Demonstration Test Program for Long�term Dry Storage of PWR

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    Demonstration Test Program for
Long–term Dry Storage of PWR Spent Fuel

                   2 June 2010
                 M. Yamamoto,
       The Japan Atomic Power Company
        The Kansai Electric Power Co., Inc.
          Kyusyu Electric Power Co., Inc.
         Mitsubishi Heavy Industries, Ltd.


1. Introduction
2. Demonstration Test Program
   Test Overview and Process
   Fuel Assemblies for Test
   Outline of Test Container
   Verification Method of Fuel Integrity
   Confirmation during Storage Tests
3. Designing of Test Container
   Current Knowledge and Experience
   Simulated Environment of Actual Casks
4. Summary

1. Introduction
  Mutsu interim spent fuel storage facility in Japan is preparing for the
   maximum 50-year storage of spent fuel in dry metal casks for both
   transportation and storage.

  To reduce risk of radiation exposure to workers and waste materials, the
   facility has no hot cells, and the spent fuel will be confirmed for their
   integrity indirectly by monitoring casks during storage and
   transported after the storage without opening the cask lid.
                             Lots of fuel cladding
                             integrity investigations
Lots of demonstrations &                                Dry storage experiences
                             in Japan
experiences in overseas                                 of BWR fuel in Japan

    Long-term storage test for “fuel integrity” in domestic research facility
    to accumulate knowledge and experience on long-term integrity
    of PWR spent fuel during dry storage.
     To make assurance doubly sure on safety of transportation after storage.

2. Demonstration Test Program (1/5)
 Test Overview and Process

   Time Schedule of Demonstration Test of PWR Fuel Storage
Fiscal year     2009   2010     2011    2012     2013 2023 2033 2043 - - -
                                                 –2022 –2032 –2042 –2052
Planning               Planning
& Designing              Designing
                           Safety analysis
Manufacture                               Manufacturing of test container
& Preparation                             Thermal test
                            (48GWd/t fuel)   (55GWd/t fuel) Preparation & Fuel inspection
                                                            Loading to container
Storage test           48GWd/t type fuel test
& Inspection              55 GWd/t type fuel test
                          Gas sampling                                              ---

2. Demonstration Test Program (2/5)
 Fuel Assemblies for Test
  Up to two spent fuel assemblies (Type 48GWd/t and 55GWd/t ) will be
  48GWd/t : Some of the fuel rods were used for PIE tests, and now it is
   stored in the pool of the hot laboratory in Tokaimura (NDC).
  55GWd/t : a proper spent fuel will be prepared in the future.
                 Fuel assemblies Assumed for Tests
                     Type 17×17 48GWd/t Fuel       Type 17×17 55GWd/t
                            Assembly                  Fuel Assembly
 Burn-up (MWd/t)        42,800 (past record)       ≤55,000 (assumption)
  Cooling period               19 years                   >10 years
                        (as of October, 2012)       (as of October, 2022)

 Cladding material           Zircalloy–4               MDA or ZIRLO
     Remarks             15 empty fuel rods*                Non
       *Fuel rods used in PIE are never used for long-term storage tests.

  2. Demonstration Test Program (3/5)
   Outline of Test Container
                                                                            item          Description
                                                                          Compo-       - Lid
                                                                          nents         (Steel, Resin,
                                                                                         Double metal
  Outer thermal                                                                          gasket)
      insulator*                                                                       - Body
  Inner thermal                                                                         (Steel, insulator,
       insulator                                                                         Resin)
                                                                                       - Basket
        Mid-body                                         Cross section                  (Steel, Boron-Al)
                                                                                       - Outer thermal
Inner container                                                                          insulator
                                                     PWR spent
                                                                          Size         - Height :
                                                     fuel assemblies                     Approx. 5.2m
                                                     Basket spacer                     - Outer diameter
   Neutron shield                                    (Boron-Al)                          Approx. 2.2m
                                                      Basket              Contents     Max. 2 PWR
                                                      (Stainless steel)                spent fuel
                                                       Trunnion                        assemblies
                                                                          Cover gas    Helium (negative
*Note: Outer thermal insulator installed at loading only 48GWd/t F/A is                pressure)
       removed when 55GWd/t fuel assembly is added.

2. Demonstration Test Program (4/5)
 Verification Method of Fuel Integrity
                         Loading to test                   * The following inspections of
[ 48GWd/t fuel assembly] container*                        sampled cover gas are to be
     Inspection of fuel            Start of Storage Test   carried out at the start of storage
     before storage test            under Dry Condition    test after fuel loading;
     – Visual inspection                                    – Kr-85 radioactivity analysis
       of fuel assembly                                    – Gas composition analysis
                                10 years
                                                       Analysis and monitoring
[ 55GWd/t fuel assembly] Loading to test               during storage test
     Inspection of fuel                                – Kr-85 radioactivity analysis
     before storage test
                                                       – Gas composition analysis
      – Visual inspection
        of fuel assembly                               – Monitoring of surface temperature of
                                                         test container
                                                       – Monitoring of containment boundary
                                                         pressure of test container

                                                                         Increase of Kr-85 level
                                       End of Test
                                                                     Suspension of Test
                                    Inspection of fuel
  Flow Diagram of                                                  Investigation of cause
                                    after storage test
  Test Program
                                 – Visual inspection of fuel assembly

2. Demonstration Test Program (5/5)
 Confirmation during Storage Tests
 Sampling of cover gas in test container
  - Confirm detection of fuel leakage
  - Induction of cover gas into sampling pod
  - Scheduling every 5 years
  - Radioactive gas (Kr-85) analysis with a Ge detector
  - Gas components analysis with a mass spectrometer

  Temperature monitoring
   - Estimate temperature history of fuel rods
   - Installation of thermocouples on the outer surface in the middle area.
   - Calculation of the fuel rods temperature with a previously-verified
      assessment tool by thermal performance tests.

