Hydrophilic Chelators for Aqueous Reprocessing of Spent Nuclear Fuel

ABSTRACT

Significant improvements in aqueous reprocessing are a key need in closing the future nuclear fuel cycle and addressing concerns with past industrial reprocessing technologies. Despite much-dedicated efforts over the past several decades, the separation of the large variety of elements and isotopes, such as minor actinides, found in the fuel is unanimously challenging. This review summarizes and classifies various aqueous chelators that have already been implemented or could potentially be used in the aqueous reprocessing of spent nuclear fuel. A variety of processes are briefly introduced, and the application of aqueous chelators is analyzed, with a focus on the elements targeted for separations, as well as aqueous/organic phase composition and acidity, and inherent physico-chemical properties. Comparisons among these agents are made to provide a clear outline of their unique characteristics. Different aqueous chelators function in different ways and thus are applied with different purposes. However, there exist limitations, even for the most widely applied polyaminocarboxylate ligands, and functional groups have been relentlessly modified over the years to achieve more efficient, sustainable, and cost-effective separations.

KEYWORDS:

• Spent nuclear fuel
• separation
• Liquid-Liquid extraction
• hydrophilic chelators

Abbreviations

ADHA: p-amino-N,N-dihexylacetamide; An: actinides; ALSEP: actinide lanthanide separation process; ARTIST: amide-based radio-resources treatment with interim storage of TRU; AP: activation product; Bimet: (2S,2ʹS)-4,4’-(ethane-1,2-diylbis(sulfanediyl)) bis(2-aminobutanoic acid); BiPPBiCTA: N²,N⁶-bis(phenyl)-pyridine-2,6-bis(carbothioamide); BTP: 2,6-bis(1,2,4-triazin-3-yl) pyridine; BTBP: 6,6’-bis(1,2,4-triazin-3-yl)-2,2’-bipyridine; BTPhen: 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline; CAM: catecholamide; CCD: chlorinated cobalt dicarbollide; CDTA: (1,2-cyclohexylenedinitrilo)tetraacetic acid or trans-1,2-cyclohexandiamine-tetraacetic acid; CEA: French Commissariat à l’énergie atomique; CHALMEX: Chalmers extraction process; (Clph)₂PSSH: bis(chlorophenyl)dithio-phosphinic acid; CMPO: octyl(phenyl)-N,N-diisobutyl carbamoyl methyl phosphine oxide; COEX^TM: U-Pu co-extraction; CP: corrosion product; CTH: Chalmers tekniska högskola; CyMe₄-BTBP: 6,6’-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]-triazin-3-yl)-[2,2’]-bipyridine; d-CMPO: diphenyl-N,N-di-n-butylcarbamoyl-methyl-phosphine oxide (Ph₂Bu₂CMPO); DEHiBA: N,N-di-(ethyl-2-hexyl)isobutyramide; DGA: Diglycolamide; DIAMEX: Diamide extraction; DIDPA: di-isodecylphosphoric acid; DMDOHEMA: N,N’-dimethyl-N,N’- dioctylhexylethoxy malonamide; DOGA or DMOGA: N,N’-dimethyl-3-oxa-glutaramic acid; DPA: dipicolinic or pyridine-2,6-dicarboxylic acid; DTPA: diethylenetriaminepentaacetic acid; DTTA-DAG: diethylenetriamine-N,N”-di(acetylglycine)-N,N’,N”-triacetic acid; DTTA-PyM: N-(2-pyridylmethyl) diethylenetriamine-N,N’,N”,N”-tetraacetic acid; EDTA: ethylenediaminetetraacetic acid; EEDTA: also BAETA, 2,2’,2”,2”‘-[oxybis(2,1-ethanediylnitrilo)] tetraacetic acid; EGTA: ethylene glycol tetraacetic acid; EXAm: Extraction of Ameriium; FHA: formohydroxamic acid; (LL)FPs: (long lived) fission products; GANEX: Group Actinide extraction; H₄TPAEN: