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Figure 6: Principle design characteristics of the reference accelerator
2.4 Inert Matrix Fuels (IMF) for transmutation in ADS systems
Fuels developments for the ADS have concentrated on fertile free (inert matrix) fuels for highest
transmutation rates. Some of the tests on these fuels are discussed below.
2.4.1 IMF – MgAl2O4 (EFTTRA T4)
EFFTRA T4 was the first European experiment to investigate the irradiation behaviour of Am in an
IMF fuel [8]. The chosen inert matrix was magnesium aluminate spinel (MgAl2O4) and the Am was
introduced using an infiltration procedure. The resulting fuel consisted of a micro-dispersion of Am
bearing particles, with diameters less than 3 μm. The mass of Am in the pellets was about 10 wt%
which given the density of spinel corresponds to an actinide loading of about 0,2 g.cm -3 The irradiation
was performed in the HFR Petten for 358 EFPD with transmutation and fission of 96 and
28% of the original Am being achieved. Ceramographs of the sample before and after irradiation
(see Fig. 7) indicate a tremendous increase in porosity, with the pores originating at the location of
the Am bearing particles. These bubbles are a result of He build up during irradiation, and to a large
part they contribute to the very large volumetric swelling of the fuel (ca. 20%), which also produced
severe cladding deformation, but without rupture. The main conclusion of the experiment, apart
from eliminating spinel as an IMF, lies in the need to manage effectively He produced in the fuel,
e.g. low density fuels with closed or open porosity, operation at higher temperature to encourage
atomistic He diffusion to the plenum, or ultimately alternative fuel forms (e.g. SPHEREPAC).
2.4.2 IMF - Zirconia
PSI has performed a major investigation on zirconia based fuels. Zirconia has a monoclinic crystal
structure but can be stabilised in the cubic form by the addition of ca. 15 mole% of Y. Furthermore,
all actinides can be incorporated in the cubic structure. Several (Zr,Y,Pu)O2 based fuels, manufactured
by different processes, have been irradiated in the OECD Halden reactor [8], but PIE is not
completed yet. Within the European programme EUROTRANS, two Am based zirconia fuels are
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