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US Will Clean Area In Spain Where Hydrogen Bombs Fell (nytimes.com)
HughPickens.com writes: Rafael Minder writes in the NY Times that almost 50 years after coming close to possibly provoking a nuclear disaster, Secretary of State John Kerry, following years of wrangling between Spain and the U.S., signed an agreement to remove contaminated soil from an area in southern Spain where an American warplane accidentally dropped hydrogen bombs. In 1966 a bomber collided with a refueling tanker in midair and dropped four hydrogen bombs, two of which released plutonium into the atmosphere. No warheads detonated, narrowly averting what could have been an explosion more powerful than the atomic strikes against Japan at the end of World War II. Four days after the accident, the Spanish government stated that "the Palomares incident was evidence of the dangers created by NATO's use of the Gibraltar airstrip," announcing that NATO aircraft would no longer be permitted to fly over Spanish territory either to or from Gibraltar. The U.S. later announced that it would no longer fly over Spain with nuclear weapons, and the Spanish government formally banned U.S. flights over its territory that carried such weapons.
Neither Kerry nor Spanish Foreign Minister García-Margallo said exactly how much contaminated soil would be sent back, where it would be stored in the United States, or who would pay for the cleanup — some of the issues that have held up a deal until now. Spain has insisted that any contaminated soil be sent to the United States, because Spain does not have plants to store it. Concern over the site was reawakened in the 1990s when tests revealed high levels of americium, an isotope of plutonium, and further tests showed that 50,000 cubic meters of earth were still contaminated. The Spanish government appropriated the land in 2003 to prevent it being used.
Neither Kerry nor Spanish Foreign Minister García-Margallo said exactly how much contaminated soil would be sent back, where it would be stored in the United States, or who would pay for the cleanup — some of the issues that have held up a deal until now. Spain has insisted that any contaminated soil be sent to the United States, because Spain does not have plants to store it. Concern over the site was reawakened in the 1990s when tests revealed high levels of americium, an isotope of plutonium, and further tests showed that 50,000 cubic meters of earth were still contaminated. The Spanish government appropriated the land in 2003 to prevent it being used.
After a couple neutrons are captured. Am-241 is the most common isotope (half life of 400-odd years). Pu-239 captures two neutrons (rarely), then undergoes beta decay to become Am-241.
Since this normally requires a specially designed reactor to produce, the amount produced casually by four bombs will have been minuscule.
Which is not to say it shouldn't be cleaned up. Just that the urgency of the cleanup is pretty much consistent with taking 50 years to get around to it.
Note the amount of material being discussed (50000 m^3 of dirt). Cleanup can be done with one of those big earth movers used when strip mining in a few months, tops....
"I do not agree with what you say, but I will defend to the death your right to say it"
Because nuclear weapons tend to require carefully timed simultaneous detonations of explosives in a controlled manner in order to compress the fission core to a supercritical mass, it is unlikely that simply dropping the bomb (unarmed) or even having some of the explosives used for core compression go off will create an actual nuclear scale detonation.
However, the explosives for the explosive lens can go off and distribute radioactive material over a relatively wide area. This was more of a threat in the past, when explosives used in the bombs were somewhat more sensitive. Additionally, some explosives become more sensitive over time, so bombs stored for long periods could have somewhat more sensitive explosives and react badly to an accidental drop or crash.
All of that being said... an actual accidental nuclear explosion is extremely unlikely, but not entirely impossible in the case of an accident, and it was much, much more likely back when these bombs were dropped in Spain.
Also, there was one time where a bomb was lost where all but one of the safeties had been deactivated. And that was a mechanical breaker which could well have been flipped. Luckily, that sort of thing was much more common when SAC was actually doing regular strategic deterrent missions and bomb design had not progressed as far as it has today.