BEPU and Safety Margins in Nuclear Reactor Safety University of Pisa DESTEC-GRNSPG Nuclear Research Group in San Piero a Grado (Pisa) - Italy BEPU and Safety Margins in Nuclear Reactor Safety F. D’Auria, N. Debrecin, H. Glaeser Int. Conf. on Topical Issues in Nuclear Installation Safety: Safety Demonstration of Advanced Water Cooled Nuclear Power Plants IAEA Headquarters , Vienna 6-9 June, 2017

ACTIVITY EMBEDDED INTO A BROADER FRAMEWORK WHICH INCLUDES: PREFACE – 1 of 2 ACTIVITY EMBEDDED INTO A BROADER FRAMEWORK WHICH INCLUDES: ALARA (As-Low-As-Reasonably-Achievable) is an early principle. IA (Independent Assessment) is a requirement . IN ADDITION TO: BEPU (Best Estimate Plus Uncertainty) is a key approach [the term took its origin within the nuclear thermal-hydraulics and the Accident Analysis framework during the ‘90s]. SM (Safety Margin) is an established concept. 2/21 2

ISSUES CONNECTED WITH THE TERMS: PREFACE – 2 of 2 ISSUES CONNECTED WITH THE TERMS: ALARA: adopted for Radioprotection & disconnected from Deterministic Safety Analysis. BEPU: not commonly accepted. SM: (sometimes-somewhat) ambiguous & comprehensive and systematic definition missing. IA: pursued only in principle: this is a wish rather than an achievement. 3/21 3

FOR THE ACTIVITY (IN PROGRESS): To integrate ALARA, BEPU, SM and IA. OBJECTIVES FOR THE ACTIVITY (IN PROGRESS): To integrate ALARA, BEPU, SM and IA. FOR THE PRESENTATION: To provide snapshot insights - advancements. To emphasize advantages (of the integration). 4/21 4

LIST OF CONTENT A view for NRS (role of ALARA, BEPU, SM and IA) The BEPU features - Key elements of BEPU (V&V; Scaling; Unc.; Coupling; DB / Application) - ALARA BEPU - Expanding BEPU (or BEPU-FSAR) Enhancing the SM concept (E-SM) Issues with current IA Integrating ALARA, BEPU, E-SM and IA - The additional safety barrier 5/21 5

Making ‘concrete’ the role of ALARA A VIEW FOR NRS Region for IA Making ‘concrete’ the role of ALARA Role for BEPU SM / E-SM 6/21 6

NRC – Interim Acceptance Criteria THE BEPU FEATURES A HISTORIC OUTLINE 1970 NRC – Interim Acceptance Criteria NRC – Appendix K to 10 CFR 50.46 NRC – RG 1.157 1990 Angra-2 BE LB-LOCA NRC – RG 1.203 Atucha-2 BEPU Chapter 15 2010 7/21 2020 BEPU-FSAR 7

THE BEPU FEATURES – Accident Analysis SAFETY ANALYSIS / LICENSING – IAEA SSG-2, 2010 BEPU 8/21 8

THE BEPU FEATURES WHAT IS BEPU? 9/21 BEPU ≡ ALARA  The BEPU is a logical process which connects the understanding in NRS (and licensing) with nuclear TH.  The starting point for BEPU are the physical phenomena. This implies the DBA envelope.  BEPU implies the existence of qualified computational tools dealing with different disciplines, input decks or nodalizations and a method to evaluate the uncertainty.  BEPU needs the existence of qualified procedures for the application of the computational tools.  BEPU needs the existence of qualified code users and of maven capable of evaluating the acceptability of analysis.  BEPU needs the existence of ’legal’ acceptance criteria.  The application of BEPU implies the knowledge of the licensing process.  The structure of the FSAR must be adapted to BEPU including the design of the core, the experimental data drawn during the commissioning, the design of EOP, etc.  Any BEPU report should be a living document. BEPU ≡ ALARA 9/21 9

