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G.B. Bruna IRSN/DSR. GENERATION IV NUCLEAR REACTORS. Preliminary safety considerations on SFR GEN-IV Prototype. TRISO. SFR. VHTR. SUMMARY Introduction GIF Framework Objectives for the GEN-IV Systems Insight on the French strategy Expectations for the safety demonstration

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Generation iv nuclear reactors



Preliminary safety considerations on SFR GEN-IV Prototype





  • Introduction

    • GIF Framework

    • Objectives for the GEN-IV Systems

    • Insight on the French strategy

    • Expectations for the safety demonstration

  • Overview of the main features of the GEN-IV reactor concepts focusing on :

    • A short description

    • Advantages & Drawbacks

  • Focus on the SFR concept and its safety features

Reference : document on the web site of the IRSN :



  • Others public references:

  • / GEDEPEON May 2007

  • / PHYSOR, Chicago, 2004

GIF Framework

Objectives and Context for the GEN-IV Systems

Energy market

Financial risk

Parameters to account for …



Public acceptance



The designer

Objectives and Context for the GEN-IV Systems

Should they exist !

Design and operating feedback

Safety issues derived from licensing process

It is difficult to go beyond the main safety principles

Requirements: «  what it is wished and what it ispossible: that’s the question » !

Specific issues for GEN-IV new systems (technological orientations, challenges, etc.)

New safety objectives, new standards…

Participants in the G.I.F.

Russian Confederation

People’s Republic of China

Objectives for the GEN-IV Systems

  • Reduction of fault rate of normal operation equipments,

  • Increased protection against external attacks and hazards (plane crash, malevolence, etc.),

  • Very low probability of major core damage:

    • Design features

    • Passive protection system,

      No need for off-site emergency plan for severe accidents

    • According to a defense in depth design approach including severe accidents in the design basis.


Objectives for the GEN-IV Systems

  • Optimization of the uranium resources and the fissile material inventory (closed fuel cycle),

  • Decrease of the waste volume and storage costs,

  • Waste management taken into account in the design,

  • Multi-functionality (hydrogen, electricity, industrial heat).


Generation IV Systems


  • SFR

  • GFR

  • LFR

  • MSR

  • SCWR







Insight on the French Strategy

  • January 2006, impulse of President J. Chirac for the operation of a GEN-IV reactor prototype by 2020

  • June 2006, adoption of a new Law on the management of radioactive materials and waste, with two milestones:

    • 2012: definition of an industrial scenario for GEN-IV and ADS system

    • 2020: operation of a GEN-IV prototype

Very challenging context !

Insight on the French Strategy

  • December 2006, decisions of the French Council of Ministers, and of the « Atomic Energy Committee »including different representatives of the French Government (Research, Industry, Environment, etc.):

    • involvement of France in the design of GEN-IV systems, in the aim of an industrial deployment in the ‘40

    • priority to the fast reactor systems allowing a closed fuel cycle

    • support to the industry for advanced VHTR system design

Very challenging context !

Insight on the French Strategy

Current Systems Evolutionary Advanced and Revolutionary

About Licensing in France

  • Planning proposed by CEA for the GEN-IV prototype:

    • SFR : 2010 : « principles of innovative safety options »

      2012 : « proposal of a set of options for the prototype »

    • GFR : 2009 : « evaluation of safety options »

      2012 : « safety report »

A part of the irsn s assignment is to serve as the tso for the french nuclear safety authority

Safety Authorities

  • Generalists:

    • power reactors

    • fuel cycle facilities

    • experimental reactors

    • waste

Request forms





  • Specialists:

    • mechanical engineering

    • hydraulics, thermal eng.

    • reactor control

    • I&C

    • severe accidents

    • human factors

    • neutronics

    • seismic studies, etc.









