Yes, CARTRIDGE is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, R 1, T 1, R 1, I 1, D 2, G 2, E 1.

Is it a valid word?

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

ammunition consisting of a cylindrical casing containing an explosive charge and a bullet; fired from a rifle or handgun
a light-tight supply chamber holding the film and supplying it for exposure as required
a module designed to be inserted into a larger piece of equipment
an electro-acoustic transducer that is the part of the arm of a record player that holds the needle and that is removable