The operators of the Mühleberg and Beznau nuclear power plants have been ordered to implement safety improvements by August.
The Swiss Federal Nuclear Safety Inspectorate said on Wednesday that the emergency cooling water systems at both plants were “insufficiently protected against earthquakes and floods”.
The inspectorate has told the plants in cantons Bern and Aargau to present measures to remedy the situation by August 31, 2011.
By March 31, 2012, both plants must also demonstrate that they can cope with both an earthquake as well as an earthquake combined with the rupture of nearby dam walls.
Nuclear plants in Leibstadt in canton Aargau and Gösgen in canton Solothurn were also sanctioned by the inspectorate because cooling system temperature indicators do not appear in the command post in the event of an emergency.
swissinfo.ch and agencies