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SAFETY AND LICENSING OF SPENT FUEL STORAGE AND
TRANSPORT-Safety issues within spent fuel
transport by AREVA
Stéphane BRUT François DERLOT Laurent MILET 31
May- 4 June 2010
TN INTERNATIONAL
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INTRODUCTION

• Some of the main Safety issues raised during
  last years within French spent fuel transport
• Leaking fuel assembly transport How to transport
  and demonstrate safety of package loaded with
  fuel assemblies with suspicion of water trapped
  in the cladding?
• Double Barriers design for spent fuel packages
  what kind of design to comply with the
  regulation?
• Double Operations controls associated to the
  water exclusion assumption how to fulfilled
  requirement regarding leakage of water as a
  result of error?

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Leaking fuel assembly transport

• What is the problem ?
• Cladding rupture on irradiated fuels involve
• Loss of containment with loss of internal
  pressure
• Potentially allow water to penetrate inside the
  claddings
• Water radiation hydrogen
  generation

• Accumulation of hydrogen in a sealed cavity may
  reached limits of inflammability non acceptable
  from a safety point of view

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Leaking fuel assembly transport

• French history with leaking fuel assembly
  transports
• December 2007 Request by French competent
  Authority for a systematic measurement of
  hydrogen rates for packages transporting at least
  one non-sealed fuel rod
• From this request systematic measurement of
  rates of hydrogen upon arrival at recycling
  facility (LA HAGUE) for packages transporting
  fuel identified as ruptured.
• Measurements gave a hydrogen rate far below
  safety limits of inflammability (around 3)
• Beginning 2009 upon French Authority request , TN
  International carried out linear extrapolation of
  hydrogen generation to include real periods of
  transport margin depending of the status of
  transport (national, continental transport,
  intercontinental)
• Results according this approach some transports
  that were checked as conform at the recycling
  site arrival would be determined as non conform
  regarding safety criteria
• French competent authority requested a new
  procedure for new transport
• Measuring of hydrogen rate before transport and
  at least two days after closing the cavity
• Carrying out linear extrapolation taking into
  account real period transport and safety margin

• New procedure extremely restrictive for transport

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Leaking fuel assembly transport

• TN International action plan to improve leaking
  fuel assembly transport
• 3 ways in progress
• Using a neutral gas to increase inflammability
  threshold.
• Helium atmosphere increase in the same condition
  the inflammability level from 3 to 5
• An application in under progress with French
  Competent Authority
• To characterize a hydrogen generation law less
  penalizing as linear extrapolation.
• To develop solution such as catalytic recombiner.
• Such a solution experimented on a TN17T package
  for the wet transport of spent fuel at TIHANGE
  (Belgium) showed a stabilization of hydrogen
  rates about 0.6
• Aim of TN INTERNATIONAL is to implement this
  technology on a first dry transport of spent
  leaking fuel in France before long.

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Double barriers design for packages

• 2005 IAEA regulation request regarding
  sub-criticality
• Sub-criticality of a package may be demonstrated
  assuming water exclusion from the containment
  system, if and only if the design is based on a
  multiple high standard water barriers.
• Nevertheless it is widely agreed by competent
  authorities that a double watertight high quality
  standard is enough to comply with this
  requirement.
• Application to spent fuel cask of such a
  requirement
• Usually spent fuel casks are constituted of a
  thick vessel made of steel or cast iron regarding
  radiation level that may involve 2 types of
  design
• Double-lid design
• Double-vessel design

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Double barriers design for packages

• Double-lid design

Advantages - strength of the body - high thermal conductivity of the shell - simplification of design of drying orifices - optimization of mass, dimensions and so cost
Drawback - to demonstrate the containment barrier when material subject to brittle fracture at low temperature
Thick shell in steel or iron cast
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Double barriers design for packages

• Double-vessel design

Advantage - Two complete different barriers
Drawbacks Gap between the two vessel reduce the thermal performance If drying of the cavity is request in case of loading or unloading underwater operation, difficulties to design and perform drying orifices through the two barriers Risk of water trapped between the two vessels in case of loading or unloading underwater operation Increase of mass, size , of the package to compare a double lid design More complicated to design, manufacture and use than a double-lid
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Double operations Controls associated to the
water exclusion assumption

• 2005 IAEA regulation request regarding
  sub-criticality
• According 677 sub-criticality shall be
  demonstrated assuming water flooding within all
  spaces of the packaging, except if the design
  incorporates special features to prevent such
  leakage of water into or out of certain void
  spaces, even as a result of error.
• Such features than can prevent inleakage
• May be either a single barrier design licensed
  according 1985 IAEA regulation and submitted to
  multilateral approval or a multiple barrier
  design licensed according 2005 IAEA regulation
• Are based on design components (leaktight
  sealing,) that we can call Confinement
  Components" by analogy to regulatory Confinement
  system regarding criticality safety. And
  confinement operation may be defined as any
  operation that may result in reducing the
  efficiency of a confinement components as a
  result of error, standing for a human or a tool
  failure.
• To prevent error resulting in leakage of water,
  French competent Authority require that
  confinement operation need to be performed twice
  independently (different operators and tool).

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Double operations Controls associated to the
water exclusion assumption

• Application of double controls system to drying
  operations by AREVA
• For packages loaded in pools, water is removed by
  draining then vacuum drying of the cavity . To
  prevent ice formation, vacuum pressure shall be
  maintained over 6mbar abs. Drying criteria is
  usually a pressure rise limit during a short time
  Control of the pressure is the key
  operation
• Double control is then implemented
• by measuring continuously the pressure though a
  double recording measuring device
• Then a different operator from the one performing
  the test check the pressure level and the
  pressure rise on the second device

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Double operations Controls associated to the
water exclusion assumption

• Usually designs confinement components are
• Shell (s) and welded bottom
• Lid (s) equipped with seals and secured by bolts
• Orifice covers equipped with seals and secured by
  bolts
• Application of double control by AREVA
• Draining and drying of the cavity see previous
  slide
• Fastening of bolts to the required torque
  2 operators with a different tool for a single
  barrier or one different operator and tool for
  each barrier in case of double barriers
• Check of the leak tightness of the lid and
  orifices 2 operators for pressure
  measurement for a single barrier or one different
  operator for each barrier in case of double
  barriers

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Double operations Controls associated to the
water exclusion assumption

• To be noticed
• That in case of sub-criticality demonstration
  based on a complete flooding of all of the void
  space of the cavity , double controls system are
  not required
• That multiplying operations and controls has
  significant effect on the radiation dose of
  operators. Such a program should not be extended.