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
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
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
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.