For anybody that is remotely interested!
Since the 1st atomic test at Alamogordo in New Mexico, there have been more than 2000 other tests. There have been over 200 small to large accidents at nuclear facilities since we have started tinkering with the atom. Currently there are more than 400 nuclear reactors in operation around the world. Not counting the ones floating around in space powering satellites etc. 65 new ones are under construction and another 165 in the planning stages.
Radiation is different from things like poison in that it does not accumulate within the body. What determines your odds of survival from radiation poisoning is primarily your livers ability to break down the poison. The reason not everyone dies at the same dose is because of the variations of each person's body. As the dosage is increased the odds of surviving becomes smaller and smaller until you reach the limit of what the body can process. At a certain point you will have a dosage that no human can survive. Most low dosed ionization radiation poisoning presents itself in the form of cataracts in the eyes, smaller brains, malformation of sperm or complete sterility. So if your best buddy down below is rotted away at an alarming rate, you now know why.
Now, with radiation it's not a matter of health, but purely an exercise of luck. Alpha, beta, and gamma radiation all damage the body in the same way. When a particle or a wave collides with your DNA in such a way that the cell can not survive or it disrupts sequencing then that will cause cancer. We're exposed to the cosmic background radiation every day and each individual particle/wave of radiation in your everyday life is no more or less dangerous than the radiation from a nuclear bomb. Imagine you're laying on a football field and someone in the stands is blindly throwing needles onto the field. It's unlikely that the needles will hit you, and even less likely that the needles would kill you. However if you have say 100000 people each throwing needles onto the field it becomes much more likely that you will get hit by one and likewise more likely that one of the needles will hit you in such a way as to be fatal. Because this is a matter of luck and not a matter of health there is no hypothetical limit to the number of needles that can be thrown onto the field, or the amount radiation a person can survive. Your odds of survival may be infinitesimally small, but there will never be a point where the odds of dying are exactly 100%. Caveat to that being the point where the radiation itself imparts so much energy into your body that you are physically torn apart or burn up. But if you're ever in that position there are probably a dozen or so other things which would have already killed you, so I wouldn't worry about it.
And just as a little side note. The technology for the MRI scanner was developed at CERN, and uses radioactive material that comes straight out of nuclear facilities. And if they weren’t using it inside the scanner at the hospitals, it would be deemed nuclear waste.