Databank

POSIVA Report 1996-15

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Name:

The Hyrkkölä Native Copper Mineralization as a Natural Analogue for Copper Canisters

Writer:

Nuria Marcos

Language:

English

Page count:

62

ISBN:

951-652-014-6; 1239-3096

Summary:

Working report: THE HYRKKÖLÄ NATIVE COPPER MINERALIZATION AS A NATURAL ANALOGUE
FOR COPPER CANISTERS




The Hyrkkölä U-Cu mineralization is located in southwestern Finland, near the Palmottu analogue
site. The age of the mineralization is estimated to be between 1.8 and 1.7 Ga. Petrological and
mineralogical studies have demonstrated that this mineralization has many geological features that
parallel those of the sites being considered for nuclear waste disposal in Finland. A particular
feature is the existence of native copper and copper sulfides in open fractures in the near-surface
zone. This allows us to study the native copper corrosion process in analogous conditions as
expected to dominate in the nuclear fuel waste repository. The occurrence of uranyl compounds at
these fractures permits also considerations about the sorption properties of the engineered barrier
material (metallic copper) and its corrosion products.

From the study of mineral assemblages or paragenesis, it appears that the formation of copper
sulfide (djurleite, Cu1.934S) after native copper (Cu0) under anoxic (reducing) conditions is
enhanced by the availability of dissolved HS- in the groundwater circulating in open fractures in
the near-surface zone. The minimum concentration of HS- in the groundwater is estimated to be of
the order of 10-5 M (~10-4 g/l) and the minimum pH value not lower than about 7.8 as indicated by
the presence of calcite crystals in the same fracture.

The present study is the first one that has been performed on findings of native copper in reducing,
neutral to slightly alkaline groundwaters. Thus, the data obtained is of most relevance in
improving models of anoxic corrosion of copper canisters.
THE HYRKKÖLÄ NATIVE COPPER MINERALIZATION AS A NATURAL ANALOGUE
FOR COPPER CANISTERS




The Hyrkkölä U-Cu mineralization is located in southwestern Finland, near the Palmottu analogue
site. The age of the mineralization is estimated to be between 1.8 and 1.7 Ga. Petrological and
mineralogical studies have demonstrated that this mineralization has many geological features that
parallel those of the sites being considered for nuclear waste disposal in Finland. A particular
feature is the existence of native copper and copper sulfides in open fractures in the near-surface
zone. This allows us to study the native copper corrosion process in analogous conditions as
expected to dominate in the nuclear fuel waste repository. The occurrence of uranyl compounds at
these fractures permits also considerations about the sorption properties of the engineered barrier
material (metallic copper) and its corrosion products.

From the study of mineral assemblages or paragenesis, it appears that the formation of copper
sulfide (djurleite, Cu1.934S) after native copper (Cu0) under anoxic (reducing) conditions is
enhanced by the availability of dissolved HS- in the groundwater circulating in open fractures in
the near-surface zone. The minimum concentration of HS- in the groundwater is estimated to be of
the order of 10-5 M (~10-4 g/l) and the minimum pH value not lower than about 7.8 as indicated by
the presence of calcite crystals in the same fracture.

The present study is the first one that has been performed on findings of native copper in reducing,
neutral to slightly alkaline groundwaters. Thus, the data obtained is of most relevance in
improving models of anoxic corrosion of copper canisters.

Keywords:

File(s):

The Hyrkkölä Native Copper Mineralization as a Natural Analogue for Copper Canisters (pdf) (2.9 MB)


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