There seem to be a generic feeling of "nuclear is fine" in reaction to all the anti-nuclear bashing going on, but few people seem to be really paying attention to the case at hand.
From what I read these reactors are not just old, they are built on an area that can have up to M7 earthquakes. The seismic risk was taken into account when building the power plants, but after a new security audit following Fukushima, it appears the risk was vastly underestimated, and from there all plans of building replacement plants in the area got nerfed.
Basically these reactors are not actually deemed to be safe, it's just not practical to shut them down now without any alternative plan to cover for the electric needs of the whole country, when there is enough chance of no major earthquakes until they get decommissioned.
> In 2011, in response to Fukushima, ENSI called for a rapid review of seismic safety at all nuclear power plants in Switzerland. The results were to be submitted within a year and concentrated on the most important aspects. They showed that all Swiss nuclear power plants are sufficiently protected against earthquakes and flooding potentially caused by a breach in a dam following a seismic event. Further investigations also revealed that all nuclear power plants in Switzerland have a safety margin.
https://www.ensi.ch/en/2016/05/31/updated-seismic-hazard-ass...
An audit commanded by the Health departments to non goverment related parties points at the vastly under-estimated seismic risk: http://www.atomschutzverband.ch/xs_daten/Fakten/93_3_Experti...
BTW the operation of nuclear power plant in Switzerland seems to be allowed as long as the ENSI accepts it as safe. Without any knowledge in the matter, I highly doubt there's no tremendous pressure and work done on the ENSI to be more lenient towards risk.
Just like in Japan.