Papers by Jan-Erik Holmberg
Probabilistic Safety Assessment and Management, 2004
Planering och analys av möjligheter att införa rapportens idéer i en verklig PSA-studie för att d... more Planering och analys av möjligheter att införa rapportens idéer i en verklig PSA-studie för att demonstrera hur djupförvarsnivåerna 1 och 2 mer explicit kan inkluderas i en PSA, än de är i dagens PSA studier. En annan tänkbar uppgift är också att utveckla resultatpresentationen och säkerhetsvärderingen av erhållna resultat. Med dessa utvecklingssteg kan PSA bli ett verktyg för att identifiera relativa och absoluta svagheter i aktiviteter som syftar till att förhindra eller kontrollera onormala händelser.
PSA 2008, Challenges to PSA during the nuclear renaissance. International Topical Meeting on Prob... more PSA 2008, Challenges to PSA during the nuclear renaissance. International Topical Meeting on Probabilistic Safety Assessment & Analysis. Knoxville, Tennessee, 7 - 11 Sept. 2008. 10 p. Vol.3, 1606 - 1615 Teollisuuden Voima Oy (TVO) owns and operates in Southern Finland two BWR units (OL1 and OL2) and has one PWR unit (OL3) under construction. The Finnish Regulatory Body STUK requires that the design of new nuclear power plants as well as the operation of the operating nuclear power plants shall be supported by PSA. Recently, a project has been carried out for the operating units OL1 and OL2, in order to systematically evaluate the TechSpecs with PSA. This study encompasses allowed outage times (AOTs) for power operation, surveillance testing and, also, outages. The paper discusses the insights and results of the analyses. Examples of such insights are that there is no single predominant methodology for this kind of evaluation, and therefore AOT calculations may to be studied from dif...
PSAM 9. International Conference on Probabilistic Safety Assessment & Management. Hong Kong, Chin... more PSAM 9. International Conference on Probabilistic Safety Assessment & Management. Hong Kong, China, 18 - 23 May 2008. Paper 0443 Probabilistic criteria are used to judge the acceptability of PSA results. Highest level criteria set limits to acceptable societal risk, which requires performance of level 3 PSA. In many countries - including e.g. Finland and Sweden - performance of level 3 PSA is not required, and probabilistic decision criteria (limits or targets) are defined only at core damage frequency and large release frequency level. The definition of probabilistic criteria for level 2 PSA has been one of the key issues discussed in the Nordic study on validation of safety goals. There is a need to discuss and define more precisely the decision criteria related to unacceptable releases, as they seem to be understood differently in different organizations. For instance, the inclusion or exclusion of long-term effects makes a big difference as well as the inclusion or exclusion of ...
Safety, Reliability and Risk Analysis: Theory, Methods and Applications – Martorell et al. (eds),... more Safety, Reliability and Risk Analysis: Theory, Methods and Applications – Martorell et al. (eds), 227 – 232 The Enhanced Bayesian THERP (Technique for Human Reliability Analysis) method has been successfully used in real PSA-studies at Finnish and Swedish NPPs. The method offers a systematic approach to qualitatively and quantitatively analyze operator actions. In order to better know its characteristics from a more international perspective, it has been subject to evaluation within the framework of the ‘‘HRA Methods Empirical Study Using Simulator Data.’’ This paper gives a brief overview of the method with major findings from the evaluation work including identified strengths and potential weaknesses of the method. A number of possible improvement areas have been identified and will be considered in future development of the method ESREL 2008 & 17th SRA Europe Annual Conference. Valencia, Spain, 22 - 25 Sept. 2008.
Proceedings of SIAS 2010 We have surveyed methods applicable to the reliability analysis of digit... more Proceedings of SIAS 2010 We have surveyed methods applicable to the reliability analysis of digital instrumentation and control systems. Our specific field of application is the control systems of a nuclear power plant (NPP). This paper summarizes our findings, and outlines needs for future research work. Traditional fault tree/event tree methods have a limited scope of application, namely in the analysis of protection systems. Dynamic flowgraph methodology, Markov models and model checking hold promise for capturing the time dependent dynamic behaviours ubiquitous in the more general setting. The 6th International Conference Safety of Industrial Automated Systems, SIAS 2010. Tampere, 14 -15 June 2010.
Proceedings of PSAM 10 — International Probabilistic Safety Assessment & Management Conference, 7... more Proceedings of PSAM 10 — International Probabilistic Safety Assessment & Management Conference, 7–11 June 2010, Seattle, Washington, USA, Paper 48 Most of the probabilistic safety assessments (PSA) for Nuclear Power Plants were originally created to make conservative estimates of the core damage frequencies for internal events, which might occur during power operation. The PSA models have then been expanded to replace conservative estimates with more realistic assumptions and to include other types of initiating events, modes of operation and end states. The development has resulted in very large and detailed models, which are hard to understand completely, even for an experienced PSA engineer. Today, the trend to increase the level of detail and the scope of the PSA models continues as a consequence of regulatory requirements. Hence the Nordic PSA Group (NPSAG) has initiated a project with the aim of identifying methods to reduce the complexity of the PSA models. This paper present...
