Yes, DISSECTION is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, S 1, S 1, E 1, C 3, T 1, I 1, O 1, N 1.

Is it a valid word?

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

cutting so as to separate into pieces
a minute and critical analysis
detailed critical analysis or examination one part at a time (as of a literary work)