1. BASIC PROFESSIONAL TRAINING COURSE Module III Basic principles of nuclear safety Case Studies
Version 1.0, May 2015
This material was prepared by the IAEA and co-funded by the European Union. 

2. CASE STUDIES
During the course three major nuclear accidents were described:
Three Mile Island;
Chernobyl;
Fukushima.
The sequence of events in all three accidents were described in sufficient detail as to allow a fairly detailed analysis of safety culture by the course participants.

3. SAFETY CULTURE IMPACT ASSESSMENT
Safety culture is that assembly of characteristics and attitudes in organizations and individuals which established that, as an overriding priority, nuclear plant safety issues receive the attention warranted by their significance.
Safety culture is:
Attitudinal and structural;
Relates to organizations and individuals.
Safety Culture goes beyond regulatory requirements and legal responsibilities of an operating organization.

4. SAFETY CULTURE INSAG-4

5. WORK IN WORKING GROUPS
Students should be divided into groups of 4 – 5 students. Each group should address all components of safety culture:
Policy level;
Managers commitment;
Response of individuals.
Alternatively, students could be divided into groups and each group would address only one of the above components.
Decision on which way to go is left to the lecturer to select.
Each group should spend 2 – 3 hours discussing the topics and prepare a short presentation for the plenary session.

6. Safety Culture has two major components:
Managerial framework;
Response of individuals working within and benefiting from the framework.
For each Safety Culture component, all Safety Culture elements should be addressed. The below table shows components and elements and prompts.
Prompts are meant as a straining point for discussion.
For each element event specific issues should be identified and elaborated/justified.

7. SAFETY CULTURE IMPACT ASSESSMENT: POLICY LEVEL COMMITMENT
SC Component
SC Elements
Prompts
Event Specific Issues
I. Policy Level Commitment
a) Statements of Safety Policy
Regulatory safety policy statement
Corporate safety policy statement
Plant safety policy statement
Quality directive of support organizations
II. Managers’ Commitment
III. Individuals’ Commitment
Event analyses will reveal SC deficiencies in an organization.

8. SAFETY CULTURE IMPACT ASSESSMENT: MANAGERS’ COMMITMENT
The same should be done for the Management commitment:
Definition of responsibilities;
Definition and control of safety practices;
Qualifications and training;
Rewards and sanctions;
Audit, review and comparison.

9. SAFETY CULTURE IMPACT ASSESSMENT: INDIVIDUALS’ COMMITMENT
The same should be done for the Individual response:
Questioning attitude;
Rigorous and prudent approach;
Communication.

10. PRESENTATION IN THE PLENARY
For all three safety culture components and for all elements, event specific issues should be identified by 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.

11. ADDITIONAL ELEMENTS FOR DISCUSSION IN PLENARY
Common traps and pitfalls for event investigation:
Safety is seen as external requirement and consists of compliance with rules and regulations;
It’s often irresistible to change procedures as a corrective measure;
It takes too long before the event is analysed!
Investigations are often not thorough:
i.e.- they conclude too early,
- they fail to find ROOT causes.

12. ADDITIONAL ELEMENTS FOR DISCUSSION IN PLENARY – cont.
Elements of an effective event investigation programme:
Management support;
Utility culture, must want to improve;
Voluntary reporting scheme;
Personnel trained in investigation techniques;
Prompt investigation;
Tracking and Trending of precursors;
Effective learning from Operating Experience.

13. BASIC PROFESSIONAL TRAINING COURSE Module III Fundamental safety functions Case studies
Version 1.0, May 2015

14. INDIVIDUAL WORK OR WORKING GROUPS
Students should be divided into groups of 4 – 5 students. Each group should calculate and discuss the fundamental safety functions Removal of Heat and Confinement of Radioactive Material.
Alternatively, students could work individually.
Decision on which way to go is left to the lecturer to select.
Each group should spend 2 hours discussing the topics and prepare a short presentation for the plenary session.

15. FUNDAMENTAL SAFETY FUNCTIONS Three fundamental safety functions
Reactivity Control
Removal of Heat
Confinement of Radioactive Material 
Fundamental safety functions reduce the likelihood of release 

16. FUNDAMENTAL SAFETY FUNCTIONS Decay heat removal after the accident
Emergency core cooling system of a 2000 MWth reactor failed after the accident. What is the minimum amount of water that needs to be injected into the reactor vessel to keep the core flooded after 1 day, 1 week and 1 month? Calculate and choose the correct answer!
Heat of vaporization of water at atmospheric pressure is 2260 kJ/kg.
For calculation consider Decay Heat Power curve (dotted line) in Light Water Reactors, ANSI/ANS Std given as an attachment.
Time after reactor shutdown
Required water flow m3/h
1 day
50m3/h
21 m3/h
80 m3/h
1 week
90m3/h
10 m3/h
50 m3/h
1 month
170 m3/h
5 m3/h
20 m3/h

17. FUNDAMENTAL SAFETY FUNCTIONS Decay heat curve
Decay heat is produced by the decay of radioactive fission products after reactor shutdown:
Principal reason of safety concern in LWRs;
Adequate cooling must be maintained at all times to remove decay heat and prevent cladding failure in the reactor or in spent fuel storage.
Decay heat curve for a typical LWR, that has been operating for a long time (given in % of full power P)

18. Decay Heat Power in Light Water Reactors, ANSI/ANS Std. 5
Decay Heat Power in Light Water Reactors, ANSI/ANS Std , issued by the American Nuclear Society.

19. FUNDAMENTAL SAFETY FUNCTIONS Confinement of Radioactive Material
On the cross-section view of the fuel rod identify the barriers that prevent the spread of radioactive materials!
Describe the barriers and explain how they achieve their purpose!
What is their effectiveness?

20. FUNDAMENTAL SAFETY FUNCTIONS Confinement of Radioactive Material
On the cross-section view of a PWR plant identify the barriers that prevent the spread of radioactive materials.
Describe the barriers and explain how they achieve their purpose.
Discuss their effectiveness.
The views expressed in this document do not necessarily reflect the views of the European Commission.