A thousand above ground nuclear weapons tests - some as damaging as a worst case Fukushima reactor (China Syndrome) - raised the background radiation level 1%. Castle Bravo for instance clearly released more radiation than Fukushima could have. No appreciable radiation will come to the US.
Lets look at the radiation released at Fukushima: 13,600 TBq of Cesium-137. There was some Iodine-131 and some Cesium-140 released as well but this has half-lifed itself out of significance. The ocean volume is 1386000000 cubic kilometers. Dividing the released radiation by the ocean volume: 13,600 TBq/1386000000 km3 = .0000098 Bq m-3. For comparison, the ocean background radiation is 2-3 Bq/m-3 for Brazil and 35.2 Bq m-3 for the Baltic Sea.
See the following for radiation and food: http://truenorthreports.com/facts-an...ation-exposure.
The ICRP in 1928 adopted the linear no-threshold model for radiation and there is no conclusive science evidence that it is a valid model. There is a lot of evidence that it is not. Normal background radiation is 2 mS (milliSieverts) per year - 15% is produced by your own body. This is a global average, the rate varies by location: the US background rate is 3.6 mS/yr, the Australian rate is 2.4 mS/yr, and the rate for Ramsar (Iran) 260mSv. The radiation level for optimum health is 120-200 mSv (milliSievert) annually (hormesis hypothesis). The radiation level has to reach 2 Sieverts/year before cancer mortality is as high as the death rate from normal background radiation. Allowing radiation levels up to 2 S/yr will save lives.
Japanese government raised the level of permissible exposure to schoolchildren twenty fold, from 1mSv/year to 20mSv. Given the above facts this is a wise decision.
The dismantlement issue is a created issue.
1. The allowed radiation level for reactor steel is set 100,000 times lower than the radiation level for natural gas pipe steel.
2. The radiation level allowed at Yucca mountain was barely above the background (granite) radiation level.
3. Using fast reactors or thorium reactors the spent fuel issue could be solve by burning spent fuel. 95-99% of high level waste could be eliminated.
4. The linear no-threshold model of radiation is provably killing people and forcing unnecessary and expensive nuclear cleanup.
The issue that gets missed in the nuclear debate is that we shouldn't be using pressurized reactors at all. There are alternative reactor designs, LFTR (Liquid Floride Thorium Reactor) or LMFR (liquid metal fast reactor) that would be better for installations in populated areas since they are not pressured reactors - there is no water to boil off. The LFTR doesn't need active cooling - the reactor expands until it reaches steady state. The LFTR reactor has no core, the solution in the reactor is a mix of salt and fuel that cools when it expands. There is also the subcritical Thorium reactor (ADS) design that is absolutely safe since a particle accelerator is needed to operate the reactor.