of the Si. The potential
positive effect of both modifications (silicon + oxide layer) will also be studied since two kinds
of matrix are tested: pure Al and Al + 2.1wt% Si.
The second objective of IRIS4 is to test the fuel at the OSIRIS’ maximum authorized
irradiation conditions (by the French Nuclear Regulatory Commission) i.e. a maximum heat
flux of about 290 W/cm² and an outer cladding temperature of about 100°C. The IRIS4
irradiation targets a minimum burn-up of 50% 235 U.
This paper presents the IRIS4 fabrication, the irradiation parameters and deals with the first
plate thickness measurements after 4 cycles.
2. IRIS4 Plates fabrication and characterization
Since the main objective of IRIS4 was to test the influence of a tailored oxide layer on fissile
particle in a UMo/Al dispersion fuel, a preliminary lab-scale study at CEA was made to define
a reliable and optimised oxidation treatment procedure to obtain the desired uranium oxide
layer characteristics, keeping in mind to not strongly modify the current manufacturing rolling
[11]. A compromise between the oxide layer uniformity around atomised UMo particles, the
decrease of the uranium density and the integrity of the barrier allowed to specify an oxide
layer thickness of 1.5 µm ± 0.5 µm.
After a scale-up oxidising treatment step performed by AREVA-CERCA, four full-size AlFeNi
cladded fuel plates made of oxidised atomised UMo particles were fabricated by AREVA-
CERCA [12]. The plates have a high uranium meat loading of ~7.8 gU.cm -3 and a uranium
enrichment of about 19.8 % 235 U. The meat consists of oxidised U7.3wt%Mo atomised
particles dispersed in either a pure (A5) aluminium matrix (plates 8053 and 8054) or an Al
matrix to which 2.1 wt% Si is added (plates 8043 and 8044). The IRIS4 fuel meat
characteristics are similar to those of the IRIS2 [1] and IRIS3 [6] experiments with a fuel
volume fraction close to 50%. The as-fabricated porosity is comprised between 1.1 to 4.5
vol%.
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