Page 11

DISCUSSION

It was hinted previously that stiffer sidewalls increase the relative upward

displacement due to thermal gradients. Therefore, although cooling fins lower the
sidewall temperature and reduce the gradients, they were not effective for the studied
shell design.

Furthermore, it is well known that the cradles of the AP30/AP35 are fully

reinforced, so their sidewalls will be significantly stiffer than the studied design. The in
plane bending showed in Figure 4 will be drastically reduced. It is likely that the
magnitude of the relative upward displacement for these cells will be much larger than
what has been computed for the 300 kA base case (see Figure 6).

Forced-air cooling was found to be the most effective measure to reduce the

relative upward displacement. For instance, it was reduced from 17 to 5 mm for the 300
kA cell (Figure 6). In fact, for the cell at 500 kA (Figure 9), the sidewalls were too cold
with respect to the shell floor, leading to a downward relative displacement.

CONCLUSIONS

Simple "Empty-Shell" finite element models were used to assess the impact of

two different shell sidewall cooling enhancement measures fins and forced-air on the
relative upward displacement of the shell floor.

It was shown that a good mesh for thermo-electrical simulations may not be

adequate for a mechanical analysis, more so if non-linearities are present. The quality of
the global solution depends on the ability to capture local phenomena such as in plane
bending and plasticity.

It was hinted that stiffer sidewalls lead to larger relative upward displacements.

This is one of the reasons why cooling fins were not very successful in this aspect.
Forced-air cooling reduced the relative displacement to almost nil for the 300 kA cell and
even caused a downward relative displacement for the 500 kA cell. A proper amount of
cooling must therefore be performed to avoid having the shell floor warmer than the
sidewalls.

Since it is likely that the magnitude of the relative upward displacement is larger

in the AP50 than in the studied design, it is plausible that the forced-air cooling system is
primarily used to solve this problem. After all, easier solutions are available to control
the ledge thickness of the cell.