NUREG/CR-4551, Vol. 1, Rev. 1 "Evaluation of Severe Accident Risks: Methodology for the

296 Pages·2007·11.22 MB·English

NUREG/CR-4551
SAND86-1309
Vol. 1, Rev. 1
Evaluation of
Severe Accident Risks:
Methodology for the Containment,
Source Term, Consequence, and
Risk Integration Analyses
Prepared by
E. D. Gorham, R. J. Breeding, J. C. Helton, T D. Brown,
W. B. Muffin, F T Harper, S. C. Hora
Sandia National Laboratories
Operated by
Sandia Corporation
Prepared for
U.S. Nuclear Regulatory Commission
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NUREG/CR-4551
SAND86-1309
Vol. 1, Rev. 1
AN, XX
Evaluation of
Severe Accident Risks:
Methodology for the Containment,
Source Term, Consequence, and
Risk Integration Analyses
Manuscript Completed: October 1993
Date Published: December 1993
Prepared by
E. D. Gorham, R. J. Breeding, J. C. Helton', T D. Brown,
W. B. Muffin2, F. THarper, S. C. Hora3
Sandia National Laboratories
Albuquerque, NM 87185-5800
Prepared for
Division of Safety Issue Resolution
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC FIN A1322
'Arizona State University, Tempe, AZ 85287
2Technadyne Engineering Consultants, Inc., Albuquerque, NM, 87112
3University of Hawaii, Hilo, HI 96720-4091

ABSTRACT
NUREG-1l50 examines the risk to the public from five nuclear power plants. The
NUREG-IIS0 plant studies are Level III probabilistic risk assessments (PRAs) and,
as such, they consist of four analysis components: accident frequency analysis,
accident progression analysis, source term analysis, and consequence analysis.
This volume summarizes the methods utilized in performing the last three
components and the assembly of these analyses into an overall risk assessment.
The NUREG-1150 analysis approach is based on the following ideas: (1) general and
relatively fast-running models for the individual analysis components, (2) well-
defined interfaces between the individual analysis components, (3) use of Monte
Carlo techniques together with an efficient sampling procedure to propagate
uncertainties, (4) use of expert panels to develop distributions for important
phenomenological issues, and (5) automation of the overall analysis. Many
features of the new analysis procedures were adopted to facilitate a
comprehensive treatment of uncertainty in the complete risk analysis.
Uncertainties in the accident frequency, accident progression and source term
analyses were included in the overall uncertainty assessment. The uncertainties
in the consequence analysis were not included in this assessment. A large effort
was devoted to the development of procedures for obtaining expert opinion and the
execution of these procedures to quantify parameters and phenomena for which
there is large uncertainty and divergent opinions in the reactor safety
community.
iii

TABLE OF CONTENTS
FOREWORD ........................... ................................. xi
ACKNOWLEDGMENTS ........................ .............................. xv
ACRONYMS AND INITIALISMS ......... ................... ... ......... xvii
1.0 INTRODUCTION 1....1......1...................
1.1 Background ..................... ......................... 1.1
1.2 Objectives of the NUREG-1150 Study ..... ................. 1.2
1.3 Quality Control and Reviews .......... ................. .. 1.4
1.4 Organization of this Volume .......... ................. .. 1.6
1.5 References ................... ......................... 1.7
2.0 REPRESENTATION OF RISK IN NUREG-1150 .......... ................ 2.1
2.1 Representation of Risk ............. ................... 2.1
2.2 References ................. .......................... .... . 2.3
3.0 IDEAS UNDERLYING THE COMPUTATIONAL FRAMEWORK ..... ........... .. 3.1
3.1 General and Relatively Fast-Running Models ... ......... .. 3.1
3.2 Well-Defined Interfaces ...... ................. ....... .. 3.3
3.3 Monte Carlo Techniques ............... ............... . ... 3.5
3.4 Use of Expert Panels ............. .................... 3.7
3.5 Automation of Overall Analysis .............. ......... .. 3.7
3.6 References ..................... ......................... 3.10