  • Integrating knowledge, summaries

  • Research and development requirements

A part of the IRSN’s assignment is to serve as the TSO for the French Nuclear Safety Authority

Licensing procedures



Licensing procedures


















Authorisation DECREE

SOR: Safety Option Report PSAR: Preliminary Safety Analysis Report

GOR: General Operating Rules PrSAR: Provisional Safety Analysis Report

EP: Emergency Plan FSAR: Final Safety Analysis Report

General expectations for the safety demonstration of GEN-IV systems

  • Enhanced safety compared to GEN-III and GEN-III+ (EPR, AP1000, etc.) At least equivalent criteria (probabilistic approach for severe core damage) and confidence level in the safety demonstration

  • From the IRSN point of view, the current safety approach must be adopted:

    • defense in depth principle,

    • « deterministic » approach, supported by extended PSA insight (including “safety margins” assessment)

  • For systems which have been already built and operated (such as HTR, SFR, LFR, etc) design and operating experience, must be accounted for by the designers to increase the safety.

Safety margins approach

A’ systems



Loss of Safety margins




General expectations for the safety demonstration of GEN-IV systems

« Safety margins » Approach

Definition of the “Risk Space”

and its sensitivity to NPP design changes

General expectations for the safety demonstration of GEN-IV systems

  • The demonstration of the exclusion of events consequences of which are not accounted for in the design (« practically eliminated »):

    • big graphite fire in VHTR, big sodium fire in SFR ?

    • complete break of pipes in VHTR, SFR, GFR ?

    • melting of the core for TRISO type fuel, for SFR, GFR ?

      Which kind of demonstration (« lines of defence », PSA, …) and which confidence level ?

What is not taken into account ?

General expectations for the safety demonstration of GEN-IV systems : main challenges

  • The definition of the most severe accident retained in the BDBA scope, with dedicated safety systems, the prevention, the mitigation of the consequences, mainly concerning the containment/confinement

  • Co-generation: the safety approach retained for coupled VHTR and industrial installations for production of industrial heat, hydrogen, etc.

    What are the events generated by industrial facilities which must be taken into account as operating conditions or external hazards in the safety assessment ?

    Does it exist a safety assessment for such facilities?

    Is their safety assessment consistent with the assessment for nuclear reactors ?

General expectations for the safety demonstration of GEN-IV systems

  • Ambitious targets for the radioprotection and the radiological consequences for the public and workers in operation (DBA, BDBA) and in presence of hazards,

  • A clear identification of

    • the containment/confinement barriers and safety systems,

    • their functional requirements vs. operating, incidental and accidental conditions and hazards

General expectations for the safety demonstration of GEN-IV systems : main challenges

  • The core characteristics, mainly those involved in thesafety studies (neutronics, feedback coefficients, etc.)

  • The study of the most severe reactivity accidents (if not included in the BDBA): prevention, detection andconsequences

  • The extensive use of PSA, with topics which need improvements (data bases for equipment, reliability for passive systems, probability evaluation for rare hazards, etc.)

PART II systems : main challenges

  • Main features of the reactor concepts

  • Maturity of concepts

  • Advantages & Drawbacks

Summary review 1 2

Elements of comparison between GEN-IV concepts systems : main challenges

Summary Review (1/2)

Summary review 2 2
Summary Review 2/2 systems : main challenges

  • No system is able satisfying all the GIF criteria

  • The six concepts do not enjoy the same maturity level : the SFR and the HTR enjoy the most advanced technologies

  • The VHTR does not permit a closed fuel cycle (as far as current designs and technology are concerned), it needs enriched uranium fueling, but shows some major advantages:

    • a resistant barrier around the fuel,

    • a safety founded on a natural behavior of the reactor,

    • a capacity to be coupled to industrial processes (heat, H2, etc.)

  • The SFRallows a closed fuel cycle andenjoys:

    • a proved technology,

    • a widespread operating experience,

      nevertheless it needs some major improvements (neutronics, risks dues to the sodium, ISI, etc.)

