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

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Presentation on theme: "1 SAFETY ASPECTS IN DECOMMISSIONING A RAHMAN RWE NUKEM Ltd (UK) Name, company and chapter."— Presentation transcript:

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

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

3 3 Nuclear safety – radiological Non-nuclear safety – industrial, chemical.

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

5 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 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 7 HIERARCHY OF LAYERS Technical layers of defence Human factors

8 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 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 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 11 TECHNICAL LAYER Redundancy

12 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 13 Radiological Protection To protect individuals, society and the environment from the harmful effects of radiation

14 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 15 DOSE LIMITS Based on ICRP – 60 in Both European BSS and the International BSS are based on ICRP – 60.

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

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

18 18 POSSIBLE DOSES External dose Internal dose Body wounds

19 19 PROTECTION FROM EXTERNAL IRRADIATION

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

21 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 22 VISIPLAN ALARA PLANNING TOOL

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

24 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 25 SUPERVISED AREA Area labelled and physically demarcated Working instructions available Area monitoring Unclassified persons work under a system of work

26 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 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 28 AREA MONITORING Required for both supervised and controlled areas. Individual dose estimations from External doses Activity concentration in air Surface contamination

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

30 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 31 ELECTRONIC DOSIMETER

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

33 33 PROTECTIVE CLOTHING

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

35 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 36 NUCLEAR SAFETY IN DECOMMISSIONING Knowledge of the facility Nature of operations Knowledge of any hot spots Tools to be used Operator training

37 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 38 CHEMICAL HAZARDS Chemicals – acids, alkalis Asbestos, lead etc. Solvents used in decontamination process Sodium in fast reactors

39 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 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 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 42 INDUSTRIAL PPE Steel toe-capped shoes Hard hats Heavy duty gloves

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


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