4.0 STRUCTURE OF THE NUREG-1150 PLANT STUDIES ........... .............. 4.1
4.1 Accident Frequency Analysis .......... ................. .. 4.1
4.2 Accident Progression and Containment Response Analysis . . 4.4
4.3 Source Term Analysis ............... .................... 4.5
4.4 Consequence Analysis ............. .................... 4.7
4.5 Propagation of Uncertainties ........... ................ 4.10
4.6 Calculation of Risk ................ ..................... .. 4.16
4.7 References ..................... ......................... 4.18
5.0 INTERFACE OF ACCIDENT SEQUENCE FREQUENCY ANALYSIS WITH
THE ACCIDENT PROGRESSION ANALYSIS .......... ................. .. 5.1
5.1 Introduction ................. ........................ 5.1
5.2 Initiating Events .............. ...................... .. 5.1
5.3 Accident Sequence Analysis ........... ................. 5.2
5.4 Plant Damage States .............. ..................... .. 5.8
5.5 Core Vulnerable Sequences ............ .................. .. 5.10
5.6 Products of the Accident Frequency Analysis . . ......... .. .5.10
5.7 References ..................... ......................... 5.16
6.0 ACCIDENT PROGRESSION AND CONTAINMENT RESPONSE ANALYSIS .. ...... 6.1
6.1 Introduction ................... ........................ 6.1
6.2 Description of the Accident Progression Event Trees ....... .. 6.2
6.3 Quantification and Evaluation of the APETs ....... ......... 6.7
6.4 Grouping of Event Tree Outcomes ........ ............... .. 6.8
v
TABLE OF CONTENTS (continued)
6.5 Products of Accident Progression Analysis ......... . 6.12
6.6 References . . . . . . . . . . . . . . . . . . . . . . . . * 6.20
7.0 SOURCE TERM ANALYSIS ............. 7.1
7.1 Introduction ... 7.1
7.2 Decomposition of Release Fractions . . . 7.3
7.3 Development of Source Term Data Base . . 7.6
7.4 Mapping from Accident Progression Bins to Source Term Data
Base . . . . . . . . . . . . . . . . . . 7.7
7.5 The XSOR Codes ............. 7.8
7.6 Source Term Partitioning ........ 7.9
7.7 Source Term Risk Results ........ 7.10
7.8 References . . . . . . . . . . . . . . . 7.13
8.0 OFFSITE CONSEQUENCE ANALYSIS ............... 8.1
8.1 Introduction . . . . . . . . . . . . . . . . . . . . 8.1
8.2 Assessment of Pre-Accident Inventories ....... 8.1
8.3 Transport, Dispersion, and Deposition of Radioactive
Material . . . . . . . . . . . . . . . . . . . . . . 8.2
8.4 Calculation of Doses . . . . . . . . . . . . . . . . 8.3
8.5 Mitigation of Doses by Emergency Response Actions . . 8.3
8.6 Health Effects Modeling .......... ................ 8.4
8.7 Products of Offsite Consequence Analysis .... . . 8.5
8.8 References . . . . . . . . . . . . . . . . . . . . . 8.8
9.0 CHARACTERIZATION AND COMBINATION OF UNCERTAINTIES ........ 9.1
9.1 Overview . . . . . . . . . . . . . . . . . . . . . . 9.1
9.2 Types of Uncertainty . . . . . .. . . . . . . . . . 9.5
9.3 Use of Expert Opinion . .. . . .. . . .. . . . . 9.7
9.3.1 Steps to Elicit Expert Judgment ........ 9.8
9.3.2 Selection of Issues ...... ............ 9.8
9.3.3 Selection of Experts ...... .... 9.15
9.3.4 Elicitation Training .......... 9.15
9.3.5 Training Topics ........ .............. 9.15
9.3.6 Presentation of Issues ......... 9.16
9.3.7 Preparation and Discussion of Analyses 9.17
9.3.8 Elicitation ...... ................. . 9.17
9.3.9 Recomposition and Aggregation of Results 9.17
9.3.10 Review . . . . . . . . . . . . . . . . . 9.18
9.3.11 Documentation .......... ............... 9 .18
9.4 References . . . . . . . . . . . . . . . . . . . . . 9.19
APPENDIX A DESCRIPTION OF SUITE OF CODES USED TO CALCULATE
RISK
A.1 Introduction . . . . . . . . . . . . . . . . . . . . A.1
A.2 Input From Level I Analysis ............. A.I
A.3 Latin Hypercube Sample ............... A. 6
A.4 Accident Progression Analysis .... ... .... A.7
A.5 Source Term Analysis . . . . . . . . . . . . . . . . A.9
vi
TABLE OF CONTENTS (continued)
A.6 Consequence Analysis . . . . . . .. . . . . . . . . . A.II
A.7 Risk Integration . . . . . . . . . . . . . . . . . . . A.12
A.8 References . . . . . . . . . . . . . . . . . . . . . . A. 13
APPENDIX B RISQUE CODE DESCRIPTION
B.1 Description of the RISQUE Code ..... B.
