* Five blocks well equipped to weather crises
* 8 "open points" and 3 instructions to be tackled
* Switzerland says it will be toughter than EU
FRANKFURT, Jan 10 (Reuters) - Switzerland's safety precautions for its nuclear reactors must be further reviewed and more proof that they can withstand major earthquakes must be filed by the end of March, its nuclear safety authority ENSI said on Tuesday.
The assessment was made in the context of stress tests which the country demanded last June in line with the European Union following the Fukushima nuclear disaster in Japan last year.
Switzerland was among seven EU neighbours that agreed to follow the bloc's lead by imposing new safety checks.
"These safety measures will be based on toughter risk assumptions than assumed in EU stress tests," the authority said in a statement on its website. "ENSI will assess the plants' assurances. Results are due by end-June."
Should they be viewed as insufficient to offer protection against natural disasters, in particular the combination of earthquakes and failure of dams near power stations, ENSI could in theory require plants to stop production, it said.
All in all, the findings publicised by ENSI, which it had sent to the EU Commission on Dec. 31, 2011, were favourable.
They said Switzerland's five reactor blocks were well prepared to cope with flooding, loss of cooling systems and internal power, extreme weather and emergency operations.
The report will now be subject to a peer review, final results of which will be tabled in June 2012.
It did identify eight open points regarding the functioning of reactor containments, cooling cycles and venting systems after earthquakes, internal power blackouts and physical restrictions in such cases on cooling water intake - for example damaged bridges after disasters.
In three instructions with a Sept. 30 deadline, ENSI required all rectors to show how robust their outer shells are.
Goesgen and Leibstadt have to test and document venting systems, and Goesgen and Muehleberg must show whether water bottlenecks would be under control under all circumstances.
Muehleberg must bring additional proof by the end of January of the performance of its automatic switch-off system and Muehleberg must show by that date that the Wohlensee dam can resist earthquakes. This had originally been due by end-Nov.
Switzerland in 2010 derived 56.5 percent of its power from hydroelectricity and 38.1 percent from nuclear plants, while thermal plants supplied 5.4 percent.
Its nuclear sector is watched closely in central Europe, where power markets are converging. (Reporting by Vera Eckert, editing by William Hardy)