Ceramics Synroc

Figure 20. (A) SEM micrograph taken in SE mode of the microvoid in the fracture surface of the ceramic synroc C, and SAM Cs maps of the same area (B) before and (C) after removal of I. ) nm by ion etching. (D) Micrograph of the fracture face containing Cs-rich regions and corresponding SAM Cs maps (E) before and (F) after removal of. 7.5 nm by ion beam etching 1104].

According to researchers, furnaces for ceramic immobilization processes typically cost less than 1000 (D16044B, p. 155). According to the researchers, the SYNROC approach is only cost effective for large-scale applications (a large-scale application is assumed to produce 30-cm-diameter disks, each weighing approximately 30 kg). Cold press applications of the SYNROC process are more cost effective (D160429, pp. 255-256). No cost information is available for the Ceramification and SMITE processes. 

Fig. 3. Backscattered electron image of a zoned murataite-5C crystal in a Synroc-type ceramic containing 20 wt% HLW surrogate produced by ICCM at SIA Radon (Sobolev et al. 1997c). Scale ban 5 pm. Numbers mark locations of analyses listed in Table 3. ACT concentrations in the core are approximately 10-20 times higher than at the edge.

Sobolev, I. A., Stefanovsky, S. V., Omelianenko, B. I., Ioudintsev, S. V., Vance, E. R. Jostsons, A. 19974. Comparative study of Synroc-C ceramics produced by hot-pressing and inductive melting. Materials Research Society Symposium Proceedings, 465, 371-378. 

Additional work has been carried out on the behaviour of actinides in Synroc-type ceramics (Ringwood et al. 1988 Reeve et al. 1989 Hart et al. 1992 Smith et al. 1996 19976). 

The alteration of several titanate ceramics in pure water at 90 °C has been investigated by Leturcq et al. (2001). These experiments were performed under conditions of high surface area to volume ratio and lasted for over one year without replacement of the solution. Starting materials included melted Synroc-like materials and hot pressed Synroc-C. This study reported the normalized elemental mass losses, defined by the equation ... 

In an important study of accelerated radiation damage effects in polyphase Synroc samples doped with 244Cm, Mitamura et al. (1992, 1994) studied the behaviour of Mo, Sr, Ca, Cs, Ba, and Cm for up to 56 days in distilled water at 90 C. These ceramics were doped with either Na-free simulated Purex waste (PW-4b) or simulated waste containing 1.65 wt% Na20 (e.g., JW-A type). We should note here that the... 

We have included here, for comparison, the results of a study of zirconolite-rich Synroc nominally composed of 80 wt% Ce- or Pu-doped zirconolite plus 10 wt% hollandite and 10 wt% rutile (Hart et al. 1998). Inclusion of this study in this section is significant because the two additional phases are both highly durable in their own right and the experiments were conducted at two different temperatures (90 and 200 °C) and in three different aqueous solutions (pure water, silicate, and brine). The authors found no major differences in the release rates of Ca, Ce, Hf, Ti, Zr, Pu, and Gd apart from those for Ce and Ti, which appeared to be somewhat higher in the brine. On average, for all elements, the increase in temperature caused the release rates to increase by a factor of approximately seven. Release rates were generally below 10 2 g/m2/d for Ca, 10 3 g/m2/d for Ce and Gd, and 10 4 g/m2/d for Ti, Zr, Hf, and Pu (except for the brine at 200 °C, which gave a Ti release rate of 2 x 10 3g/m2/d). Hart et al. (2000) also determined the release rate of Pu in an LLNL-type zirconolite ceramic. After nearly one year in pure water at 90 °C the release rate of Pu decreased from 2 x 10-3 g/m2/d to less than 10-5 g/m2/d (Fig. 7). 

Solomah, A. G. Matzke, Hj. 1989. Leaching studies of synroc crystalline ceramic waste forms. In Lutze, W. Ewing, R. C. (eds) Scientific Basis for Nuclear Waste Management XII. Materials Research Society Symposium Proceedings, 127, 241-248. 

An alternative route for ceramic production is hot uniaxial or isostatic pressing of precursors [27]. The demonstration plant for Synroc fabrication based on hot uniaxial pressing in bellows containers was designed at the Australian Nuclear Science and Technology Organization (ANSTO). Synroc powder is heated to 1150-1200 C and pressed at 14-21 MPa into pancakes , which can be stacked on top of one another in the disposal canister. To improve product quality, a special precursor is prepared using wet milling or sol-gel techniques. 

Based on the leaching data [40,69,83] as well as data on radiation resistance of fast neutron irradiated [84-85] and actinide-doped Synrocs [86-88], as well as individual synthetic phases and their natural analogues study [14-18,89-91] zirconolite- and pyrochlore-based ceramics have been proposed for immobilization of excess plutonium and the other actinides. Moreover, additional phases, which were not part of the Synroc formulation, have been considered because of their chemical durability and radiation resistance (e.g., murataite, zircon, garnet, monazite, britholite). Of particular interest are the zirconate pyrochlores, many of which are extremely radiation resistant [8,92]. Zirconolite-based ceramics. Zirconolite, ideally CaZrTi207, is a major actinide host phase in the Synroc-type ceramics. Study of natural and synthetic samples... 

Reeve DD, Levins DM, Woolfrey IL, Ramm EJ (1984) Immobilisation of high-level radioactive waste in SYNROC. In Advances in Ceramics, Vol. 8. Wicks G, Ross WA (eds) American Ceramic Society, Columbus, Ohio, p 200-208... 

In Russia, besides the Radium Institute, research on the synthesis of crystal ceramics is carried out mainly for the immobilization of actinide-containing wastes at the RPA Radon , the Bochvar VNIINM, and some other organizations. The research activities are at the stage of laboratory experiments with a use of simulators of actinides. As a rule, ceramics of the titanate composition of the SYNROC type are synthesized, or some other phases (for example, monazite). Two methods of synthesis used are the cold crucible or hot pressing. 

---