The Safety Case Radioactive Waste and Spent Fuel Management Unit Sustaining Cradle-to-Grave Control of Radioactive Sources (INT-9182) Meeting on the development, revision and implementation of the safety case and safety assessment Indonesia, 15 – 19 May 2017 The Safety Case Radioactive Waste and Spent Fuel Management Unit Department of Nuclear Safety And Security IAEA

The Safety Case IAEA Safety Requirements include several requirements for a safety case, including quantitative safety assessments IAEA GSG-3 and SSG-23 give guidance on the safety case, its various components and its uses

The Safety Case The Safety Case is a tool for integrating all information on the disposal system, for managing the development, operation and closure of the disposal facility, and for demonstrating that the Safety Objective and Requirements are fulfilled The safety case is: the collection of scientific, technical, administrative and managerial arguments and evidence supporting the safety of a facility a formal set of documents produced by the operator and reviewed by the regulator

Example Safety Case Documentation Structure: UK

Example Safety Case Documentation: Finland The scope and extent of the safety case and safety assessments should reflect the scale of the hazard and the nature of the facility

The Safety Case The safety case should: Describe all safety-relevant aspects of the site, the design of the facility, and the necessary managerial and regulatory controls Be prepared and updated by the operator at each step in the development of a disposal facility Be submitted to the regulatory body for review Be sufficiently detailed and comprehensive to provide the necessary information for the regulatory body and the decisions at each step Demonstrate the level of protection provided for people and the environment Provide assurance to the regulatory body and other interested parties that safety requirements will be met

The Safety Case and Safety Assessment Safety assessment is an integral part of the safety case It provides an understanding of the safety of the facility under normal conditions and for the case of accidents / disturbing events, considering the time frames over which the radioactive waste remains hazardous It includes a systematic quantification of radiation doses and risks that may arise from the facility for comparison with regulatory (e.g., dose and risk) criteria

The Safety Case The facility shall: Be constructed in accordance with the design in the safety case and analysed in the safety assessment Be operated in accordance with the conditions of the licence and the safety case Accept wastes and waste packages disposal which conform to waste acceptance criteria that are consistent with and derived from the safety case

Safety Case Components

A. Safety Case Context The safety case context comprises: Regulatory requirements and criteria for the safety case The particular decision step in the lifecycle of the facility Key system characteristics e.g., the nature of the waste and the site The purpose of the safety assessment The assessment timeframes (e.g., a few years to perhaps a few decades for a waste store, longer for disposal facilities), philosophy (e.g., conservative, realistic) and end-points (e.g., potential doses to workers, to the public)

B. Safety Strategy The safety strategy comprises: A high-level integrated approach adopted for achieving safe storage or disposal of radioactive waste An overall management strategy for the activities required in planning, operation, closure and decommissioning of a facility Should identify the intended safety functions, the timeframes over which they will be available and how degraded performance of a safety function (e.g., a barrier) will be compensated for by another mechanism or component of the system (robustness, defence in depth)

C. System Description The system description: Related terms: Provides information on the system Demonstrates system understanding Provides the basis for safety assessment Helps to determine needs for further system characterisation and facility design work Related terms: The system description includes much of what is sometimes called the “assessment basis”

C. System Description The system description should provide information on: The facility design and why it has been designed that way The wastes (e.g., origin, quantities and properties, radionuclides) The engineering (e.g., waste conditioning and packaging, disposal units, engineered barriers, disposal facility cap or cover, drainage) The extent and properties of any zone disturbed by excavations or construction The site - e.g., geographical extent and location, geology, tectonic and seismic conditions The biosphere - e.g., climate and atmosphere, water bodies, human activities, biota, topography

D. Safety Assessment Evaluates some or all of the potential radiological and non-radiological impacts to humans, non-human species and the environment depends on the situation and regulations Involves an process of: Scenario development Conceptual, mathematical and computer model development Gathering of data and model parameter values Safety assessment calculations Analysis and review of assessment results Iterative refinement

D. Safety Assessment The ISAM methodology for safety assessment developed under an IAEA Coordinated Research Project (CRP) on disposal Very similar safety assessment methodology for pre-disposal developed in the SADRWMS Project Applied in a wide range of countries

D. Safety Assessment Scenario development Scenarios are descriptions of alternative possible events and evolutions of the system It is common to develop a set of scenarios for consideration in safety assessment as a way of assessing uncertainties Scenarios can be derived in several ways e.g. by using Safety Functions, Postulated Initiating Events, and/or Features Events and Processes (FEPs) The assessment should consider all of the things that could influence the system and affect the safety of the facility It is best practice not to speculate too much on future human behaviour To make the assessment practical, the number of scenarios should not be too great – the assessment is illustrative

D. Safety Assessment Model development Conceptual, mathematical and computer models A conceptual model is a set of assumptions concerning the geometry of the system and the chemical, physical, hydrogeological, biological and mechanical behaviour of the system A mathematical model is a representation of the conceptual model using mathematical equations Computer model is a software implementation of the mathematical model – it is important to verify that the computer code functions correctly Model testing should be undertaken to help build confidence that the model is “fit for purpose” Uncertainties and use of alternative conceptual models

D. Safety Assessment Gathering data and model parameter values Literature and experimental data Generic and site-specific data There are always uncertainties and a need for extrapolation Expert judgement and expert elicitation Deterministic and probabilistic approaches Essential to have QA and fully traceable documentation of the parameter values used and why they were selected for the assessment

D. Safety Assessment Safety assessment calculations Traceable, reproducible, QA Clearly documented data flows and relationships between models Analysis and review of assessment results Results from different scenarios Sensitivity studies Careful comparisons with regulatory criteria Uncertainties

E. Iteration and Design Optimisation

F. Management of Uncertainties There are always uncertainties and there can be alternative ways of dealing with them e.g: Gather more experimental data Use a less conservative modelling approach Re-design a component of the physical system Each of the alternatives will have pros and cons e.g. in terms of cost, timescale, likelihood of successfully reducing the uncertainty of concern

G. Limits, Controls and Conditions The safety case should be used to derive appropriate limits, controls and conditions, e.g: Limits on the total waste inventory, on acceptable concentration levels for specific radionuclides in the waste, and other waste acceptance criteria (WAC) Controls and conditions on construction and on the manufacture, materials and quality of engineering Conditions for a monitoring and surveillance programme WAC Transport Disposal Storage Treatment & Conditioning General requirements

H. Integration of Safety Arguments Simply showing that safety assessment results comply with quantitative regulatory criteria is not sufficient  multiple lines of reasoning Lines of reasoning may include discussion of: The use of best available techniques The history of design and optimisation Waste isolation and containment Passive safety Robusness and defence in depth QA and peer review Conservatisms in safety assessment Application of limits, controls and conditions

H. Integration of Safety Arguments In summary, a safety case is required and should be developed and used to: Integrate and synthesise available information, analyses and assessments Acknowledge any limitations of currently available information Guide the next steps in the development and use of the store or disposal system, and highlight the main reasons why this should be allowed Describe an approach to the management of uncertainty through which any open questions and uncertainties will be addressed

Recent Safety Cases Near-Surface Disposal Geological Disposal Borehole Disposal LLW, UK L/ILW, Sweden DSRS, Malaysia LLW, Belgium Spent Fuel, Finland The scope of the Safety Case should follow the Graded Approach