ENSI confirms Swiss plants can withstand earthquake

12 July 2012

Switzerland’s nuclear regulator has confirmed that the country’s four nuclear power plants can withstand severe earthquakes, but it has asked all plants to provide additional information so that it can complete its analysis.

In May 2011, the Swiss Federal Nuclear Safety Inspectorate (ENSI) set out requirements for nuclear plant operators to provide evidence that they could manage in the event of a once-in-10,000-years earthquake and any associated flooding from nearby dam failures. Utilities had until the end of March 2012 to submit this information to the regulator.

ENSI said that it accepted the earthquake analyses for all four Swiss nuclear power plants (Beznau, Gösgen, Leibstadt and Mühleberg), but is said that the earthquake analysis submitted for Gösgen NPP in March 2012 ‘was partly deficient,’ and that it needed to be revised. Gösgen submitted a re-worked report in late June 2012, which appears to satisfy ENSI’s requirements.

Measures are in place to provide cooling of the reactor cores and spent fuel pools in case of a once-in-10,000-years earthquake and associated flooding, ENSI said.

Such an event would not pose a radiation threat to humans or the environment, according to ENSI, which said that the regulatory dose limit of 100 millisievert would be ‘easily satisfied’ in such incidents.

ENSI said that reactors can continue to operate, but it has asked all four nuclear operators to provide additional information this year so that it can complete its analysis.

Gösgen has until the end of October 2012, to submit additional analyses on core cooling and the seisimic resistance of its spent fuel pool. It must also provide a more detailed analysis of the interactions between components in the reactor pressure vessel (globally and during an earthquake scenario).

Finally, Gösgen must consider the effects of flooding caused by potential dam failure in case of earthquake, although ENSI said this will be requested as part of a separate procedure.

Leibstadt and Mühleberg must demonstrate, by 31 December 2012, that the fuel elements can not be lifted or move aside during a once-in-10,000-years earthquake.

ENSI said that dams protecting the Mühleberg plant from a possible flood should withstand a severe earthquake, but said that it must complete seismic safety calculations under the requirements outlined in a new report issue by the Swiss Federal Office of Energy.

Mühleberg must also complete calculations of seismic safety for dams in the radius of the plant under the requirements contained in the review reports of the SFOE. The documents are reworked to provide the SFOE and ENSI until 31 October 2012.

The plant must also conduct an analysis to improve the sealing function on the insulating plate between the spent fuel pool and the reactor cavity by 31 December 2012.

Finally, Beznau must verify that the main steam relief valves can be controlled continuously from the emergency control centre during an earthquake. It has until 30 September 2012 to ensure that short-term measures to prevent water leaking from the spent fuel pool under certain conditions are sufficient.

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