Yes, INTUMESCENCE is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, T 1, U 1, M 3, E 1, S 1, C 3, E 1, N 1, C 3, E 1.

Is it a valid word?

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

swelling up with blood or other fluids (as with congestion)
the increase in volume of certain substances when they are heated (often accompanied by release of water)

Not playable in Scrabble US: INTUMESCENCY.