Needs for Safety Assessment & the Safety Assessment Process

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making Needs for Safety Assessment & the Safety Assessment Process Workshop Information Lecturer Lesson II 2.1 and II 3_2 IAEA Workshop City , CountryXX - XX Month, Year

Needs for Safety AssessmentRegulatory View • CONTENT: • Needs for Safety Assessment • Deterministic and Probabilistic Approach • Safety Assessment Process • Slovene (SNSA) Practice IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment Safety assessment - safety analysis • Safety assessment is the systematic process that is carried out throughout the design process to ensure that all relevant safety requirements are met by the proposed or actual design of the plant. Safety assessment includes, but is not limited to, the formal safety analysis. • A safety analysis of the plant design, applying methods of deterministic and probabilistic analysis shall be provided which establishes and confirms the design basis for the items important to safety and demonstrate that overall plant design is capable of meeting the prescribed and acceptable limits for radiation doses and releases for each plant condition category and that defence-in-depth is achieved. Source: IAEA IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment • Licensing and renewing of operating plant, • Periodic safety review, • Plant modification, upgrading and modernization projects, • Assessment of operational experience, • Updating of safety analysis report, • Updating of operational limits and conditions, • Updating the safety relevant programs and procedures (?) IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment • Licensing and renewing of operating plant: • Rare in the plant life-time but the most extensive assessment work, • Usually includes different areas of analysis and assessment: • New methods and codes • Determination of new operating conditions • Verification of new operating parameters (limiting safety analysis) • Other not limiting Safety analysis • System and component verification (safety and non-safety systems with support systems) • Plant maneuverability verification (verification of operation margins) • Mechanical analysis of NSSS systems and components, etc. • Performed due to plant reconstruction, life extension • Very extensive change and reassessment of all licensing documents IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment • Periodic Safety Review: • Challenges: • ageing problems, • obsolescence of components & equipements, • safety upgrading, • periodic safety re-assessment, • Safety assessment: • the level of safety of the NPP “as designed”, • the level of safety improved through modifications, • the level of safety based on operation and maintenance, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment Plant modification, upgrading and modernization projects: • Very wide category of plant changes assessment (in term of assessment extent) • Causes for plant modification and modernisation are very different • Examples: from minor safety related modification up to SG replacement, power uprate or wide plant modernisation projects • Not all modifications are subject of regulatory safety assessment and review (depends from criteria and procedures) IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment • Assessment of operational experience: • Very specific assessment work encompassing the event analysis, SSC performance evaluation, screening and reassessment due to events or findings in other plants, etc. • Performance and safety/risk indicators program, • Deterministic and probabilistic methods are used  corrective actions • Main benefits: • allocation of design deficiencies and design improvements (optimisation) • improvement of operating deficiencies (procedures, maintenance, human errors, test performance, etc.) • in-depth evaluation of operation practice, • improve the better understanding the plant response insights, etc. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment • Updating of safety analysis report: • SAR contains wide range of safety related information necessary for licence permit • SAR changes are usually one of the starting points for the safety assessment and review • Plant modifications shall be checked against SAR descriptions and analysis • Safety assessment should be performed if the plant changes impacts the assessments and/or analysis described in the SAR • Changes of safety standards which are reflected on safety analysis could cause SAR changes • SAR updating on each plant change which reflects on SAR change • New SAR revisions approximately once per year IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment Updating of operational limits and conditions (T.S.): • Envelope of plant operation • Most frequent changes • Regulatory approval is obliged • Usually the SAR changing in parallel, • Relaxation of limits and conditions (IST) • On-line maintenance of safety related systems challenge the T.S. • T.S. Exemptions IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment Updating the safety relevant programs and procedures: • EOPs, ISI Program, FP Program, FP, Emergency Procedures, SAMGs • Set up the programs and major procedures - regulatory approval, • Programs and procedure changes due to operational reasons or design changes, • Regulatory review are selective and limited, • Regulatory approval of program and procedure updates are rare, • Generally, procedures are not the part of regulatory approval process, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Safety Assessment • Designer safety assessment • Licensee safety assessment • Regulatory safety assessment and review • Safety analysis • Deterministic and probabilistic approach IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach • The mechanistic thinking era • Determinism. Everything has a cause and can be explained why it happened • Knowing everything that can happen when dealing with a machine • Analysis as a way to know how things work • The need for safety analysis IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach SAFETY ANALYSIS - DETERMINISTIC • DESIGN BASIS EVENTS: • TRANSIENTS • ACCIDENTS • OPERATOR ACTIONS • PROCEDURES • TRAINING • EQUIP. PERFORMANCE • DESIGN • MAINTENANCE ANALYSIS OF PLANT RESPONSE (MODELS) SINGLE FAILURE UNIQUE ERROR DAMAGE LIMITS NO NO OK ? MODIFICATION MODIFICATION YES DEFINITION OF OPERATIONAL REQUIREMENTS IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach • The need to limit the scope and extent of the deterministic safety analysis: • simplifying assumptions and bounding situations • design basis events • single failures • unique error of the operator • actions taken to fulfill the assumptions made in the safety analysis IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach DETERMINISTIC BASIS ENVELOPE PHYSICAL LIMIT DAMAGE 1E 0 NORMAL OPERATION NOT ACCEPTABLE AREA OPERATIONAL INCIDENTS DESIGN BASIS ACCIDENTS PROBABILITY SEVERE ACCIDENTS ACCEPTABLE AREA 1E-X IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach Defense in depth: • sound design, construction, testing, maintenance, training and guidance, • control systems, • protection system, • safety systems to deal with DBAs, • measures to deal with Severe Accidents, • emergency preparedness, • distance IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach • The Design-Basis Envelope • classes of events, • limited to “credible” events, • Events beyond the Design-Basis Accident • events • actions • impact on the safety analysis complexity IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach DETERMINISTIC DESIGN-BASIS ENVELOPE PHYSICAL LIMIT DAMAGE NORMAL OPERATION NOT ACCEPTABLE AREA OPERATIONAL INCIDENTS DESIGN BASIS ACCIDENTS PROBABILITY SEVERE ACCIDENTS NEW NOT ACCEPTABLE AREA ACCEPTABLE AREA IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Deterministic Approach • The Deterministic safety design principles • redundancy and diversity, • fail safe, • avoidance of common cause failures, • Safety-related and non-safety related • Deterministic rules and requirements • Complaints about deterministic approach IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Probabilistic Approach • Safety as an emergent property of a system. The need for a systematic view. • A system is an entity that maintains its existence and functions as a whole through the interactions of its parts, • Emergent properties. Safety. • Importance of selection of boundaries of the system. Not so long in the past the technical system, by the middle of the 70’s the human operator, by the end of the 90’s the management system, • Other significant influences in the safety not yet properly included, • Synthesis in addition to analysis, • Difficulties to model socio-technical systems, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Probabilistic Approach The strength and drawbacks of PSA. Deterministic and probabilistic approaches are complementary • Probabilistic safety analysis RISK: Scenarios What can go wrong ? Probability/Frequency What is the risk ? How likely is it ? What are the consequences ? Damages IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

