RD&D-Programme 2004 - SKB

The results of this testing should serve as a basis for optimizing the fabrication processes,
the material specification and the testing methods. Besides showing that the canister meets the
design requirements, strength analyses should also be based on the actual material properties of
fabricated canisters.
In its review of RD&D 2001, SKI concluded that SKB should to a greater extent verify the
mechanical properties of the inserts by examining some fabricated inserts more thoroughly.
SKI also offered the viewpoint that simulation programs should be run to achieve a satisfactory
result in the casting of the insert.
Newfound knowledge since RD&D 2001
Extensive material testing has been conducted on a number of cast inserts, both with cast-on test
bars and with test pieces from the actual inserts. To determine variations in properties between
different specimen locations, test bars for tensile testing and microstructure examination have
been made from discs cut from different locations in the inserts, see Figure 5-4. Examples of
specimen locations are shown in Figure 5-5.
SKB has found a relatively wide range of variation in material properties in several individual
inserts. The greatest variation in tensile testing is found in values for elongation at rupture.
The ductility of this type of cast iron is highly dependent on the microstructure of the graphite
and whether there are material defects such as porosities in the casting. The nodularity of the
graphite (roundness as in type VI in Figure 5-3) has varied in some inserts. Some presence of
porosities and slag particles has also been found. This has been detected by both microscopy
and ultrasound.
An analysis by the Swedish Foundry Association employing e.g. computer simulations of
the casting technique at each individual foundry has indicated some improvements. This and
the foundries’ own assessments regarding process parameters has resulted in measures being
taken to obtain more uniform material properties.
An extensive development project has been started concerned with probabilistic analysis
of canister strength. The participants include SKB, the Swedish Foundry Association,
Ångpanneföreningen, the Royal Institute of Technology in Stockholm, the Joint Research
Center (JRC) in the Netherlands, Det Norske Veritas and CSM Materialteknik AB. Three
Figure 5-4. Discs cut from cast insert for material testing.
RD&D-Programme 2004 51