Ion-beam irradiation and 244 Cm-doping investigations of the radiation response of actinide-bearing crystalline waste fo
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Andrey A. Lizin Research Institute of Atomic Reactors, Radiochemical Department, Dimitrovgrad-10, Ulyanovsk reg., Moscow, Russia
Tatiana S. Livshits Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Laboratory of Radiogeology and Radiogeoecology, Moscow 119017, Russia
Sergey V. Stefanovsky Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Laboratory of Radioecological and Radiation Problems, 119071 Russia
Sergey V. Tomilin Research Institute of Atomic Reactors, Radiochemical Department, Dimitrovgrad-10, Ulyanovsk reg., Moscow, Russia
Rodney C. Ewing Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA (Received 11 September 2014; accepted 8 January 2015)
Candidate materials for actinide immobilization are subject to alpha-decay event doses that accumulate to values of more than 1020 alpha-decays per gram (tens displacements per atom, dpa) over the extended periods of geologic disposal. To evaluate the radiation-response of actinidebearing materials, two experimental techniques have been used to accelerate the damage accumulation process: ion-beam irradiations and 244Cm-doping experiments. Based on modern characterization techniques, such as high-resolution transmission electron microscopy, and experimental results that involve ion-beam irradiation and chemical doping with highly active actinides, crystalline ceramics for the immobilization of actinides can be divided into three groups on the basis of their critical doses, Dc, i.e., the dose required for amorphization at 300 K: (i) low resistance to radiation damage accumulation (Dc ; 0.2 dpa) – murataite, Ti-perovskite, Fe-garnet; (ii) resistant (0.4 , Dc , 0.6 dpa) – Al-garnet, Ti–Zr-pyrochlore, Al-perovskite; and (iii) highly resistant (Dc . 0.8 dpa) – Zr-, Zr–Ti-, and Sn-pyrochlores. Phases with low critical temperatures (Tc below 600 K) will not become amorphous in a deep geologic repository, as long as the temperature remains between 300 and 550 K, but rather, they will remain crystalline. Only Zr-rich pyrochlore is fully resistant to radiation damage and will remain crystalline over the entire period of its disposal. I. INTRODUCTION
One of the major challenges of the back-end of the nuclear fuel cycle is to determine the fate of actinides that are either separated during reprocessing or remain, in minor amounts, in the high-level waste (HLW) generated by reprocessing. Reprocessing of one metric tonne (mt) of spent nuclear fuel (SNF) yields up to 13 m3 of liquid HLW1 containing a total of up to 0.4 kg/m3 residual U, Pu and minor actinides, MA (MA 5 Np, Am, Cm). These elements emerge as major contributors to the Contributing Editor: William J. Weber a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.23 J. Mater. Res., 2015
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long-time ecological hazard (Fig. 1).2–4 The dose factors for the most dangerous fission products, 135Cs and 90Sr, are estimated to be 13 and
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