DATA BASES OPERATIONAL PRACTICES • INITIATING EVENTS: • LOCAS • TRANSIENTS • EXTERNAL INITIATORS • HUMAN RELIABILITY • PROCEDURES • TRAINING EQUIP. AVAILABILITY (FAULT TREES) ANALYSIS OF PLANT RESPONSE (EVENT TREES) (DOMINANT SEQUENCES) • SAFETY GOALS • OTHER CRITERIA NO NO MODIFICATION OK ? MODIFICATION YES DEFINITION OF OPERATIONAL REQUIREMENTS The Probabilistic Approach SAFETY ANALYSIS - PROBABILISTIC IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Probabilistic Approach • Differences between deterministic and probabilistic safety analysis • Realistic vs. conservative • Initiating events • Use of event trees and fault trees • Use of specific data • Human reliability analysis • Qualitative and quantitative results IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Probabilistic Approach • Advantages of PSA • more realism • a more holistic view • uses generic and plant specific data • more systematic representation of equipment and personnel • as any other technique can not model what is not known, but can focus reviews • highlights and treats areas of uncertainty • provide a structure for sensitivity studies IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Probabilistic Approach • Drawbacks of PSA: • improvements required in models • some influences not yet treated • may be oriented to get the results desired • lack of consideration for non-core-damage events • bottom-line-numbers may be overstressed • may accept unbalanced prevention mitigation • could be a “snapshot” in time • lack of systematic control of assumptions IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

