⁹⁹Tc‐ and ²³⁹Pu‐Doped Glass Leaching Experiments: Residual Alteration Rate and Radionuclide Behavior

Abstract

The long-term behavior of high-level nuclear glass subjected to alpha/beta radiation by long-life radionuclides must be investigated with respect to geological disposal. This study focuses on the effects of alpha and beta radiations on the chemical reactivity of R7T7 glass with pure water, mainly on the residual alteration rate regime. Glass specimens doped with 0.85 wt % 239 PuO 2 (a emitter) and 0.24 wt% 99 TcO 2 (b emitter) that simulate alpha and beta dose rate corresponding to long-term disposal conditions are leached under static conditions in argon atmosphere at 90°C, in initially pure water and at a high surface-area-to-volume ratio (S/V = 20/cm). The alteration rate is monitored by the release of glass alteration tracer elements (B, Na, and Li). Radiation effects on the leached glass and its gel network are characterized by SEM and TEM analyses. Plutonium and technetium releases are also measured by radiometry, and their chemical oxidation state is assessed by measuring the pH and reduction-oxidation potential of the leachates. The results do not highlight any significant effect of alpha/beta radiation on the residual alteration of these doped glasses. These observations are consistent with solid characterizations, which show that a protective layer can be formed under such irradiation fields. Under our experimental conditions (Eh~380 mV/ *magaly.tribet@cea.fr

Irradiation Impact on the Leaching Behavior of HLW Glasses

“…Moreover, the morphology and protective properties of the altered layer formed under these conditions are similar to those of the inactive SON68 glass, as presented in figure 3. These results are consistent with similar studies performed on nonradioactive SON68 glass under external gamma irradiation at 50 Gy.h -1 , where no direct effects of such irradiation were observed on the glass residual alteration rates [Rolland et al (2013)bis].…”

“…The use of radionuclide-doped glasses also allows to understand the radionuclide behavior during the glass leaching and to assess the retention properties of the alteration products [Rolland et al (2013)] [Advocat et al (2001)] [Jollivet et al (2005)]. Finally, doped glass leaching experiments can also be carried out under realistic disposal conditions [Valcke et al (2006)].…”

“…Gamma irradiation of inactive glasses by 60 Co sources have been used to focus on electronic effects occurring during gamma transitions, beta and alpha decays, as the main interaction mode is dominated by Compton diffusion. This kind of irradiation system reproduces very well gamma transitions and beta decays, but is less representative of the alpha emission due to its lower linear energy transfer value [Rolland et al, (2013)] [Rolland et al, (2013)bis].…”

“…Radiation effects on the leached glass and its gel network are characterized by SEM and TEM analyses. Plutonium releases are also measured by radiometry and its chemical oxidation state is assessed by measuring the pH and reduction-oxidation potential of the leachate [Rolland et al (2013)]. Data obtained from solution and solid analyses show that the residual rate is not significantly affected by the alpha dose rate (150 Gy.h -1 ) and the local irradiation field in water (i.e high linear energy transfer).…”

Open Scientific Questions about Nuclear Glass Corrosion

“…Despite a large number of studies carried out on the leaching behavior of radioactive or irradiated glasses, showing no effect of radioactivity on the initial dissolution rate and little effect on the rate drop (Advocat et al, 2001), few data are available on the residual rate. A recent study suggested no significant impact of dose rate on the residual rate of a 239 Pu-doped glass altered under a dose rate of 150 Gy.hr -1 and on a 99 Tc-doped glass providing a dose rate of 0.06 Gy.hr -1 (Rolland et al, 2013). Moreover the potential effects of radioactivity when glass is altered in the presence of nearfield materials require further work.…”