Internal and External Hazard Analyses for PSA. Workshop Information IAEA Workshop

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1 IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making Internal and External Hazard Analyses for PSA Lecturer Lesson Lesson IV IV 3_7.4 3_7.4 Workshop Information IAEA Workshop City, XX XX - City -XX, Country Month, Year Year

2 Contents Introduction General Steps of the Analysis Important Considerations Analysis of Internal Fires Analysis of Internal Floods Analysis of External Hazards Seismic Hazards Other External Hazards IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 2

3 Introduction Internal and external HAZARDS (sometimes referred to as external events) often create extreme environments common to several plant systems They often lead to initiating events (as understood in the PSA) thus they are core damage sequence initiators Internal hazards include 1) internal fires, 2) internal floods and 3) missiles External hazards include earthquakes, external floods, external fires, high winds, aircraft crash, transportation accidents, etc. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 3

4 General Steps of the Analysis CHARACTERIZATION OF THE HAZARD Understand the the hazard, its its frequency and and impact INITIATING EVENT ANALYSIS PLANT RESPONSE ANALYSIS Identify what internal initiating events can can be be caused by by the the hazard, e.g., Transients, LOCA, LOSP events Analyze the the response of of the the plant to to the the initiating events and and how this this response is is affected by by the the hazard IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 4

5 Important Considerations The treatment of dependent failures may cause difficulties if the failure correlation is not understood. The analysis needs to consider both, externally induced failures as well as unrelated failures caused by internal plant faults. Another important issue is the treatment of human actions. Stress levels and conditions in the plant may differ considerably from the ones after an internal initiating event. Because of the complexity and scope of these analyses, screening techniques may be used. The screening criteria needs to be adequate so that important scenarios are not excluded from the analyses. Hazard analyses need to be supported by local plant walk-downs in order to obtain site and plant specific information. Since plant walk-downs can be significant inputs to the analyses, it is necessary that these walk-downs are well planned and thoroughly documented IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 5

6 Steps of the Hazard Analyses for PSA Hazard identification and calculation of its frequency and impact Calculation of the risk: Definition of Initiating Events Modifications to the existing event trees and fault trees Specific CCF analysis Specific data analysis Specific HRA Quantification. Results of the analysis. Sensitivity, uncertainty and importance analyses Documentation (with special attention to assumptions and references used in the analysis) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 6

7 Overview of Initiating Events Analysis Selection Selection of of initiating initiating events events Parameter Parameter definition definition for for each each initiator initiator Screen out Screening Detailed screening by frequency Approximate screening by impact Detailed Detailed parametrization parametrization of of each each initiator initiator Sensitivity Sensitivity analysis analysis Hazard Hazard analysis analysis (frequency (frequency vs. vs. size) size) Plant response DOCUMENTATION IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 7

8 ANALYSIS OF INTERNAL FIRES IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 8

9 Fire Compartments/Zones Plant is divided into fire zones which consist of one or more rooms in various structures Cable/equipment associated with each division are located usually in separate fire zones Fire zones are physically separated from one another by fire rated floors, walls, and ceilings Correspondingly rated doors and penetration seals, HVAC ducts usually equipped by flaps Fire rating of the boundaries is XX minutes Fire suppression systems in the fire zones IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 9

10 Examples of Fire Related Phenomena impact of smoke nt on equipment and human performance ventilation duct ignition frequency, fire growth, and fire impact multi-compartment propagation damaged barrier impact of heat on equipment close to walls in adjacent compartments IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 10

11 Other Fire Related Phenomena that Need to be Considered Electrical faults (open circuits, shorts to ground, short circuits and hot shorts) which can lead to: loss of equipment function spurious actuation of equipment (e.g., undesired reconfiguration of valves or actuation of inactive systems) loss and/or false signals and indications secondary fires, etc. Explosions Collapse of structures Missiles IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 11

