There is a rumour that iodized salt will help protect you from radiation poisioning. Salt in that area is often iodized (this happens by oxidising it), as people in the area can be in danger of iodine deficieny. Mental health problems as well as thyroid problems can be associated with a lack of iodine in your diet, and so adding this to salt will prevent these risks as people can get their intake that way. I beliebe it is the thyroid problems that people are worried about in the nuclear crisis.
To actually build up enough iodine to be really protected in any significant way from radiation would most likely involve digesting an amount of salt that could well prove fatal, so it is not really likely to help you even if you do stock up on this. Painting a little iodine on you to absorb through the skin would be more effective, but obviously this is not an option for everyone so they do the next best thing.
Taking iodine protects the people from getting thyroid cancer, which is associated with exposure to radiation. Iodized salt is just the least inexpensive and easiest way to get iodine to all those people. You can find iodized slat in your local super market.
Best way to get the protective power against nuclear radiation is to take iodine tablets... But like I said at the beginning, they will only protect you against getting thyriod cancer.