the european stress test for nuclear power plants

Safety objective O1: 


Normal operation, abnormal events and prevention of accidents 


The safety objective “O1” of the WENRA safety objectives for new reactors58refers to the first and second level of defence: 

“WENRA expects new nuclear power plants to be designed, sited, constructed, commissioned and operated with the objectives of: 

  • reducing the frequencies of abnormal events by enhancing plant capability to stay within normal operation. 
  • reducing the potential for escalation to accident situations by enhancing plant capability to control abnormal events.” 

The safety goals of “O1” aim at conceptual measures for new nuclear power plants but they may also be applied to operating plants. 

Quality of material 

To reach, for example, the objective “O1” to reduce the frequency of abnormal events, the question, what kind of quality the used material has, is most relevant for safety. The question of how reliable the plant prevents leaks or malfunction of valves or pumps depends strongly on the quality of the material.59 

The requirements to assure a good material quality comprises of a lot of requirements which include the chemical and physical properties, the kind of manufacturing, the kind of welding, the process of quality assurance from manufacturing until installing the component, the kind and frequency of inservice inspections, and the kind of monitoring of the aging process of the materials. 

For testing the quality of the respective plant specific provisions the “Safety Criteria for Nuclear Power Plants” provide benchmarks that can be applied.

According to those benchmarks specific properties of the material60 must be given and a quality assurance system has to be installed. 

To manage the aging problems it has to be checked whether a comprehensive ageing management system is implemented.61 The efficiency of such a system must be demonstrated by the licensee. 

For an efficient in-service inspection according to “Safety Criteria for Nuclear Power Plants” 62 evidence must be given that all safety relevant equipment is so conditioned and arranged that in-service inspections for the identification of beginning material irregularities can be executed wherever they are needed. If this is not possible, it has to be demonstrated that precautionary measures against irregularities are implemented that guarantee the same level of safety.63 

Man-machine interface / Design of the control room 

The safety objective to reduce the potential for escalation to accident situations by an efficient control of abnormal events means that all should be done to avoid accidental situations by a preventive safety strategy. So whenever the pressure within the reactor vessel rises out of the limit for normal operation or the temperature exceeds normally allowed degrees there have to be intelligent and effective measures to analyse the problem and to lead the plant back into the limits of normal operation. Implementing the best available man-machine interface can avoid operating errors. Therefore, one way in which to achieve the defined safety goal is to implement a manmachine interface as regards information and diagnostic instruments64 that corresponds to the current state-of-the-art technology. For this to be achieved, the requirements on the ergonomic design of the control room play a key role.65 

The test of these fundamental safety requirements resulting from safety objective O1 is not part of the current “Stress test“.





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

59 The check of this part of safety objective “O1” is not part of the current „Stress test“.

 60 Module 4 \"Safety Criteria for Nuclear Power Plants: Criteria for the Design of the Reactor Coolant Pressure Boundary, the Pressure Retaining Walls of the External Systems and the Containment System\", Principles of basic safety in connection with design and manufacturing, particularly paragraphs about Material selection No. 2.3.2 (Reactor coolant pressure boundary), No. 3.3.2, (Pressureretaining walls of components of external systems) No. 5.3 (Small-diameter pipes) and No. 7.4 (Containment system). Example: 2.3.2 (2): In combination with the selected construction and the processing techniques applied, the materials used have sufficient resistance against corrosion and other ageing effects under the operating conditions. The water qualities required for corrosion resistance during specified normal operation (levels of defence 1 and 2) are specified. The water quality is monitored and deviations from the specified parameters are detected at an early stage so that disadvantageous impacts on the components are prevented.

61 Module 4 \"Safety Criteria for Nuclear Power Plants: Criteria for the Design of the Reactor Coolant Pressure Boundary, the Pressure Retaining Walls of the External Systems and the Containment System\" Operation, Principles No. 2.5.1 (1+8) (Reactor coolant pressure boundary) No. 3.5.1 (1+9) Pressure-retaining walls of components of external systems) and Handling of indications on components and pipes No. 8 (4), Example: 2.5.1 (8): For systematic identification, observation or prevention of ageing impacts on the integrity of the components of the pressure-retaining walls, an ageing management system is implemented.

62 Module 1 „Safety Criteria for Nuclear Power Plants: Fundamental Safety Criteria”; Technical criteria, No. 3.1 (12) Module 4 \"Safety Criteria for Nuclear Power Plants: Criteria for the Design of the Reactor Coolant Pressure Boundary, the Pressure Retaining Walls of the External Systems and the Containment System\", Non-destructive in-service inspections: No. 2.5.3 (Reactor coolant pressure boundary), No. 3.5.4 (Pressure-retaining walls of components of external systems), No. 7.5.2 (Containment system),; Example: 2.5.3 (1) Non-destructive in-service inspections are performed regarding potential damage mechanisms in a representative manner with qualified procedures considering all types of welded joints and base material areas. Selection and suitability of the test procedures and techniques is justified under consideration of the technical progress.

63 Module 1 „Safety Criteria for Nuclear Power Plants: Fundamental Safety Criteria”, Technical criteria, No. 3.1 (12a)

64 WENRA: Safety Objectives for New Power Reactors – Study by WENRA Reactor Harmonization Working Group (RHWG), December 2009, Appendix 3

65 Module 1 „Safety Criteria for Nuclear Power Plants: Fundamental Safety Criteria”, Criteria for control rooms, No. 3.8 (4): The ergonomic design of the control room and the emergency control room supports the safety-oriented behaviour of the personnel.