12 Methodology Qualitative screening Fire frequency analysis Quantitative screening Quantitative detailed analysis Interpretation of Results, Sensitivity, Uncertainty Analysis IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 12

13 Overview of Fire PSA Main Tasks Plant Plant Information Information Collection Collection Plant Plant Walkdowns Walkdowns Cable Cable Routing Routing Information Information and and Cable Cable Location Location Database Database Initiating Initiating Events Events Caused Caused by by a Fire Fire and and Compilation Compilation of of PSA PSA Components Components List List Fire Fire Zone Zone Definition Definition Multi-Compartment Multi-Compartment Fire Fire Analysis Analysis SCREENING qualitative quantitative Human Human Error Error Probability Probability Analysis Analysis Fire Fire Frequency Frequency Evaluation Evaluation Control Control Room Room and and Cable Cable Spreading Spreading Room Room Analysis Analysis + Circuit Circuit Analysis Analysis Detailed Analysis and and Verification Walkdown Risk Risk Contributors Identification, Uncertainty and and Sensitivity IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 13

14 Qualitative Screening MAIN TASKS: Define and locate independent fire zones Define post fire stable states and functions/systems required Define fire initiating events in each zone Identify equipment/cables in each fire zone Screen out fire zones based on the minimal qualitative impact (non-safety related equipment) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 14

15 Qualitative Screening MAIN TASKS: Define and locate independent fire zones Define post fire stable states and functions/systems required for such states Define fire initiating events in each zone Identify equipment/cables in each fire zone Screen out fire zones based on the minimal quantitative impact (using conservative assumptions), i.e. CDF < 1E-7/year IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 15

16 Examples of Fire Initiating Events for Each Fire Zone Examples of initiators caused by a fire: Total or Partial Loss of Off-Site Power LOCAs (PORV, RPV Head Vent and Pressurizer Vent spurious opening, etc.) Transient without Loss of AFW/MFW Transient with Loss of AFW/MFW Steam Line Breaks (TBV, ADV opening) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 16

17 Components and Cables vs.. Fire Zones Data Base Search 1 COMPONENT Name Result 2 List of Components and Cables Located in the Compartmo m p ent XX 000 records Power Cable Data DATA BASE DATA SELECTION PR OC EDURES I&C Cable Data Component L ocation Data Result 1 Info rm ation fo r Identification of IEs in plant compartments List of Compartments Where Associated Cables are Located Search 2 COMPARTMENT Name Compartments Containing Different Trains of Cables Info rm ation fo r Initial S creenin g Task Fire zones/compartments definition Definition of pathways for fire effect propagation IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 17

18 Example of Fire Assumptions Used for Screening Process Given a fire all equipment in the fire zone (compartment) is assumed to fail Lack of credit for manual fire suppression Credit for fire propagation pathways Assumed standard fire protection program to be implemented to prevent inter-zone fire propagation IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 18

19 Steps of the Fire Analysis For each compartment not screened out: Identification of potential fire sources and targets, fire loads, detection and suppression equipment, passive protections, fire spreading paths, equipment located in the compartment, cable routings Fire barriers and propagation analysis Evaluation of fire frequency IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 19

20 Steps of the Fire Analysis (Cont( Cont.) For each compartment not screened out (cont.): Analysis of fire growth, including consideration of automatic/manual fire fighting actions, and effects of fire heat and smoke (including propagation to neighbouring compartments) Identification of initiating events which can be caused by fire in each compartment Analysis of the impact of fires on equipment (mechanical, I/C, electrical) with special emphasis on cables and hence system functions which may be affected by fires Analysis of the impact of fires on human performance (modification of existing Level 1 internal IE HRA) Modification of existing PSA models to reflect the identified fire scenarios Quantification and analysis of results IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 20

21 CDF Calculation CDF contribution is calculated for each fire zone IE frequency established for given fire zone is multiplied by CCDP for CDFi associated with that zone CDFi = IEi * CCDPj Contributions from all fire zones are summed: ΣCDFi = Σ( IEi * CCDPj) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 21

