Switzerland’s Mühleberg enters formal decommissioning

22 September 2020

BKW, the owner-operator of Switzerland’s Mühleberg nuclear plant, said that it is making headway with dismantling, the plant, which was finally shut down in December 2019, despite the coronavirus. 

All requirements for the "final" decommissioning have been met as well as for the transition to decommissioning phase 1, the company said. This was confirmed by the Federal Nuclear Safety Inspectorate (Ensi) after examining the documents submitted, and after an inspection.

The pandemic has, so far, had no impact on the schedule. The single unit 373MWe boiling water reactor, which began operations in 1972, was the first in Switzerland to be shut down after 47 years of operation. Work to ensure the independent cooling of the fuel storage pool in the reactor building has now been completed, BKW noted.

Decommissioning will take 15 years and BKW does not expect the site to be in use again until 2034.

BKW said it undertook the work using its own employees “who have extensive knowledge of the system and valuable specialist knowledge”. It added: “Service providers and experts with international experience in the dismantling of nuclear power plants are called in for highly specialised one-off tasks. The most important of these orders have already been awarded and the necessary external services have been secured."

BKW said financing for the decommissioning and disposal of the radioactive waste ensured. BKW is paying the necessary costs in full. Costs are estimated at about €2.7 billion ($3.2bn).

Ensi said that, although the plant stopped operating in December, it has only been formally considered permanently out of service since 15 September 2020, when the operating licence was replaced by a decommissioning order from the Federal Department of the Environment, Transport, Energy and Communication (DETEC).

The Mühleberg NPP was only considered to be ready for decommissioning after all fuel elements hade been transferred from the reactor to the fuel storage pool, and the measures required to establish safe technical post-operation had been implemented, Ensi said.

The most important measures in this context were changes to the system so that the fuel storage pool can be cooled independently and redundantly. These system changes are summarised under the term “Arbek” (self-sufficient redundant fuel storage pool cooling). They essentially consist of five sub-systems:

  • an operating system,
  • a safety system for cooling the fuel storage pool,
  • an emergency water make-up system,
  • a locking system
  • measures to protect the fuel element storage pool and the necessary operating and safety systems from the effects of the dismantling operation.

The work was carried out under the operating licence, because the still operating and safety systems were required to dissipate the residual heat from the fuel elements. In addition, in contrast to the decommissioning work, according to Ensi's assessment, this work had to be carried out promptly and absolutely in order to bring the plant to a long-term safe condition after the final cessation of power operation.

Preparatory measures for the decommissioning phase were subject to approval by Ensi and included:

  • Preparation for decommissioning: The dismantling of the large individual components in the machine house, especially the turbines;
  • Dismantling of the large individual components in the machine house, especially turbines; and
  • Establishment of material treatment plants, e.g. devices for decontaminating components.

The preparatory measures were also carried out under the operating licence and in parallel with the work to establish technical post-operation  and before the final decommissioning phase.

Much of this work was subject to approval by Ensi through regular on-site inspections and technical discussions. In June 2020, Ensi approved the first phase of decommissioning after a thorough review of the documentation. “With the final decommissioning and the beginning of the first decommissioning phase, another milestone has now been reached on the way to the complete dismantling of the nuclear power plant,” Ensi said.

The plant will be dismantled in three phases.

Phase 1 will continue until all the plant’s fuel assemblies have been removed, and should be completed by 2024. Phase 2 will be completed with the lifting of controlled zones, probably around 2030. The third and final phase will involve work to demonstrate that the system is no longer a source of radiological hazard, which is scheduled for 2031. Demolition of the   conventional plant will be regulated uner a second DETEC decommissioning order.

Switzerland voted to phase out nuclear power in May 2017. Switzerland’s five commercial reactors provided 45% of electricity in winter when hydro reservoirs are low.  According to the Swiss Nuclear Forum, Mühleberg’s closure will reduce electricity output by 5%.

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