Yes, TANTALUS is a Scrabble word!

Letter values in Scrabble US: T 1, A 1, N 1, T 1, A 1, L 1, U 1, S 1.

Is it a valid word?

TANTALUS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(Greek mythology) a wicked king and son of Zeus; condemned in Hades to stand in water that receded when he tried to drink and beneath fruit that receded when he reached for it