  Pressure monitoring
   - Confirm maintenance of containment of the test container
   - Monitoring of helium gas pressure at the lid boundary.
   - Installation of pressure gauges to a buffer tank leading to gap of double
      metal gaskets.

3. Designing of Test Container (1/4)
 Current Knowledge and Experience
                          Evaluation of Degradation Events
Conditions to             Technical Evidence             Actual Conditions of      Test Conditions
be considered                                               Stored Cask                (target)
                No embitterment due to hydride          Around 230°C            Around 230°C
 Thermal        reorientation, failure due to creep     (Gradually decrease     (Gradually decrease
degradation     strain, recovery of irradiation         with decrease in        with decrease in
                hardening, or stress corrosion crack    decay heat)             decay heat)
                under 100MPa or less
                circumferential stress at 275°C

                Negligible oxidation/hydrogen           He gas atmosphere       He gas atmosphere
 Chemical       absorption during storage (inert gas    Moisture:               Moisture:
degradation     atmosphere) compared to that             10% or less             10% or less
                during in-core irradiation
                Negligible neutron irradiation          Burn-up of stored       Burn-up of contained
 Radiation      influence during storage                fuel:                   fuel:
degradation     Saturation of mechanical strength        Maximum 47GWd/t         5GWd/t or more
                due to neutron irradiation at
                relatively low burn-up (around
                Maintenance of integrity under          During storage:         During storage:
Mechanical      normal test conditions of transport      static position         static position
degradation     (free drop) (Acceleration :20 to 45G)   During earthquakes:     During earthquakes:
                                                        Acceleration of 1G      Acceleration of 1G

3. Designing of Test Container (2/4)
 Simulated Environment of Actual Casks
 Chemical degradation
 The test container is filled with helium gas having negative pressure as
  with actual dry cask cavity.
 Vacuum drying operation is carried out before backfilling of helium gas.
 Amount of moisture is confirmed.

Radiation degradation
 Mechanical strength of cladding tubes shows saturation and ductility
  shows slow deterioration at low burn-up (around 5GWd/t).
 Test fuel Burn-up is 42.8GWd/t. (Irradiation dose is 1021 to 1022n/cm2)

Mechanical degradation
 The test container is statically positioned in a vertical direction.

3. Designing of Test Container (3/4)
Simulated Environment of Actual Casks --- Temperature

 Thermal degradation
 The maximum temperature of fuel cladding tubes during the storage test is
  set as around 230°C regarding to design value of actual casks.
 Gradual decrease of fuel temperature is simulated considering to the
  condition of actual casks.

  temperature 1
         (°C)                3
         210                          55GWd/t fuel assembly

                                                     Schematic drawing of Max.
                             48GWd/t fuel assembly
                                                       Temperature transition
             0            10      Test Time (year)

3. Designing of Test Container (4/4)
 Simulated Environment of Actual Casks --- Temperature
            Heat load and max. temperature of cladding at initial test conditions
                          Beginning of test        Addition of 55GWd/t fuel assembly
     Loaded fuel               48GWd/t              48GWd/t (cooling for 29 years) &
     assemblies         (cooling for 19 years)      55GWd/t (cooling for 10 years) .
      Heat Load                547 W                      1472 W (455+1017 W)
     Initial max.           Approx. 250°C                     Approx. 230°C
  temperature of fuel      (at 48GWd/t fuel             (at 55GWd/t fuel assembly)
      cladding                 assembly)

                                                      Thermal analyses were
                                                       conducted for estimation of max.
                                                       temperature of fuel claddings
                                                       covered with He gas.
                                                      The obtained temperatures will
                                                       meet the aimed temperature
                                                       around 230°C or more.
 Thermal Analyses of Test Container (during loading of 48&55GWd/t fuel assemblies)

4. Summary
  Some Japanese utilities are planning to conduct a long-term storage
   test for up to 60 years by placing PWR fuel assemblies in a test
   container simulating temperature and internal gas of actual casks to
   accumulate knowledge and experience on long-term integrity of
   PWR spent fuel assemblies during dry storage.

  The storage test plans such as test methods and inspection items,
   and container design have been prepared. In the future, safety
   analyses, licensing and manufacturing of the test container are to be
   done, and the storage test of 48GWd/t fuel assembly will start in
   fiscal 2012.

  Thermal design of the test container is important. Its temperature is
   controlled with thermal insulators and heat-transfer performance is
   confirmed by heat transfer tests at the completion of the container.

  Others ----- Japan Nuclear Energy Safety Organization (JNES) plans to
   participate in this test from a regulator’s standpoint. We will discuss its
   details in the future.

Supplemental OHP
 Confirmation of containment

                                                           Web data                Server      PC

                       P1    T1        P2        T2
                                                           Controlled area    Non–controlled area
                  V6        V7    V8        V9

                                                             V4          V3
                  V10                                 V5
   Inert gas                 Buffer tank                                 V2
 inlet / outlet                                                          V1

                                                                                    Lid part
                        Schematic Drawing of
                         Pressure Monitoring


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