CONSTITUTIVE ELEMENTS THE BEPU FEATURES WHAT IS BEPU? CONSTITUTIVE ELEMENTS V & V; UNC; COUPLING; DB; SCALING 10/21 10

KEY ELEMENTS OF BEPU V & V 11/21 DRAFT-IAEA V&V – 2017 VERIFICATION ESTABLISHED QA PRACTICE VALIDATION: STARTING FROM SETF & ITF CCVM + FFTBM FOR ACCURACY QUANTIFICATION RECENT CONCEPTS: ASSESSMENT OF VALIDATION (MINIMUM) INDEPENDENT ASSESSMENT FOR CODE USER 11/21 11

HIERARCHY & KNOWLEDGE MANAGEMENT ‘BRIDGES’ & ACHIEVEMENTS KEY ELEMENTS OF BEPU SCALING HIERARCHY & KNOWLEDGE MANAGEMENT ‘BRIDGES’ & ACHIEVEMENTS OECD/NEA/CSNI S-SOAR – 2017 11/21 12/21 12

KEY ELEMENTS OF BEPU UNCERTAINTY IAEA SRS-52 – 2008 13/21 13

KEY ELEMENTS OF BEPU CODE COUPLING EC-NEA CRISSUE-S – 2004 14/21 14

(TH) DATABASE / APPLICATION ARN (REGULATORY BODY) - APPROVED 2012 KEY ELEMENTS OF BEPU (TH) DATABASE / APPLICATION NA-SA / UNIPI ARN (REGULATORY BODY) - APPROVED 2012 5/21 15/21 15

ENHANCING THE SM CONCEPT E-SM CONTRIBUTED BY BEPU-FSAR A ‘FEW’ 10E4 E-SM DEFINITIONS 16/21 16

ENHANCING THE SM CONCEPT E-SM CONTRIBUTED BY BEPU-FSAR 17/21 17

ISSUES WITH CURRENT IA ISSUES NPP COMPLEXITY (efforts needed for IA ‘too large’ out of industry) SAFETY DEPENDING UPON DETAILS (details un-known out of industry; issue is proprietary information) INDUSTRY ENGAGED IN CONTINUOUS CHANGES / IMPROVEMENTS (changes not necessarily qualified, e.g. passive systems) IA ONLY POSSIBLE WITH LATEST BE TECHNIQUES (expertise may not be available out of industry) EXPERT ANALYSTS NOT NECESSARILY AWARE OF LICENSING DETAILS (the licensing framework is complex, too) 23/21 18/21 18

Integrating ALARA, BEPU, SM and IA ADDITIONAL SAFETY BARRIER NPP UNIT ALARA NRS REQUIREMENTS BEPU [BEPU-FSAR] SM [E-SM] ASSESSMENT INDEPENDENT LEGEND Philosophy Software Hardware Writing FSAR ADDITIONAL SAFETY BARRIER 19/21 19

Integrating ALARA, BEPU, SM and IA THE ADDITIONAL SAFETY BARRIER The Emergency Rescue Team (ERT) (not discussed here) and The BEPU-based Independent FSAR (BEPU & IA) coupled with The Safety Margins Detection & Control (E-SM) INTRODUCE A NEW SAFETY BARRIER WHICH MAY HELP TO RE-ESTABLISH THE PUBLIC TRUST TOWARDS NUCLEAR ENERGY 20/21 20

CONCLUSIONS ALARA at the origin of BEPU. BEPU based on V&V, Scaling, Code Coupling, Uncertainty, and Database. BEPU extended to the entire FSAR (analytical parts). E-SM (comprehensive and systematic set) derivable with support from BEPU. IA based on BEPU. SUMMARY BEPU: must be pursued. Any further delay is not justifiable for NRS. Safety Assessment (Licensing) must be independent of Vendor-Owner  BEPU-based I-FSAR & E-SM. 21/21 21