A. Abdelouas et al., SURFACE-LAYERS ON A BOROSILICATE NUCLEAR WASTE GLASS CORRODED IN MGCL2 SOLUTION, Journal of nuclear materials, 240(2), 1997, pp. 100-111
Citations number
57
Categorie Soggetti
Nuclear Sciences & Tecnology","Mining & Mineral Processing","Material Science
Surface layers on the French borosilicate nuclear waste glass, R7T7, c
orroded in MgCl2 solution were studied to determine the composition, s
tructure and stability of crystalline phases. The characteristics of t
he phases constituting the surface layer varied with the parameter S/V
X t, the glass surface area (S) to solution volume (V) ratio, times t
ime (t). At low S/V X t values (< 360 days/m; less than or equal to 36
d) the surface layer was thin and contained mainly iron hydroxide par
ticles and hydrotalcite crystals. At an intermediate S/V X t value (28
00 d/m; 5.5 y) the surface layer contained hydrotalcite- chlorite- and
saponite-type phases. At the highest S/V X t value (10(7) d/m; 463 d)
the major phases were saponite, powellite, barite and cerianite solid
solutions. About 95% of the uranium and > 98% of the neodymium releas
ed from the glass were precipitated in the surface layer. In the 463 d
ay experiment, 86% of the neodymium in the surface layer was in solid
solution with powellite, the rest with saponite. Uranium was contained
exclusively in saponite. High S/V ratios, typical of disposal conditi
ons for vitrified high-level radioactive waste, favor retention of act
inides in fairly insoluble corrosion products. Observation of similar
corrosion products on natural glasses as on nuclear waste glasses lend
support to the hypothesis that the host phases for actinides observed
in the laboratory are stable over geological periods of time.