Bad policies implemented in a single country doesn't determine environmental friendliess of a energy production technology as a whole. Obviously a nuclear power plant is not environmentally friendly if the waste is not taken care of.
"Die britischen Fässer enthalten nach Angaben der IAEA 58 Billionen Becquerel, die belgischen 2,4 Billionen Becquerel Alpha-, Beta und Gammastrahlung. Der EU-Grenzwert für Trinkwasser liegt bei 10 Becquerel pro Liter."
So, there's about 6 * 10^10 Becquerel radiation there, while the EU allows 10 per liter. If so, mixing this with 6 * 10^9 liters of water would dilute it enough to be within EU limits. That's 6 * 10^6 cubic meter. If the stuff got dropped over an area of a square kilometer in a depth of 6 meter, you would already get there.
So, I expect at worst, localized contamination of sea water.
Also, http://www.who.int/mediacentre/factsheets/fs291/en/: "The WHO guidelines for drinking water quality recommend repeated measurements to be implemented if radon in public drinking water supplies exceeds 100 Bq/l.". That puts that 10 Bq/l EU norm into perspective.
A team of journalists just discovered the barrels of nuclear waste that the UK threw in the ocean. 17,000 tons of nuclear waste just near the British island Alderney.
"It is just as environmentally friendly." Yeah, sure.
source: http://www.dw.de/atommüllfässer-im-ärmelkanal-entdeckt/av-16...
Or read this: http://en.wikipedia.org/wiki/Asse_II_mine