General Safety Approaches for Fuel Cycle Facilities FCF

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General Safety Approaches for Fuel Cycle
Facilities (FCF)
Dominique GRENECHE
AREVA NC - DRD

• ALISIA info day meeting on MSRs Paris, March 4,
  2008

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Content

• The framework of the analysis
• Safety approaches for existing FCF
• Selection of FCF considered
• Inventory of risks in these facilities
• Safety approach for these facilities
• The safety of the fourth generation FCF (G4 FCF)
• Evolution of risks to be considered
• Applicability of of new safety approches
  developed for NPPs
• Conclusions

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• Within the scope of Gen-IV activities, creation
  of a specific international working group, RSWG
  ( Reactor Safety Working Group ) to study
  safety issues for Gen-IV reactors
• To complement this effort, creation (2005) of a
  French group, gathering experts from EDF, CEA,
  AREVA the GCFS ( Groupe Consultatif Français
  de Sûreté )
• Main assigments of GCFS are to
• Develop a suitable and  technology neutral 
  safety approach for Gen-IV Nuclear Energy Systems
  (G4 NES)
• Harmonize thoughts and positions on safety of
  each G4 NES
• Ensure that RD work on safety is relevant and
  optimized
• Assist dialog with safety authorities
• The safety of Fuel Cycle Facilities (FCF) must be
  adressed in these workings this is the purpose
  of this presentation

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Content

• The framework of the analysis
• Safety approaches for existing FCF
• Selection of FCF considered
• Inventory of risks in these facilities
• Safety approach for these facilities
• The safety of the fourth generation FCF (G4 FCF)
• Evolution of risks to be considered
• Applicability of of new safety approches
  developed for NPPs
• Conclusions

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Selection of FCF considered

• NOTE AREVA operates ALL kinds of FCF (except
  final disposal)

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Specific risks associated with FCF

• FCF feature quite different kind of risks than
  reactors

• Dispersable materials powders, gases,
  solutions,
• Materials undergo physicochemical transformations
  ? potential violent reactions, corrosion, fires,
  explosions,
• High inventories of radioactive and / or fissile
  materials
• Volume, mass and physicochemical form of fissile
  materials evolve constantly in a process
  criticality risks increased
• Numerous handling operations ? increased human
  errors
• Variety of systems and processes ? numerous and
  diversified maintenance and repairs (radiological
  exposure risk increased)
• Much more flows of radioactive effluents and
  waste
• BUT ..
• Generally low pressures and low
  temperatures processes

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Inventory of risks in FCF internal nuclear
risks (1/2) non nuclear origin

• Fire hazard
• Highest risk in most facilities (chemical
  products in different forms)
• Example fire in a storage silo of zircaloy
  waste at La Hague(1981)
• A specific  Fundamental Safety Rule  (FSR) is
  devoted to this risk
• Chemical hazard
• Can lead to fires (see above), explosion (Kyshtym
  disaster in 1957)
• Can cause degradation of safety equipements (ex.
  corrosion of a containement), injuries,
  environmental effects,
• Typical example UF6 risk (ex fatal accident
  in the USA in 1986)
• Other non nuclear risks
• Handling risks
• Electrical risk
• Internal flooding

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Inventory of risks in FCF internal nuclear
risks (2/2) nuclear origin

• Criticality
• Risk that deserves the most attention (with fire)
  in FCF
• Past 50 years 22 accidents reported (ex-USSR,
  USA, last one in Japan in 1999, never in France)
• Needs very strict preventive measures (mass,
  concentrations, geometry, neutronic poisons, )
• In France, covered by a specific FSR
• Contamination
• Needs for effective and permanent containment
  system
• Multiple barriers (static dynamic) high
  performance monitoring
• In France, covered by a speecific FSR
• Irradiation appropriate shieldings, controlled
  access,
• Others internal risks
• Radiolysis (potential source of gaz such as H2 ?
  explosion, pressure)
• Heat release (ex storage of fission products)

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Inventory of risks in FCF other risks

• External hazards
• Not specific to FCF but require special treatment
  (? specific FSR)
• Aircraft crash (except terrorist attack ?
  physical protection)
• Earthquakes
• Meteorological strong winds, floods, excessive
  heat or cold, )
• Industrial environment external explosion,
  collapse of external stuctures (cranes, external
  fires, )
• Risks related to abnormal radioactive releases
• Not specific to FCF but require special treatment
  (? flows higher than in nuclear reactors)
• In France, very stringent limits for normal
  operations (specific decrees)
• Any exceeding of these limits constitutes safety
  related issues

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Safety approach for FCF (at the design level)

• Fundamental principal
• As for reactors, FIVE levels of DiD are
  considered for FCF
• This deterministic approach is supplemented, if
  necessary, with a Probabilistic Safety Assessment
  (PSA) but it is more difficult to implement for
  FCF
• Lack of extensive operational feed back
  experience for most facilities (most FCF have
  unique technical characteristics)
• Few attempts to establish and conduct PSA for FCF
  USA (NUREG-1513, 2001), IAEA (TECDOC-1267,
  2002), Japan, England, France (see references in
  the paper)

