The REPAS Study: Reliability Evaluation of Passive Safety Systems

2002 ◽  
Author(s):  
M. E. Ricotti ◽  
F. Bianchi ◽  
L. Burgazzi ◽  
F. D’Auria ◽  
G. Galassi
Keyword(s):  
Initial Conditions ◽  
Natural Circulation ◽  
Quantitative Information ◽  
External Input ◽  
Passive System ◽  
Two Phase ◽  
Passive Safety Systems ◽  
Safety Systems ◽  
Physical Laws ◽  
Physical Phenomena

The strategy of approach to the problem moves from the consideration that a passive system should be theoretically more reliable than an active one. In fact it does not need any external input or energy to operate and it relies only upon natural physical laws (e.g. gravity, natural circulation, internally stored energy, etc.) and/or “intelligent” use of the energy inherently available in the system (e.g. chemical reaction, decay heat, etc.). Nevertheless the passive system may fail its mission not only as a consequence of classical mechanical failure of components, but also for deviation from the expected behaviour, due to physical phenomena mainly related to thermalhydraulics or due to different boundary and initial conditions. The main sources of physical failure are identified and a probability of occurrence is assigned. The reliability analysis is performed on a passive system which operates in two-phase, natural circulation. The selected system is a loop including a heat source and a heat sink where the condensation occurs. The system behavior under different configurations has been simulated via best-estimate code (Relap5 mod3.2). The results are shown and can be treated in such a way to give qualitative and quantitative information on the system reliability. Main routes of development of the methodology are also depicted.

Integration of Passive System Reliability in PSA Studies

2006 ◽  
Author(s):  
Luciano Burgazzi ◽  
Michel Marques
Keyword(s):  
Safety Assessment ◽  
Natural Circulation ◽  
Fault Tree ◽  
Passive Safety ◽  
Passive System ◽  
Passive Systems ◽  
Probabilistic Safety Assessment ◽  
Passive Safety Systems ◽  
Safety Systems ◽  
Probabilistic Safety

The treatment of passive safety systems within the probabilistic safety assessment models is a difficult and challenging task. The main concern arises from the nature of the passive systems whose predominant operating principles are based on physical phenomena rather than on active components. The present study provides a consistent approach for the integration of passive safety systems into fault tree and event tree based Probabilistic Safety Assessment (PSA) model of accident sequences, in the fashion of and in combination with a front line system or a human action. With reference to the thermal-hydraulic passive systems (e.g. natural circulation systems), in addition to the component failures (i.e. mechanical and electrical faults), the impairment of the physical principle upon which the system relies, deserves special consideration. This makes the relative assessment process different as regards the system model commonly adopted in the fault tree approach (i.e. exponential failure model). For the thermal-hydraulic passive system, since the failure process is driven mainly by the occurrence of the phenomenological failure modes, each pertinent basic event will be characterized by defined critical parameters (e.g. non-condensable fraction) that are expected to drive the failure mechanisms. An application of this approach is presented, with reference to a system designed for decay heat removal of advanced Light Water Reactors, relying on natural circulation and provided with a heat exchanger immersed in a cooling pool, acting as heat sink, and connected to the pressure vessel via steam and condensate lines.

scholarly journals Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome BWR Reactor KERENA: Part II

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 109 ◽  
Author(s):  
René Manthey ◽  
Frances Viereckl ◽  
Amirhosein Moonesi Shabestary ◽  
Yu Zhang ◽  
Wei Ding ◽  
...  
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Gravitational Force ◽  
Heat Removal ◽  
Dimensional System ◽  
Thermal Gradients ◽  
Two Phase ◽  
Passive Safety Systems ◽  
External Power ◽  
Safety Systems

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modeling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I dealt with numerical and experimental methods for modeling of condensation inside the emergency condenser and on the containment cooling condenser. This second part deals with boiling and two-phase flow instabilities.

Simple Analytical U-Tube Benchmarks Appropriate for Testing of Pipe-Network Computer Codes

2002 ◽  
Author(s):  
N. I. Kolev
Keyword(s):  
Nuclear Reactors ◽  
Natural Circulation ◽  
Computer Code ◽  
Inherent Safety ◽  
Pipe Network ◽  
Safety Behavior ◽  
Network Computer ◽  
Passive Safety Systems ◽  
Computer Codes ◽  
Safety Systems

Partially heated U-tube configurations are characteristic idealizations for the so called building condensers of future nuclear reactors with passive safety systems. In this paper three simple cases of natural circulation problems are analyzed and analytical solutions are generated. This solutions are recommended for validation of pipe network computer codes. As an example the procedure is demonstrated for the IVA computer code. The usefulness of the obtained solutions is demonstrated discussing the inherent safety behavior of the building condenser of the Framatome ANP SWR 1000 power plant being under development.

