RD&D-Programme 2004 - SKB

Newfound knowledge since RD&D 2001
A literature review of copper corrosion in alkaline waters with different salinities has been
published /16-12/. The conclusion in the report was that an increase in pH will passivate the
copper surface. The stability of the passive film and its ability to prevent localised corrosion are
enhanced by increasing pH. An increase in pH up to 12–13 will therefore have little effect on
the integrity of the canister.
Since RD&D 2001, an experimental investigation of intergranular corrosion in electron beam
welds and friction stir welds has been started at Swedish Corrosion Institute. Preliminary results
indicate that the electron beam welds are not sensitive to intergranular corrosion. This agrees
with the results of previous investigations /16-13/. The work will continue during the coming
year.
An experimental study of copper corrosion under anoxic conditions in sodium chloride solution
(1 molar NaCl) has been conducted since RD&D 2001 in cooperation with Posiva /16-14,
16-15/. The results show that after an initial period of several hours with a high corrosion rate,
the corrosion rate declines and is virtually zero after about 30 days.
A project for studying the mechanisms of sulphide action on copper by means of electrochemical
and surface analysis methods has been started at the University of Western Ontario.
The main goal of this project is to develop a model for predicting the long-term behaviour of
copper canisters in a repository environment. The project will continue throughout the coming
three-year period.
A programme to investigate the prospects of bacterial corrosion of copper has been under way
for several years now. Previous results have shown that sulphate-reducing bacteria will be active
in compacted bentonite. No new evidence to contradict this has emerged during the period
/16-16/. The work will continue into the coming period.
Field experiments in the Äspö HRL involving multiyear exposure of copper – both to the
atmosphere in the underground laboratory and to various groundwaters – have been conducted
during the past three-year period. The experiments with exposure to groundwater will continue
into the next three-year period. The air-exposed samples have been evaluated and the results
show that the corrosion attacks have been less than are normally obtained in a normal urban
atmosphere /16-17/.
Programme
In addition to what has been mentioned above regarding already ongoing projects that will
continue during the coming period, a project aimed at shedding light on the properties of copper
oxide films, and particularly the influence of chloride and sulphide ions, is being started at the
Department of Physics at Uppsala University. The project will employ surface-sensitive spectrometric
methods to characterize sorbing and chemically bound sulphide and chloride species on
clean copper surfaces and copper surfaces with different surface films.
16.2.13 Stress corrosion cracking of copper canister
Tensile stresses in the copper canister are a necessary prerequisite for SCC. Since the canister is
under external pressure it is not likely that SCC could lead to canister penetration.
Conclusions in RD&D 2001 and its review
SKI says that SKB must show that the canister will not be present in an environment that can
cause SCC of the copper, or else take into account SCC in the analysis of canister lifetime.
190 RD&D-Programme 2004