“…The hypo-stoichiometric MOX with high plutonium content is known to be biphasic at low temperatures [8,9]. The two coexisting phases of (U,Pu)O 2Àx system, with p > 0.35, can be two FCC phases or FCC with cubic or rhombohedral phase [10], depending on the Pu/M, O/M and temperature. Presence of even 3 at.% uranium is known to suppress the appearance of hexagonal, Pu 2 O 3 type phase [8].…”