scholarly journals Application of REPAS Methodology to Assess the Reliability of Passive Safety Systems

2009 ◽  
Vol 2009 ◽  
pp. 1-18 ◽  
Author(s):  
Franco Pierro ◽  
Dino Araneo ◽  
Giorgio Galassi ◽  
Francesco D'Auria
Keyword(s):  
Monte Carlo ◽  
Safety Assessment ◽  
Probability Distributions ◽  
Passive Safety ◽  
Passive System ◽  
Passive Systems ◽  
Passive Safety Systems ◽  
Passive Safety System ◽  
Uncertain Input ◽  
Safety Systems

The paper deals with the presentation of the Reliability Evaluation of Passive Safety System (REPAS) methodology developed by University of Pisa. The general objective of the REPAS is to characterize in an analytical way the performance of a passive system in order to increase the confidence toward its operation and to compare the performances of active and passive systems and the performances of different passive systems. The REPAS can be used in the design of the passive safety systems to assess their goodness and to optimize their costs. It may also provide numerical values that can be used in more complex safety assessment studies and it can be seen as a support to Probabilistic Safety Analysis studies. With regard to this, some examples in the application of the methodology are reported in the paper. A best-estimate thermal-hydraulic code, RELAP5, has been used to support the analyses and to model the selected systems. Probability distributions have been assigned to the uncertain input parameters through engineering judgment. Monte Carlo method has been used to propagate uncertainties and Wilks' formula has been taken into account to select sample size. Failure criterions are defined in terms of nonfulfillment of the defined design targets.

Integral Testing of the AP600 Passive Emergency Core Cooling Systems

1993 ◽  
Vol 207 (4) ◽  
pp. 259-268 ◽  
Author(s):  
L E Hochreiter ◽  
S V Fanto ◽  
L E Conway ◽  
L K Lau
Keyword(s):  
Natural Circulation ◽  
Cooling Mode ◽  
Passive Safety Systems ◽  
Pressure Test ◽  
Integral Systems ◽  
Analysis Computer ◽  
Computer Codes ◽  
Core Cooling ◽  
Safety Systems

In support of the development of AP600, Westinghouse is conducting two integral systems tests to examine the performance of the passive safety systems. A full-height, full-pressure test is being performed to simulate a small loss-of-coolant, steam generator tube rupture and large steam line break events. A one-quarter scale, low-pressure test is being performed to simulate transients with emphasis on the transition to the natural circulation post-accident, long-term cooling mode and to demonstrate the long-term cooling capability. Each of the tests will provide detailed experimental results for verification of the accident analysis computer codes.

scholarly journals Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome KERENA BWR Reactor: Part I

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 35 ◽  
Author(s):  
Amirhosein Moonesi Shabestary ◽  
Frances Viereckl ◽  
Yu Zhang ◽  
Rene Manthey ◽  
Dirk Lucas ◽  
...  
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Gravitational Force ◽  
Heat Removal ◽  
Dimensional System ◽  
Thermal Gradients ◽  
Two Phase ◽  
Passive Safety Systems ◽  
External Power ◽  
Safety Systems

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modelling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I deals with numerical and experimental methods for modelling of condensation inside the emergency condensers and on the containment cooling condenser while part II deals with boiling and two-phase flow instabilities.

Validation of the System Code APROS for Fast Transients

2013 ◽  
Author(s):  
Manuel Raqué ◽  
Heiko Herbell ◽  
Thomas Schulenberg
Keyword(s):  
Initial Conditions ◽  
Numerical Models ◽  
Natural Circulation ◽  
Initial Pressure ◽  
Test Facility ◽  
Heating Rates ◽  
Transient Phenomena ◽  
Numerical Predictions ◽  
Reflection Time ◽  
Physical Phenomena

The thermal-hydraulic system code APROS Version 5.09 [1] is being applied in the European project SCWR-FQT to evaluate the performance of the safety systems for a nuclear test facility operated with supercritical water. In order to validate the commercial code for predictions of transient phenomena, two adequate hydraulic experiments from literature have been simulated. The experiment of Fujii and Akagawa [2] investigated hydraulic shocks as they will occur in case a pipe, which is stationary passed through by water, is abruptly closed. A simple numerical model with adapted time and space nodalization was able to reproduce the observed physical phenomena, such as the magnitude of the initial pressure wave and reflection time, in detail. In a second experiment, a test series was performed by Becker et al. [3] and Mathisen [4] in order to examine the natural circulation in a closed loop for different heating rates and system pressures. For a stepwise power increase, the typical mass flow characteristic for boiling channels was recorded until the onset of flow oscillations. In further runs, the effect of different initial conditions on the flow stability was analyzed. This paper compares the numerical predictions with both experimental results. The numerical models could describe the physical phenomena with appropriate accuracy.

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