22 Examples of Screening Results 404 fire zones in 10 buildings evaluated 187 fire zones screened out qualitatively 217 fire zones evaluated quantitatively 195 fire zones screened out with CDF < 1E-6/yr 22 fire zones refined further for detailed analysis with realistic assumptions IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 22

23 ANALYSIS OF INTERNAL FLOODS IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 23

24 Overview of Flood PSA Main Tasks Plant Plant Information Information Collection Collection and and Plant Plant Walkdowns Walkdowns Identification Identification of of Flood Flood Sources Sources in in Plant Plant Compartments Compartments Flood Flood Frequency Frequency Evaluation Evaluation Identification Identification of of Flood Flood Scenarios Scenarios (equipment (equipment damage damage and and flood flood propagation propagation paths) paths) SCREENING qualitative quantitative Detailed Analysis and and Verification Walkdown Risk Risk Contributor Identification, Uncertainty and and Sensitivity IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 24

25 Steps of the Flood Analysis Identification of flooding compartments: Location of flood compartment boundaries/barriers Capacity of drainage systems Communications with other compartments Location of flood susceptible equipment Identification of flooding sources: e.g., ruptures in water systems (service water, etc.) Location and total volume of potential flood sources IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 25

26 Steps of the Flood Analysis (Cont( Cont.) Screening analysis Designation of independent flood areas/compartments Identification of flood susceptible equipment, flood propagation pathways Identification of potential initiating events due to flood e.g., flooding of switchgears, I&C systems, MCR, etc. Flood frequencies assessment Qualitative screening of non risk significant flood areas Quantitative screening scenarios with CDF < 1E-7/year screened out from consideration using usually conservative criteria, e.g. all affected equipment in the flooding scenario would fail IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 26

27 Steps of the Flood Analysis (Cont( Cont.) Detailed analysis of flooding risk Determination of realistic flood frequency (pipe break frequency) Determination of size of flood sources (flow rate, inventory) Considering of flood mitigating features (drainage, doors, alarms, procedures...) Identification of significant Flood Damage States Timing calculations (flood level vs. time) for recovery Human reliability analysis (HRA) re-assessment Development of Event Tree / Fault Tree models for each scenario (often based on ET/FTs from internal events PSA) Quantification of corresponding ETs/FTs with flood affected equipment failed and analysis of results including sensitivity and uncertainty analysis IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 27

28 Examples of Screening Results 37 flood areas in 19 buildings evaluated 25 flood areas screened out qualitatively 5 flood areas screened out quantitatively (IE frequency < 1E-6/year) 6 flood areas refined further for detailed analysis and quantification IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 28

29 Examples of Results Flood Damage State FDS 3: CDF = 9.44E-7/year This scenario initiates as a flood in the Turbine Building. Flood growth is unmitigated and propagation occurs into the 6 kv transformer building (Building 500). At flood elevations above 0.0 m, this flood is postulated to fail the 220V DC, 0.4 kv AC or 6 kv AC non-safety switchgear, causing a loss of breaker control and leading to a Loss of Off-Site Power transient. For the quantification, no credit was taken for recovery of offsite power. The IE frequency for this FDS is 1.1E-4/year. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 29

30 ANALYSIS OF SEISMIC HAZARD IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 30

31 Seismic Hazard Analysis Overview Seismic Hazard Analysis Seismic Inputs - History, Geology Seismic Hazard Curves Ground and Floors Response Spectra Component and Structures Fragility Analysis Fragility Screening Analysis Modification of PSA and Quantification IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 31

