We've had this discussion before. KI protects against a very specific radiation effect. It blocks the thyroid so you don't get thyroid cancer down the road. It's not going to protect you in any other way from radiation exposure. It's not a panacea. The only thing that will protect you is shielding from the radiation source. 450 REMs is an LD50 and 800 REMs is LD100, KI will not protect from that.