Isometric pyrochlore oxides (A 2 B 2 O 7 ) offer a wide range of applications, including electrolytes, sensors, the immobilization of radioactive nuclides, and so on because of their extraordinary structural and physical properties. In the present study, neutron irradiation experiments were used to investigate the irradiation-induced defects in a complex oxide, La 2 Zr 2 O 7 . The grazing incident X-ray diffraction (GI-XRD) and Raman spectroscopy have been used to examine the defects in La 2 Zr 2 O 7 pyrochlore. To obtain more information about the defects in the La 2 Zr 2 O 7 system, positron annihilation spectroscopy was performed. GI-XRD study exhibits the significant amorphization processes and lattice contraction in La 2 Zr 2 O 7 .

Neutronics of a reactor for accelerator driven subcritical system (ADS) based on spallation neutrons is expected to be different compared to that of a thermal and a fast reactor. The spallation neutrons produced in a collision of 1 GeV proton with the thick lead target have a wide energy spectrum up to the beam energy. These neutrons upon interaction with the elements of Th-U fuel influence the fuel cycle by adding new radio-nuclides, change in magnitude of cross sections, change in the yield of neutron producing and neutron absorbing nuclides. Scenario of neutron poisons may entirely be different. For the study of a fuel cycle, elementary cross sections are calculated using the TALYS-1.0 code up to 200 MeV as well as from the CASCADE code beyond 200 MeV up to the maximum energy of neutrons. The spectrum average cross sections (sp. av. cs.) are calculated using the PREPRO-07 code. For the extreme situation of original spallation neutron spectrum, values of sp. av. cs. for some reactions like, Th-232 (n, 6n) = 7.77 mb, Pa-233 (n, 3n) = 35.17 mb, U-238 (n, 6n) = 2.82 mb, U-235 (n, 3n) = 27.8 mb and Np-237 (n, 3n) = 20.8 mb. These reactions are not possible in a conventional thermal and a fast reactor. It is revealed that sp. av. cs. of (n,gamma) reaction of fuel element is drastically reduced compared to a thermal spectrum e. g. in case of Th-232, it reduces to 90.1 mb from 3.11 b; in case of Pa-233, it reduces to 247 mb from 22.4 b and in case of U-238, it goes down to similar to 67.4 mb from 7.78 b. From the study it is inferred that the fuel cycles of an ADS reactor will be extensive and the neutron poisons of the thermal and the fast reactors will be much less effective in case of the original un-moderated energetically wide spallation neutron spectrum. In this regard a much careful study will be required.