SCWR systems : main challenges

Westinghouse concept inel
Westinghouse concept (INEL) systems : main challenges

Westinghouse concept inel1
Westinghouse concept (INEL) systems : main challenges


  • Direct conversion cycle: the vapor which enters the turbine is produced into the core (no benefit for the safety)

  • Fast neutrons (breeder reactor) or thermal neutrons concept


  • The heat exchange between the fuel and the water is not uniform  Great uncertainties on the fuel cooling (especially for the super-critical water)

  • Difficulties with the core design and layout: need for multi-enrichment zones

  • At the stage of feasibility studies / Non nuclear design and operating feedbacks

MSR systems : main challenges

Molten salt reactor
Molten Salt Reactor systems : main challenges

Molten salt reactor1
Molten Salt Reactor systems : main challenges


  • No risk of core melting !

  • Possible on-line extraction of the PFs  low consequences in the case of salts leakages

  • Thorium fuel: abundant « fertile » material

  • Less waste produced by MWe

Molten salt reactor2
Molten Salt Reactor systems : main challenges


Salts are corrosive ( non-metallic materials) and the solubility of the PFs is various in the salts

Melting temperature of the salts > 500°C

Irradiation of the primary circuit structures

Neutronics: complexity (fissions in all the primary circuit !)

This concept has not passed the experimental stage

LFR systems : main challenges

Lead fast reactor
Lead Fast Reactor systems : main challenges

  • ADVANTAGES: systems : main challenges

  • The reactor can be operated with natural or depleteduranium

  • Lead boiling is almost impossible (T>2000°C)

  • No strong pressurization

  • Passive behavior in case of accidental transients  reactor control without immediate acting of protective systems or operators

  • Good compatibility with water (secondary coolant), and no fire risk with air

INCONVENIENTS and/or INCUMBENT systems : main challengesDIFFICULTIES:

  • Molten lead is very corrosive (pumps, clad, vessels, etc.)

  • Difficulty to wash and decontaminate the equipment immerged in the lead  maintenance ?

  • Significant hydrodynamic pressures (BREST: ~ 1,6 bar)

  • ISI: not possible for internal structures (BREST)

  • Difficulties for an core unloading, in case of emergency ?

  • Activation of lead and bismuth: production of long life  waste

  • Not satisfying operating feedback (submarines)

  • Maturity: not advanced

HTR/VHTR systems : main challenges

High or very high temperature reactor
High or Very High Temperature Reactor systems : main challenges

Htrs design and operating experience
HTRs : Design and Operating Experience systems : main challenges

Us experience
US Experience systems : main challenges

Peach Bottom 1 – 1966 -1973

U/Th (high enrichment)

40 MWe

Helium : 350°C / 750°C

Us experience1
US Experience systems : main challenges

Fort Saint-Vrain – 1976-1989

842 MWth et 330 MWth

Spherical coated particles and put into hexagonal graphite blocks

Helium : 350°C / 750°C

German e xperience

AVR systems : main challenges

German Experience

AVR (KFA – Jülich) / 1966 -1987

P = 46 MWth / 15 MWe

Tmax helium : 850°C (up to 950°C in 1974)

Htrs design and operating experience1
HTRs : Design and Operating Experience systems : main challenges

New low power experimental reactors


China / 10 MWth / pebbles

Tsinghua University


Japan / 30 MWth / prismatic blocks


Technical orientations for new power reactors plants technical and technological challenges
Technical Orientations for New Power Reactors Plants Technical and Technological Challenges

  • EUROPE: ANTARES (VHTR- 600 MWth), + R&D project RAPHAEL

  • SOUTH AFRICA: PBMR (400 MWth  pebbles)

  • RUSSIAN FEDERATION: GT- MHR (600 MWth  prismatic blocks of compacts)

  • JAPAN: GTHTR-300 (600 MWth  prismatic blocks of compacts)

  • CHINA (Chinergy): HTR-PM (195 MWe)

The VHTR Technical and Technological Challenges

The VHTR is seen as more efficient than reactors in operation in several aspects:

  • A higher thermodynamic efficiency and a wider scope of applications, because of the very high temperature gas supply,

  • A different commercial approach, to serve the market segment of medium-scale electricity production, as opposed to the traditional nuclear plants for large-scale production of electricity.

