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Sensitivity and Uncertainty Analysis of Boiling Water Reactor Stability Simulations
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. (ARTS)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The best estimate codes are used for licensing of Nuclear Power Plants (NPP), but with conservative assumptions. It is claimed that the uncertainties are covered by the conservatism of the calculation. Nowadays, it is possible to estimate certain parameters using non-conservative data with the complement of uncertainty evaluation, and these calculations can also be used for licensing. As NPPs are applying for power up-rates and life extension, new licensing calculations need to be performed. In this case, evaluation of the uncertainties could help improve the performance, while staying below the limit of the safety margins.

Given the problem of unstable behavior of Boiling Water Reactors (BWR), which is known to occur at certain power and flow conditions, it could cause SCRAM and decrease the economic performance of the plant. Performing an uncertainty analysis for BWR stability would give better understating of the phenomenon and it would help to verify and validate (V&V) the codes used to predict the NPP behavior.

This thesis, reports a sensitivity/uncertainty study of numerical, neutronics, and thermal-hydraulics parameters on the prediction of the BWR stability within the framework of OECD Ringhals-1 (R1 stable reactor) and OECD Oskarshamn-2 (O2 unstable reactor) stability benchmarks. The time domain code TRACE/PARCS was used in the analyses. This thesis is divided in three parts: space-time convergence; uncertainty; sensitivity.

A space-time convergence study was done for the numerical parameters (nodalization and time step). This was done by refining nodalization of all components and time step until obtaining space-time converged solution, i.e. further refinement doesn’t change the solution. When the space-time converged solutions were compared to the initial models, much better solution accuracy has been obtained for the stability measures (decay ratio and frequency), for both stable (R1) and unstable (O2) reactors with the space-time converged models.

Further on, important neutronics and thermal-hydraulics parameters were identified and an uncertainty calculation was performed using the Propagation of Input Errors (PIE) methodology. This methodology, also known as the GRS method, has been used because it has been extensively tested and verified by the industry, and because it allows identifying the most influential parameters using the spearman rank correlation method.

Using the uncertainty method’s results, an attempt has been done to identify the most influential parameters affecting the stability. A methodology using the spearman rank correlation coefficient has been implemented, which helps to identify the most influential parameters on the stability (decay ratio and frequency). Additional sensitivity calculations have been performed for better understanding of BWR stability and parameters that affect it.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xiv, 94 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:84
Keyword [en]
BWR Stability, Sensitivity, Uncertainty
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
SRA - Energy
Identifiers
URN: urn:nbn:se:kth:diva-105866ISBN: 978-91-7501-565-1 (print)OAI: oai:DiVA.org:kth-105866DiVA: diva2:572638
Public defence
2012-12-17, FA32, Alba Nova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework ProgrammeStandUp
Note

This work has been preformed thanks to the support of the Swedish Radiation Safety Authority (SSM) and EU project NURISP. QC 20121129

Available from: 2012-11-29 Created: 2012-11-28 Last updated: 2013-04-18Bibliographically approved
List of papers
1. Sensitivity and Uncertainty of OECD Benchmark Ringhals-1TRACE/PARCS Stability Prediction
Open this publication in new window or tab >>Sensitivity and Uncertainty of OECD Benchmark Ringhals-1TRACE/PARCS Stability Prediction
2012 (English)In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 180, no 3, 383-398 p.Article in journal (Refereed) Published
Abstract [en]

Unstable behavior of boiling water reactors (BWRs) is known to occur during operation at certain power and flow conditions. This paper reports on an uncertainty study of the impact of various parameters on the prediction of the stability of the BWR within the framework of the Organisation for Economic Co-operation and Development Ringhals Unit 1 (Ringhals-1) Stability Benchmark. The time domain code TRACE/PARCS was used in the analysis. The paper is divided into two parts: a sensitivity study on numerical parameters (nodalization, time step, etc.) and an uncertainty analysis of the stability event. The sensitivity study was based on a space-time converged solution, and the most important neutronic and thermal-hydraulic parameters were identified for parameterization. The uncertainty calculation was then performed using the well-established propagation of input errors methodology. Finally, the Spearman Rank method was used to identify the most influential parameters affecting the stability of Ringhals-1.