32 Method of Analysis The method used requires specialist estimates inputs: SEISMOLOGY: occurrence frequencies and magnitudes of earthquakes that can affect the site STRUCTURAL MECHANICS: effects of earthquakes on the plant structures/components HAZARD CURVES, which give the frequency of exceedance as a function of ground motion acceleration FRAGILITY CURVES representing the probability of component failure as a function of the same ground motion acceleration used in the hazard description The estimates of the IMPACT OF SEISMIC EVENTS ON CDF is determined by integrating the work of these specialists by PSA personnel with modifications to the Event Trees and System Fault Trees developed in the modeling of internal events IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 32

33 Overview of Seismic PSA Procedure IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 33

34 Major Subtasks Development of a seismic hazard curves Structure and component seismic response determination Assignment of structure and component fragility Random failure data development Event/Fault tree modification and solution Risk quantification incorporating results of subtasks above IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 34

35 IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 35

36 Seismic Hazard Curves Major Subtasks Developing the seismic hazard curves consists of the following steps: Compilation of an earthquake catalogue Identification of seismic source zones Development of an empirical intensity-frequency relationship for each seismic zone Establishment of a distance-intensity relationship for each zone (attenuation equation) Establishment of a relationship between site-intensity and PGA The final output of the analysis is a set of seismic hazard curves which depict the annual frequency of exceeding different levels of ground motion (typically, the peak ground acceleration PGA) at the NPP site IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 36

37 Example of Seismic Hazard Curves IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 37

38 Load Analysis An earthquake may be characterized by a relatively small number of parameters (typically PGA for earthquakes). Its impact on the plant is much more difficult to characterize, because of the structure itself influences the transmission of loads from the ground motion to the components located at different elevations at the plant structures. Acceleration amplification factor by the cantilever action of tall buildings. Damping effect of seismic snubbers Careful attention should be paid to the frequency content of the response spectrum of the earthquake. High magnitude earthquakes - rich in low frequency (0,5-5 Hz) - strong effect on the structures Local earthquakes with low magnitude - have high frequency ( > 10 Hz) components of ground motion - strong effect on the equipment in the structures IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 38

39 Floor Response Spectra 3D Finite Element Model development for the reactor building and other essential plant structures Dynamic analysis using e.g. modal superposition method and the corresponding software, e.g. NISA II (developed by Engineering Mechanics Research Corp., USA). Load analysis in terms of floor response spectra generation at several locations in the buildings where different safety related equipment is mounted Pumps electrical relay and junction boxes rod drive mechanism IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 39

40 Example of the Floor Response Spectra at m Level IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 40

41 Fragility Analysis The objective of this task is to determine the probability of failure of specific components or structures, given the loads experienced by an earthquake. Fragility is defined as the probability of failure as a function of the size of the input load. Usually, the input load is parameterized in terms of a single variable (e.g. PGA for earthquakes). The results of the evaluation of the probabilities of failure resulting from an earthquake are given as fragility curves which give the probability of failure as a function of the same parameter used to characterize the seismic hazard, namely PGA. Key part of the fragility analysis must be to determine the extent to which the fragility is uncertain because of approximation in the parameterization of the load size. For example, although PGA is widely used to parameterize earthquake size, it is an incomplete attribute. At a given site, different types of earthquake can produce the same PDA value. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 41

42 Fragility Analysis (Cont( Cont.) The entire fragility family for a component corresponding to a failure mode can be expressed in terms of the best estimate of a median input motion parameter and two random variables: A = A m ε r ε U where A m is the median ground acceleration capacity, and ε r and ε U are two lognormally distributed variables with logarithmic standard deviations of βr and β U respectively. The first variable, ε r, essentially represents randomness in earthquake energy content, whereas ε U represents the uncertainty in determining the parameter. Fragility evaluations are presented for each of the components and structures identified as being significant, in terms of the parameters A m, βr, and βu. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 42

43 Fragility Screening Analysis The screening criterion is based on the concept of "High Confidence of Low Probability of Failure" (HCLPF) ground motion acceleration. The HCLPF ground motion acceleration for a structure or a component is the acceleration at which there is a 95% confidence that the failure probability will be less than Any component or structure that has a HCLPF greater than a predetermined cutoff value derived from the hazard curves can be discarded from further inclusion in the analysis. This cut-off value may be taken from a representative hazard curve, for example the mean hazard curve. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 43

