TECHNICAL REPORT 9214  Nagra
NAGRA NTB 9214  5 
fluid that has no shear strength in the final creep state calculation. Figure 1.1
depicts the defonned shape of the overpack at different times as calculated
by PSI/NAGRA.
OAP investigated further nonlinearity in the fonn of sliding motion at the
interfaces between the titanium overpack and the lead filler and between
the lead filler and the block of high level nuclear waste. In the case of
frictionless interfaces, sliding motion is quite noticeable between the lead
filler and the titanium overpack at the corner region. On the other hand,
sliding motion is almost negligible at the interfaces after a period of 50 years
when a small friction coefficient is considered and, therefore, a longtenn
transient creep calculation would resemble the one where the interfaces are
perfectly bonded.
1.2.2 Thickwalled overpack with uniformly corroded profile
This test was chosen in order to show the elastoplastic calculation capabilities
of the finite element codes. It was required to predict the external pressure
which causes a reduction of 10 mm in the internal diameter (440 mm) of
a 60 mm thick overpack. The 10 mm correspond to the overpack collapsing
onto the canister with high level nuclear waste.
Table 4: Pressure for 10 mm of reduction in the internal diameter of the
uniformly corroded overpack.
I Partner
OAP DYNA3D
SCKCEN CASTOR BE2D
CEA CASTEM  INCA
STEAG COSMOS/M
ENSA ANSYS
PSI/NAGRA ADINA
I Calculation 1)
threedimensional
onl y elastic
small displacement
large displacement
standard
standard
twodimensional
Pressure I
I [MPa]
80.5

81.6
112.5
78.4
82.3
77.7
1): An elastoplastic twodimensional calculation in a small displacement
fonn ulation was used as a standard.
There is a good correlation in the elastic range, although there is a degree
of divergence in the plastic range. The variation in the stresses could have
been due to different modelling strategies used by the partners (axisymmetric,
twodimensional plane strain or threedimensional), different mesh
patterns across the thickness, different number of Gaussian integration points
(ranging from 3*3 to 1*1 *1) or different techniques used by the codes for
calculating the stresses at the nodal points from the stresses at the Gaus