Plutonium oxidation states in the Waste Isolation Pilot Plant repository

Formation of mono- and binuclear complexes of Nd3+ with d-gluconate ions in hyperalkaline solutions – Composition, equilibria and structure

“…The radiotoxicity of spent nuclear fuel is predominated by actinides (Am 3+ , Cm 3+ , Pu 3+, and Pu 4+ ) in radioactive waste repositories [10], where anoxic conditions are typical [11], ensuring that reduced oxidation states of actinides prevail under these conditions [10][11][12][13]. The formation of hydroxo-and carbonato-complexes of radioactive actinides increase solubility [10], which can be further enhanced by complexation of gluconate present [9].…”

“…Zanonato et al found that NdL x (L: ligand, x = 1, 2, 3) complexes form in the case of an acetate ligand, and stronger complex formation is typical at elevated temperatures [20]. When a more comprehensive pH range (5)(6)(7)(8)(9)(10)(11) was studied, Nd 3+ was found to express a significant red shift upon deprotonation and complexation of Dglucosamine [22], and precipitation appeared at pH > 8.6 at several different metal to ligand ratios [22]. Levitskaia et al referred to the precipitation as Nd(OH) 3 [22] since Nd 3+ is known to form insoluble Nd(OH) 3 around pH = 8 [23][24][25].…”

Plutonium Co-precipitation with Calcite

“…For example at the Waste Isolation Pilot Plant (WIPP), both Pu(III) and Pu(IV) are expected to be Pu-dominant oxidation states. 9 In the higher oxidation states (V and VI), U, Np, and Pu form the highly mobile linear trans-dioxo actinyl cations U(VI)O 2 2+ , Np(V,VI)O 2 (+,2+)…”

“…Both the management of contaminated sites and disposal of high-level radioactive waste in geological repositories pose unique scientific, engineering, and societal challenges. Under environmental and repository conditions, the early actinide elements uranium (U), neptunium (Np), and Pu are able to exist in a wide range of oxidation states. − In the lower oxidation states (III/IV), these elements are present as spherically coordinated ions and are generally characterized by low solubility. Pu­(IV) undergoes rapid hydrolysis in circumneutral-alkaline conditions, resulting in limited solubility and mobility; , however, under anoxic conditions, reducing materials [Fe­(II) compounds, sulfides, humic substances, and microorganisms] can reduce Pu­(IV) to Pu­(III), which is more soluble than Pu­(IV) .…”

“…Lower oxidation states are expected to control Pu behavior in reducing nuclear repository scenarios. For example at the Waste Isolation Pilot Plant (WIPP), both Pu­(III) and Pu­(IV) are expected to be Pu-dominant oxidation states . In the higher oxidation states (V and VI), U, Np, and Pu form the highly mobile linear trans -dioxo actinyl cations U­(VI)­O 2 2+ , Np­(V,VI)­O 2 (+,2+) , and Pu­(V,VI)­O 2 (+,2+) .…”