Synthesis and Study of 239 Pu-Doped Ceramics Based on Zircon, (Zr,Pu)Sio 4 , and Hafnon, (Hf,Pu)SiO 4
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Synthesis and Study of 239Pu-Doped Ceramics Based on Zircon, (Zr,Pu)Sio4, and Hafnon, (Hf,Pu)SiO4 B.E. Burakov, E.B. Anderson, M.V. Zamoryanskaya, M.A. Yagovkina, E.E. Strykanova and E.V. Nikolaeva V.G.Khlopin Radium Institute, 28, 2-nd Murinskiy ave., St.Petersburg, 194021, Russia, Email: [email protected] ABSTRACT Zircon, ZrSiO4, as well as its Hf-analogue hafnon, HfSiO4, have been proposed for use as durable Pu host phases for the immobilization of weapons grade Pu and other actinides. Four samples of Pu-doped ceramics based on the zircon and hafnon structures were synthesized through sintering in air using precursors containing 5-6 and 10 wt% 239Pu. Synthesized ceramic samples were studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), microprobe method, MCC-1 leach test at 25 and 90°C. Inclusions of separated a PuO2 phase in the matrix of zircon-based ceramic and presumably, (Pu,Hf)O2 phase in the hafnon-based ceramic were observed for samples obtained from precursors doped with 10 wt% Pu. No separated Pu-phases in significant amounts were identified in the matrices of both ceramics obtained from the precursors doped with 5-6 wt% Pu. It was found that normalized Pu mass losses (without correction on ceramic porosity) for samples doped with 10 wt% Pu which contain separated inclusions of PuO2 or (Pu,Hf)O2 after 14/28 days were approximately (in g/m2) - for zircon: 0.2/0.2 - at 90°C and 0.03/0.04 - at 25°C and for hafnon: 0.02/0.04 - at 90°C and 0.01/0.01 - at 25°C. The losses of Pu from samples doped with 5-6 wt% are 1-2 order of magnitude less. It was suggested that optimal amount of Pu which could be incorporated by zircon and hafnon lattices does not exceed 7 wt%. An important additional conclusion is that Pudoped ceramic based on zircon or hafnon can be successfully fabricated excluding hot pressing method. INTRODUCTION Zircon, ZrSiO4, has been proposed as a durable Pu host phase for the immobilization of weapons grade Pu and other actinides [1-5]. Hafnium and Zr may be substituted for each other into the zircon an hafnon structures forming a solid solution in the system: ZrSiO4-HfSiO4. It has been suggested that Pu4+ can substitute in large quantities for Zr4+ or Hf4+ forming a ternary solid solution, (Zr,Hf,Pu)SiO4. Zircon is a relatively inexpensive material to produce taking into account that metallic Zr is widely used in the nuclear industry for fuel cladding fabrication. Spent fuel is also a large potential source of Zr for the synthesis of zircon based ceramic waste forms. Hafnium compounds are more rare and expensive; however, the use of Hf in a zircon solid solution, (Zr,Hf,Pu)SiO4, is important in order to provide sufficiently high neutron absorption for avoiding criticality in Pu waste forms. Although hafnon is iso-structural with zircon, it might be expected that some properties of hafnon, such as its capacity for Pu incorporation, its chemical durability, etc., are potentially better than those of zircon. Therefore,
hafnon-based ceramics should not be ignored as pros
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