Expert: You may be interested to know radioactive rainfall occurs around nuclear plants during normal operations.
Associated Press, Dec. 3, 2013: Experts on [the Japan government's contaminated water] panel also proposed establishing a special team to focus on how to deal with massive amounts of tritium, the only isotope that cannot be removed chemically by existing technology. [...] U.S. officials evaporated tritium water at the Three Mile Island plant following the 1979 accident, but the method is not recommended for Fukushima, where there is too much and it is likely to come back as tritium rain.
In fact, the method has been recommended for Fukushima
Joonhong Ahn, professor in UC Berkeley’s nuclear engineering department: Water that’s been treated to remove radionuclides apart from tritium, which can’t be filtered out, can be evaporated [...] “Amounts of tritium would be small, so that radioactivity that would be discharged into the atmosphere would be acceptably small” [...] discharging low-level contaminated water at the Fukushima station into the sea may need to be used in addition or as an alternative to evaporation.
Arjun Makhijani, President of the Institute for Energy and Environmental Research, at the Community Symposium on Decommissioning San Onofre, Oct. 19, 2013 (26:45 in): You might also be interested to know that all nuclear power plants, that are of the variety of light water reactors, release tritium to the atmosphere, so you can expect radioactive rainfall around nuclear power plants. We have asked the NRC to require monitoring of rainfall — because people have private wells in many places – but they have refused to require it.
Watch Makhijani at the symposium here