Yes, PORTION is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, R 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

something determined in relation to something that includes it
something less than the whole of a human artifact
the allotment of some amount by dividing something
assets belonging to or due to or contributed by an individual person or group
your overall circumstances or condition in life (including everything that happens to you)
money or property brought by a woman to her husband at marriage
an individual quantity of food or drink taken as part of a meal

Also: component part.