There should be no pieces/chunks of anything in the pan, period. The converter is outside the transmission. If you had broken parts in the converter it would be pretty difficult to drive the car.
The debris that looks like sand is likely friction material. On older units there will always be some of that in the pan as the frictions wear but if you have a broken ring you might be getting uneven/excessive wear.
Like said above it looks like the shards could be part of a snap ring. The snap rings provide the proper clearance for the frictions and hold them in place in the drum. If you have a broken one it’s only a matter of time before you lose gears. The frictions will wear out and won’t grab.
Why do you have the pan off?
Also, how do you drive the car?