If you would like to learn more about the IAEA’s work, sign up for our weekly updates containing our most important news, multimedia and more.
Development of Methodologies for the Assessment of Passive Safety System Performance in Advanced Reactors
Closed for proposals
Project Type
Project Code
I31018CRP
1481Approved Date
Status
Start Date
Expected End Date
Completed Date
15 May 2013Description
This CRP aims on development of a common approach to assess performance of passive safety systems. Such an approach could facilitate design optimization and safety qualification of the future advanced reactors, contributing to their enhanced safety levels and improved economics. The project is expected to pool together efforts of all principal developers of the relevant approaches and methodologies worldwide, and also to attract capable new participants.
Objectives
The objective is to determine a common method for reliability assessment of passive safety system performance. Such a method would facilitate application of risk-informed approaches in design optimization and safety qualification of the future advanced reactors, contributing to their enhanced safety levels and improved economics.The CRP will be implemented as a programmatic activity of the IAEA sub-programme 1.1.5 “Technology Development for Advanced Reactor Lines” (involving collaboratively the projects 1.1.5.1, 1.1.5.2, and 1.1.5.4) and the IAEA project 3.2.3.3 “Fostering technical developments and trends in safety analyses”, starting with the IAEA Program and Budget Cycle 2008 – 2009. The sub-programme 1.1.5 has the objective to achieve progress in the development of advanced nuclear power technologies that have competitive economics and meet stringent safety objectives through international information exchange and coordinated research, and the Project 3.2.3.3 has the objective to facilitate, among others, technical developments of new trends and issues in safety analyses, and to share with Member States. Given its aforementioned overall objectives, the CRP clearly responds to the objectives of the IAEA sub-programme 1.1.5 and project 3.2.3.3.Inter- and intra-departmental coordination in the AgencyThe proposed CRP foresees a broad intra-departmental and inter-departmental cooperation. The project would be implemented in conjunction with the Nuclear Energy Department’s Technical Working Groups on Advanced Light Water Reactors (LWRs), Heavy Water Reactors (HWRs), Gas Cooled Reactors (GCR) and Fast Reactors (FR) of NENP and the Safety Assessment Section and Engineering Safety Section of the Department of Nuclear Safety and Security. Specifically, the IAEA Safety Assessment Section of the Department of Nuclear Safety and Security would be engaged to provide peer reviews of the PSA methodologies applied and of the results obtained in PSA studies for advanced NPP designs.One of the methodological approaches that could be addressed within this project, the RMPS approach developed within the EU framework programmes, is currently undergoing a trial application to the assessment of the passive system design of the CAREM type reactor of Argentina within an IAEA CRP "Natural circulation phenomena, modelling and reliability of passive systems that utilize natural circulation", coordinated jointly within the Technical Working Groups on Advanced Technologies LWRs and HWRs within NENP.The CEA has proposed in the framework of INPRO a collaborative project called “Reliability Assessment of Passive Gaseous Provisions”. This proposal, dedicated to the issues of passive decay heat removal from a fast gas cooled reactor concept being developed by the CEA, could be a task of the present CRP or close cooperation between the two efforts could be established.
Specific objectives
The scope of the problems associated with further development of methodologies for reliability assessment of passive safety systems was elaborated at the IAEA technical meeting “Status of Validation and Testing of Passive Safety Systems for Small and Medium Sized Reactors (SMRs)” held in Vienna on 12-16 June 2006 and through direct communications with the developers of such methodologies. In line with these discussions, the specific research objectives of this CRP are:Identify requirements for a method of reliability assessment of passive safety systems for future advanced NPPs ;Work out a set of definitions for reliability assessment of passive safety systems and their treatment by PSA, e.g., ‘reliability of a passive safety system’, ‘safe end state’ of accident sequences, ‘mission time’, etc. (a consensus should also be reached on whether proving the ability of passive systems to perform their function is clearly related to the selection of a certain PSA modelling approach);Identify a benchmark problem for comparison and validation of methodologies for reliability assessment of passive safety system performance, including such issues as systematic failure modes and effects analysis (FMEA), component failure rates, treatment of dependencies in fault tree (FT) models, impact from internal and external hazards, etc.;Select reliability assessment methodologies and perform trial applications, including evaluation of the uncertainties, for a selected benchmark problem;Compare the results and prepare recommendations for a common analysis-and-test based unified approach ;Draft suggestions for further elaboration of IAEA Safety Standards.
Activities, inputs, outputs, outcome
Impact
The principal conclusion of this CRP is there is a clear need to obtain more data, especially related to thermal hydraulics. This necessitated additional development, testing and research. It is essential that passive and evolutionary components, Common Cause Failures (CCF) of high redundancy systems and intersystem CCF of such reactors are adequately addressed. The technical challenges for advanced reactors also include the potential need to address very different systems and phenomenology, the potential unavailability of important reliability and experimental data, the potential unavailability of knowledge on new key phenomena, and the potential unavailability of accident analysis models.
The other broad based conclusions are derived from the CRP are as follows:
• Failure of passive components and structures now more important in advanced reactor designs. The new and advanced methodologies described in the report for the assessment of passive safety system reliability are considered as important tools and approaches to achieve improved safety for the future advanced nuclear power plants and particular attention should be paid to the status of development of the methodologies and the obtained results.
• The general consensus was that a more practical approach would be very helpful for the robust design and qualification of advanced nuclear reactors. The further promotion of international collaboration which needs to be enhanced in order to model the unique features of new reactors in key areas such as digital/software based instrumentation and control (I&C) reliability and passive system high degree reliability modelling.
• Passive systems and passive PSA are becoming more and more important as technology evolves. The key element as to furthering development and use of passive systems is the decision to proceed with licensing and construction of an advanced reactor design.
• Facilitate information exchange and promote international collaborative research and development in the area of advanced nuclear reactor technologies needed to meet, in a sustainable manner, the increasing energy demands of the 21st century.
Relevance
Advanced nuclear reactor designs incorporate several passive systems in addition to active one, not only to enhance the operational safety of the reactors but also to eliminate the possibility of hypothetical severe accidents. While the wording ‘passive safety design options’ denotes various possible combinations of
inherent and passive safety features and reasonable combinations of active and passive systems incorporated in reactor design, these are the passive systems, such as those incorporating moving fluids or expanding solid structures, direct action devices, or stored energy sources (i.e. passive systems of categories B, C, and D, that generally require validation and testing to demonstrate and prove their reliable operation and, if necessary, adjust their design. While individual process are well understood, the combinations of these processes, which define actual performance of such systems, may vary depending on changes in the conditions of state, boundary conditions and failure or malfunctioning of components within the system, the circuit or the plant. Therefore, the issue of process performance reliability becomes important for passive systems.