Yes, AQUANAUTS is a Scrabble word!

Letter values in Scrabble US: A 1, Q 10, U 1, A 1, N 1, A 1, U 1, T 1, S 1.

Is it a valid word?

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

an underwater swimmer equipped with a face mask and foot fins and either a snorkel or an air cylinder
a skilled worker who can live in underwater installations and participate in scientific research

Also: skin-diver.