What parts of clam are likely to be preserved?

The pearl is kept and the edible part of the clam is kept until ate

It is the pearl.

Fun fact. To find how much a pearl is worth will vary depending on size, color, shape, surface quality, the type of pearl it is, were it is from etc.
The average pearl is worth $300 to $1,500.

I hope this helps.

Because its reliable.   there is no pollution  the chances of a radiation leak is low