Plutonium Environment in Lanthanide Borosilicate Glass
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1264-Z11-09
Plutonium Environment in Lanthanide Borosilicate Glass Sergey V. Stefanovsky, Andrey A. Shiryaev,1 Yan V. Zubavichus2 and James C. Marra3 SIA Radon, 7th Rostovskii lane 2/14, Moscow 119121 RUSSIA 1 Institute of Physical Chemistry and Electrochemistry RAS, Leninskii pr. 31, Moscow 119991 RUSSIA 2 RRC “Kurchatov Institute”, Kurchatov sq. 1, Moscow RUSSIA 3 Savannah River National Laboratory, Building 773-A, Aiken 29808 U.S.A. ABSTRACT Two lanthanide borosilicate (LaBS) glasses containing 9.5 and 5.0 wt.% PuO2 prepared at 1500 °C consisted of a vitreous phase and minor crystalline PuO2 (or PuO2-HfO2 solid solution with minor HfO2) and britholite-type phases. X-ray absorption spectra of Pu LIII edge in the as-prepared and stored for various periods LaBS glasses were recorded, analyzed and compared with the spectra of crystalline PuO2. Pu in the as-prepared glass existed in predominantly tetravalent form (Pu4+ ions) but its storage in air results in partial oxidation as was seen from shift of peak energy values. In the structure of the asprepared glass, Pu4+ ions had a co-ordination number (CN) close to 6 (~6.3) and were located within the axially squeezed octahedra with five equidistant oxygen ions at a distance of 2.265±0.015 Å and one – at a shorter distance (2.130±0.010 Å) from the Pu4+ ion. The PuPu(M) distance (second co-ordination shell) was 3.675±0.015 Å. “Aging” of the LaBS glass with transformation of some fraction of Pu into penta- or/and hexavalent form was accompanied by a structural transformation. INTRODUCTION Lanthanide borosilicate (LaBS) glasses were proposed for immobilization of actinide-containing waste and excess weapons plutonium [1-4] due to their capability to incorporate of up to ~10 wt.% actinide oxides whereas conventional borosilicate glasses may dissolve them in amount of only up to ~2 wt.% [5]. LaBS glasses are also more durable in water solutions than conventional borosilicate glasses [4]. The as-prepared LaBS glasses may contain trace of undissolved PuO2 [6] and britholite [7,8]. Thermal treatment at 1250 °C and even storage at room temperature for 1 year and longer time resulted in crystallization of PuO2-HfO2 solid solution [6] and extra PuO2 and britholite [7,8]. Pu in LaBS glasses is predominantly tetravalent [7,8] and being partitioned between vitreous and crystalline phase (mainly PuO2) has different co-ordination environments which can also vary with time. Investigation of the structure of the LaBS glasses in more detail will be published in a separate paper. In this paper we describe Pu environment in two LaBS glasses containing 9.5 and 5.0 wt.% PuO2. EXPERIMENTAL Two LaBS glasses (Table I) were prepared from reagent-grade Al2O3, H3BO3, SiO2, La2O3, Nd2O3, Gd2O3, CaCO3, SrCO3, ZrO2, HfO2, MnO, Fe2O3, LiOH⋅H2O, NaNO3 intermixed in an agate mortar and mechanically treated/activated in an AGO-2U planetary mill. Mechanically activated precursor was soaked with a plutonium nitrate solution and the mixture was dried under an infrared (IR) lamp, calcined in a Pt ampoule at
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