atw 2017-09

atw Vol. 62 (2017) | Issue 8/9 ı August/September
DECOMMISSIONING AND WASTE MANAGEMENT 546
Steel
St 12
# 1.0330
GGG 40.3
# 0.7043
Canister materials for wastes
with negligible heat production
Experiments with fine-grained steel
(material number 1.0566) were performed
under anaerobic conditions at
35 °C in solution 1 and 2 (see Tab. 2).
Measured mass losses and corrosion
rates are shown as function of time.
Figure 9 shows significant scatter
of the corrosion rates in both brines.
Especially one of the parallel samples
in MgCl 2 -rich solution at the time step
of 548 days showed by a factor of 2
higher corrosion rate in comparison to
the other samples. The sample did not
show local corrosion phenomena such
as pitting corrosion, however, the
Corrosion
medium
| | Fig. 6.
Mass loss of steel 1.0566 in MgCl 2 -solution depending on S/V ratio at
150 °C.
| | Fig. 8.
XRD pattern of corrosion products of steel 1.0566 in NaCl (top) and MgCl 2
solution (middle) at 90 °C.
Exposure
time
days
­corrosion attack produced shallow
pits. The distribution of these shallow
pits explains the scatter of data. As
mentioned above, the corrosion rate
was independent of the solution.
Untreated plane samples of St 12
(material no. 1.0330) [7] and nodular
cast steel GGG 40.3 [15] were investigated
under dry interim storage
­conditions (aerobic conditions). The
steels showed uniform corrosion rates
but also localized corrosion processes
(pitting). The general corrosion rate
was determined to about 10 µm/yr.
This rate decreased with increasing
time as well as pitting corrosion. Under
conditions in ventilated galleries
General
corrosion rate
µm/a
| | Tab. 3.
Corrosion phenomena of untreated plane samples of St 12 (material no. 1.0330) and nodular cast steel (material no. 07043) under
aerobic conditions (iron ore mine Konrad) [7].
| | Fig. 7.
General corrosion rate of nodular cast steel GGG40.3 at 150 °C as function
of time.
| | Fig. 9.
General corrosion rates of fine-grained steel 1.0566 as function of time in
MgCl 2 -rich p and NaCl solution s at 35 °C.
Maximum
penetration depth
µm
Konrad 1250 m level @ 45 °C 133 21.2 280
covered by iron ore 378 305.0 740
Konrad water 121 18.0 120
@ 50 °C 381 23.5 130
Konrad 1250 m level @ 45 °C 90 650 1600
covered by iron ore 180 460 1700
365 430 1200
Konrad water 90 250 -
@ 50 °C 180 260 200
365 270 100
in the iron ore mine Konrad, corrosion
rates of < 100 µm/yr. were observed.
The measurements were performed
by contacting the steel samples with
crushed iron ore implying definite
­water contents. For the conditions of
the iron ore mine, higher uniform
­corrosion rates up to about
600 ­µm/yr. as well as pitting corrosion
rates of 1.7 mm/yr. were measured.
These tests were made in the closed
gallery with a relative humidity of
80 % at 42 °C on the -1,250 m level of
the Konrad Mine. The results of the
tests are summarized in Table 3.
Summary and conclusions
During the period between 1980 and
2004, a huge number of corrosion
tests were performed at KIT-INE. The
database contains more than 5,600
datasets for metals. Due to the fact
that high temperature conditions
were expected in the disposal, most
of the experiments were performed
at temperatures between 150 and
200 °C. Most of the corrosion experiments
were carried out in closed autoclaves
simulating the deep disposal
redox conditions. The attacking
­solutions were selected according
the host rocks under investigation at
this time.
It needs to be mentioned that
­different host rocks together with the
rock specific disposal concepts significantly
influences the selection of the
Decommissioning and Waste Management
Corrosion of Canister Materials for Radioactive Waste Disposal ı Bernhard Kienzler