44 ANALYSIS OF EXTERNAL HAZARDS IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 44

45 Facts on External Hazards External hazards can make a significant contribution to the plant risk It is widely recognized that such hazards should be included in the PSA External hazards arise from outside the plant and are accidental in nature External hazards have a potential for affecting many different pieces of equipment simultaneously IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 45

46 Hazard Identification and Characterization Identification of the possible types of external hazards to which the plant is exposed Determination of the frequency of those hazards that are considered important Example: The seismic hazard is usually represented in the form of a frequency of exceedance as a function of some measure of acceleration IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 46

47 Hazard Identification and Characterization These external events are always site-dependent, and are often design-dependent Generally earthquakes, floods, high winds and man induced hazards have emerged as being risk-significant. However, because of the site dependency, the consideration of only these hazards could make the analysis incomplete The following table is meant to be illustrative only. Common sense must be used, as a starting point, to eliminate those initiators that simply do not occur at the site or have a very low probability. After this first rough screening process, a more sophisticated screening analysis will be required (by impact and by frequency) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 47

48 ORIGIN PRINCIPAL PHENOMENA ASSOCIATED TOPIC Natural Events From the Earth Earthquakes Capable faults, liquefaction, vibratory ground motion Volcanoes Ejected missiles, lava, mud flow, poisonous volcanic ash gases, Soil failures Slope instability, subsidence, swelling clays, karst collapse From water River floods Dam failure, extreme rainfall, snowmelt Coastal floods Tsunami, seiche wind generated high waves From air Transportation (airports, railways, highways,,river traffic) Nearby hazardous facilities (pipelines, petrochemical, facilities, factories, etc.) Extreme meteorological conditions High winds Lightning Meteorites Man induced events Temperature, rain, snow Hurricanes, tornadoes, cyclones, sand storms, fire Aircraft impact, explosion, missiles, vibrations Drifting clouds, explosions, missiles, vibration, toxic gases IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 48

49 External Events PSA Methodology A SUCCESSIVE SCREENING PROCESS, with detailed analyses being performed only for those events, which cannot be eliminated by the screening process. The successive screening methodology allows a comprehensive approach, concentrating the efforts in the areas with the most risk potential. The successive screening analysis used involves the following steps: Identification of candidate OEE that may impact the plant Qualitative external event screening Plant specific qualitative and quantitative screening with supporting detailed analysis IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 49

50 Qualitative Screening Identification of candidate external events that may impact the plant based on generic list of OEEs : Identification of industrial activity in the near vicinity of the plant site Hazardous material use/storage locations within 10 km of plant - survey and inventory, location, quantity Transportation of hazardous materials near the plant site vicinity Highway transport Railway transport Waterway transport (if applicable) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 50

51 Qualitative Screening (Cont( Cont.) On-site inventory of hazardous materials Inventory of hazardous flammable materials and gases Inventory of toxic materials and gases Gather historical record of meteorological extremes and severe natural phenomena Temperatures Severe winds Floods/dam failure incidents Assemble comprehensive list of candidate external events that may impact the plant IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 51

52 Qualitative and Site-Independent Screening The generic list list of of potential OEEs can can be be screened to to eliminate events from further consideration and and to to consolidate the the other remaining events to to the the maximum extent possible. The The largely qualitative screening criteria, which were applied on on a site site specific basis, included the the following: Cr it er ion 1: Cr it er ion 2: The event is not as sever e as t he plant design basis def ined in t he plant docum ent at ion. The event is included in anot her event def init ion. Cr it er ion 3: The event cannot occur near a plant. Cr it er ion 4: Cr it er ion 5: The cor e dam age event has a sit e-independent f r equency of 1.0E-7/ year or less. The event is analyzed in t he special analysis. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 52

