Yes, ARSENAL is a Scrabble word!

Letter values in Scrabble US: A 1, R 1, S 1, E 1, N 1, A 1, L 1.

Is it a valid word?

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

all the weapons and equipment that a country has
a military structure where arms and ammunition and other military equipment are stored and training is given in the use of arms
a place where arms are manufactured