Search

This paper reported the irradiation response of a 55 wt.% MgO-45 wt.% Nd 2 (Zr 1- x Ce x) 2 O 7 (abbreviated to M-NZC x , x = 0, 0.3 and 1) composite ceramics used as candidate inert matrix fuel under 500 keV He2+ ions with fluence of 1 × 1016–5 × 1017 ions/cm2. The irradiation-induced lattice expansion, amorphization of MgO and NZC x phases and order-disorder transition of Nd 2 (Zr 1- x Ce x) 2 O 7 pyrochlore were systemically explored via GIXRD, Raman and TEM techniques. And the detailed irradiation response at different depths of the typical M-NZC 0.3 sample was especially investigated via GIXRD and TEM. The results showed that the lattice expansion ratios (Rs) of MgO (M), ordered pyrochlore (P) and disordered defect-fluorite (F) structures of NZC x pyrochlore in the samples under the same dose of He2+ irradiation were regular, which were ranged as the following order: Rs M < Rs P < Rs F. And there was a belt-shaped damage aggregation zone located near interphase boundary at the maximum damage depth of M-NZC 0.3 sample, which could be explained by the defect-absorption of boundary. And this defect-absorption of boundary was also found at any depth of M-NZC 0.3 sample. This work systematically analyzed α-decay irradiation response of different phases in M-NZC x composite ceramics applying for inert matrix fuel. [ABSTRACT FROM AUTHOR]

In this work, the heavy-ion irradiation responses of MgO-Nd 2 Zr 2 O 7 (M-NZO) composite ceramics used for inert matrix fuel were experimentally investigated. And the micro and macro radiation damage of M-NZO samples was systemically unveiled after 5 MeV Xe20+ irradiation and quantified by two exposure units, displacements per atom (dpa) and phonons per atom (ppa). The newly ppa represent the number of phonon modes available in the radiated material, which are high relative to thermal properties and the resulting morphological fragmentation after irradiation. In detail, MgO phase mostly retains its pristine structure without extensive amorphization irradiated at high dpa values, meanwhile, Nd 2 Zr 2 O 7 phase also presents satisfactory radiation resistance through the distinctive order-disorder structural transformations that alleviate radiation-induced strain. Besides, MgO grains with lower ppa value dissipate ions energy more efficiently than Nd 2 Zr 2 O 7 , and exhibit higher radiation tolerance at macroscopic morphological scale. Overall, M-NZO composite ceramics have good radiation tolerance under heavy-ion bombardment, in which the lower ppa value and higher thermal conductivity of MgO make itself possess superior resistance to irradiation-induced damage than Nd 2 Zr 2 O 7. [ABSTRACT FROM AUTHOR]

In recent years, the MgO-Nd 2 Zr 2 O 7 composite ceramics inert matrix (IM) was proposed as a candidate for the transmutation of Pu and minor actinides (MA) in light water reactors (LWR) or accelerator driven sub-critical system (ADS). To take full advantage of the pyrochlore structure of Nd 2 Zr 2 O 7 to accommodate different types of MA and Pu, in this work, Y and Ce co-doped ω MgO-(1- ω)(Nd 1- x Y x) 2 (Zr 1- x Ce x) 2 O 7 (M-NYZC) composite ceramics used as a candidate IM for inert matrix fuel were prepared by solid-state one-step sintering method at 1500 °C for 3 h. The phase structure and microstructure of M-NYZC composite ceramics were characterized by XRD and SEM-EDS. Also, the thermal physical properties of M-NYZC composite ceramics including the thermal expansion coefficient and thermal conductivity were investigated systematically. Results from XRD and SEM-EDS showed that the magnesium oxide and NYZC pyrochlore solid solution are intermixed well with each other, and the M-NYZC samples present uniform element distribution with a grain size of about 1 μm. Also, the as-prepared samples possessed well densified microstructure, and the average relative density of all samples could exceed 95 %. Moreover, the thermal expansion coefficient and thermal conductivity of 0.5M-0.5NYZC (x = 0, 0.15, 0.2, 0.5, 0.9) samples were located in the range of 13.4 × 10-6–14.4 × 10-6 K-1 and 16.34–3.70 W·m-1·K-1 respectively. By comparison, the thermal physical properties of 0.5M-0.5NYZC samples are superior to that of traditional UO 2 and MOX fuels. It is suggested that the M-NYZC composite ceramics prepared in this study can meet the thermal physical performances of inert matrix fuel. [ABSTRACT FROM AUTHOR]

In this work, the helium irradiation effects were systematically investigated on MgO-Nd 2 Zr 2 O 7 (hereafter M-NZO) composite ceramics used for inert matrix fuel, in which the ion fluences range from 5 × 1016 to 3 × 1017 ions/cm2 at room temperature. It was demonstrated that M-NZO composite ceramic shows superior radiation tolerance after He implantation. Specifically, MgO had almost no phase transition and extensive amorphization. And Nd 2 Zr 2 O 7 phase possessed slightly pyrochlore-fluorite-amorphization structural transformation, while part of Nd 2 Zr 2 O 7 maintained the ordered pyrochlore structure and co-existed with the irradiation-induced disordered fluorite structure. Importantly, GIXRD results indicated that MgO phase presents higher resistance to radiated damage than Nd 2 Zr 2 O 7 phase. Besides, SEM images illustrated that MgO particles have substantially less fragmentation than Nd 2 Zr 2 O 7 particles due to the higher thermal conductivity of MgO. It reconfirmed that MgO phase resists irradiation damage better than Nd 2 Zr 2 O 7 phase in post-irradiated M-NZO composite ceramics. [ABSTRACT FROM AUTHOR]

MgO-Nd 2 Zr 2 O 7 composite ceramic is a promising candidate as an inert matrix material for the transmutation of Pu and minor actinide. In this work, the MgO-Nd 2 Zr 2 O 7 composite ceramics (hereafter M-NZO) with 30–70 wt% mass percent of MgO were successfully prepared at 1500 °C for 24 h via direct solid-state reaction one-step method. This method achieved the integration of Nd 2 Zr 2 O 7 pyrochlore synthesis and M-NZO composites sintering, which shows a significant improvement in the simplification of the preparation process than the traditional two-step method. The structural properties and compactness of the as-prepared composite ceramics were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). It was confirmed that the as-prepared M-NZO ceramics are composed of only crystalline MgO and Nd 2 Zr 2 O 7 phases, and the mass fractions of two phase are almost the same as the designed nominal chemical composition. The composite ceramics showed remarkable densification and the relative density is higher than 98.2%. [ABSTRACT FROM AUTHOR]