PSAM 9. International Conference on Probabilistic Safety Assessment & Management. Hong Kong, Chin... more PSAM 9. International Conference on Probabilistic Safety Assessment & Management. Hong Kong, China, 18 - 23 May 2008. Paper 0428 The paper will deal with the consistency of judgement in the usage of probabilistic safety goals for nuclear power plants, as analysed in a sub-project within an on-going Nordic (Sweden/Finland) project. The project has relations to an on-going OECD/NEA WGRisk task on probabilistic safety criteria in member countries. Two important issues when dealing with safety criteria is the problem of consistency of judgement in a situation when safety goals are applied to PSA results which change over time, or which are made up of contributors with major differences in uncertainties. In many cases changes in PSA results over time are due to scope extensions or increases of level of detail, which will lead to an increase of the frequency of the calculated risk measures (CDF or off-site release). Changes in plant specific data and in analysis methods will also cause ch...
Proceedings of PSAM 10 — International Probabilistic Safety Assessment & Management Conference, 7... more Proceedings of PSAM 10 — International Probabilistic Safety Assessment & Management Conference, 7–11 June 2010, Seattle, Washington, USA, Paper 47 Probabilistic safety criteria, including safety goals, have been progressively introduced by regulatory bodies and utilities. They range from high level qualitative statements to technical criteria. They have been published in different ways, from legal documents to internal guides. They can be applied as legal limits down to “orientation values”. The OECD/NEA Working Group on Risk (WGRISK) prepared a questionnaire on the probabilistic risk criteria for nuclear power plants. Answers were received from 13 nuclear safety organizations and 6 utilities. The reported probabilistic risk criteria can be grouped into 4 categories, in relation with the tools to be used for assessing compliance: core damage frequency, releases frequency, frequency of doses and criteria on containment failure. Introduction of probabilistic safety criteria is general...
Nuclear Engineering and Technology
To assess the risk of nuclear power plant operation and to determine the risk impact of digital s... more To assess the risk of nuclear power plant operation and to determine the risk impact of digital systems, there is a need to quantitatively assess the reliability of the digital systems in a justifiable manner. The Probabilistic Risk Analysis (PRA) is a tool which can reveal shortcomings of the NPP design in general and PRA analysts have not had sufficient guiding principles in modelling particular digital components malfunctions. Currently digital I&C systems are mostly analyzed simply and conventionally in PRA, based on failure mode and effects analysis and fault tree modelling. More dynamic approaches are still in the trial stage and can be difficult to apply in full scale PRA-models. As basic events CPU failures, application software failures and common cause failures (CCF) between identical components are modelled.The primary goal is to model dependencies. However, it is not clear which failure modes or system parts CCF:s should be postulated for. A clear distinction can be made...
Proceedings of PSAM 10 — International Probabilistic Safety Assessment & Management Conference, 7... more Proceedings of PSAM 10 — International Probabilistic Safety Assessment & Management Conference, 7–11 June 2010, Seattle, Washington, USA, Paper 245 A guidance document has been developed as part of a four-year Nordic project dealing with the use of probabilistic safety criteria for nuclear power plants. The Guidance sums up, on the basis of the work performed throughout the project, issues to consider when defining and applying probabilistic safety criteria. The Guidance describes the terminology and concepts involved, levels of probabilistic safety criteria and relations between these, how to define a criterion, how to apply a criterion, on what to apply the criterion, and how to interpret the result of the application. It specifically deals with what makes up a probabilistic safety criterion, i.e., the risk metric, the frequency criterion, the PSA used for assessing compliance, and the application procedure for the criterion. It will also discuss the concept of subsidiary criteria...
IEC 61508 [1] is a standard for Functional safety of electrical/electronic/programmable electroni... more IEC 61508 [1] is a standard for Functional safety of electrical/electronic/programmable electronic safety related systems. This standard defines concepts for analyses of these types of systems. On a general level the standard is defining the concept of Safety Integrity Levels, SILs. SIL sets the requirements on the process how the equipment is manufactured, tested etc. The same is relevant for the software being developed. To meet the requirements of a SIL – the software shall meet some predefined criteria. The software reliability estimates in the current probabilistic safety assessments (PSA) for nuclear power plants (NPP) are often engineering judgments – often lacking a proper justification. The use of probabilities for software reliability is based on some common understanding rather than a proper reference. The backgrounds for this figure is however not clear, as what it really means. Does it mean failure of an individual processor, CCF between different processers or failure ...
To assess the risk of nuclear power plant operation and to determine the risk impact of digital s... more To assess the risk of nuclear power plant operation and to determine the risk impact of digital systems, there is a need to quantitatively assess the reliability of the digital systems in a justifiable manner. Due to the many unique attributes of digital systems, a number of modelling and data collection challenges exist, and consensus has not yet been reached. The OECD/NEA CSNI Working Group on Risk Assessment (WGRisk) has set up a task group called DIGREL to develop a taxonomy of failure modes of digital components for the purposes of probabilistic safety assessment (PSA). An activity focused on development of a common failure modes taxonomy is seen as a step towards standardised digital I&C reliability assessment techniques. Needs from PSA will guide the work, meaning e.g. that I&C system and its failures are studied from their functional significance point of view. The taxonomy will be the basis of modelling and quantification efforts. It will also help to define a structure for...
http://www.nks.org/en/nks_reports/view_document.htm?id=111010213008953
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Papers by Jan-Erik Holmberg