1. SAFETY ASPECTS IN DECOMMISSIONING
A RAHMAN
RWE NUKEM Ltd (UK)
Name, company and chapter

2. SAFETY ASPECTS IN DECOMMISSIONING
Safety is a culture extending from
Design
Construction
Operation
Final shutdown
Decommissioning and
Waste management

3. SAFETY ASPECTS IN DECOMMISSIONING
Nuclear safety – radiological
Non-nuclear safety – industrial, chemical.

4. DECOMMISSIONING Starts at the end of operational phase
Hazards from nuclear and non-nuclear activities
Lower overall hazards than the operational phase
ends with de-licensing

5. SAFETY OBJECTIVES
General nuclear safety objective – protect individual, society and the environment
Radiation protection objective – exposure below dose limits, ALARA
Technical safety objective – practical measures to prevent accidents

6. DEFENCE IN DEPTH
Multiple layers of protection – multi-barrier protection
Layers must be independent
Failure probabilities of independent layers are multiplicative
Layers may be technical and/or human factors

7. HIERARCHY OF LAYERS
Technical layers of defence
Human factors

8. TECHNICAL LAYERS OF DEFENCE
Quality design
Safety systems – protective systems, control systems, interlocks etc
Safety monitoring systems – installed monitors, portable monitors, alarms etc

9. SAFETY ASSESSMENT Various methods exist:
Failure Mode and Effects Analysis (FMEA)
Event Tree Analysis (ETA)
Fault Tree Analysis (FTA)
Hazard and Operability (HAZOP)
Hazard Assessment (HAZAN)
Evaluation of risk
Risk = Probability of an adverse effect or
probability x consequences

10. TECHNICAL LAYERS OF DEFENCE
Redundancy – two or more protective layers in parallel
Diversity – alternative types to eliminate common mode failure
Independence – to eliminate common cause failure
Systems to comply with single failure criteria.

11. TECHNICAL LAYER
Redundancy

12. HUMAN FACTORS
Working procedures and practices – safety orders, safety manuals, written system of work etc
Training of workforce
Quality assurance and control
Management review of safety standards

13. Radiological Protection
To protect individuals, society and the environment from the harmful effects of radiation

14. Implementation of Radiological Protection
Statutory dose limits to individuals
Individual doses to comply with ALARA principle
Collective doses to comply with ALARA principle
Steps to prevent accidents
Steps to mitigate accident consequences

15. DOSE LIMITS
Based on ICRP – 60 in 1990.
Both European BSS and the International BSS are based on ICRP – 60.

16. STATUTORY DOSE LIMITS Quantity Dose limits / mSv.y-1
workers Apprentices and Public
students
Effective dose for 18 y 1
6 for y
Eq. dose in:
lens of the eye
skin
hands and feet

17. DOSIMETRIC QUANTITIES
Absorbed dose,
Equivalent dose,
Effective dose,

18. POSSIBLE DOSES
External dose
Internal dose
Body wounds

19. PROTECTION FROM EXTERNAL IRRADIATION

20. ALARA PRINCIPLE A L A R P Unacceptable level of risk > 10-3 y-1
Basic Safety Objective (BSO)
Basic Safety Limit (BSL)
Risk level: 10-3 y-1
Risk level: 10-5 y-1
Broadly acceptable level of risk < 10-5 y-1
A L A R P
Unacceptable level of risk > 10-3 y-1

21. DOSE PREDICTION TOOLS
Computer codes to predict individual and collective doses
Coupling workplace environment with 3D modelling to predict total dose
Useful in training
Useful in ALARA Application

22. VISIPLAN ALARA PLANNING TOOL

23. PROTECTION OF OCCUPATIONAL WORKERS
Classification of workplaces
Classification of workers
Monitoring of workplaces (area monitoring)
Individual dose monitoring
Control measures

24. CLASSIFICATION OF WORKPLACES
Workplaces with dose levels  1 mSv.y-1
Supervised area: dose levels  1mSv.y-1 but < 6 mSv.y-1.
Controlled area: dose levels  6 mSv.y-1.

25. SUPERVISED AREA Area labelled and physically demarcated
Working instructions available
Area monitoring
Unclassified persons work under a system of work

26. CONTROLLED AREA Dose levels  6 mSv.y-1.
Area labelled and physically demarcated
Barriers produced and entry restricted
Classified workers work
Area monitoring
Work under the written system of work

27. CLASSIFICATION OF WORKERS
Category A: dose  6 mSv.y-1.
work mainly in controlled areas
Category B: dose  1 mSv.y-1.
work mainly in supervised areas

28. AREA MONITORING Required for both supervised and controlled areas.
Individual dose estimations from
External doses
Activity concentration in air
Surface contamination

29. Instrumentation AREA MONITORING Installed -monitors  in air monitors

30. INDIVIDUAL DOSE MONITORING
For both category A and category B workers:
TLDs, film badges
Personal dosimeters – QFDs, portable dosimeters etc.
Alpha-in-air portable dosimeter
Record keeping: at least 30 years or until 75 years of a worker

31. ELECTRONIC DOSIMETER

32. PERSONAL PROTECTIVE EQUIPMENT (PPE)
Protective clothing
Respiratory protection

33. PROTECTIVE CLOTHING

34. PROTECTIVE CLOTHING
Overshoes, gloves, caps and overalls
Shoes, gloves, pressurised suits containing own air supply or airline

35. RESPIRATORY PROTECTION
Simplest face mask
Passive respirators (gas masks) where breathing is through a suitable filter material
Positive pressure respirators where pumped air supply to the face mask

36. NUCLEAR SAFETY IN DECOMMISSIONING
Knowledge of the facility
Nature of operations
Knowledge of any hot spots
Tools to be used
Operator training

37. NUCLEAR SAFETY DURING DECOMMISSIONING
Open and frequent communication
Support from health physics and safety department
Strict quality control
Adaptation of tools
Management of the facility with flexibility and adaptability

38. CHEMICAL HAZARDS Chemicals – acids, alkalis Asbestos, lead etc.
Solvents used in decontamination process
Sodium in fast reactors

39. HAZARDOUS MATERIALS
Chemical solvents, complexing agents such as EDTA, DPTA
Alkali metals (NaK)
Asbestos in thermal insulation
Lead dust from Pb shielding
Mercury vapour

40. PROTECTION AGAINST CHEMICAL HAZARDS
Characterisation of chemical hazards
Appreciation of hazards involved
National and international regulations on chemical hazardous materials
Guidance, operating procedures, safety instructions
Emergency arrangements

41. INDUSTRIAL HAZARDS
Decontamination, dismantling involving cutting, lifting, packaging etc
Custom-built tools and machines used
Lack of training in new methods
Hoist and lifting equipment used
Crane collapse, dropped load, collisions
Electrocution

42. Steel toe-capped shoes Hard hats Heavy duty gloves
INDUSTRIAL PPE
Steel toe-capped shoes
Hard hats
Heavy duty gloves

43. SAFETY DOCUMENTATION
Safety documentation covering design, construction, commissioning, operation and decommissioning
Decommissioning Plan (DP)
Decommissioning Safety Case (DSC)
Post Decommissioning Report (PDR)