Immobilisation of actinides in phosphate matrices

Abstract

In the field of the immobilisation of high-activity-level and long-life radwaste (HAVL) for a deep underground repository, several phosphate matrices were already proposed as good candidates to delay the release of actinides in the near-field of such disposal. Among them, thorium phosphate-diphosphate (TPD), monazites/brabantites, britholites, and TPD/monazite composites were extensively studied. The synthesis of samples doped with actinides (Th, U...) through wet and dry chemistry methods then their complete characterisation are reported. Their chemical durability is also examined. These materials appear as promising matrices to immobilise tetravalent and/or trivalent actinides. To cite this article: N.

Synthesis and characterization of thorium-bearing britholites

“…Zirconolite Ca 1-x and β-TPD/monazite composites and finally apatites (with general formula Me 10 (XO 4 ) 6 Y 2 with Me = Ca 2+ , Ln 3+ , An 3+ or An 4+ , X = Si or P and Y = F or O) were considered for the simultaneous incorporation of An(III) and An(IV) [2]. Indeed, in natural apatites, particularly those coming from the Oklo fossil nuclear reactors (Gabon), the structure was able to immobilize over the lanthanides, a large variety of cationic substitution (as example by U, Th, Pu) [3,4].…”

Comparison of microstructure and chemical durability of Ce0.9Gd0.1PO4 ceramics prepared by hot-press and pressureless sintering

“…Chemical durability is an important factor for waste form when it was been evaluated the safe disposal of nuclear waste in a geological repository [16,17,21,24,29,37]. At present, the researchers prepared monazite ceramics (sintered over 1300 1C) and compared the dissolution of the monazite ceramics with that of natural samples, finding that synthetic monazite samples showed almost the same chemical durability as natural analogs [28,29,38,39].…”

“…At present, the researchers prepared monazite ceramics (sintered over 1300 1C) and compared the dissolution of the monazite ceramics with that of natural samples, finding that synthetic monazite samples showed almost the same chemical durability as natural analogs [28,29,38,39]. In order to investigate the stability of the monazite-based ceramics prepared by the lowtemperature HPS process, the Ce 0.9 Gd 0.1 PO 4 ceramics were sintered by HPS and PLS at different temperatures and holding times.…”

“…At present, the preparation [11-13, 20-24, 28-31], radiation resistance [17,26,27] and chemical durability [16,23,[28][29][30][31][32][33] of monazite ceramics containing various actinides and/or lanthanides (used as surrogates of actinides) were already extensively researched. These monazite ceramic waste-forms were generally sintered by the conventional pressureless sintering (PLS) process, the sintering temperature is relatively high (1300-1450 1C) and holding time is relatively long (4-10 h).…”

Effect of sintering technique on mechanical property and chemical durability of Ce0.5Pr0.5PO4 ceramics

“…Considering the long-term safety aspects of geological disposal, minor actinides (Np, Am and Cm) are of particular concern due to their high toxicity and long half-lives [1,2]. Extensive studies are performed in several countries on the immobilization of minor actinides in highly durable matrices [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Monazite ores are the major source of light rare earth elements, which show high actinides loadings, chemical durability, mechanical stability and radio-resistance [5,6,8,16,17,20,21,[23][24][25][26].…”