ENSI orders upgrades at Swiss NPPs

9 May 2011

Operators of Switzerland’s four nuclear power plants have been asked to make improvements to the spent fuel pools and earthquake and flooding resistance of their plants, following a post-Fukushima safety review. The Swiss Federal Nuclear Safety Inspectorate (ENSI) says that although there is no immediate danger to the population, the plants must show how they will resolve the deficiencies by the end of August 2011.

On 18 March, ENSI ordered Swiss nuclear power stations to conduct an immediate review of their plants' earthquake and flood protection systems. The operators of these plants had to submit a report on their findings by 31 March 2011. Following on a review of these inital reports ENSI has identified a number of weaknesses, mainly surrounding the spent fuel pool.

In the cases of Beznau and Mühleberg, the review found that “the fuel pool cooling is not sufficiently protected against earthquakes and flooding,” and that “the emergency measures to restore the cooling after earthquakes or flooding are incomplete.”

At Mühleberg the emergency cooling system has no alternative to cooling water from the river Aare, while at Beznau the earthquake behavior of the fuel storage building needs improvement.

At Gösgen and Leibstadt modifications to the instrumentation and control system will be required as the level and temperature of the fuel pool are displayed in the main control room, but not in the emergency control center.

Operators will need to submit an outline of the improvement measures to address these shortcomings by 31 August 2011. They will also need to provide ENSI with additional evidence of earthquake and flood protection for the spent fuel pool, as well as evidence that the pools are protected from hydrogen explosions.

By end of June 2011, operators must supply proof of their ability to cope with the worst flood likely in 10,000 years. By 31 March 2012 they must demonstrate control of a 10,000-year earthquake, taking into account earthquake-induced damage from nearby dams.

ENSI said that the work to evaluate and implement any safety measures deemed necessary at Swiss nuclear power plants could take several years, but it could be carried out while the plants are operational.

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