The Chemical Durability of Some Hlw Glasses: Effects of Hydrothermal Conditions and Ionising Radiation
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THE CHEMICAL DURABILITY OF SOME HLW GLASSES:
EFFECTS OF HYDROTHERMAL
CONDITIONS AND IONISING RADIATION D.R. COUSENS, R.A. LEWIS,
S. MYHRA, R.L.
SEGALL, R.St.C. SMART AND
P.S. TURNER School of Science, Griffith University, Nathan, Queensland 4111. Australia.
ABSTRACT The time dependence of leaching and dissolution under hydrothermal conditions at 250*C has been investigated in an autoclave designed for continuous sampling; it
is found that the rates are in accord with those
obtained by the commonly used procedures.
The effect of pressure by itself
has been studied in an ultracentrifuge; ambient rates for Si and Na loss remain unchanged up to about 40 MPa followed by a monotonic increase to about 1.5 times the ambient rates at 160 MPa.
The surface layers formed as
a result of chemical attack have been examined (XRD, is found that Zn present in
IR, XPS and PIXE).
It
the glass or in the solution is retained in the
siliceous layer which in some circumstances contains a crystalline zinchydroxy-silicate phase.
A method for enhancing rates of displacement damage
by a factor of -106 has been developed.
Powdered borosilicate glass and
glass doped with U02 have been neutron-irradiated in a high-flux reactor. Damage is thereby introduced in the bulk as a result of 1 OB(n,c) 7 Li and (n,fission) events and subsequent slowing-down of energetic charged ions. Irradiation doses equivalent to 106 years HLW storage have been achieved. The resultant stored energy of -102 kJ kg-I is released over the range 300 to 800 K.
The initial leaching/dissolution rates are found to be increased by a factor of about three by irradiation; the changes in longer-term rates are difficult to determine due to the effects of back-reactions and changing particle size geometry and size distribution, but significant enhancement is found.
Rates for fission and activation products are similar to those for
bulk species. INTRODUCTION It
is likely that high-level nuclear wastes from the commercial operation
of power reactors will be immobilized by incorporation in a glassy matrix. The present pre-eminence of glasses over other waste forms is largely due to the considerable research and development effort during the last twenty years which has sought to ensure that no major unsuspected short-comings
164 will be found.
The work discussed below has been undertaken in
order to test
the validity of some specific techniques which are in widespread use for studying the effects of hydrothermal conditions on glasses.
Also, experiments
have been designed and carried out to evaluate the role of surface layers in the dissolution of HLW glasses.
Durability tests have been performed on
glasses subjected to extreme pressure and high doses of ionising radiation. The object of these separate experiments is
to establish that the chemical
durability of glasses under extreme conditions can be evaluated and that the results exhibit no unusual features.
The experiments have been optimized
in each case so as to potentially yield an effect which ca
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