The most fundamental problem with the proposed DGR is simply its proximity – under a kilometer (half-mile) – to Lake Huron. This raises the possibilities of water getting into the storage shaft and nuclear waste getting out into the lake.
Lake Huron and the other Great Lakes supply the drinking water for approximately forty million people in the US and Canada. In addition, the Great Lakes and the Saint Lawrence River, by which they drain into the northern Atlantic Ocean, are a unique and critical ecosystem for northeastern North America, constituting 21% of the world’s supply of fresh water. Situating the proposed facility on the Great Lakes means that any major problems with it could become a disaster larger than Chernobyl or Fukushima.
This is not a merely theoretical problem. It has been acted out in real life, as most nuclear facilities are located near bodies of water that are used in cooling the nuclear material. If we look at other catastrophes involving nuclear waste, not only has disaster been caused by flooding of the site (as at Fukushima), but the main avenue of environmental contamination in general has been the discharge of radioactive waste into bodies of water.
For instance, the 1957 nuclear waste explosion at Kyshtym created a radioactive plume that spread over hundreds of kilometers, creating a contaminated area known as the East Urals Radioactive Trace (EURT), and prompting the evacuation of about ten thousand people. Although the Soviet government attempted to quarantine the use of water from the river, it proved impossible over such a large area – just as it would with the Great Lakes – with a 1992 study concluding that 8,015 people had died as a result of the accident. It is rated as the third worst nuclear accident ever (after Fukushima and Chernobyl).
Yet the nuclear facility responsible for the accident was also discharging high-level waste directly into the neighboring lake and river, and this turns out to have caused comparable damage to the more dramatic explosion. In fact, some studies suggest that “frequent use of the floodplain for food and fodder production increase the intake and dose estimates by about a factor [of] three over the other irradiated residents.”
[Read more here]
One can see a similar pattern in Britain, comparing their two biggest nuclear disasters. When the land-locked Windscale nuclear reactor caught fire in 1957, the only large-scale response needed was the destruction of locally produced milk. In contrast, the explosion in the Dounreay underground waste storage shaft in 1977 drew attention to the contamination of the local seabed by radioactive fuel rod filings. This contamination has led to closing the local beaches and the abandonment of the formerly very productive salmon fishery. The current cost for the cleanup alone currently stands at over £2 billion, or about $3 billion (Canadian or US).
Read more here
Finally, the leaking nuclear waste in the underground storage facility in Asse, Germany is mostly contained because it is inland and far from any body of water, but the main concern is that the leaking radioactive material will spread via the groundwater flowing through the mine.