  • A minimized environmental impact owing to the robustness of the fuel that retains fission products under both normal and accidental conditions,

  • A better resource utilisation and a contribution to waste minimization owing to

    • Its thermal efficiency,

    • Its quite high burn-up,

    • Its large capacity to transmute Actinides [both Plutonium and Minor Actinides].

Core design

“ The VHTR Core: A Very Heterogeneous System” Technical and Technological Challenges

Core design

Core heterogeneities (1) Technical and Technological Challenges[]

Core heterogeneities (2 Technical and Technological Challenges) []

Control rod penetrations Technical and Technological Challenges

Reactor vessel

ANTARES( free references : [] and []) []

Helium fan

Primary circuit and exchangers

Isolating valves

Heat removal system after reactor shut down

Wall of the reactor building

Plates type exchanger

  • ADVANTAGES: Technical and Technological Challenges

  • Resistant first barrier up to 1600°C

  • Very low power density (few MW/m3)

  • Large inertia due to the important quantities of graphite; fuel temperature 1600°C in case of non protected loss of active systems for the heat removal

  • Design and operating feedbacks noticeable (Peach Bottom, AVR, THTR, Fort Saint Vrain, etc.)

  • Advanced maturity, but for limited reactor powers

INCONVENIENTS and/or INCUMBENT DI Technical and Technological ChallengesFFICULTIES:

  • Fuel cycle open (but some studies aiming at the closure of the cycle have been performed)

  • Weak efficiency of the coolant

  • Significant pressures

  • High or very high temperatures for the structures (internal structures, etc.): materials to develop, specific risks ?

  • Risk and consequences of big breaks on primary circuit (mechanical consequences, graphite oxidation or fire, etc. ?)

  • In service inspection: ?

  • Risks for the reactor due to industrial linked process

GFR Technical and Technological Challenges

Gas fast reactors
Gas fast reactors Technical and Technological Challenges


  • ADVANTAGES: Technical and Technological Challenges

  • Fuel developed for a good resistance at high temperatures (ceramic clad), in case of an accidental loss of heat removal

  • Very low « void effects » in GFR, vs. SFR

  • Helium is chemically neutral

  • A the equilibrium, only the necessity of natural uranium for the fuel re-processing / Possible transmutation of M.A.

Projet rnr g cea
Projet RNR-G (CEA) Technical and Technological Challenges


  • Quite high power density (50 to 100 MW/m3)

  • Very low thermal inertia of the coolant

  • Redundant emergency heat removal circuits (3x100%)

  • The accident of depressurization needs a third barrier under pressure (P ≈10 bar)

  • In service inspection: ?

  • No operating feedbacks

  • Maturity; to develop…

SFR Technical and Technological Challenges

Sodium fast reactor
Sodium Fast Reactor Technical and Technological Challenges

Sodium fast reactor1
Sodium Fast Reactor Technical and Technological Challenges

  • Design and operating feedbacks:

  • Rapsodie, Phénix, Superphénix, « RNR1500 » project

  • PFR


  • SNR 300

  • BN 350, BN 600

    FBTR (India)

  • EFR project

Loop vs Pool

Coupled vs. Modular

Specific requirements for SFR Technical and Technological Challenges

  • Designers need explicit feedbacks on the design and operation of integrated and loop types SFR (Phénix, Superphénix, PFR, Monju, BN 350 and 600, etc.)

  • Expertise of structures and materials, irradiated or not, from Rapsodie, Phénix, etc. would be of great interest (what is planned for PFR, etc. ?)

  • Lessons learned from existing probabilistic studies (Superphénix, etc.) would be useful

Specific requirements for SFR Technical and Technological Challenges

  • Need for the designers to acquire and account for specific experience upon operating experience of past and existing reactors such as Superphénix, PFR, Monju, BN 350 et 600, etc.

