Beznau 1: Source of irregularities identified – proof of integrity will be provided by the end of 2016

03.05.2016 - The source of irregularities in the Unit 1 reactor pressure vessel of the Beznau nuclear power plant has been identified. However, providing proof that the integrity of the reactor pressure vessel is still given will take significantly more time than Axpo originally anticipated. In particular, the procurement of comparable material samples with a similar inclusion density in order to complete the investigations is extremely challenging. Axpo currently expects the proof of integrity process to be completed by the end of 2016.

The extensive examinations carried out on the reactor pressure vessel of Unit 1 at the Beznau nuclear power plant (KKB) have confirmed current findings, indicating that there are no safety-related reservations for the continued safe operation of the plant.

Since the summer of 2015, Axpo has conducted sophisticated ultrasound measurements, extensively reviewed the fabrication process, and carried out a root cause analysis of the detected irregularities.  

No hydrogen flaking

The extensive investigations produced the following findings:

• Hydrogen flaking can be ruled out
  
• The number, form and location of the inclusions are characteristic and conclusive for non-metallic inclusions for aluminium oxide
  
• The findings found on the reactor pressure vessel are manufacture-related
  
• Inclusions cannot attributed to reactor operation
  
• The reactor pressure vessel fulfils the ASME acceptance criteria in force at the time of manufacture as well as the current regulations

Axpo has submitted the respective test reports and findings to the Swiss Federal Nuclear Safety Inspectorate (ENSI) for review; an international team of experts is supporting the authorities in this process.

In the course of wide-ranging material tests last year, Axpo already examined identified test material, which was, however, only partially suitable. As a result the search for additional test material has been intensified.

A complex procedure

Proving that the integrity of the Unit 1 reactor pressure vessel has not been compromised has turned out to be more time consuming than Axpo originally anticipated.

The delays are the can be attributed to the following:

• Procurement and testing of suitable additional samples is very time-consuming
  
• Test and analysis processes are extremely complex, and in some cases, can take several months
  
• Axpo is strongly dependent on the availability staff from specialised companies
  
• Numerous legal and commercial issues must be clarified with partners and suppliers in connection with ownership and utilisation rights

In light of these facts, Axpo currently expects a restart approval from ENSI towards the end of 2016.

The renewed postponement of the restart results in increased costs. Depending on the issues that will have to be clarified in the course of the on-going process, investigation expenses and the loss of revenues from electricity sales since August 2015 will cost Axpo about CHF 200 million.