Yes, INVASION is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, V 4, A 1, S 1, I 1, O 1, N 1.

Is it a valid word?

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

the act of invading; the act of an army that invades for conquest or plunder
any entry into an area not previously occupied
(pathology) the spread of pathogenic microorganisms or malignant cells to new sites in the body