Yes, CLATHRATE is a Scrabble word!

Letter values in Scrabble US: C 3, L 1, A 1, T 1, H 4, R 1, A 1, T 1, E 1.

Is it a valid word?

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

having a latticelike structure pierced with holes or windows
designating or relating to a compound in which one component is physically enclosed within the crystal structure of another

Not playable in Scrabble US: CANCELLATE, CANCELLATED.