The Probabilistic Approach • The fear for the simple increment of requirements using PSA • deterministic framework rather prescriptive in requirements, • potential “acumulative” approach, • use of PSA to select among alternatives to achieve required safety level and not to find best solution in terms of safety, DANGER OF “COMPLEMENTARY” USE OF PSA 1. PLANT STATUS 2. DETERMINISTIC REQ. 3. BEST CONFIG. ACCORDING TO THE PSA 4. “COMPLEMENTARY REQ. OUTSIDE CONTAINMENT INSIDE CONTAINMENT IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Towards a Risk-informed Approach • The practical difficulties of a risk-based regulatory framework • not prudent today to use a risk-based framework • some elements of defense-in-depth should be maintained • The importance of efficiency in a deregulated electricity production market. The role of PSA in improving efficiency • uses of PSA, with present framework or to improve the framework • Improvements of efficiency of the present regulatory framework • focus In-Service-Inspection (ISI) • improve Technical Specifications • improve In-Service-Testing • maintenance reliability goals • focus planning, assessment, inspection, research and development, etc. ROOM FOR IMPROVEMENT DEPENDS ON PRESCRIPTIVENESS OF REGULATORY FRAMEWORK IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Towards a Risk-Informed Approach • The main elements of a risk-informed framework • Scope of changes in the deterministic framework • Importance of expectations • The main elements • philosophy of defense-in-depth • insights from PSA • knowledge derived from operating experience assessment IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

SAFETY ASSESSMENT PROCESS IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Objectives of Reg. BodyReview & Assessment Process • One of the regulatory body’s principal functions, • Understanding of the: • design of the facility or equipment, • the safety concept on which the design is based, and • the operating principles • Determination whether the facility or activity complies with the safety objectives, principles and criteria, • Available information demonstrates the safety of the facility or proposed activity, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Objectives of Reg. BodyReview & Assessment Process • The information contained in the operator’s submissions is accurate and sufficient to enable verification of compliance with regulatory requirements, • The technical solutions, and in particular any novel ones, are proven or qualified by experience or testing or both, and are capable of achieving the required level of safety IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

BASIS FOR REVIEW & ASSESSMENT Range of sources for formulating the content and structure of the safety objectives and safety requirements to be used as basis in the review and safety assessment process: • national laws and regulations, • the requirements and experience of relevant national industries, • technical results of research and development organizations, • expertise and requirements used by other persons and bodies involved in the reviewing and assessing similar facilities, • advice obtained from consultants and advisory bodies associated with regulatory body, • safety standards and guidance published by national and international org. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review and Assessment Process • The operator and the regulatory body should establish a formal relation based on independence and mutual respect, • It is the responsibility of the operator to make arrangement with its contractors to ensure the availability of all required information, • The use of consultants should not relieve the R.B. of its responsibilities for making decisions or recommendations, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Areas for Review and Assessment At any phase of the plant life cycle listed below, the concentration of review and assessment may be on specific aspects, but it is important to note that the safety argument presented by the operator should at all phases deal with the full range of topics to an appropriate level • Siting • Design, construction, manufacture and installation, • Commissioning • Operation • Decommissioning IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review & Assessment During Operation In routine operation the regulatory body shall require the operator to report regularly on: • the compliance with safety objectives, • specified regulatory requirements and • on efforts to enhance safety, The regulatory body shall: • review and assess the reports • perform inspections to confirm whether compliance with safety requirements is maintained and • whether the facility is suitable to continue in operation IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review & Assessment During Operation The requirements for reassessment may arise owing to: • experience relevant to safety gained at similar facilities and other relevant nuclear and non-nuclear facilities, • information from relevant tests and research and development programmes, • proposed modifications of the facility or the way it is to be operated, • changes in the regulatory framework, regulation and guides IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review & Assessment During Operation While the need for reassessment may arise in a number of ways systematic safety reassessment termed Periodic Safety Reviews (PSRs) should be carried out by the operator at predetermined regular intervals to review the cumulative effects of the facility: • ageing, • modifications, • implications of operating experience, • technical developments IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review and Assessment Review and assessments should be carried out by employing a systematic plan, an outline of which could be: • definition of the scope of the review and assessment process, • specification of the purpose and technical bases for the review and assessment process (acceptance criteria), • identification of the additional information needed for the review and assessment, • performance of step-by-step review and assessment procedure to determine whether the applicable safety objectives and requirements on each aspect or topic have been met, • decisions made regarding the acceptability of the operator’s safety argument or need for further submissions which will then need review and assessment IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review and Assessment The general aim of safety analysis, whether deterministic or probabilistic, is to verify that for each identified barrier between the source of radioactivity and people or environment, the safety measures are sufficient at the following tree levels, providing a progressive character for the safety analysis: • prevention of failure of the barrier itself and prevention of failure of related systems during normal operation and fault conditions, • monitoring of any parameter significant to the integrity of the barrier, to allow initiation of either manual or automatic actions in order to prevent any evolution towards an unsafe condition, • safety action preventing or limiting release of radioactivity if the barrier has failed and mitigating consequences if applicable. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Review and Assessment The requirements on the SSC’s and operations can be derived from the safety analysis and considered against the existing or suggested provisions.These requirements should cover also, among other things: • application of the defense in depth principle, • the single failure criterion, • requirements for redundancy, diversity and segregation, • the preference for a passive over an active or human-machine interface, • criteria related to human factors and the human machine interface, • radiological risk criteria for workers and the public, • minimization of waste generated. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Safety Analysis and Fault Conditions Consideration of fault conditions strongly influences the design limits for safety systems It will also strongly influence the operational instructions and procedures that operating personnel should follow In addition, the potential radiological consequences for workers, the public and the environment in fault conditions may be much more severe than those during routine operation For this reason the largest part of the review and assessment effort may be expected to be directed to the safety analysis of fault conditions Safety analysis can be considered as two major steps: • identification of postulated initiating events (PIEs) and their frequencies, • evaluation of how these PIEs develop and their consequences. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

