1. Diversity analysis for advanced reactor design
Vincent SOREL & Boris GONUL EDF/Basic Design Department
International Conference on Topical Issues in Nuclear Installation Safety:
Safety Demonstration of Advanced Water Cooled Nuclear Power Plants
IAEA Headquarters, Vienna, Austria
6–9 June 2017

2. Summary Abstract Functional analysis Preliminary system analysis
Detailed component reliability analysis
Diversity provision
Conclusion
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

3. Abstract Safety requirements:
Requirement 7 of IAEA SSR-2/1: The levels of Defence-In-Depth shall be independent as far as practicable... In particular, safety features for design extension […] shall be independent to the extend practicable to those used for more frequent accidents.
Requirement 24 of IAEA SSR-2/1: The design of equipment shall take due account of the potential for common cause failures (CCF) of items important to safety, to determine how the concepts of diversity, redundancy, physical separation and functional independence have to be applied to achieve the necessary reliability.
Proposal of an innovative multi-stage approach performed at the reactor design stage to analyse and specify diversity and reliability requirements for independent design features to back-up core melt prevention safety features affected by CCF.
Starting from functional analysis of accidents Ending to specifications of detailed equipment diversity provisions.
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

4. Functional analysis
Identification of diversity requirements is based on a case-by-case systematic functional analysis of the most frequent Postulated Initiating Event (PIE)
assuming the main redundant safety features are affected by CCF,
and determining where and how diversity is required to achieve the safety goals.
In an early design approach when no details on severe accident mitigation features are known, only the reactor core damage risk could be considered so that diversity requirements apply to features belonging to the third level of DiD.
The analysis of CCF affecting safety features is driven by probabilistic criteria
PIE : Postulated Initiating Event
CDF : Core Damage Frequency
FI: PIE frequency
Pf : Front line mission failure probability
Pd : Diverse line mission failure probability
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

5. functional analysis (2)
Examples of reliability targets for diverse line with CDF < 10-8 /ry
Example of functional analysis of a PIE:
PIE: Small LOCA, reactor at full power; (FI~ 10-3/ry)
Fundamental Safety Function: Decay Heat Removal;
Safety function: Ensure RCS water inventory by make-up;
Front line: Medium Head Safety Injection (MHSI) trains; (PF = 10-3)
Diverse line: Diverse Safety Injection trains (with or without RCS depressurization). (PD < 10-2)
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

6. System Reliability analysis (1)
Simplified 3-train architecture for Medium Head Safety Injection (MHSI)
Equipments: Motor (M) / pump (P) / motor-operated valve, MOV (V)
Selection of the most important component within the diversified redundant train
Diversified train
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

7. System Reliability analysis (2)
The quantification of the total system reliability is based on the respective component reliability
Table Legend: M: Motor; P: Pump; V: MOV; N: without diversity; Y: with diversity
Conclusions:
Using MOV or Motor diversity would not lead to a significant reliability increase (e.g., between 1% and 3%) compared to the configuration without any diversity.
Diversifying the Pump within the third redundant safety injection train leads to a significant increase in the function reliability (~ 86%). M P V
Qtot
% (Q0- Q)/Q0) N
Q0 = 6.20 x 10-4 - Y
Q = 6.18 x 10-4
0.3%
Q = 6.01 x 10-4
3.1%
Q = 8.35 x 10-5
86.5%
Q= 8.15 x 10-5
86.9%
Q = 6.49 x 10-5
89.5%
Q= 6.28 x 10-5
89.9%
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

8. System Reliability analysis (3)
Pump of the third Medium Head Safety Injection (MHSI) train is the most important component to diversify
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

9. Detailed component reliability analysis
The objective is to analyse in detail a component candidate for diversity
Functional analysis of the component (e.g. Pump)
Identification of internal parts
Research of independent failure mode
Estimation of failure gravity based on severity, probability and possibility of failure detection
Identification of the critical internal part
Analysis of the potential CCF associated to “internal part” and failure mode  Identification of the CCF coupling factors
Elimination of CCF coupling factors by introducing diversity at : design, quality, manufacturing or maintenance levels
Operating experience
on similar equipment
Failure Mode and Effect Analysis (FMEA)
FMEA upgrade
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

10. Example of component diversity provision
Example for a medium safety injection pump
The here above diversity provisions are not unique and shall ensure the elimination of critical CCF between redundant safety features
Critical internal
macro-part
Most severe
Failure mode
Main
coupling factor
Example of safety pump
diversity provision
Coupling
Breakage due to a bad fitting
Design
Use of different coupling design :
Flexible v.s. Gear coupling
Mechanical seals
Use of different mechanical seal assembly
Bearings
Assembly
Do not perform the bearing maintenance
at the same time
Bolting
Incorrect preload
Or use of welded connections for diversified pump
Flange
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

11. Conclusion
An innovative approach developed with strong synergy between safety team and machinery teams
Methodology applicable at the design stage of a new reactor and based on industrial best practices and operating experience
First diversity provision overview limited to component parts, are identified in a couple of months
Diversity provision allows considering critical CCF between redundant components as eliminated
ABSTRACT
FUNCTIONAL
ANALYSIS
PRELIMINARY SYSTEM RELIABILITY ANALYSIS
DETAILED COMPONENT RELIABILITY ANALYSIS
DIVERSITY
PROVISIONS
CONCLUSION
Diversity analysis for advanced reactor design | IAEA-CN June 2017

12. THANK YOU