53 Candidate External Events for Screening EVENT SOURCE SCREENING CRITERION REMARKS Aircraft Impact PRA Procedures Guide 4 Based upon plant-specific review Avalanche PRA Procedures Guide 3 No potential for occurrence Coastal Erosion PRA Procedures Guide 3 No potential for occurrence Drought PRA Procedures Guide 1 Little effect on the ultimate heat sink Dam Failure PRA Procedures Guide 2 Included in external flooding review Extreme Winds and Tornadoes PRA Procedures Guide NONE Plant-specific review required Fog PRA Procedures Guide 2 Effects on transportation accident rates included in the data for these events Frost PRA Procedures Guide 2 Impacts of snow and ice govern Hail PRA Procedures Guide 2 Other types of missiles govern High, Tide, Lake Level, or River Stage PRA Procedures Guide 2 Included in external flooding review High Summer Temperature PRA Procedures Guide 1 Little effect on the ultimate heat sink Hurricane PRA Procedures Guide 2 Included in the external flooding and extrem e winds review Ice Cover PRA Procedures Guide 1 Little effect on the ultimate heat sink Industrial or M ilitary Facility Accident PRA Procedures Guide NONE Plant-specific review required IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 53

54 Qualitative Screening out Events Examples of screened out External Events: Screening criterion 3 Avalanche, Coastal Erosion, Landslide, Sand Storm, Seiche, Storm Surge, Tsunami, Waves, Volcanic Activity Screening criterion 4 (e.g. 1E-07/year) Meteorite Screening criterion 5 (special analysis) Internal Fires Internal Floods Seismic Hazard Analysis Note:! Screened out events are always site-specific! IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 54

55 Events Usually Requiring Plant Specific Review Aircraft Impact (commercial, military, private) Gas Pipeline Failure Extreme Winds and Tornadoes Industrial or Military Facility Accident External Fires External Floods Hazardous Material Transportation Accidents (highway, railway, waterway) Main Turbine-Generated Missiles IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 55

56 Plant Response Analysis Analysis of the probability of core melt Analysis of containment integrity Example: the impact of the earthquake on the plant structures and components is usually represented by fragility curves, that is curves representing the probability of failure as a function of strength of the earthquake. These failures have to be combined with the unrelated failures caused by internal plant faults or human errors IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 56

57 Analysis of In-Plant Accident Phenomena and Ex-Plant Consequences Some external hazards could compromise containment and accident mitigation systems and/or their supporting systems Some external hazards can cause significant off-site damage and therefore the emergency response personnel may not be available and the communications, evacuation and sheltering may be affected Consequently, the impact of external events on the results of a Level 2 and a Level 3 PSA may be more significant than on those of a Level 1 PSA IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 57

58 References IAEA-SAFETY SERIES No. 50-P-4, IAEA, Procedures for Conducting Probabilistic Safety Assessments of Nuclear Power Plants (Level 1), (1992) IAEA-Safety Report Series No. 10, Treatment of Internal Fires in Probabilistic Safety Assessment for Nuclear Power Plants, (1998) IAEA-SAFETY SERIES No. 50-P-7, Treatment of External Hazards in Probabilistic Safety Assessment for Nuclear Power Plants, (1995) IAEA-TECDOC-724, Probabilistic Safety Assessment for Seismic Events, (1993) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 58

59 References (Cont.) NRC Genetic Letter 88-20, Supplement 4 NUREG/CR-2300, PRA Procedures Guide, January, 1983 NUREG/CR-5042, Evaluation of External Hazards to Nuclear Power Plants in the US, Other External Events. Supplement 2, February, 1989 NUREG 1407 Procedural and Submittal Guidance of Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities, June, 1991 NUREG/CR-4839, Methods for External Events Screening Quantification - RMIEP Methods Development, July, 1992 IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 59