Alpha-Decay Effects in 241 Am-Doped Gadolinium Zirconate
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Alpha-Decay Effects in 241Am-Doped Gadolinium Zirconate S.V. Stefanovsky1,2, A.G. Ptashkin1, S.V. Yudintsev3, B.F. Myasoedov2 1
SIA Radon, 7th Rostovskii lane 2/14, Moscow 119121 Russia, [email protected]
2
Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Leninskii av. 31, Moscow 119071 Russia
3
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Staromonetny 35, Moscow 119117 Russia
ABSTRACT Sample of zirconate ceramic with a composition corresponding to formula Gd1.7241Am0.3Zr2O7 was synthesized by heat-treatment of mechanically activated and compacted in pellet oxide mixture at 1500 °C for 30 min. The d values on XRD pattern of the sample soon after synthesis (D = 7.9×1015 α-decays/g or 0.001 dpa) demonstrated fluorite structure with the most intensive peak with d111 =3.042 Å (a = 5.269 Å) and very weak diffuse reflections due to d-pyrochlore. At a dose of 7.9×1017 α-decays/g or 0.11 dpa the reflections were broadened by approximately 20% and their relative intensity slightly reduced. At higher doses all the weak superstructure reflections disappeared and the growth in intensity and narrowing of the main reflection occurred. Lattice parameter a increased with the dose and reached 5.343 Å (d111 = 3.085 Å) at a dose of 4.6×1018 α-decays/g or 0.42 dpa. At a dose of 5.5×1018 α-decays/g or 0.78 dpa positions of reflections were shifted to lower d-spaces (d111 value reduced to 3.071 Å) and the half-width of the major reflection was 67% of initial. For the 241Am-doped Gd-zirconate the structure recovery rate exceeds disordering rate and no amorphization occurred at doses higher than ~0.2-0.3 dpa. INTRODUCTION Radiation resistance of waste forms with respect to α-decay was being extensively studied since the middle of 1970s [1]. Numerous studies were performed in the frame of excess weapons plutonium disposition programs [1,2]. Currently they are important for an advanced nuclear fuel cycle with high level waste (HLW) partitioning. Shorter-lived Cs/Sr fraction should be incorporated in glass or glassceramics whereas long-lived actinide (or actinide/rare earth) fraction is suggested to be immobilized in high-stable ceramic forms. The compounds with a cubic fluorite or fluorite-derived structure demonstrated the highest radiation resistance with respect to both α-decay of short-lived actinides incorporated in their structure and accelerated ions (see reviews [1-6] and original works, for example, [712]). A number of works were performed on pyrochlore structure ceramics doped with 238Pu (T1/2 = 87.8 yrs) and 244Cm (T1/2 = 18.1 yrs) isotopes (see above-mentioned works [1-12]) but only few studies on α-decay damage due to incorporated 241Am (T1/2 = 432.5 yrs) or 243Am (T1/2 = 7370 yrs) isotopes are known [1319]. Doping with 238Pu or 244Cm allows to obtaining relatively fast results (for a period of up to 1-2 yrs) but dose rates in this case are much higher than those taking place at long-term storage of actual actinide waste forms. Doping with 241Am more corresponds to
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