TECHNICAL REPORT 92-14 - Nagra

nagra

TECHNICAL REPORT 92-14 - Nagra

NAGRA NTB 92-14 - 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 non-linearity 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 long-tenn

transient creep calculation would resemble the one where the interfaces are

perfectly bonded.

1.2.2 Thick-walled overpack with uniformly corroded profile

This test was chosen in order to show the elasto--plastic 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

SCK-CEN CASTOR BE-2D

CEA CASTEM - INCA

STEAG COSMOS/M

ENSA ANSYS

PSI/NAGRA ADINA

I Calculation 1)

three-dimensional

onl y elastic

small displacement

large displacement

standard

standard

two-dimensional

Pressure I

I [MPa]

80.5

-

81.6

112.5

78.4

82.3

77.7

1): An elasto--plastic two-dimensional 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,

two-dimensional plane strain or three-dimensional), 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-

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