Plutonium Leaching from a Reference Nuclear Waste Glass in Synthetic Interstitial Claywater
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PLUTONIUM LEACHING FROM A REFERENCE NUCLEAR WASTE GLASS IN SYNTHETIC INTERSTITIAL CLAYWATER
Lian Wang, and P. Van Iseghem S.C.K./C.E.N, Boeretang 200, 2400 Mal, Belgium A. Maes, Laboratorium voor Colloidale Schelkunde, Kardinaal Mercierlaan 92, 3001 Leuven, Belgium
ABSTRACT The steady-state concentration of Pu was measured upon leaching Pu doped glass in synthetic interstitial claywater (SIC) and humic acid free interstitial solution (IS). The solubility of Pu02.xH20(am) was determined in the same chemical condition. The results then were compared with the Pu solubility calculated by using a published solubility product and complex stability constants. The humic acid (HA) influence on the Pu leaching from the glass and the colloid formation were investigated. INTRODUCTION In Belgium, the boom clay formation has been chosen as a potential repository for nuclear waste. Pu is a important element in the field1 1 of nuclear waste disposal in terms of its radio-toxicity and long half-life i . This paper aims both to study the release behaviour of Pu from NWglass PWG124 in SIC solution, which has a composition representative of the in-situ interstitial water in the boom clay repository, and to determine the steadystate concentration of Pu released from the NW glass under the simulated disposal condition. EXPERIMENTAL Leaching of Pu from NWglass in SIC and IS solutions The Pu doped reference glass PWGl24* was used in the leaching tests because of its relatively large PuO2 content (1 wtZ). A quantity of 0.4g of the glass 1 with grain size of 125-250 p.mwas leached in 5 ml of solution (SA/V=1000 m- ). This high SA/V ratio was used to accelerate the leaching process and Pu saturation was expected within the leaching time. Two leaching solutions, SIC* and IS, were used to investigate the influence of humic acid on Pu dissolution. The real in-situ claywater sampled in the underground gallery in S.C.K/C.E.N also used in the leaching tests to compare the results of those from the SIC solutions. The leaching tests were conducted in the N2 glove box at 901C in a teflon cup. The duration of the tests was ranged from 6 to 400 days. After the leaching, the leachate then were filtered and ultrafiltered through a 0.45 PM filter and a 30,000 MWcut-off membrane, 2 nm in pore size, in order to investigate the distribution of the Pu in different particle size fractions. The Pu concentrations measured in the 2 rnmfiltrate was assumed to correspond to the soluble portions. The difference in Pu concentration between the 0.45 pm and 2 nm filtrate is considered as the colloidal fraction in the leaching * The compositions of the glass and SIC solution are given in Reference 2.
Mat. Res. Soc. Symp. Proc. Vol. 294. @1993 Materials Research Society
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solution. The Pu concentrations were measured by total a activity counting combined with the 241Am determination by gamma-spectrometry: [PU]Tot.1 = [( activity]Tot 1 - [a activity]Am_241 Solubility of PuO0-xH9 O (am) If a solid phase containing the radionuclide is present in a repository, the eq
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