Ageing of Eurobitum Bituminised Radioactive Waste under Gamma Irradiation
- PDF / 154,865 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 96 Downloads / 252 Views
Ageing of Eurobitum Bituminised Radioactive Waste under Gamma Irradiation Fabian Rorif1, Elie Valcke, Patrick Boven, Hans Ooms, Jozef Peeters, and Steven Smets SCK•CEN, the Belgian Nuclear Research Centre, Foundation of Public Utility Boeretang 200, 2400 Mol, Belgium 1 Present address: IAEA, Wagramerstrasse 5, P.O.Box 100, A-1400 Vienna ABSTRACT The extent of the physico-chemical processes of concern in the study on the acceptability of the Belgian Eurobitum bituminised waste for underground disposal will depend on the degree of ageing of the bituminous matrix. Therefore, the ageing of non-radioactive simulates of Eurobitum under gamma irradiation was studied both in the presence and absence of oxygen. Chemical changes in the bitumen structure were measured in the mid-infrared region with the attenuated total reflectance infrared technique (ATR/FTIR) and evaluation of the peaks at 1700 cm-1 (C=O) and 1600 cm-1 (C=C). Even for the highest total absorbed doses (~800 kGy at ~150 Gy/h), the effect of the irradiation in Eurobitum was found to be small and was, in any case, smaller than for samples heated for three hours at 130°C in air. INTRODUCTION Eurobitum bituminised radioactive waste Since the late sixties, bitumen has been widely used as a matrix for the immobilisation of low and intermediate level radioactive waste because of its good binding capacity, low permeability, low solubility in water, and good chemical and biological inertia. Eurobitum has been produced by the Eurochemic/Belgoprocess reprocessing facility (Dessel, Belgium), and with its total volume of ~3000 m3, it is the most important medium-level long-lived waste form in Belgium. It consists of ~60 weight% (wt%) blown bitumen Mexphalt R85/40, ~26 wt% NaNO3, ~5 wt% CaSO4, and ~4 wt% CaF2, for the most abundant salts, and ~1 wt% residual water. The rest of the waste is a complex mixture of Ca3(PO4)2, Ni2[(Fe,Mn)(CN)6], and oxides and hydroxides of Fe, Zr, and Al. The total radionuclide inventory (238-242Pu, 241Am, 137Cs, 90Sr...) is lower than 0.001 weight% [1]. The option presently considered for the medium-level long-lived waste like Eurobitum is deep disposal in a clay host rock, such as the Boom Clay formation, provided that its compatibility with the host rock is demonstrated [2]. Long-term behaviour of Eurobitum in underground disposal conditions Opposite to the glass matrix, the resistance to leaching of the bitumen matrix is not considered in safety assessments: an instantaneous release is assumed, and the durability of the Eurobitum waste form is regarded as a safety reserve. The main barrier function is performed by the Boom Clay host formation. The research programme focuses thus on the compatibility of the bituminised waste with the Boom Clay i.e. the study of processes that may potentially affect or disturb the performance of the Boom Clay host formation [2,3]. These processes of concern are:
i) The production of water-soluble organic ligands, due to radiolytic, chemical, and microbial degradation of bitumen, that might facilitate the mig
Data Loading...
