1. Version 1.0, May 2015 BASIC PROFESSIONAL TRAINING COURSE Module VIII Integrated risk informed decision making Case Studies This material was prepared by the IAEA and co-funded by the European Union.

2. Basic Professional Training Course; Module VIII Integrated risk informed decision making IRIDM The following slides present the basic elements of IRIDM. Whether these slides should be presented to students by the lecturer or be used for exercises in working groups where students should elaborate on these elements is left for the lecturer to decide. In case thy are used for exercise, students should be divided in smaller groups and each group should tackle one aspect of IRIDM. Each group should spend 2 – 3 hours discussing the topics and prepare a short presentation for the plenary session. 2

3. Basic Professional Training Course; Module VIII Integrated risk informed decision making If used for working groups Each working group should present their findings in a plenary session. 1 – 2 hours should be devoted to group presentations and discussions. Each presenting group should prepare a set of slides. All participants and the lecturer should comment on working group findings. At the end the lecturer should summarize the evaluation of working groups. 3

4. Basic Professional Training Course; Module VIII Integrated risk informed decision making Basic elements of IRIDM The process of decision making takes into account many aspects in a robust and unambiguous way. These include: − Deterministic considerations; − Probabilistic considerations; − Organizational factors (management systems and operational experience); − Security considerations; − Existing standards and good practices; − Other considerations including radiation doses for personnel, economic factors, research results. Weighting coefficients are assigned for each factor. A multi-disciplinary team of experts is formed. 4

5. Basic Professional Training Course; Module VIII Integrated risk informed decision making Deterministic Considerations Deterministic Safety Analyses: − Postulated Initiating Events (PIEs); − Bounding scenarios to be considered; − Levels of defense-in-depth; − Safety margins from design basis analysis; − Other deterministic considerations important for IRIDM: − Requirements for equipment qualifications; − Physical and material analysis and non-destructive examinations; − Prevention of CCFs; − Fail-safe design; − Provision of adequate redundancy and diversity for safety functions and systems; − Physical separation of redundant systems. 5

6. Basic Professional Training Course; Module VIII Integrated risk informed decision making Probabilistic Considerations Probabilistic Safety Analyses: − Define 3 levels of PSA: − Levels 1 and 2 important for safety of the plant; − Level 3 important for decisions relating to siting and emergency planning. − Recent advances in PSA methodology are inclusions of: − Organizational factors; − Passive system reliability; − External hazards; − Failures in digital system software. 6

7. Basic Professional Training Course; Module VIII Integrated risk informed decision making Organizational factors (management systems and operational experience) Management systems: − Management for safety include: − Leadership; − Control; − Competence; − Communication and cooperation between staff. − Management for safety should include: − Planning; − Review and audit to ensure that the following are correctly carried out in order to improve the human input to safety: − Maintenance, inspection and testing of equipment; − Staffing levels and training; − Management oversight. Operational experience: − Learning from events – root cause analyses. 7

8. Basic Professional Training Course; Module VIII Integrated risk informed decision making Security considerations Proper integration of safety and security requirements. Examples where security measures: − Support safety; − Have negative impact on safety. Security measures during different plant operating modes. Security measures during additional plant activities (modifications, outages, etc.). 8

9. Basic Professional Training Course; Module VIII Integrated risk informed decision making Existing standards and good practices Standards and codes prepared by: − Governmental agencies; − Engineering organizations; − National and international standard groups; − Quality assurance bodies. Engineering safety margins based on experience and research are examples of good practices. More good practices can be found in the IAEA mission reports. A systematic process should be put in place to capture good practices from: − The plant itself; − Other similar plants and industry in general. 9

10. Basic Professional Training Course; Module VIII Integrated risk informed decision making Other considerations During operation there are small but nevertheless risks to workers and the public from radiation doses. Efforts should be made to reduce them. Effect of plant operational changes on: − The normal operational doses; − Doses during maintenance and modifications; − Requirements to minimize radioactive waste and discharges; Should be constantly evaluated. Costs and economic effects should also be part of the decision making. 10

11. Basic Professional Training Course; Module VIII Integrated risk informed decision making PART TWO 11

12. Basic Professional Training Course; Module VIII Integrated risk informed decision making Dose-frequency curve In the main body of this Module we have introduced Dose – frequency curve. More likely is the event to happen, more stringent are the requirements. In addition some countries specify a frequency limit for the release of 137 Cs or the equivalent. In addition some countries specify limit for applying countermeasures such as banning food and evacuating the population. 12

13. Basic Professional Training Course; Module VIII Integrated risk informed decision making Dose-frequency curve 13

14. Basic Professional Training Course; Module VIII Integrated risk informed decision making Example for ANSI/ANS-51.1 An example where the acceptance criteria depend on the frequency of the occurrence can be found in the ANSI Standard ANSI/ANS-51.1. Depending on the plant condition the allowable dose limit is determined. More unlikely is the condition to occur, more relaxed is the allowed dose limit for whole body. 14

15. Basic Professional Training Course; Module VIII Integrated risk informed decision making Dose Limit for Whole Body at Site Boundary American National Standard ANSI/ANS-51.1-1983 Dose Limit for Whole Body at Site Boundary

16. Basic Professional Training Course; Module VIII Integrated risk informed decision making Offsite radiological dose criteria for plant conditions

