What the stress tests are
Following the Fukushima nuclear accident in Japan in 2011, the European Council called for a review of the safety and security of nuclear power plants in the EU.
In response, ENSREG, with the support of the European Commission, developed a comprehensive and transparent methodology for risk and safety assessments, known as nuclear safety stress tests.
These tests are targeted reassessments of the safety margins of nuclear power plants.
What the stress tests cover
The stress tests scope focuses on extraordinary triggering external events, including earthquakes, floods and other initiating events potentially leading to multiple loss of safety functions. These include situations such as the loss of external electricity supply requiring severe accident management.
All the operators of nuclear power plants in the EU had to review how their plants would respond to these extreme situations.
Many other non-EU countries have voluntarily conducted comprehensive nuclear risk and safety assessments, based on the EU stress test model. ENSREG, supported by the Commission, can organise peer reviews based on previous agreements with national regulators in non-EU and EU candidate countries.
Alongside the safety assessments, there was also a review of the security of nuclear power plants. An ad hoc group on nuclear security was set up for this purpose. However, these security aspects fall outside ENSREG’s remit and are not covered here.
How the stress test process works
- Self-assessment by operators
Nuclear power plant operators in the EU and beyond conduct stress tests to find out how their plants would respond to a range of extreme events, such as earthquakes and floods. The findings of the stress test are then set out in a report.
- Review by regulators and peer review teams
National nuclear safety regulators review the operators’ reports and prepare summary national reports. These summary reports are then reviewed by peer review teams set up by ENSREG.
- National action plans
After the reviews, national authorities in the participating countries draft national action plans on implementing the recommendations from the reviews. These plans can be systematically updated until all recommendations are fully implemented. During the initial EU-wide exercise, ENSREG also produced an EU-level action plan. Lastly, ENSREG’s peer review team concludes the stress test exercise by producing a final peer review report.
- Status reports and follow-up
Implementation of the national action plans and ENSREG peer review team recommendations is monitored over time. Since 2011, some countries have gone through several rounds of reviewing and producing action plans. Progress is monitored through regular status reports, usually submitted every 2 years.
Stress tests documents
- EU stress tests specifications
- National reports, reviews and action plans – EU countries
- National reports, reviews and action plans – non-EU countries (Armenia, Belarus, Switzerland, Türkiye, Ukraine, UK)
- EU-level summary report, 2012
- Status report on national action plans, 2023
ENSREG has a working group dedicated to nuclear safety stress tests. Find more information on the group here.