Compositions – Radioactive compositions
Patent
1983-12-20
1986-12-30
Terapane, John F.
Compositions
Radioactive compositions
252628, 252631, 252633, G21F 928, G21F 912, G21F 916
Patent
active
046327789
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a procedure for transforming radioactive wastes into ceramics.
Treatment of the radioactive waste solutions accruing in nuclear energy production aims at transforming the wastes into a safe form for ultimate disposal. In this context, safety implies low solubility of the final waste product, and good mechanical as well as thermal and radiation stability.
In solidifying low and medium-active power plant wastes, the commonest procedures are embedding in concrete and in bitumen. The greatest drawback of the inexpensive and simple embedding in concrete is the high leach rate of radio nuclides from the solidified product. Bituminized products have a lower degree of solubility, but the process is a lot more difficult and risky, e.g., because of risk of ignition. The only procedure widely used in solidifying the high-active waste from reprocessing of spent fuel is vitrifying the waste, particularly in borosilicate glasses. However, experiments carried out with ceramic final waste products such as titanate, zirconate and niobate-based ceramic transformation products have proved that these are superior to glass products in stability, and are gaining ground in research.
Titanates, in particular sodium titanate, are the most important base materials for ceramic products for ultimate disposal. The radioactive wastes are bound to them in the material synthesis, by ion exchange or by mechanical mixing in calcinate form. Thereafter, the product may be transformed into ceramics under high pressure and at high temperature. The most promising ceramic final waste product is SYNROC (A. E. Ringwood et. al., Immobilization of High Level Nuclear Reactor Wastes in Synroc: A Current Appraisal, Research School of Earth Sciences, Australia National University, Publication No. 1975, 1981). It is composed of three minerals, the main components of which are TiO.sub.2 (60%) and ZrO.sub.2 (10%). These minerals are analogous to minerals occurring in nature, and they have been found to have exceedingly low solubility and to tolerate radiation extremely well.
The drawback encumbering the ceramizing procedures studied so far is their complexity and high cost. Expensive initial materials awkward to pre-treat and expensive compressing apparatus are used in them.
SUMMARY OF THE INVENTION
The present invention aims at improvement of the procedures known in the art. A more specific aim of the invention is to provide a procedure which is simple in its process technology, and economical, and wherein inexpensive and readily available initial materials are used, for instance conventional raw materials of the ceramic industry. The invention is applicable in connection with both low- and high-active wastes. The other objects of the invention and the advantages gainable with its aid will become apparent in the disclosure of the invention.
The aims of the invention are achieved by means of a procedure which is mainly characterized in that the procedure comprises the following steps: ion exchanger, ceramizing substance, and waste product.
By means of the procedure of the invention, a number of remarkable advantages are achieved. The invention describes a ceramizing procedure for inorganic ionic exchangers based on inexpensive and readily available initial materials, on conventional raw-materials of the ceramic industry and on a simple process technology, appropriate for both low- and high-active wastes. The raw materials for bricks and tiles are cheap and readily and continuously available. The manufacturing technology of tiles is simple, and the firing temperature of tiles is relatively low, thus preventing evaporation of certain radioactive substances during the baking process. It is possible to add to the tiles synthetic or natural additives, such as vermiculite or apatite, which improve the stability of certain substances in the tiles. In tile firing, no complex pressing apparatus is required, and this greatly reduces the cost and simplifies the process. Clay tile containing titanate is gl
REFERENCES:
patent: 2616847 (1951-04-01), Ginell
patent: 3093593 (1963-06-01), Arrance
patent: 3249551 (1966-05-01), Bixby
patent: 4297304 (1981-10-01), Scheffler et al.
Heinonen Olli
Lehto Jukka K.
Miettinen Jorma K.
Caress Virginia
Imatran Voima Oy
Terapane John F.
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