Keyword
BWR stability, sensitivity, uncertainty
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-106211 (URN)000311914300007 ()2-s2.0-84867962329 (Scopus ID)
Note

QC 20121129

Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
2. Space–time convergence analysis on BWR stability using TRACE/PARCS
Open this publication in new window or tab >>Space–time convergence analysis on BWR stability using TRACE/PARCS
2013 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 51, 295-306 p.Article in journal (Refereed) Published
Abstract [en]

Unstable behavior of Boiling Water Reactors (BWRs) is known to occur during operation at certain power and flow conditions. Even though BWR instability is not a severe safety concern, it could cause reactor scram and significantly decrease the economic performance of the plant. This paper aims to (a) quantify TRACE/PARCS space–time discretization error for simulation of BWR stability, (b) establish space (nodalization) and time discretization necessary for space–time converged model and (c) show that the space–time converged model gives more reliable results for both stable and unstable reactor. The space–time converged model is obtained when further refinement of numerical discretization parameters (nodalization and time step) has negligible effect on the solution. The study is significant because performing a space–time convergence analysis is a necessary step of qualification of the TRACE/PARCS model, and use of the space–time converged model increases confidence in the prediction of BWR stability.

Keyword
BWR stability, Coupled TRACE/PARCS analysis, Space–time convergence
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-106209 (URN)10.1016/j.anucene.2012.08.018 (DOI)000311660700035 ()2-s2.0-84868371547 (Scopus ID)
Note

QC 20121129

Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
3. Sensitivity analysis of input uncertain parameters on BWR stability using TRACE/PARCS
Open this publication in new window or tab >>Sensitivity analysis of input uncertain parameters on BWR stability using TRACE/PARCS
2014 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 67, 49-58 p.Article in journal (Refereed) Published
Abstract [en]

The unstable behavior of Boiling Water Reactors (BWR), which is known to occur at certain power and flow conditions, could cause SCRAM and decrease the economic performance of the plant. For better prediction of BWR stability and understanding of influential parameters, two TRACE/PARCS models of Ringh-als-1 and Oskarshamn-2 BWRs were employed to perform a sensitivity study. Using the propagation of input errors uncertainty method's results, an attempt has been made to identify the most influential parameters affecting the stability. Furthermore, a methodology using the spearman rank correlation coefficient has been used to identify the most influential parameters on the stability parameters (decay ratio and frequency).

Keyword
BWR stability, Sensitivity, Parameters identification
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-106210 (URN)10.1016/j.anucene.2013.10.016 (DOI)000333512200007 ()2-s2.0-84894652331 (Scopus ID)
Conference
Scientific Workshop on Advanced Stability Analysis for Nuclear Reactors, 2012, Dresden, Germany
Note

QC 20140428. Updated from accepted to published.

Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
4. Predicting actual reactor conditions: Why timedomain simulation is necessary for BWR stability
Open this publication in new window or tab >>Predicting actual reactor conditions: Why timedomain simulation is necessary for BWR stability
Show others...
2013 (English)In: International Journal of Nuclear Energy Science and Technology, ISSN 1741-6361, Vol. 7, no 4, 319-342 p.Article in journal (Refereed) Published
Abstract [en]

Despite two decades of development and successful use of coupled thermal-hydraulics/neutron-kinetics (TH/NK) codes for the analysis of design basis accidents, the application of coupled codes to BWR stability transients remains a formidable challenge. While the issues in physical models and numerical methods can be identified, quantified and managed through special developments and separate-effect tests, other aspects (e.g. coupling, modelling assumptions) can only be addressed through benchmarking on full plant stability tests. However, often incomplete information causes uncertainties, whose significance on the modelling and simulation must be evaluated. The objective of this paper is to define validation data needs that allow prediction of the transient behaviour should an unstable condition occur. It is shown that the confidence in exploiting advantageous features of the coupled TH/NK system codes in dealing with core-plant interaction, transient effects and local perturbations can only be evaluated with well-characterised, well-documented plant stability tests and stability events.

Keyword
BWR stability, Coupled codes, Reactor simulation, RELAP5/PARCS, TH/NK, Time domain, Validation
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-92646 (URN)10.1504/IJNEST.2013.054369 (DOI)2-s2.0-84879066810 (Scopus ID)
Note

QC 20131120. Updated from manuscript to article in journal.

Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2015-04-27Bibliographically approved

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