Determination of the Forward Rate of Dissolution for SON68 and PAMELA Glasses in Contact With Alkaline Solutions
- PDF / 377,918 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 168 Views
Determination of the Forward Rate of Dissolution for SON68 and PAMELA Glasses in Contact With Alkaline Solutions K.Ferrand, K.Lemmens SCK•CEN, Boeretang 200, B-2400 Mol, Belgium ABSTRACT In the new Belgian disposal design, the nuclear waste glass will be surrounded by a 3 cm thick carbon steel overpack and a 70 cm thick concrete buffer. An initially high pH is expected after water intrusion in the concrete buffer and this may have an effect on the radionuclide release from the waste glass. This study was performed in order to determine the forward rate of dissolution for SON68 and PAMELA glasses (SM513 LW11 and SM539 HE 540-12), conducting dynamic tests at 30°C in contact with alkaline solutions. In these experiments, the silicon concentration in solution was determined by UV/Visible spectrophotometry according to the blue β-silicomolybdenum method. The forward rates of dissolution were quite similar for the three glasses except at the highest pH for which a slightly higher value was found for SM539 glass. For SON68 glass, a good agreement with the previously established interpolation law was observed until pH 11.5, but at higher pH, the interpolation law slightly overestimates the dissolution rate [1]. INTRODUCTION In Belgium, the study of a preliminary reference design for the disposal of vitrified HLW and spent fuel in an underground repository described in detail in the SAFIR 2 report has revealed some uncertainties regarding the engineered barrier system performance. The main uncertainties were due to the possibility of localised corrosion or stress corrosion that might threaten the integrity of the overpack during the thermal phase [2]. Consequently, NIRAS/ONDRAF has recently selected a new reference design based on the so-called Supercontainer design. It comprises three main components: the stainless steel liner, a Portland Cement concrete and the carbon steel overpack. The canisters of HLW or spent fuel are enclosed in a carbon steel overpack with a thickness of 3 cm, preventing the contact with (near field) ground water during the thermal phase. A Portland Cement concrete of about 70 cm of thickness has been chosen for the buffer because it will provide a highly alkaline chemical environment allowing to passivate the surface of this overpack and to inhibit its corrosion. On the other hand, once the overpack is locally perforated, the high pH of the incoming water may have an impact on the lifetime of the vitrified waste [3]. Most published data and national programs are related to clayey backfill materials and few studies are reported in alkaline media [4, 5]. Hence, to evaluate the durability of the glass matrix in a such environment, a series of experiments has to be conducted. This paper presents the results of the experiments performed to determine the forward rate of dissolution for SM539 and SM513 PAMELA glasses and for the SON68 glass at 30°C in alkaline solutions. The forward dissolution rate is defined as the dissolution rate in diluted conditions, and can be considered as the maximum dissolution r
Data Loading...
