SEVERE ACCIDENT ANALYSIS USING DYNAMIC ACCIDENT PROGRESSION EVENT TREES ...

245 Pages·2006·3.35 MB·English

SEVERE ACCIDENT ANALYSIS USING DYNAMIC ACCIDENT PROGRESSION
EVENT TREES

DISSERTATION

Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in Nuclear
Engineering of The Ohio State University

By
Aram P. Hakobyan, B.S. Nuclear Physics, M.S. Nuclear Engineering
* * * * *

The Ohio State University
2006

Dissertation Committee:
Approved by
Professor Tunc Aldemir, Adviser
Professor Richard Denning _______________________________
Professor Xiaodong Sun Dr. Tunc Aldemir, Adviser
Nuclear Engineering Graduate Program
Professor Umit Catalyurek

ABSTRACT

In present, the development and analysis of Accident Progression Event Trees
(APETs) are performed in a manner that is computationally time consuming, difficult to
reproduce and also can be phenomenologically inconsistent. One of the principal
deficiencies lies in the static nature of conventional APETs. In the conventional event
tree techniques, the sequence of events is pre-determined in a fixed order based on the
expert judgments. The main objective of this PhD dissertation was to develop a software
tool (ADAPT) for automated APET generation using the concept of dynamic event trees.
As implied by the name, in dynamic event trees the order and timing of events are
determined by the progression of the accident. The tool determines the branching times
from a severe accident analysis code based on user specified criteria for branching. It
assigns user specified probabilities to every branch, tracks the total branch probability,
and truncates branches based on the given pruning/truncation rules to avoid an
unmanageable number of scenarios.
The function of a dynamic APET developed includes prediction of the conditions,
timing, and location of containment failure or bypass leading to the release of radioactive
material, and calculation of probabilities of those failures. Thus, scenarios that can
potentially lead to early containment failure or bypass, such as through accident induced
failure of steam generator tubes, are of particular interest. Also, the work is focused on
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treatment of uncertainties in severe accident phenomena such as creep rupture of major
RCS components, hydrogen burn, containment failure, timing of power recovery, etc.
Although the ADAPT methodology (Analysis of Dynamic Accident Progression
Trees) could be applied to any severe accident analysis code, in this dissertation the
approach is demonstrated by applying it to the MELCOR code [1]. A case study is
presented involving station blackout with the loss of auxiliary feedwater system for a
pressurized water reactor. The specific plant analyzed is the Zion Nuclear Power Plant,
which is a Westinghouse-designed system that has been decommissioned.

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Dedicated to my friend Armen Mikoyan, wife Armine, and son Vahan

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ACKNOWLEDGMENT

I wish to thank my adviser Tunc Aldemir, for intellectual and financial support, for
always showing the right direction, for everything he has done to make this
accomplishment possible.
I wish to thank my research adviser Richard Denning, for all those priceless advises
he has provided throughout this research work that helped me to find an excellent
practical application for my theoretical skills.
I am grateful to Umit Catalyurek and Benjamin Rutt for their significant
contribution to this research project with computer programming and database
management.
I thank the whole OSU Nuclear Engineering Program, for the knowledge and skills
I gained while studying and working here that helped me complete this dissertation work.
Finally, I want to thank my wife Armine for the moral support, and the great
patience she showed during all these years I had been working on my research.
The research presented in this dissertation was partially supported by a contract
from the Sandia National Laboratory (SNL). The information and conclusions presented
here in are those of the author and do not necessary represent the views or positions of
the SNL. Neither the U.S. Government nor any agency thereof, nor any employee, makes
any warranty, expressed or implied, or assume any legal liability or responsibility for any
third party’s use of this information.
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VITA

May 18, 1974 ………………………….. Born – Yerevan, Armenia

1996 …………………………………… B.S. Nuclear Physics, Yerevan State University

1996 – 2001……………………………. Engineer,
Armenian Nuclear Power Plant

2002 – present ………………………….Graduate Research Associate,
The Ohio State University

2003 …………………………………… M.S. Nuclear Engineering,
The Ohio State University

PUBLICATIONS

Research Publications

1. A. Hakobyan, M. Fiorino, C. Li, R. Wagrey, D. Mills, C. Segovia “Implementation of
Silicon Carbide Detectors to IRIS Reactor”, Proceedings of ANS Winter Meeting, New
Orleans, Nov 17 – 20 (2003)

2. A. Hakobyan, M. Biro, T. Aldemir, “Representation of measurement uncertainty in
flux/power shape construction from monitored data”, Proceedings of ANS Annual
Meeting, San Diego, June 5 - 9 (2005)

