Yes, CASSAVA is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, S 1, S 1, A 1, V 4, A 1.

Is it a valid word?

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

a starch made by leaching and drying the root of the cassava plant; the source of tapioca; a staple food in the tropics
cassava root eaten as a staple food after drying and leaching; source of tapioca
any of several plants of the genus Manihot having fleshy roots yielding a nutritious starch

Also: cassava starch.