the european stress test for nuclear power plants


The limits of the test

The “Stress test” of the European nuclear power plants as defined by the European Nuclear Safety Regulators Group does not meet the requirements of the EU council nor the expectations of the European public for a comprehensive safety assessment. It doesn’t provide a method for comparing the safety of the different plants, nor does it answer how safe European plants actually are. 

The prevention of nuclear accidents – which is the centre of the nuclear safety provisions – is practically excluded by the test. The scope of the “test” focuses on which measures are left in the case an accident having happened:

  • The scenarios which are under review are incomplete. Internal scenarios such as fire-scenarios, electrical surges, leakage of pipes, malfunction of valves, human failures and combinations of those events are not included in the scope of the test. External scenarios like airplane crashes are also excluded.
  • The quality of the safety related systems and components of the plants like the material of pipes, of the reactor vessel, of valves and pumps, of control and instrumentation equipment is not under investigation.
  • Degradation effects, in particular those caused by the aging of plants / material fatigue, are not considered
  • The safety management of nuclear power plants, which is of utmost importance, is not included.
  • The test relies on the safety cases of the licenses of the individual plants, which in many cases are out of date.

The test specifications do not define assessment criteria to check a plant’s safety features. No criteria are defined to determine the so-called “robustness” of the plant. Furthermore the “Stress test“ does not comply with normally applied qualified and comprehensible methods of technical studies and review practices. It is basically dependent on the confidence in the operators’ reports. The experts involved in the “Stress test“ are the same experts that have been responsible for nuclear safety in the past. The European Commission is not able to make up for this lack of independence because it has no technical expertise itself. Therefore the whole process is open to abuse, only demonstrating to the public how safe the plants are. 

Within this limited scope and taking into account the deficiencies of the method and the process the proposed “Stress test” could nevertheless be useful in giving additional information, and potentially an initial estimation of the ability of individual plants to withstand a few important extreme external events (in particular earthquakes and floods).

The lesson of Fukushima - recommendations

The first practical experience of the Fukushima accident is that nuclear accidents can happen everywhere, and that the residual nuclear risk cannot be eliminated. 

Beyond this experience the most important lesson of the Fukushima accident was that a plant and its management must be checked against well-known modern standards for nuclear safety, because in the instance of Fukushima, it was not, and consequences of such a review had not been drawn. Most of the issues concerning the on-going “Stress test“ in the European Union can be deduced from existing codifications of nuclear safety requirements including publications of the International Atomic Energy Agency. Most of the technical safety issues which now appear to as new lessons from the Fukushima accident, have already been discussed in national and international forums. However this knowledge had not been applied to Fukushima and it has not yet been applied to the European plants. The lesson is to apply the knowledge now. This leads to a two-step-approach: 

The current limited approach of the “Stress test“ should be complemented by the assessment of aeroplane crashes (see I.2.3). Acceptance criteria that enable a classification of different grades of robustness should be defined (see I.3.4 and II.2.1). The requirements for the reports on the existing defence-in-depth-concepts of the plants should be structured to give more transparency and to get a sound basis for comparing the safety provisions of the plants (see I.3.1 and II.2.2). More precise and more stringent requirements for the underlying data and documents should be defined (see I.3.5 and II.2.3). Reports and the main underlying documents should be open to the public. The results of the peer review process (questions and answers) should be completely documented and published (see I.3.7 and II.2.3).

The “Stress test“ should be complemented by a second part that assesses the preventive measures of the nuclear power plants against nuclear accidents (see II.3). 

The safety objectives of WENRA (Western European Regulators Association) for new reactors are an appropriate basis to structure the missing assessment of the preventive measures. Advanced technical safety requirements, which comprise of targets for meeting these objectives, are available (see Annex I). For every safety objective the most advanced requirements that are applicable for operating reactors should be applied. As result of such a process a questionnaire which comprises of the most important benchmarks for a safety check of the defence -in-depth system would be a sound basis for the needed second complementary part of the “Stress test”. This methodology would provide a comprehensive risk assessment which could inform the European Union about the safety status of its nuclear power plants.