3. A. Hakobyan, K. Metzroth, T. Aldemir, “An online probabilistic diagnostic and
prognostic approach to accident management”, Proceedings of International Topical
Meeting on Mathematics and Computation, Reactor Physics and Nuclear and Biological
Applications, Avignon, France, September 12 – 15 (2005)

4. A. Hakobyan, R. Denning, T. Aldemir, S. Dunagan, D. Kunsman, “Treatment of
Uncertainties in Modeling the Failure of Major RCS Components in Severe Accident
Analysis”, Proceedings of ANS Annual Meeting, Reno, NV, June 4 – 8 (2006)

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5. A. Hakobyan, R. Denning, T. Aldemir, S. Dunagan, D. Kunsman, “A Methodology for
Generating Dynamic Accident Progression Event Trees for Level-2 PRA”, Proceedings
of PHYSOR-2006 Meeting, Vancouver, CA, September 10-14 (2006)

6. B. Rutt, U. Catalyurek, A. Hakobyan, K. Metzroth, T. Aldemir, R. Denning, S.
Dunagan, D. Kunsman, “Distributed Dynamic Event Tree Generation for Reliability and
Risk Assessment”, Proceedings of CLADE 2006 Workshop, Paris, France, June 19
(2006)

FIELDS OF STUDY

Major Field: Nuclear Engineering

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TABLE OF CONTENTS

Page
Abstract ..............................................................................................................................ii
Dedication ..........................................................................................................................iv
Acknowledgements ............................................................................................................v
Vita .....................................................................................................................................vi

List of Tables .....................................................................................................................x
List of Figures....................................................................................................................xi
Nomenclature..................................................................................................................xviii

Chapters:

1. Introduction .................................................................................................................1

1.1 Problem description ..............................................................................................1
1.2 Objective and scope ..............................................................................................3
1.3 Dissertation overview ...........................................................................................4

2. Probabilistic risk assessment (PRA) ..........................................................................6

2.1 Historical remarks ................................................................................................6
2.2 Conventional PRA tools .......................................................................................7
2.2.1 Event tree analysis ................................................................................9
2.2.2 Accident progression event trees.........................................................11
2.3 Dynamic event tree methodology .......................................................................17

3. ADAPT methodology ...................................................................................................24

3.1 Mechanization of APET generation process ......................................................24
3.2 Uncertainty treatment in severe accident phenomena ........................................28
3.2.1 Creep rupture of major RCS components............................................30
3.2.2 Hydrogen combustion..........................................................................37
3.2.3 Containment overpressure failure.........................................................41
3.2.4 Power recovery ....................................................................................45
3.2.5 Pressurizer relief valve failure..............................................................56
3.3 Branch probability calculation ............................................................................58

4. Severe accident analysis code .......................................................................................62
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4.1 Description of severe accident codes..................................................................62
4.2 MELCOR severe accident simulation code........................................................67
4.2.1 General information............................................................................67
4.2.2 MELCOR execution and file structure...............................................70
4.2.3 MELCOR modules.............................................................................73
4.2.3.1 Control functions (CF) package...........................................76
4.2.3.2 Flow paths (FL) package.....................................................81
4.2.3.3 Executive (EXEC) package.................................................84
4.2.3.4 Burn (BUR) package...........................................................88

5. Test case.........................................................................................................................91

5.1 Reference power plant nodalization....................................................................91
5.2 Initiating event and accident progression ...........................................................96
5.3 MELCOR input deck...........................................................................................98

6. Application of ADAPT methodology..........................................................................103

6.1 Computational infrastructure.............................................................................103
6.1.1 System overview..............................................................................103
6.1.2 Database support .............................................................................106
6.1.3 Scheduler .........................................................................................107
6.1.4 Prototype implementation................................................................109
6.2 Linking ADAPT with severe accident simulation code ....................................112

7. Results and Analysis...................................................................................................122

7.1 Dynamic versus static APET analysis...............................................................122
7.2 Dynamic APET results from ADAPT example case........................................125
7.2.1 Early power recovery........................................................................125
7.2.2 Pressurizer SRV failure with power recovery at two hours..............129
7.2.3 Pressurizer SRV failure with power recovery at four hours.............132
7.2.4 Pressurizer SRV failure with power recovery at six hours...............141
7.2.5 Pressurizer SRV failure with power recovery at eight hours............151
7.2.6 Pressurizer SRV failure with no power recovery.............................162
7.2.7 No pressurizer SRV failure ..............................................................171
7.2.7.1 Power recovery at four hours ............................................171
7.2.7.2 Steam Generator tube rupture............................................179
7.2.7.3 Containment overpressure failure......................................186
7.3 General analysis of ADAPT results .................................................................197

8. Conclusion...................................................................................................................202

List of References............................................................................................................205

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