  • Perform post operation analysis of irradiated materials from Rapsodie, Phénix, etc. (what is planned for PFR, etc. ?)

  • Account for and take advantage from existing PSA studies (Superphénix, etc.)

  • Include the design and technological advances from « RNR 1500 » et EFR design experience

  • Collect all available information upon FR fleet, worldwide

  • Identify all progress axis and share the R&D effort

Overview of sfr design and operation safety aspects based on french experience
Overview of SFR design and operation Technical and Technological Challenges safety aspectsbased on French experience



Main events

  • Sodium-water reactions (PX) Technical and Technological Challenges

  • Stability and vibrations of internal structures (SPX)

  • Assembly plugging (SPX)

  • Leak of the drum vessel (SPX)

  • Negative Reactivity Trips (AU/RN) (PX)

  • Air ingress in the cover gas (SPX)

  • Argon leak on an intermediate exchanger argon bell (SPX)

Main Events

Main safety aspects 1 4
Main Safety Aspects 1/4 Technical and Technological Challenges

  • Sodium void effects

  • Residual power removal

  • Severe accidents and initiators

  • Sodium confinement

  • Inspectability of structures

  • What to learn from Phenix End-of-Life Experiments

Main safety a spects 2 4
Main Technical and Technological ChallengesSafety Aspects 2/4

  • Residual power heat removal

  • Phénix and Superphénix: residual power underestimated at the design stage

  • Heat removal by overestimated radioactive transfers

    for Superphénix, installation of RUR

    for Phénix, de-rating from 600 to 400 MWth

  • « Total loss of electric supply »: demonstration of a global natural convection is not straightforward

Main safety aspects 3 4
Main Safety Aspects 3/4 Technical and Technological Challenges

  • Severe accidents and initiators

Void and compaction effects:

As early as the design stage for Phénix and Superphénix, consideration of core meltdown  included in authorization decrees

  • Several aspects:

    • prevention (PSA required for SPX)

    • choice of a « symbolic » sequence (SPX) or arbitrary in $/s (PX)

    • thermal and mechanical energy calculations (500 MJ for PX and 800 MJ for Superphénix)

Main safety aspects 4 4
Main Safety Aspects 4/4 Technical and Technological Challenges

  • What to learn from Phenix End-of-life Experiments

Two series of experiments are planned befor the decommissionig of Phenix Reactor :

  • Reactor Physic basisc tests such as:

    • assembly deplacement,

    • introduction of voided zone …

    • rod drop,

  • Operation test (experimental search of the « equilibrium temperature » in natural convection)

  • ADVANTAGES: Technical and Technological Challenges

  • At the equilibrium, fueled with recycled Pu and natural uranium only / Transmutation of M.A. (Am, Cm, Np)

  • Margin of  200°C / sodium boiling in normal conditions

  • No significant pressures in the circuits in sodium

  • Very efficient coolant, large inertia of the reactor in case of loss of convection in the circuits

  • In case of a first barrier leakage or damaging, the sodium acts like a filter for volatile fission products (iodine, cesium, etc.)

  • Sodium circuits under low pressures (few bars)

  • Important and useful design, operating and licensing feedbacks, with Phénix, PFR, Superphénix, etc.: advanced maturity

  • INCONVENIENTS and/or INCUMBENT DIFFICULTIES: Technical and Technological Challenges

  • High power density (300 MW/m3 for Superphénix)

  • Possibility of positive reactivity injection in case of a sodiumvoiding (boiling, bubble ingress, etc.)

  • Chemical sodium risks: strong reactions with water, and air (with important consequences in case of spray fires)

  • Large plutonium inventory

  • Very hard in service inspection:

  • Difficulties for an emergency core unloading

Needs for the gen iv sfr
Needs for the GEN-IV SFR Technical and Technological Challenges

Search for cores with low « void effects »

Better assessment of local meltdown propagation risks in the core and re-criticality risks is needed

Sodium: a few risks are still to be identified

Easy access and control must be provided