Leibstadt, Switzerland
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Zvoncek P.,Leibstadt Nuclear Power Plant | Nusbaumer O.,Leibstadt Nuclear Power Plant | Torri A.,Risk Management Associates Inc.
Nuclear Engineering and Technology | Year: 2017

This paper describes the development process, the innovative techniques used and insights gained from the latest integrated, full scope, multistate Level 2 PSA analysis conducted at the Leibstadt Nuclear Power Plant (KKL), Switzerland. KKL is a modern single-unit General Electric Boiling Water Reactor (BWR/6) with Mark III Containment, and a power output of 3600MWth/1200MWe, the highest among the five operating reactors in Switzerland. A Level 2 Probabilistic Safety Assessment (PSA) analyses accident phenomena in nuclear power plants, identifies ways in which radioactive releases from plants can occur and estimates release pathways, magnitude and frequency. This paper attempts to give an overview of the advanced modeling techniques that have been developed and implemented for the recent KKL Level 2 PSA update, with the aim of systematizing the analysis and modeling processes, as well as complying with the relatively prescriptive Swiss requirements for PSA. The analysis provides significant insights into the absolute and relative importances of risk contributors and accident prevention and mitigation measures. Thanks to several newly developed techniques and an integrated approach, the KKL Level 2 PSA report exhibits a high degree of reviewability and maintainability, and transparently highlights the most important risk contributors to Large Early Release Frequency (LERF) with respect to initiating events, components, operator actions or seismic component failure probabilities (fragilities). © 2017


Papra M.,Paul Scherrer Institute | Papra M.,Leibstadt Nuclear Power Plant | Buchi F.N.,Paul Scherrer Institute | Kotz R.,Paul Scherrer Institute
Fuel Cells | Year: 2010

Hydrogen fuelled vehicles with a fuel cell based powertrain are considered to contribute to sustainable mobility by reducing CO2 emissions from road transport. In such vehicles the fuel cell system is typically hybridised with an energy storage device such as a battery or a supercapacitor (SC) to allow for recovering braking energy and assist the fuel cell system for peak power. The direct parallel combination of a polymer electrolyte fuel cell (PEFC) and a SC without any control electronics is investigated in the present study. It is demonstrated that the combination enhances the dynamics of the PEFC significantly during load changes. However, due to the lack of a power electronic interface the SC cannot be utilised to its optimum capacity. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Podofillini L.,Paul Scherrer Institute | Dang V.N.,Paul Scherrer Institute | Nusbaumer O.,Leibstadt Nuclear Power Plant | Dres D.,Leibstadt Nuclear Power Plant
Reliability Engineering and System Safety | Year: 2013

Probabilistic Safety Assessment (PSA) typically focuses on the errors leading to the non-performance of required actions (Errors of Omission, EOOs). On the other hand, Errors Of Commission (EOCs) refer to inappropriate, undesired actions that aggravate an accident scenario. The challenges to their treatment in PSA relate to both their identification (which error events should be included in the PSA) and to the quantification of their probabilities. This paper presents the results from a plant-specific study to identify potential EOC vulnerabilities and quantify their risk significance. The study addresses a Boiling Water Reactor (BWR) in Switzerland. It is one of the first EOC analyses ever made for BWRs. The Commission Error Search and Assessment (CESA) method was used to identify EOC scenarios. The EOC probabilities were estimated using the elicitation approach developed as part of the ATHEANA method (A Technique for Human Event Analysis), with input from interviews with plant personnel (with oral as well as written questions). The basis for the quantification was a qualitative analysis of the scenario, the operator response and its procedural basis, and of the opportunities for the EOC and its recovery. The results suggest that the contribution to risk of the most important EOCs is comparable to that of the most important errors of omission, i.e. the required actions typically treated in a PSA; thus, they highlight the significance of EOCs in the overall risk profile of the plant. This study demonstrates the feasibility of a systematic treatment of EOCs for large-scale applications and contributes to understanding the importance of EOCs in the plant risk profile. © 2012 Elsevier Ltd. All rights reserved.


