Durability of High-Level Waste Glass in Flowing Groundwater Under Gamma-Irradiation
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DURABILITY OF HIGH-LEVEL WASTE GLASS GAMAS-IRRADIATION
IN FLOWING GROUNDWATER UNDER
Hiroshi Kamizono, Masa-aki Hashimoto. and Sei-ichiro Matsumoto Japan Atomic Energy Research Institute Tokai-mura. Ibaraki-ken, 319-11 Japan
Yukito Tamura.
Tamio Sagawa.
ABSTRACT Durability of simulated high-level waste glass in continuouslyflowing J-13 tuff groundwater has been examined at 900C under gammairradiation. The results obtained are compared with those without gamma-irradiation. The effects of groundwater radiolysis on the glass durability are discussed based on the Eh-pH excursion obtained in the present system. It is found that the groundwater tends to be reduced under gamma-irradiation, however, this may not influence the solubility of multivalent cations leached from the glass. 1. INTRODUCTION Disposal sites suitable for the isolation of high-level waste glass (HLW glass) may be constructed in geologic formations below the land surface. During the first several hundreds of years after the disposal, a considerable amount of 137Cs emits gamma-radiation to the surrounding area. If the glass comes into contact with groundwater during this period, leaching behavior of the glass will be affected by radiolysis of groundwater. There are many studies on the effects of gamma-irradiation on the HLW glass durability in water. Various effects on the water chemistry and hence leaching behavior from the glass are reported (see, for example, Ref. 1-4). However, in most studies leach experiments are carried out
under
static
conditions,
and
therefore
in
examine the dynamic gf ects of gamma-irradiation
the
present
study we
on the HLW glass
in
flowing groundwater. The glass is exposed to a constant gamma-irradiation of about 104 R/h which is nearly equal to the irradiation rate after about 250 years of disposal. This assumption must be reasonable when the stainless steel canister outside the glass iý damaged after at least 250 years of disposal. A rate of about 4 x 10 R/h gamma-irradiation is also examined whether or not the irradiation is effective after the decay of most of the gamma emitters. 2. EXPERIMENTAL 2.1 Preparation of Simulated HLW Glass The simulated HLW glass containing 11.8 wt% of simulated fission products was prepared. The composition of the glass is given in Table I. Reagents for the simulated HLW, which were mostly in the form of nitrates, were mixed with additives, melted at 1200 0 C for 2 hours, poured into graphite molds, kept at 600 0 C for 2 hours and then slowly cooled to room temperature. The resultant glass blocks were cut tto pin2 pple-sl5ced specimens and cljscoid specimens, which were 8. 0 x 2.3 x 0.25 cm and 5. 0 x 0.7 cm in size. (The pineapple-sliced specimen means a thin, flat and round plate with a hole in its center, and the discoid specimen is a thin, flat and round plate without a hole.) Finally the surface of these specimens was polished by #600 SiC papers.
Mat. Res. Soc. Symp. Proc. Vol. 353 0 1995 Materials Research Society
72
Table I Composition of Simulated High-Level Waste
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