17. Basic Professional Training Course; Module VIII Integrated risk informed decision making Offsite radiological dose criteria for plant conditions – cont. For Normal operation and anticipated operational occurrences (AOO) – Plant Condition 1 and 2 - the dose limit is set at the value prescribed in 10 CFR 50. If NPP is found in Plant Condition 3, the allowed dose limit is set at 10% of the value prescribed in 10 CFR 100. For Plant condition 4, dose limit is set to 25% of 10 CFR 100. For Plant Condition 5, allowed dose limit is set at 100% of the value from 10 CFR 100. 17

18. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant condition frequencies PC-1 Normal Operation; PC-2 Anticipated Operational Occurrences (AOO): − F > 10 –1. PC-3 AOO: − 10 –1 ≤ F ≤ 10 –2. PC-4 Accident condition: − 10 –2 ≤ F ≤ 10 –4. PC-5 Accident condition: − 10 –4 ≤ F ≤ 10 –6. 18

19. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant Condition 1 The following Postulated Initiating Events are categorized in Plant Condition (PC) 1 – Normal Operation (NO): − Startup; − Shutdown (hot and cold); − Refueling; − Hot standby; − Power operation; − During any of the above with additional failures such us: − Fuel cladding defects within TS limits; − Operation with specific equipment out of service or under testing within plant TS limits; − Operation with SG tube leakage within plant TS limits. 19

20. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant Condition 2 The following Postulated Initiating Events are categorized in Plant Condition 2 - Anticipated Operational Occurrences (AOO): − Inadvertent control assembly withdrawal; − Partial loss or interruption of reactor coolant flow; − Partial loss of safety-related equipment cooling or area cooling; − Control rod drop; − Reactor coolant system depressurization by inadvertent operation of an active component (e.g. a safety or relief valve); − Minor reactor coolant system or connecting system leakage; − Fire limited to one fire area; − Minor power conversion system leakage; − Reactor-turbine load mismatch, including loss of load, excess load and turbine trip. 20

21. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant Condition 2 – Cont. − Inadvertent chemical shim dilution; − Loss of feedwater flow; − Partial loss of feedwater heating; − Reactor trip; − Inadvertent emergency core cooling system actuation; − Inadvertent reactor coolant system depressurization by normal or auxiliary pressurizer spray cooldown; − Single operator error; − Single failure of an active component or control component; − Single failure in the electrical system; − Loss of instrument or service air compressor; − Generator trip; − SG tube leakage in excess of TS but less than the equivalent of a full tube rupture. 21

22. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant Condition 3 The following Postulated Initiating Events are categorized in Plant Condition 3 (AOO): − Reactor coolant system leakage that would not prevent a controlled reactor shutdown and cooldown; − Power conversion system leakage that would not prevent a controlled reactor shutdown and cooldown; − Loss of offsite AC power, including voltage and frequency disturbances; − Operation with a fuel assembly in any disoriented or misplaced position; − Inadvertent withdrawal of any single control assembly during refueling; − Inadvertent primary containment spray actuation; − Minor fuel handling accident; − Complete loss or interruption of reactor coolant flow excluding RCP locked rotor; − Full rupture of one SG tube. 22

23. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant condition 4 The following Postulated Initiating Events are categorized in Plant Condition 4 (Accident Conditions): − Small LOCA; − Drop of a spent fuel assembly involving only the dropped assembly; − Leakage from spent fuel pool in excess of normal makeup capabilities; − Single RCP locked rotor; − Blowdown of reactor coolant through multiple safety or relief valves; − Rupture of any non-seismic Category I vessel containing r/a material; − Control rod withdrawal error such that TS limits could be exceeded; − Any design basis moderate energy line crack or high energy line break outside primary containment except: − in the main steamline upstream of the turbine stop valve or − the main feed line downstream of the feedwater control valve. 23

24. Basic Professional Training Course; Module VIII Integrated risk informed decision making Plant Condition 5 The following Postulated Initiating Events are categorized in Plant Condition 5 (Accident Conditions): − Major LOCA, up to and including the largest justified pipe rupture in the reactor coolant pressure boundary; − Single control rod ejection; − Major power conversion system pipe rupture, up to and including the largest justified pipe rupture; − Drop of a spent fuel assembly onto other spent fuel assemblies. 24

25. Basic Professional Training Course; Module VIII Integrated risk informed decision making Practical exercises In case that practical exercises are to be organized, students can be divided into working groups. Each group is asked to try to identify possible initiating events in the following categories grouped by a principal cause: − Reactivity anomalies due to control rod malfunctions; − Reactivity anomalies due to boron dilution or cold water injection; − Coastdown of the main circulation pump; − Loss of primary system integrity (LOCAs); − Interfacing system LOCAs; − Loss of integrity od secondary systems; − Loss of power supply; − Malfunctions in the primary system; − Malfunctions in the secondary system; 25

26. Basic Professional Training Course; Module VIII Integrated risk informed decision making Practical exercises − ATWS; − Accidents in fuel handling; − Accidents in auxiliary systems; − Accident due to external events. For each identified IE, they should try to estimate the frequency and based on that the plant category where to be classified. Each group should be given 2 hours to complete the task. At plenary (1h) each group reports their findings. 26 The views expressed in this document do not necessarily reflect the views of the European Commission.