Yes, TENSION is a Scrabble word!

Letter values in Scrabble US: T 1, E 1, N 1, S 1, I 1, O 1, N 1.

Is it a valid word?

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

(psychology) a state of mental or emotional strain or suspense
the physical condition of being stretched or strained
a balance between and interplay of opposing elements or tendencies (especially in art or literature)
(physics) a stress that produces an elongation of an elastic physical body
feelings of hostility that are not manifest
the action of stretching something tight

Also: latent hostility.