The Effect of Cellulose Degradation Products on the Solubility and Sorption of Pu and Am in Alkaline-Plume-Affected and
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7KH(IIHFWRI&HOOXORVH'HJUDGDWLRQ3URGXFWVRQWKH6ROXELOLW\DQG6RUSWLRQRI3XDQG$P LQ$ONDOLQH3OXPH$IIHFWHGDQGLQ8QDIIHFWHG%RRP&OD\ F. Rorif 1, E. Valcke 1, M.A. Glaus 2 1 SCK•CEN, Waste and Disposal Department, Boeretang 200, B-2400 Mol 2 PSI, Waste Management Laboratory, CH-5232 Villigen, PSI $%675$&7 The potential effect of water-soluble degradation products (DPs) formed from cellulosecontaining cemented radioactive waste on the behaviour of Pu(IV) and Am(III) in AlkalinePlume-Affected (APA) and in unaffected Boom clay was assessed. After solubility measurements in APA Real Clay Water, sorption experiments of Pu(IV) and Am(III) onto APA Boom clay were performed in the presence or not of DPs or pure α-isosaccharinic acid (α-ISA). Moreover, the sorption of α-ISA onto the unaffected clay was studied. ,1752'8&7,21 In Belgium, one type of the radioactive waste presently considered for deep disposal is cellulose-containing cemented radioactive waste [1]. In the highly alkaline (pH > 12.5) and anoxic conditions, expected to prevail in the cementitious repository for periods of the order of 100 000 years [2], chemical degradation of cellulose will produce water-soluble, low molecular weight organic degradation products ('3s) [3]. At high pH and high concentration, certain DPs were shown to increase the solubility and reduce the sorption of tri- and tetravalent long-lived radionuclides (51s), thus possibly facilitating their migration (HJ., [4,3]). Amongst these DPs, α-isosaccharinic acid (D,6$) as a key ligand was also unambiguously highlighted. Therefore, we investigated the effect of cellulose DPs on the behaviour of Pu(IV) and Am(III) in Boom clay (%&), LH, the main barrier in the Belgian nuclear waste disposal concept [1]. We showed that the effects of DPs or pure α-ISA (up to 10-3 M) on the solubility and sorption of Pu(IV) and Am(III) were fairly small in undisturbed BC (far-field conditions, see Table 1) [5,6]. However, the large amounts of cementitious material in the repository are expected to affect the properties of the surrounding BC (HJ, pH increase, change of the ionic and mineralogical composition of the liquid and solid phase). Since preliminary calculations suggested that the thickness of disturbed clay could be several meters, the effect of α-ISA and other DPs in Alkaline-Plume-Affected ($3$) Boom clay was studied. Moreover, this knowledge allows validating the robustness approach (no sorption, high solubility) for the near field as a very conservative one. We also studied the sorption of α-ISA onto undisturbed BC starting from two different α-ISA solutions to examine the influence of the preparation (two different pH’s for the lactone dissolution) in terms of kinetics of the lactone ring-opening and closing [7]. Indeed, α-ISA exists mainly as an open-chain at higher pH, whilst at lower pH the lactone-form predominates. 1($5),(/'&21',7,216 '(6&5,37,21$1'6,08/$7,21 As a first step, the conditions in the alkaline plume affected field had to be defined. It was assumed that a sy
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