KKB 1: Replika bringt Durchbruch für Integritätsnachweis – Sicherheitsnachweis liegt im Herbst vor
13.09.2016 - In spring 2016, Axpo confirmed the presence of aluminium oxide inclusions in the reactor pressure vessel (RPV) of the Beznau nuclear power plant 1 (Beznau 1). The materials tests carried out on a test body, a replica of Ring C built by Axpo, now confirm these findings and validate the theory that the irregularities were introduced during the manufacturing process rather than during operations. The replica allows Axpo to run the full programme to test the physical integrity of the RPV in Unit 1, including fracture-mechanical tests. The corresponding safety case will be submitted to the Swiss Federal Nuclear Safety Inspectorate ENSI in autumn.
The tests carried out over the past months showed that the test material selected last year did not fully meet the high quality standards needed to demonstrate physical integrity. Axpo therefore instructed an internationally renowned forge in England to build a replica of Ring C of the RPV – the ring with the most inclusions – according to the documented manufacturing conditions that applied to the Le Creusot forge in the 1960s. ENSI was informed of this process and also attended the subsequent materials tests.
The following has now been confirmed:
- The replica is representative. It has practically the same chemical and mechanical features as Ring C of the RPV in Unit 1.
- Initial ultrasound measurements have confirmed that inclusions that are almost identical to those in Ring C were formed during the manufacturing process.
- The replica is suitable for running the scheduled programme to confirm the physical integrity of the RPV in full, including destructive tests.
Further extensive investigations and assessments are scheduled for the coming months. Axpo will have proved the safety of the RPV when
- all tests and analyses have been concluded with positive results in accordance with the road map accepted by ENSI,
- the material-specific effect of the inclusions on the base material has been identified,
- the fracture toughness of the material can be proved, and
- the question regarding the remaining safety buffer has been answered.
There continue to be no safety concerns about the continued operation of Beznau 1. Just the opposite in fact: Axpo is more convinced than ever that it can provide the proof and safety case required for restarting the power plant. Axpo will submit the safety case in autumn. ENSI will then examine the safety case and take a decision on restarting the plant.
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