Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – By fixation in stable solid media
Patent
1997-09-18
1999-09-14
Langel, Wayne
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
By fixation in stable solid media
423252, C01F 1500, G21F 900
Patent
active
059536780
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to novel thorium phosphates more particularly usable for the long-term storage of radioactive products such as radioactive and nuclear waste.
The problem of nuclear waste is linked with the reprocessing of spent nuclear fuels supplied by nuclear power stations after use. Thus, the processing of such fuels leads to the separation of the radioelements into different categories, on the one hand uranium and plutonium, and on the other hand fission products (mainly .sup.90 Sr and .sup.137 Cs) and minor actinides (Np, Am and Cm). At present fission products and minor actinides are stored together being incorporated into a specially developed glass.
Within the framework of the new policy of managing nuclear waste, consideration is being given to the separation of the fission products from the minor actinides in order to store them separately and the possibility has been studied of using matrixes other than glass for storing said actinides.
Thus, other matrixes are being investigated, which are able to contain actinides in large quantities, whilst still having solubility properties lower than those of glass matrixes.
EP-A-594 485 describes a thorium phosphate preparation process making it possible to render insoluble thorium 232, as well as its daughter products and in particular radium 228, and to purify effluents containing such compounds. Thorium phosphate has an extremely low leachability and is therefore suitable for the durable, long-term storage of thorium 232 and radium 228. The thorium phosphate obtained in this process complies with the formula: Th.sub.3 (PO.sub.4).sub.4.
The present invention relates to a novel thorium phosphate not only suitable for the long-term storage of radioactive products such as thorium and its daughter products, but also for the long-term storage of minor actinides and other fission products.
According to the invention, this novel thorium phosphate complies with the formula: Th.sub.4 P.sub.6 O.sub.23 (I), which can also be written: Th.sub.4 (PO.sub.4).sub.4 (P.sub.2 O.sub.7) (II).
This novel thorium phosphate can be prepared from a thorium compound and a phosphating agent either by a wet process, or by a dry process, provided that use is made of quantities of the thorium compound and the phosphating agent corresponding to a molar ratio Th/P from 1/4 to 2/3.
When said synthesis is carried out by the wet process, the following stages can be performed:
a) preparation of an aqueous solution optionally containing another solvent miscible with water, e.g. alcohol or acetone and containing a thorium salt and a phosphating agent in quantities such that the atomic ratio Th/P is 1/4 to 2/3,
b) dry evaporation of the solution at a temperature below 200.degree. C. and
c) subjecting the dry product to a heat treatment at least partly performed at a temperature from 850 to 1300.degree. C.
The aqueous starting solution can be acid, neutral or basic and can be a dilute or concentrated medium. The pH of this medium is more particularly dependent on the phosphating agent used and can be adjusted by the addition of appropriate acids or bases.
As examples of bases reference can be made to ammonia and its organic or mineral derivatives e.g. (C.sub.2 H.sub.5).sub.4 NOH and NH.sub.2 --NH.sub.2. The acid can be hydrochloric, nitric or acetic acid.
The thorium salts used for the preparation of this solution are preferably water-soluble thorium salts, e.g. the chloride ThCl.sub.4, the nitrate Th(NO.sub.3).sub.4, 4H.sub.2 O, thorium acetate Th(CH.sub.3 COO).sub.4, thorium oxalate Th(C.sub.2 O.sub.4).sub.2 or any other thorium salt soluble in an acid medium.
The phosphating agent used can be of different types. Examples of such agents are phosphoric acid H.sub.3 PO.sub.4 or ammonium dihydrogenorthophosphate NH.sub.4 H.sub.2 PO.sub.4.
When synthesis takes place in an acid medium, generally there is a slow evaporation of the solution (e.g. at 150.degree. C.) to obtain a dry product. This dry product firstly undergoes a treatment at a moderate temperature (400 to 50
REFERENCES:
patent: 3351436 (1967-11-01), Sarver
patent: 5403565 (1995-04-01), Delloye et al.
Chemistry of Materials, vol. 8, No. 1, Jan. 1996, pp. 181-188, Benard P. et al., "Th4(PO4)P207, a new thorium phosphate: synthesis, characterization and structure determination".
New Journal of Chemistry, vol. 20, No. 3, Mar., 1996, pp. 301-310, XP000575193, Dacheux N. et al.: "Solid solutions of uranium and thorium phosphates: synthesis, characterization and x-ray photoelectron spectroscopy."
New Journal of Chemistry, vol. 19, No. 3, pp. 275-285, XP002007017, Merigou C. et al., "Synthesis and Physico-chemical characterization of thorium monophosphate". (date unknown).
Chem. Abstracts, vol. 85, No. 14, Oct. 4, 1976, Columbus, Ohio; Abstract No. 103175, Tananaev I. et al. "Study of thorium phosphates".
Journal of the Less-Common Metals, vol. 102, Lausanne, CH, pp. 179-186, XP002007018, Bamberger, C.E. et al.: The synthesis and characterization of crystalline phosphates of thorium, uranium and neptunium. (date unknown).
Materials Research Society Symposium Proceedings. Scientific Basis for Nuclear Waste, Management XVIII. Symposium Held Oct. 23-27, 1994, Kyoto, Japan, vol. 33, Pittsburgh, PA, pp. 799-806, XP002007019, Genet et al.: "Thorium and Uranium phosphate syntheses and lixiviation tests for their use as hosts for radwastes".
Brandel Vladimir
Dacheux Nicolas
Genet Michel
Lindecker Catherine
Centre National de la Recherche
Langel Wayne
LandOfFree
Thorium phosphates, method for preparing same, and use thereof f does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thorium phosphates, method for preparing same, and use thereof f, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thorium phosphates, method for preparing same, and use thereof f will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1520298