QA in the Review and Assessment The system to record, audit, review and monitor all aspects of the assessment process should be established to ensure: • that it is being carried out in a suitable and efficient manner, • that any changes to the process made necessary owing to improvements in knowledge or techniques or otherwise are implemented IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

REGULATORY REVIEW AND ASSESSMENT - SLOVENE (SNSA) PRACTICE - IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Regulatory Review and Assessment - General Considerations • One of the principal and continues functions of RB, • Primary basis for the review and assessment is the information submitted by the operator, • The purpose of the review and assessment is to reach a situation in which it is possible for RB to make decisions or serious of decisions, • Review and assessment is performed by the team of specialists inside RB or put together from outside of RB , • Findings of Review and Assessment may lead to specific inspections and /or enforcement actions. This requires effective communications and interactions between different parts of the RB, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Some Elements of Review and Assessment Practise in Slovenia APPLICABLE LEGISLATION FRAMEWORK • Allows application of regulations of the country of origin when national regulation is not available • SAR is the basic licensing document as far as nuclear safety • SAR should be continuously supplemented during plant life with data and analysis about all changes • 3 categories of plant changes are established: • notification after completion, • notification before implementation, • approval before implementation. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Some Elements of Review and Assessment Practice in Slovenia (Cont.) APPLICABLE LEGISLATION FRAMEWORK (Cont.) • Third party independent evaluation is mandatory • General licensing procedure is prescribed by law • Granted authorization are formally recorded in the decisions, • Decisions can impose conditions and limitations on operators subsequent activities, • Auditing of the issued decisions implementation are performed usually by the SNSA inspectors, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Some Elements of Review and Assessment Practice in Slovenia (Cont.) • Review and assessment judgement are based mainly on: relevant regulation, guides, procedures and standards (mainly US origin), relevant experience and practice from other countries (US and EU), “Generic” analysis, etc. • TSO’s review report is used as an important input for decision-making, • SNSA by itself do not perform independent analysis to support assessments and decision making, but in some cases SNSA orders analysis from TSO-s, • SNSA encourages by limited (co)-financing the research and development at TSOs on some important areas; models and results are available at SNSA facilities, IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Some Elements of Review and Assessment Practice in Slovenia (Cont.) Licensing procedure is launched at least in following cases: • major modifications, • unreviewed safety question discovered by assessment (10CFR 50.59), • changes in the organization structure, • technical specification changes, • changes of important programs and procedures (such as, ISI Program, Fire Protection Program, Radiation Monitoring Program, Emerg. Preparedness Program, etc.) which are defined in the SAR, but are not the part of SAR. • Hearing during the regulatory review but before decision (open issues consideration and negotiation) • The part of the regulatory decision is a short elaborate (SER) about all elements which are important for decision making process IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Some Elements of Review and Assessment Practice in Slovenia (Cont.) • The plant change safety assessment: • should identify the major areas to be reviewed, • to allow R.B. to develop its own view of the proposed change, • for example: • evaluation of the reasons for the proposed modification and impact on safety, • identification of the codes and standards to be applied, • assessment of modification design basis, • assessment of modification compliance with design basis (in terms of system analysis and impact on accident and risk analysis), • previous experience, oper.experience feedback, reference NPP • should allow to set up priorities according to the safety relevance due to resource limits • evaluation/review should be adequately supported by written justification. IAEA Training Course on Safety Assessment of NPPs to assist Decision Making

Needs for Safety Assessment & the Safety Assessment Process