SYNROC nuclear waste

Hart, K. P., Vance, E. R. et al. 1998. Leaching behaviour of zirconolite-rich synroc used to immmobi-lise high-fired plutonium oxide. In McKinley, I. G. McCombie, C. (eds) Scientific Basis for Nuclear Waste Management XXI. Materials Research Society Symposium Proceedings, 506, 161-168. 

From a practical point of view, these compounds are models of crystalline matrices for nuclear waste disposal. One such storage material is SYNROC, a synthetic mineral whose major constituents are the complex oxides hollandite, zirconolite, and perovskite. We have chosen perovskite as a model structural family because of its efficient packing and its accommodation of a wide range of cations, both in size and oxidation state (5). 

The SYNROC process (Ringwood 1978) for treating nuclear wastes is another example of immobilization. Certain chemicals are added to the nuclear waste, which is then sintered and produces a mixture of minerals (a SYNthetic ROCk) that are known to be stable under the range of geological conditions that can be expected at the disposal site. 

Knyazev, O. A., Nikonov, B. S., Omelianenko, B. I., Stefanovsky, S. V., Yudintsev, S. V., Day, R. A. Vance, E. R. 1996. Preparation and characterization of inductively-melted Synroc. In Proceedings of the International Topical Meeting on Nuclear and Hazardous Waste Management SPECTRUM 96. ANS, Seattle, 2130-2137. 

Kksson, S. E. 1983, The immobilisation of cesium in synroc hollandite. Radioactive Waste Management and the Nuclear Fuel Cycle, 4, 53-72. 

Barium hollandite, Bai.4(Al,Ti)2.28Ti60i6, is an important component of Synroc, a synthetic material developed for the immobilisation of high-level waste from nuclear reactor fuel. The hollandite component of Synroc takes up alkali metal ions such as radioactive Cs by substitution for Ba in the structural channels. This uptake has been studied by Cs MAS NMR which shows a single resonance at 211 ppm from Cs in the channel sites in the absence of paramagnetic ions (Hartman et al. 1998). Replacement of Al by Ti in the channel walls causes the Cs NMR peak to broaden and shift to 640 ppm, and also provides a sensitive means of monitoring the formation of water-soluble CsAlTi04 which, if present, would compromise the aqueous durability of Synroc. 

Pells GP (1991) Radiation-induced electrical conductivity in MgAl204 spinel. J Nucl Mater 184 183-190 Ringwood AE, Kesson SE, Ware NG, Hibberson W, Major A (1979) Immobilisation of high level nuclear reactor wastes in SYNROC. Nature 278 219-223... 

Highlights. Treatment of the radioactive waste from nuclear reactors is one of the points that receive wide public attention and the disposal and burial of HLW in particular is a contentious issue due to the concerns about leakage to the environment. The technical solutions that are currently used to treat the waste that were listed earlier (concentrate-and-contain, dilute-and-disperse, and delay-and-decay) are not suitable for HLW, where safer solutions like vitrification or Synroc are sought. The characterization of the LLW and MLW waste is not as complicated as that of spent fuel but stiU greatly more complex than analysis of fresh fuel. Some of the procedures and methods used in other parts of the NFC are suitable for LLW and MLW. The composition of HLW must be determined in order to estimate the decay rate of the radioactivity and to classify the required protective measures that depend on the radionuclides and their products (emitters of alpha, beta, gamma, and neutrons). 

---