1. 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

2. 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.
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3. 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.
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4. 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).
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5. 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
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6. 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
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7. 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
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2020
BEPU-FSAR 7

8. THE BEPU FEATURES – Accident Analysis
SAFETY ANALYSIS / LICENSING – IAEA SSG-2, 2010
BEPU
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9. 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
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10. CONSTITUTIVE ELEMENTS
THE BEPU FEATURES
WHAT IS BEPU?
CONSTITUTIVE ELEMENTS
V & V; UNC;
COUPLING; DB;
SCALING
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11. 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
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12. HIERARCHY & KNOWLEDGE MANAGEMENT ‘BRIDGES’ & ACHIEVEMENTS
KEY ELEMENTS OF BEPU
SCALING
HIERARCHY & KNOWLEDGE MANAGEMENT
‘BRIDGES’ & ACHIEVEMENTS
OECD/NEA/CSNI
S-SOAR – 2017
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13. KEY ELEMENTS OF BEPU
UNCERTAINTY
IAEA
SRS-52 – 2008
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14. KEY ELEMENTS OF BEPU
CODE COUPLING
EC-NEA
CRISSUE-S – 2004
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15. (TH) DATABASE / APPLICATION ARN (REGULATORY BODY) - APPROVED 2012
KEY ELEMENTS OF BEPU
(TH) DATABASE / APPLICATION
NA-SA / UNIPI
ARN (REGULATORY BODY) - APPROVED 2012
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16. ENHANCING THE SM CONCEPT E-SM CONTRIBUTED BY BEPU-FSAR
A ‘FEW’ 10E4 E-SM
DEFINITIONS
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17. ENHANCING THE SM CONCEPT E-SM CONTRIBUTED BY BEPU-FSAR
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18. 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)
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19. 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
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20. 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
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21. 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.
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