the european stress test for nuclear power plants

Recommendation No. 5: 

Prevention of nuclear accidents 

The “Stress test“ should - in a second phase - assess the ability of the nuclear power plants to prevent accidents. This means the assessment of the defence-in-depth safety provisions to prevent accidents for all foreseeable initiating events and to give an answer to the question whether these provisions meet the current state-of-the-art. 

This key question for the safety of nuclear power in the European Union is a crucial one: 

Nearly none of the 135 operating European nuclear power plants (NPPs) comply with strict requirements of an accident preventing defence-in-depth concept which corresponds to the up-to-date standards. 

The plants differ substantially in age, design and condition. The differences concerning the realisation of the defence-in-depth correspond to substantial differences of their residual risks. 

An assessment to reveal residual risks needs testable safety criteria. Binding European criteria for such a safety assessment is currently not available. A commonly agreed and applicable basis for complementing the current “Stress test“ are the “Safety Objectives for New Power Reactors”49, published by the Western European Nuclear Regulator’s Association (WENRA) in 2009. The safety objectives for new NPP’s50 were defined on the basis of a systematic analysis of the “Fundamental Safety Principles” developed by IAEA in 2006 51 and some other studies related to safety improvements for new reactors.52 

The seven “Safety objectives for new reactors” are aimed at the design for new plants. By this they represent the current state-of-the-art safety provisions for nuclear power plants. Beside very few really new requirements, such as measures to cope with a core-melt, they contain safety goals for a strict application of the defence-in-depth concept that can directly be applied to operating plants. As far as new features are required they include those questions that have become relevant with the Fukushima accident and are at least partly addressed in the current “Stress test“. 

Applying those criteria to existing power plants is apparently not far from WENRA’s view. According to WENRA, these safety objectives should also be “used as a reference for identifying reasonably practicable safety improvements for ‘deferred plants’ 53 and existing plants in case of periodic safety reviews” 54. This statement was again strengthened in the WENRA “Pilot study on Long term operation of nuclear power plants” published in March 2011.55 

The safety objectives are not applicable without a set of more precise assessment criteria (benchmarks). These have to be defined. To get the benchmarks for the test, what requirements should be met to achieve the safety objectives as best as possible and to optimise the safety provisions for operating plants, advanced criteria in international and national level are available. Without excluding other technical requirements, rules or guides, the German “Safety Criteria for Nuclear Power Plants” 56 could in a far extent provide testable criteria to assure the level of needed provisions. As a result of that test the deviations (“deltas”) of the older plants from current state-ofthe- art-requirements on prevention of accidents would be identified. 

Annex 1 outlines content and methodology of this missing second phase of the Stress test.

49 WENRA: Safety Objectives for New Power Reactors – Study by WENRA Reactor Harmonization Working Group (RHWG), December 2009 

50 Published in their final wording in WENRA: Statement on Safety Objectives for New Nuclear Power Plants, November 2010 

51 IAEA: Safety Standard Series No. SF-1, Fundamental Safety Principles, 2006 

52 For example: -NEA/CNRA/R(94)2, A Review for regulatory requirements for advanced nuclear power plants, 1994 -EUR 20163 EN, ISO study project on development of a common safety approach in the EU for large evolutionary pressurized water reactors, October 2001 -Several utilities and individual countries documents of the last 20 years 

53 NPPs originally based on reactor design similar to currently operating plants, the construction of which halted at some point in the past, and now being completed with more modern technology. 

54 WENRA: Statement on Safety Objectives for New Nuclear Power Plants, November 2010 

55 WENRA: Pilot study on Long term operation of nuclear power plants” Study by WENRA Reactor Harmonization Working Group (RHWG), March 2011 56 Federal Ministry for the Environment, Nature Conservation and Nuclear Safety: Safety Criteria for Nuclear Power Plants, Revision D, June 2009, Note: This is a translation of the German document entitled: \"Sicherheitskriterien für Kernkraftwerke\", BMU, April 2009.