Internal and External Hazard Analyses for PSA

1. Internal and External Hazard Analyses for PSA Workshop Information Purpose: To present and explain the Internal and External Hazard Analysis Learning objectives: To get a global overview of Internal and External Hazard Analysis (Internal Fire, Internal Flood, Earthquake) within PSA framework, to understand specific characteristics of Internal and External Hazard Analysis and the main phenomena and methodologies applied to Internal and External Hazards and to know qualitative and quantitative screening process Duration: 1 and 1/2 hours Resources: screen, video projector, PC, PowerPoint 2000� Purpose: To present and explain the Internal and External Hazard Analysis Learning objectives: To get a global overview of Internal and External Hazard Analysis (Internal Fire, Internal Flood, Earthquake) within PSA framework, to understand specific characteristics of Internal and External Hazard Analysis and the main phenomena and methodologies applied to Internal and External Hazards and to know qualitative and quantitative screening process Duration: 1 and 1/2 hours Resources: screen, video projector, PC, PowerPoint 2000�

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

3. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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. The lecture can start with a brief introduction to explain the concepts and the main characteristics of the internal and external hazards and their risk relevanceThe lecture can start with a brief introduction to explain the concepts and the main characteristics of the internal and external hazards and their risk relevance

4. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 4 General Steps of the Analysis The lecturer should explain the general steps of the internal and external hazards analysis although latterly the specific characteristic of each hazard analysis will be developed The lecturer should explain the general steps of the internal and external hazards analysis although latterly the specific characteristic of each hazard analysis will be developed

5. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer should emphasise the main differences that exist between internal and external event analysis that justify different methodological analysis approachesThe lecturer should emphasise the main differences that exist between internal and external event analysis that justify different methodological analysis approaches

6. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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) The lecturer should explain the main steps of a Hazard Analysis in the framework of the PSA. The different steps will be developed lately.The lecturer should explain the main steps of a Hazard Analysis in the framework of the PSA. The different steps will be developed lately.

7. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 7 Overview of Initiating Events Analysis Employing this slide the lecturer can explain the initiating events analysis as a part of the hazard analysis. The lecturer should emphasise the screening process in order to select the relevant initiators and simplify the analysis.Employing this slide the lecturer can explain the initiating events analysis as a part of the hazard analysis. The lecturer should emphasise the screening process in order to select the relevant initiators and simplify the analysis.

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

9. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer should explain the different points of the internal fires analysis. The first step is the definition of fire compartments/zones. The criteria for defining the zones should be described. The information related to the zones that is necessary to take into account in the fire analysis should be described: cable/equipment contained in the zone, doors, penetrations, detection and suppression fire systems, etc.The lecturer should explain the different points of the internal fires analysis. The first step is the definition of fire compartments/zones. The criteria for defining the zones should be described. The information related to the zones that is necessary to take into account in the fire analysis should be described: cable/equipment contained in the zone, doors, penetrations, detection and suppression fire systems, etc.

10. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 10 Examples of Fire Related Phenomena This slide will be used to describe briefly some of the fire related phenomena that must be considered in the fire analysis.This slide will be used to describe briefly some of the fire related phenomena that must be considered in the fire analysis.

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

12. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 12 Methodology Qualitative screening Fire frequency analysis Quantitative screening Quantitative detailed analysis Interpretation of Results, Sensitivity, Uncertainty Analysis This slide defines the main points of the fire analysis methodology that is developed in the following slidesThis slide defines the main points of the fire analysis methodology that is developed in the following slides

13. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 13 Overview of Fire PSA Main Tasks The lecturer can use this slide to give a global explanation of the fire analysis main tasks and its relationships.The lecturer can use this slide to give a global explanation of the fire analysis main tasks and its relationships.

14. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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) The lecturer will explain the main tasks that is necessary to carry out as part of the qualitative screening activity with this slide and the next one. The screening criteria should be explained clearly The lecturer will explain the main tasks that is necessary to carry out as part of the qualitative screening activity with this slide and the next one. The screening criteria should be explained clearly

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

16. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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) This slide presents some examples of typical initiating events that can be caused by a fire. The lecturer may develop this subject explaining with some example the way the fire can provoke the initiating eventsThis slide presents some examples of typical initiating events that can be caused by a fire. The lecturer may develop this subject explaining with some example the way the fire can provoke the initiating events

17. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 17 Components and Cables vs. Fire Zones Data Base The lecturer may use this slide to explain the utility of creating a data base with data related to the fire zones defined and the cables contained in them to make searches and make the analysis easierThe lecturer may use this slide to explain the utility of creating a data base with data related to the fire zones defined and the cables contained in them to make searches and make the analysis easier

18. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer should describe the conservatisms used in the screening analysisThe lecturer should describe the conservatisms used in the screening analysis

19. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer should describe the steps of the detailed fire analysis for the compartments not screened out. A specific example could be useful to clarify the explanationThe lecturer should describe the steps of the detailed fire analysis for the compartments not screened out. A specific example could be useful to clarify the explanation

20. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 20 Steps of the Fire Analysis (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

21. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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:SCDFi = S( IEi * CCDPj) The lecturer should explain the calculation of the core damage frequency contribution due to fire eventsThe lecturer should explain the calculation of the core damage frequency contribution due to fire events

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

23. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 23

24. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 24 Overview of Flood PSA Main Tasks The lecturer can use this slide to give a global explanation of the flood analysis main tasks and its relationshipsThe lecturer can use this slide to give a global explanation of the flood analysis main tasks and its relationships

25. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer should describe the different steps of the flood analysis with special emphasis in the screening process and the quantitative and qualitative criteria for screening out zonesThe lecturer should describe the different steps of the flood analysis with special emphasis in the screening process and the quantitative and qualitative criteria for screening out zones

26. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 26 Steps of the Flood Analysis (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 The lecturer should describe the conservatisms used in the screening analysisThe lecturer should describe the conservatisms used in the screening analysis

27. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 27 Steps of the Flood Analysis (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 The lecturer should describe the steps of the detailed flooding analysis for the compartments not screened out. A specific example could be useful to clarify the explanationThe lecturer should describe the steps of the detailed flooding analysis for the compartments not screened out. A specific example could be useful to clarify the explanation

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

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

30. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 30

31. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer can use this slide to give a global explanation of the seismic hazard analysis main tasksThe lecturer can use this slide to give a global explanation of the seismic hazard analysis main tasks

32. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 32 Method of Analysis The method used requires specialist estimates inputs: The inputs required for the seismic analysis should be described The inputs required for the seismic analysis should be described

33. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 33 Overview of Seismic PSA Procedure The lecturer can use this slide to give a global explanation of the seismic PSA procedureThe lecturer can use this slide to give a global explanation of the seismic PSA procedure

34. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The main subtasks of the seismic PSA analysis should be described. Additionally, a specific example can be used. The main subtasks of the seismic PSA analysis should be described. Additionally, a specific example can be used.

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

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

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

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

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

40. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 40 Example of the Floor Response Spectra at + 3.20 m Level

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

42. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 42 Fragility Analysis (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 = Am er eU where Am is the median ground acceleration capacity, and er and eU are two lognormally distributed variables with logarithmic standard deviations of �r and �U respectively. The first variable, er, essentially represents randomness in earthquake energy content, whereas eU 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 Am, �r, and �u.

43. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 0.05. Any component or structure that has a HCLPF greater than a pre-determined 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.

44. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 44

45. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer should emphasise the importance of analysing the external hazards and the necessity of calculating its contribution to the CDFThe lecturer should emphasise the importance of analysing the external hazards and the necessity of calculating its contribution to the CDF

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

47. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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)

48. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 48

49. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 The lecturer can use this slide to give a global explanation of the external events PSA methodologyThe lecturer can use this slide to give a global explanation of the external events PSA methodology

50. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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)

51. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 51 Qualitative Screening (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

52. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 52 Qualitative and Site-Independent Screening The generic list of potential OEEs can be screened to eliminate events from further consideration and to consolidate the other remaining events to the maximum extent possible. The largely qualitative screening criteria, which were applied on a site specific basis, included the following:

53. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 53 Candidate External Events for Screening

54. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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 !

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

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

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

58. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 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)

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