Sodalite as a vehicle to increase Re retention in waste glass simulant during vitrification

Abstract

Technetium (Tc) retention during Hanford waste vitrification can be increased if the volatility can be controlled. Incorporating Tc into a thermally stable mineral phase, such as sodalite, is one way to achieve increased retention. Here, rhenium (Re)-bearing sodalite was tested as a vehicle to transport perrhenate (ReO 4-), a nonradioactive surrogate for pertechnetate (TcO 4-), into high-level (HLW) and low-activity waste (LAW) glass simulants. After melting HLW and LAW simulant feeds, the retention of Re in the glass was measured and compared with the Re retention in glass prepared from a feed containing Re 2 O 7. Phase analysis of sodalite in both these glasses across a profile of temperatures describes the durability of Resodalite during the feed-to-glass transition. The use of Re sodalite improved the Re retention by 21% for HLW glass and 85% for LAW glass demonstrating the potential improvement in Tcretention if TcO 4 were to be encapsulated in a Tc-sodalite prior to vitrification. 1 Introduction As a byproduct of the effort to produce plutonium for the US nuclear weapons arsenal from 1943 to 1988, a vast quantity of waste was produced at the Hanford Site in Washington State. This waste contains fission products and reagents from chemical separation processes

Chemical Trends in Solid Alkali Pertechnetates

“…This will be particularly important to the development of many next-generation nuclear waste forms and new vitrification starting materials. A number of these innovative materials have only been investigated with analogues Re compounds or are just beginning to be synthesized with Tc. , Understanding the stability and chemistry of the alkali pertechnetates will be essential to the design and fine-tuning of these materials so they will efficiently and effectively retain Tc in all of its alkali forms.…”

Perrhenate sodalite growth from alkali silicate melts by noble metal catalysis

“…have been synthesised [3][4][5][6][7][8][9][10][11]. In particular, incorporation of perrhenate (ReO 4 − ) to the sodalite cage structure has been the focus of several studies due to its similarity to pertechnetate (TcO 4 − ) and applications in nuclear waste management [12][13][14][15][16][17]. Synthesis of perrhenate sodalite (referred to as Re-sodalite hereafter) has been achieved via a low temperature hydrothermal process (175 °C) involving preliminary solution chemistry methods [12][13][14][15][16][17].…”

Effect of Technetium-99 sources on its retention in low activity waste glass

“…For example, a mineral-forming precursor could be added directly into waste streams before being fed to the melter, or to the off-gas condensate. If the thermal stability and chemical durability of the selected mineral are sufficient, incorporated Tc may remain within the mineral structure through melting of the glass, thus inhibiting Tc volatility [9]. If used in the off-gas system, the resulting Tc mineral (not containing sulfur or halides) could be recycled back to pretreatment, serve as a standalone waste form, or be incorporated into a low-temperature waste form that is being considered for immobilizing secondary wastes from the WTP [10,11].…”

“…Rhenium (Re) is used as a Tc surrogate due to the similarities of the pertechnetate and perrhenate species, and Re-containing sodalite (with Re 7+ ) has demonstrated the utility of using a durable mineral phase to increase Re retention in glass [9,15]. However, attempts to synthesize minerals, such as spinel that can incorporate tetravalent Tc, with tetravalent Re were not successful, presumably because of differences in ionic size and redox potential.…”

“…, various fractions of mineral additives had already reacted by 600°C including ~50% of the quartz to form an early glass-forming melt. The glass formed at 600°C contained 22.9 % of the total Re in the KReO 4 feed[9] and 20.6 % of the total Tc in the KTcO 4 feed (seeFigure 6top plot). Although it is likely that a similar fraction of glass-forming melt was formed at 600°C in the Tc-goethite feed, the experimental and characterization methods used in the present study could not determine the split factors of insoluble Tc into Tc-minerals and the glassy phase.…”