Use and Conduct of Safety Analysis IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making Workshop Information IAEA Workshop Lecturer Lesson II 3_1 Lecturer Lesson II 3_1 City, Country XX - XX Month, Year

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 2 Items for Discussion Definitions of “Safety Assessment” Reasons for Conducting Safety Assessments Safety Assessments during Design Stages Safety Assessments for Initial NPP Licensing Safety Assessments for Operations Safety Assessments of Operating Events Safety Assessments of Modifications Safety Assessment Periodic Updates Elements Common to All Safety Assessments

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 3 IAEA Requirements on Legal and Governmental Infrastructure State “Prior to granting of an authorization, applicant shall be required to submit detailed demonstration of safety, which shall be reviewed and assessed by regulatory body …..”. “Regulatory body shall issue guidance on format and content of documents to be submitted by operator in support of applications for authorization.” “Operator shall be required to submit to or make available to regulatory body, in accordance with agreed time-scales, all information specified or requested.” “Information should be presented in form of report, herein after referred to as Safety Report.”

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 4 What is a Safety Assessment? Report which describes design, and features important to safety. Report which demonstrates overall safety. Report which demonstrates compliance with regulatory criteria. Report that forms input to regulator’s decision to issue a license. Report that forms basis for limits of future operation

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 5 How Does One Assess Safety? NPP Safety is based on assuring with “high reliability” that performance is within “allowable limits”. Allowable limits defined in National Regulations or International Standards. High reliability of performance typically based on meeting Single Failure Criteria or other probabilistic criteria.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 6 Allowable Limits NPP safety limits typically focus on radiological exposure (isotopes, activities, exposure duration, dose pathways, etc.) Safety limits are based on assuring offsite radiological doses to public less than levels which might cause immediate or long term health risks. (ICRP limits are recommended.) Offsite doses are function of: core radionuclide inventory, release scenario, mitigation features, emergency planning.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 7 High Reliability of Performance Radiological doses are impacted by release scenario and functioning of mitigation features. Design features of NPPs must assure that large consequence releases are highly unlikely (e.g.: violent breach of reactor pressure vessel). Reliability of mitigation features (e.g. ECCS, or containment) must be sufficiently high to be credited in reducing accident doses. High reliability is based on compliance with Codes and Standards.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 8 There are Many Reasons for Conducting Safety Assessment Assure Conceptual Design is Safe and Meets Applicable Regulatory Criteria Assure Basis for Issuing NPP Licenses Assure Operations and Operating Experience Consistent with Safety and Regulatory Basis Assure Safety of Proposed Modifications Others ?

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 9 Safety Assessment of Conceptual Design Performed to evaluate key technical aspects (power level, fluid volumes, containment vs. confinement, etc.) which are different than previous reactors. Level of detail on high reliability features, siting factors typically not very great. Safety Assessment is used by designers and not for seeking license from regulatory body.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 10 Initial NPP Licensing Safety Assessments Safety Assessment presents a comprehensive description of NPP to be licensed. 10–20 Volumes! Safety Assessment must demonstrate all safety and regulatory criteria satisfied. Proposed site of NPP meets regulatory criteria and is acceptable. Site-related issues are properly factored into design. Construction program and Quality Assurance will assure NPP constructed properly. Plans for commissioning, operation, radwaste treatment, and decomissioning are acceptable.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 11 Safety Assessment for Operations Performed to evaluate whether new modes of Operation are consistent with License or can be demonstrated as safe (e.g. part loop operation, increased power level, full core off-load etc.) 1-2 Volumes. Extensively references existing Safety Assessment used as Licensing Bases. Formally submitted to regulatory body for review/approval if NPP operating organization seeks to amend original license.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 12 Operating Event Safety Assessment Performed to evaluate if new operating experience is consistent with License or can be demonstrated as safe (e.g. unanticipated transient event, observed pipe cracking, unusual component wear). <1 Volume. Extensively references existing Safety Assessment used as Licensing Bases. Formally submitted to regulatory body for review and approval if NPP operating organization seeks to amend original license.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 13 Safety Assessments of Modifications Performed to determine if proposed modification alters frequency or consequences of DBAs, or creates accidents not previously considered in License review (e.g. degraded accident response, reduced mitigating system reliability, new release scenario). Performed by support organization to NPP much like safety assessment at conceptual design stage. ~1Volume. Extensively references existing Safety Assessment used as Licensing Bases. Formally submitted to regulatory body for review and approval if NPP operating organization seeks to amend original license.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 14 Safety Assessments Periodic Updates Safety Assessment presents a comprehensive update to description of NPP to be re-licensed. 10–20 Volumes! Safety Assessment must demonstrate all safety and regulatory criteria satisfied – including changes to regulations and effects of plant safety improvements. Operating experience demonstrates conservative design margins and continuous plant reliability improvement. Site-related issues consistently factored into upgrades. Construction program and Quality Assurance have consistently assured NPP upgraded properly. Plans for operation, radwaste treatment, and decommissioning remain acceptable.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 15 Elements Common to All Safety Assessments Regulatory body must define in regulations or guidelines: circumstances where safety assessment is required format and contents to be submitted. Technical approaches of key phases of Safety Assessment must be agreed-upon between operating organization and regulatory body before work starts. This includes usage of: Key thermalhydraulic or engineering mechanics computer codes Industrial standards/methods to be used to address safety margins Data bases or other sources of information to be used

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 16 Elements Common to All Safety Assessments Quality of safety assessment is improved by Independent Peer Review with audit calculations. Safety assessment and review schedules must be agreed between operators and regulatory body – and tied to licensing decisions by regulatory body. Submitting 10 volume analyses to regulatory body on night before plant restart not acceptable safety practice. Very large (10-20 volume) safety assessments and formal reviews must be conducted in parallel fashion – to preclude need for extensive re-work.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 17 Some Personal Opinions (Not IAEA Recommendations) Each time Safety Assessment submitted to Regulatory Body for review, it should be accompanied with a Bank Check according to volume of work (e.g. $$ ). This assures funding availability to pay for reviews. Also assures ‘half-completed’ Safety Assessment isn’t submitted repeatedly by NPP thus using regulatory body as operating organization’s Quality Inspector. Preparation and reviews will quickly become accountable and more business-like for both parties. An Independent Review should cost approximately 10 to 15% of the costs of producing Safety Assessment.

IAEA Training Course on Safety Assessment of NPPs to Assist Decission Making 18 Some Additional References IAEA 50-SG-G2, “The Format and Content of Safety Analysis Reports for Nuclear Power Plants” (old and being updated) (1979) IAEA DS-309, “The Format and Content of Safety Analysis Reports for Nuclear Power Plants” (in DRAFT, due out in 2002). US NRC Regulatory Guide 1.70, “The Format and Content of Safety Analysis Reports for Light Water Nuclear Power Plants” (Version 1978).