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Elements of deterministic approach (1/2)

• Safety functions (3 for reactors)

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Elements of deterministic approach (2/2)

• Protection of vital functions Three types of
  systems are implemented
• These systems are often doubled (even tripled)
  and diversified so as to prevent a single event
  (eg, fire or flooding) from simultaneously
  affecting several systems performing the same
  function
• They are also designed to comply with the  fail
  safe  principle

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Content

• The framework of the analysis
• Safety approaches for existing FCF
• Selection of FCF considered
• Inventory of risks in these facilities
• Safety approach for these facilities
• The safety of the fourth generation FCF (G4 FCF)
• Evolution of risks to be considered
• Applicability of of new safety approches
  developed for NPPs
• Conclusions

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Considerations regarding G4 FCF (1/3)

• Uranium conversion facilities
• All processes make use of conventional chemical
  transformation steps dissolution, liquid/liquid
  exchanges, evaporation, precipitation,
  calcination, fluorination, crystallisation, etc
• No major changes in the nature of these
  processes are anticipated in the future
• Thus, the types of risks (mainly chemical risks)
  should be the unchanged for G4 uranium conversion
  facilities
• Enrichment
• Almost unique technology will dominate the world
  market in the next decades centrifuge
• Thus, no major change is anticipated in risk
  analysis, even criticality risk for enrichment
  greater than 5 (HTRs), because UF6 inventory in
  these facilities is very low
• If, after centrifuge plants, completely new
  technologies such as laser enrichment are
  developed, in-depth revision of safety analysis
  should be needed

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Considerations regarding G4 FCF (2/3)

• Fuel fabrication
• Mixed-OXide fuels (MOX) should remain the
  reference fuel for SFR and LFR and powder mixing
  process (MELOX type) should remain the basic
  process no major change in safety issues
• However, many other options are under
  consideration for G4 systems, which should raise
  quite new safety challenges
• Fuels other than oxide are studied metal,
  carbides, nitrides, inert matrix, etc
• Some G4 reactors will require completely new
  fuels
• HTR coated particles (of which manufacture, for
  example, called upon the use of potentially
  explosive gases
• GFR radically innovative concepts such as plate
  design with ceramic cladding and dispersed fuel
  (current CEA design)
• Recycling of minor actinides will entail remote
  handling facilities and thus completely new
  safety analysis (particularly because of highly
  radioactive products entering the manufacturing
  process)

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Considerations regarding G4 FCF (3/3)

• Reprocessing
• Two large categories of processes
• Aqueous, PUREX being the dominant process (and a
  mature technology)
• Non acqueous, which include mainly 3 types
• Pyrometallurgical (high temperature processing of
  metallic fuels)
• Pyrochemical (high temperature processing of
  oxides or carbides fuels)
• Fluorides volatility (conversion to fluorides and
  then fractional distillation)
• Safety of aqueous processes are now well
  controlled because of very large industrial
  experience feedback (La Hague plant in France)
• Conversly, most of non aqueous processes have not
  been developed at a large scale and would raise
  specific new safety issues
• Interim storage
• Two types of facilities underwater (pools) and
  dry storage (vaults, casks, )
• Both of them benefit from significant
  safety-related experience feeback
• Risk analysis should not undergo significant
  modification, except if long term storage of
  extremely radioactive and thermogenic product are
  developed (Cs, Sr, Cm, )

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Applicability of new safety approaches to FCF

• Principals for safety analysis of G4 nuclear
  systems are developed in paper N 7168 of
  ICAPP2007 issued by the GCFS  Safety approach
  for the design and the assessment of future
  nuclear systems 
• They are fully applicable to G4 FCF and include
  
• Defense-in-Depth (as a basic principle)
• notion of  safety architecture  with  lines of
  protection , that is a coherent combination (in
  terms of performances and reliability) of
  protection  provisions  (active or passive
  systems, intrinsic characteristics, operation and
  control procedures, etc.)
• Notion of  practical elimination  of accidents
  that cannot be considered physically impossible
  but that can lead to unacceptable radioactive
  releases into the environmemt

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Content

• The framework of the analysis
• Safety approaches for existing FCF
• Selection of FCF considered
• Inventory of risks in these facilities
• Safety approach for these facilities
• The safety of the fourth generation FCF (G4 FCF)
• Evolution of risks to be considered
• Applicability of of new safety approches
  developed for NPPs
• Conclusions

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Conclusion

• Risks to be taken into account in the FCF are of
  nature rather different from those which are
  encountered in power reactors and their relative
  importance varies much from one type of facility
  to another
• However, present as well as future safety
  approaches implemented for power reactors are
  applicable to FCF
• Probabilistic Safety Analysis remains
  nevertheless little practice in FCF and still
  requires significant developments for these
  fcilities
• Future FCF should not reveal really new risks but
  industrial development of innovating processes
  or technologies could modify significantly the
  safety analysis of these facilities (example are
  Laser enrichment, new fuels for HTRs or GFRs,
  non-aqueous reprocessing)