Will a Crocea clam survive in a 102 litre nano thats 50cm high with 4x 24 watt T's ? if placed about 5 cm from the light ?

With a tank that deep, you couldn't keep one on the sandbed with that lighting, but you could probably keep one midway or more up the tank.

Light isn't always the limiting factor with clams. Water parameters and stability are generally more important.

If you put it up close to the light as stated it may be ok. As posted above there are other factors in keeping a clam. Corcea's are rock dwellers.

What size clam are you looking at ? That would make a difference as well... As clams get larger their requirements change.

The distance to the light may be enough, provided you have water quality and things like calcium/alkalinity in control.