Environmental organisations, including Greenpeace, and a citizens' lobby group have rejected a compromise plan to store radioactive waste at a site in central Switzerland.
They said there were still too many question marks surrounding the proposal to set up a temporary site for low and medium radioactive waste in canton Nidwalden.
The government and nuclear industry have been trying to find a solution to the storage problem since voters in the canton five years ago turned down an idea to build a site under the surface of the Wellenberg mountain. Swiss law requires the industry to find and run a permanent site.
In February, a government-appointed expert group came up with what looked like an acceptable compromise: still using the Wellenberg site, it proposed a long-term storage dump which could be monitored, not least through an adjacent tunnel which it said could advance knowledge in the field of storage technology.
However, the opposition to the latest proposal could put the plan on the backburner for a few more years. The recent opening of an interim ground-level site has taken some of the pressure off the nuclear industry to press ahead with other solutions.
The industry favours a permanently-sealed underground site, whereas environmental groups want a site which can be monitored, and where stored material could be retrieved by later generations if new technologies come available.
swissinfo with agencies