N,N,N’N’-tetrabis[(6-carboxypyridin-2-yl)methyl]ethylenediamine; HAN: hydroxylamine nitrate; HBA: hold-back agent; HDEHP: also D(2)EHPA, di-(2-ethylhexly) phosphoric acid; HDHP: di-n-hexyl phosphoric acid; HEDPA: hydroxyethane-1,1-diphosphonic acid, or 1-hydroxyethyanediphosphonic acid; HEDTA: hydroxyethylene-diamine-tetraacetic acid; HEH[EHP]: di-(2-ethylhexyl)phosphoric acid, or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester; HLLW: high level liquid waste; HM: heavy metal; IDA: iminodiacetic acid; LLE: liquid–liquid extraction; Ln: lanthanides; LUCA: Ln und Cm Am trennung; LWR: light water reactor; MA: Minor Actinide; Me-EDTA: also PDTA, propylenediamine-N,N,N’,N’-tetraacetic acid; Me-3,2-HOPO: N-methyl-3-hydroxypyridin-2-one; Me-TEDGA: 2-(2-(diethylamino)-2-oxoethoxy)-N,N-diethyl propanamide; Me₂-TEDGA: 2,2’-oxybis(N,N-diethyl propanamide); MOX: mixed oxide fuels; NFC: nuclear fuel cycle; NNL: National Nuclear Laboratory, UK; NTA: nitrilotriacetic acid; NUEX: new uranium extraction; OEDPA: oxyethylidene biphosphonic acid; PALADIN: Partition of actinide and lanthanide with acidic extractant, diamide, & incinerable complexants; PGM: platinum group metal; PUREX: plutonium uranium redox extraction; PyTri-Diol: 2,6-bis[1-(propan-1-ol)-1,2,3-triazol-4-yl)]pyridine; PyTri-Tetraol: 2,6-bis[1-(propan-1,2-diol)-1,2,3-triazol-4-yl)]pyridine; REE: rare earth element; SANEX: selective actinide extraction; SETFICS: Solvent extraction for trivalent f-elements intra-group separation in CMPO-complexant System; SF: separation factor; SNF: spent nuclear fuel, also called used nuclear fuel; SO₃-Ph-BTP: 2,6-bis(5,6-di(sulfophenyl)-1,2,4-triazin-3- yl) pyridine; TALSPEAK: trivalent actinide lanthanide separation with phosphorus-reagent extraction from aqueous complexes; TALSPEAK-MME: TALSPEAK- mixed monofunctional extractants; TALSQuEAK: TALS using quicker extractants and aqueous complexes; TBP: tributyl phosphate; TBDPA: tetrabutyl-diamide of dipicolinic acid; TDA: thiodiacetic acid; TGA: thioglycolic acid; TEDGA: tetraethyldiglycolamide; TEDTA: 2,2’,2”,2”‘-[sulfanediylbis(2,1-ethanediylnitrilo)]tetraacetic acid; TMDGA: tetramethyldiglycolamide; TPDGA: tetrapropyldiglycolamide; TEHP: tris(2-ethylhexyl)phosphate; TMA(O)H: tetramethylammonium hydroxide; TMOGA: N,N,N,’N’-tetramethyl-3-oxa-glutaramide; TODGA: N,N,N’,N’-tetraoctyl diglycolamide; TPH: hydrogenated tetrapropene; TREN-HOPO: tris(2-aminoethyl)amine; TREN-Me-3,2-HOPO: N,N’,N”-tris[(3-hydroxy-1-methyl-2-oxo-1,2-didehydropyrid-4-yl); carboxamidoethyl]amine; TRPO: tri-n- alkyl phosphine oxide; TRU: Transuranium; TRUEX: TRU extraction; TRUSPEAK: shortened form of TRUEX-TALSPEAK; TTHA: triethylenetetramine hexaacetic acid; T2EHDGA: N,N,N’,N’-tetra-2-ethylhexyl diglycolamide; UNEX: Universal extraction; UREX(+): Uranium extraction (plus).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author Contributions

Yufei Wang: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Software, Writing – original draft, review & editing. Katherine M. Shield: Methodology, Investigation, Writing – review & editing. Rebecca J. Abergel: Supervision, Resources, Writing – review & editing, Funding acquisition.

Additional information

Funding

We acknowledge support from the U.S. Department of Energy, Office of Nuclear Energy’s Nuclear Energy University Programs (DE-NE0008949).