Nusbaumer O.,Leibstadt Nuclear Power Plant | Rauzy A.,Ecole Polytechnique - Palaiseau
11th International Probabilistic Safety Assessment and Management Conference and the Annual European Safety and Reliability Conference 2012, PSAM11 ESREL 2012 | Year: 2012

Two well-known modeling approaches are in use in Probabilistic Risk Assessment (PSA/PRA): Fault Tree Linking (FTL) and Event Tree Linking (ETL). The question of which modeling approach is best appropriate for specific applications has been extensively, if not emotionally, debated among experts in the past two decades, addressing both modeling and quantification issues. In this article, we determine their degree of equivalence and build "methodological bridges" between the two approaches, from a mathematical and algorithmic perspective. We show that both modeling approaches are, despite appearances and under certain conditions, equivalent. Such a demonstration is made possible by recent algorithmic developments in the Binary Decision Diagram (BDD) framework. Since both Fault Tree Linking and Event Tree Linking approaches are subject to limitations and approximations, the established bridges make it possible to formulate important recommendations for PSA/PRA practitioners and quantification engine developers. In the sequel, we demonstrate a fundamental result that will allow to solve exactly any FTL models from its Minimal Cutsets, including the quantification of success paths in Event Trees, and show how this can be implemented in future quantification engines.


Nusbaumer O.,Leibstadt Nuclear Power Plant | Rauzy A.,Ecole Polytechnique - Palaiseau
Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability | Year: 2013

Two well-known modelling approaches are in use in probabilistic risk assessment: fault tree linking and event tree linking. The question of which modelling approach is m ost appropriate for specific applications has been extensively, if not emotionally, debated among experts in the past two decades, addressing both modelling and quantification issues. In this article, we determine their degree of equivalence and build 'methodological bridges' between the two approaches from a mathematical and algorithmic perspective. We show that, under certain conditions, both modelling approaches are equivalent. Since both fault tree linking and event tree linking approaches are subject to limitations and approximations, established bridges make it possible to formulate important recommendations for probabilistic risk assessment practitioners and quantification engine developers. © IMechE 2013.


Engel R.,Leibstadt Nuclear Power Plant
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2011

On March 6th 2007, the Leibstadt Nuclear Power Plant in Switzerland experienced an automatic blowdown of eight safety/relief valves installed on the main steam lines caused by a faulty electrical manipulation while performing planned maintenance during full power operation. Due to the temperature measurements inside the reactor recirculation system and the reactor pressure vessel this event, at a first glance, appeared to be Event No. 23 (Automatic Blowdown event) as an Emergency (Service Level C) Condition in accordance with the relevant reactor pressure vessel Thermal Cycle Diagram. According to the ASME Code Section III, Service Level C limits permit large deformations in areas of structural discontinuity which may necessitate the removal of a component from service for inspection or repair. This paper presents a summary of thermal-hydraulic, stress, fatigue, and fracture mechanical evaluations as well as plant inspections performed to demonstrate the impact of the event on the reactor pressure vessel and associated components and to fulfill the requirements of the Swiss Federal Nuclear Safety Inspectorate. It is shown that the primary circuit of the plant was not inadmissibly stressed by the event and that it was acceptable from a safety-related point of view to return the plant to service. Corresponding to the 7-level International Nuclear and Radiological Event Scale this event was rated afterwards as level 1 (anomaly) by the Swiss Federal Nuclear Safety Inspectorate. Copyright © 2011 by ASME.


Orlov A.,Paul Scherrer Institute | Degueldre C.,Paul Scherrer Institute | Kaufmann W.,Leibstadt Nuclear Power Plant
Journal of Solid State Chemistry | Year: 2013

The buildup of corrosion product deposits (CRUD) on the fuel cladding of the boiling water reactor (BWR) before and after zinc injection has been investigated by applying local experimental analytical techniques. Under the BWR water chemistry conditions, Zn addition together with the presence of Ni and Mn induce the formation of (Zn,Ni,Mn)[Fe 2O 4] spinel solid solutions. X-ray absorption spectroscopy (XAS) revealed inversion ratios of cation distribution in spinels deposited from the solid solution. Based on this information, a two-site ferrite spinel solid solution model is proposed. Electron probe microanalysis (EPMA) and extended X-ray absorption fine structure (EXAFS) findings suggest the zinc-rich ferrite spinels formation on BWR fuel cladding mainly at lower pin. © 2012 Elsevier Inc. All rights reserved.


