The International Nuclear Event Scale (INES) classifies safety-relevant incidents in nuclear facilities on a scale from 1 to 7. For a long time the accident at Chernobyl on 26 April 1986 was the only incident classified as a level 7 event, the maximum classification.

The accident occurred in connection with an experiment with the facility’s power supply. The subsequent release of radioactive materials resulted in the contamination of large swathes of Europe with particularly disastrous consequences for humans and the environment in today’s Ukraine and Belarus.

Switzerland was also affected by the passage of the cloud, resulting in the mobilisation of numerous emergency organisations. Authorities learned lessons in the wake of these events. 30 years after the accident challenges remain in the decommissioning of the Chernobyl nuclear power plant and disposal of the waste.

More information


Nine months after the disaster at the Fukushima nuclear power plant, Japan is working to contain radiation exposure in the region of the accident. The challenges confronting the country in this endeavour are shown by the new ENSI report on the radiological effects of the accident on 11 March 2011. ENSI already deduced some “Lessons learned for Swiss radiation protection” at the end of October.

Read more