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

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

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

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

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

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

HIERARCHY OF LAYERS Technical layers of defence Human factors

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

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

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.

TECHNICAL LAYER Redundancy

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

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

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

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

STATUTORY DOSE LIMITS Quantity Dose limits / mSv.y-1 workers Apprentices and Public students Effective dose 20 20 for 18 y 1 6 for 16-18 y Eq. dose in: lens of the eye 150 50 15 skin 500 150 50 hands and feet 500 150 -

DOSIMETRIC QUANTITIES Absorbed dose, Equivalent dose, Effective dose,

POSSIBLE DOSES External dose Internal dose Body wounds

PROTECTION FROM EXTERNAL IRRADIATION

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

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

VISIPLAN ALARA PLANNING TOOL

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

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.

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

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

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

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

Instrumentation AREA MONITORING Installed -monitors  in air monitors

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

ELECTRONIC DOSIMETER

PERSONAL PROTECTIVE EQUIPMENT (PPE) Protective clothing Respiratory protection

PROTECTIVE CLOTHING

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

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

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

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

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

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

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

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

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

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