Patent
Leibstadt Nuclear Power Plant and Kernkraftwerk Goesgen Daeniken Ag | Date: 2011-11-02

A system and a method for promoting improved air flow through a cooling tower and reduced inner air pressure losses caused by rain in the rain zone of a cooling tower. Aerodynamic modules are mounted on the lower edge of the cooling tower shell in order to deflect the downward-flowing air about the lower edge of the tower shell and into the rain zone. The aerodynamic modules can be modularly mounted, can be replaced, and do not affect the statics of the tower shell. Aerodynamic modules can also be built on the base area to deflect the incoming air over any obstacles. Troughs or dripping elements can also promote flow by reducing the rain falling in an outer area.


Orlov A.,Paul Scherrer Institute | Degueldre C.,Paul Scherrer Institute | Wiese H.,Paul Scherrer Institute | Ledergerber G.,Leibstadt Nuclear Power Plant | Valizadeh S.,Westinghouse Electrical Sweden AB
Journal of Nuclear Materials | Year: 2011

Recent Eddy current investigations on the cladding of nuclear fuel pins have shown that the apparent oxide layers are falsified due to unexpected magnetic properties of corrosion product deposits. Analyses by Scanning Electron Microscopy (SEM) or Electron Probe Micro Analysis (EPMA) demonstrated that the deposit layer consists of complex 3-d element oxides (Ni, Mn, Fe) along with Zn, since the reactor operates with a Zn addition procedure to reduce buildup of radiation fields on the recirculation system surfaces. The oxides crystallise in ferritic spinel structures. These spinels are well-known for their magnetic behaviour. Since non-magnetic zinc ferrite (ZnFe2O4) may become magnetic when doped with even small amounts of Ni and/or Mn, their occurrence in the deposit layer has been analyzed. The magnetic permeability of zinc ferrite, trevorite and jacobsite and their solid solutions are estimated by magnetic moment additivity. From the void history examination, the low elevation sample (810 mm) did not face significant boiling during the irradiation cycles suggesting growth of (Mn0.092+Zn0.752+Fe0.293+)[(Fe1.713+Mn0. 032+Ni0.132+)O4] crystals with theoretical value of the magnetic permeability for the averaged heterogeneous CRUD layer of 9.5 ± 3. Meanwhile, (Mn0.162+Zn0.552+Fe0.293+)[(Fe1.713+Mn0.042+Ni0.252+)O4] crystallizes at the mid elevation (1810 mm) with theoretical magnetic permeability for the CRUD layer of 4.2 ± 1.5 at the investigated azimuthal location. These theoretical data are compared with the magnetic permeability of the corrosion product deposited layers gained from reactor pool side Eddy current (EC) analyses (9.0 ± 1.0 for low and 3.5 ± 1.0 for high elevation). The calculated thicknesses and magnetic permeability values of the deposition layers (estimated by MAGNACROX multifrequency EC method) match together with these estimated using an "ion magnetic moment additivity" model.


PubMed | Federal office of Public Health of Fribourg, Muhleberg Nuclear Power Plant, Swiss National Accident Insurance Fund, University of Lausanne and 3 more.
Type: Journal Article | Journal: Radiation protection dosimetry | Year: 2016

Individual monitoring for both external and internal exposures is well regulated in Switzerland. The article gives an overview on the occupational exposure to external radiation of workers based on the data collected in the Swiss national dose registry (NDR) in 2013. The NDR records the monthly doses of radiation workers since the introduction of ICRP 60 recommendations and is manifested in the Swiss ordinance since 1994. Annual dose limits for effective dose are typically exceeded once a year in Switzerland, mostly in medicine. The NDR is a useful optimisation tool to identify and characterise areas with the highest exposures. While exceeded dose limits were often related to accidental acute exposure in the past, they are now more related to continuous exposure during normal work, especially in medicine.

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