B.1.1 Purpose of Code ... ........ B.
B.1.2 Calculation of Risk ....... B.
B.1.3 Structure of Code ......... B. 3
B.1.4 Input Data Requirements . . . B. 5
B.1.5 Output Data .... .......... B.9
B.1.6 Listing of Typical Data Files (Version 2--
RISQUE 2) . . . . . . . . B.II
B.1.7 Parameter Values (Dimensions) B.26
B.1.8 References . . . . . . . . B.27
B.2 Listing of the RISQUE Code ....... B.28
APPENDIX C ANALYSIS OF ACCIDENT PROGRESSION AND
CONTAINMENT RESPONSE
C.l Introduction CAI
C.2 Capabilities of the EVNTRE Code .... ........ C.
C.2.1 General Features of EVNTRE . ... C.2
C.2.2 Types of Questions ........ C. 3
C.2.3 Case Structure .......... C.5
C.2.4 Sampling and File Structure . ... C. 8
C.3 Event Tree Development ............ C.9
C.3.1 Information Required for Event Tree Development C.9
C.3.2 Definition of Time Periods .... C.ll
C.3.3 Initial Conditions ........ C.12
C.3.4 Period before Vessel Breach .... C. 14
C.3.5 Period around Vessel Breach .... C.16
C.3.6 Period after Vessel Breach .... C.18
C.3.7 Very Late Period ......... C.18
C.3.8 Summary Questions .... .......... C.19
C.3.9 Development of the Binner ........ C.19
C.3.10 Documentation ...... ............ C.21
C.4 Quantification . . . . . . . . . . . . . . . . C.22
C.5 Evaluation and Rebinning ........... C.23
Computer Evaluation of the Event Tree C.23
C.5.2 Rebinning of the APBs and other Postprocessing C.25
C.6 References . . . . . . . . . . . . . . . . . . . . . . . . C.27
vii
LIST OF FIGURES
Figure Page
1 Back-End Documentation for NUREG-1150 .... ........... .. xiii
2-1 Example Exceedance Frequency Curve ..... .............. ... 2.2
3-1 Relationship of the computer codes used in the
risk analyses for NUREG-I150 ........ ................ .. 3.9
4-1 Risk analysis parts and interfaces ..... .............. ... 4.2
4-2 Example exceedance frequency curve ...... .............. .. 4.9
4-3 Equation 4.9 expanded to show the matrices and
the individual observations in the sample explicitly ........ 4.12
4-4 Example of family of exceedance frequency curves .......... .. 4.13
4-5 Representation of risk results as an estimate of a
probability density function (right axis) and as an
estimate of a cumulative distribution function (left axis). 4.15
5-1 Systemic Event tree for TlS-Station blackout
at Surry Unit 1 ........................................... 5.3
5-2 Cumulative distribution for core damage
frequency for Surry ............... ..................... .. 5.12
6-1 Schematic representation of an accident
progression event tree ............ .................... .. 6.6
6-2 Distribution of frequencies of summary APB
groups for Surry ................ ...................... 6.13
6-3 Conditional probability of core damage arrest for internal
I initiators at Surry ............... .................... 6.17
6-4 Conditional probability of early containment failure for
internal and fire initiators at Surry ....... ........... 6.18
6-5 Mean probability of the summary APBs for each summary PDS
group for Surry - internal and fire initiators . ... ..... .. 6.19
7-1 Exceedance frequency curves for the iodine release fraction
for internal initiators at Surry ........ .............. 7.12
8-1 Example Display of Offsite Consequences Complementary
Cumulative Distribution Function ............ .............. 8.6
9-1 Principal steps in Obtaining Expert Opinion ..... ......... 9.9
A-la NUREG-1150 Level II/III PRA Calculational Scheme .... ...... A.2
A-lb' NUREG-1150 Level II/III PRA Calculational Scheme ..... ..... A.3
A-ic NUREG-1150 Level II/III PRA Calculational Scheme .... ...... A.4
A-ld NUREG-1150 Level II/III PRA Calculational Scheme .... ...... A.5
viii