Yes, CLOSURE is a Scrabble word!

Letter values in Scrabble US: C 3, L 1, O 1, S 1, U 1, R 1, E 1.

Is it a valid word?

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

approaching a particular destination; a coming closer; a narrowing of a gap
a rule for limiting or ending debate in a deliberative body
a Gestalt principle of organization holding that there is an innate tendency to perceive incomplete objects as complete and to close or fill gaps and to perceive asymmetric stimuli as symmetric
something settled or resolved; the outcome of decision making
an obstruction in a pipe or tube
the act of blocking
termination of operations

Also: gag rule, gag law, law of closure.