Yes, RADIATIONS is a Scrabble word!

Letter values in Scrabble US: R 1, A 1, D 2, I 1, A 1, T 1, I 1, O 1, N 1, S 1.

Is it a valid word?

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

energy that is radiated or transmitted in the form of rays or waves or particles
the act of spreading outward from a central source
syndrome resulting from exposure to ionizing radiation (e.g., exposure to radioactive chemicals or to nuclear explosions); low doses cause diarrhea and nausea and vomiting and sometimes loss of hair; greater exposure can cause sterility and cataracts and some forms of cancer and other diseases; severe exposure can cause death within hours
the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
the spread of a group of organisms into new habitats
a radial arrangement of nerve fibers connecting different parts of the brain
(medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance

Also: radiation sickness, radiation syndrome, radiation therapy.

Not playable in Scrabble US: ACTINOTHERAPY.