SNL and BAM collaborate on issues regarding extended interim storage of spent nuclear fuel. BAM research on metal seals, elastomer seals, and polymers does not indicate safety issues so far regarding long-term performance. SNL is focusing on closing the technical gap associated with high burnup fuel cladding through further mechanical testing, thermal analysis, and transportation loading tests.

1. 7th US/German Workshop on Salt Repository Research, Design, and Operation
Holger Völzke
Bundesanstalt für Materialforschung und –
prüfung (BAM)
Ken B. Sorenson
Sandia National Laboratories (SNL)
Washington, DC
September 7-9, 2016
Issues on Aging of Spent Fuel Storage Systems
Sandia National Laboratories is a multi mission laboratory managed and operated by Sandia Corporation, a wholly owned
subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration
under contract DE-AC04-94AL85000. SAND2016-8277 C

2. Contents
 Background of SNL-BAM collaboration
 BAM research activities associated with
extended interim storage issues and aging
management
 SNL activities associated with extended
interim storage issues and aging management
2

3. Background of SNL-BAM
collaboration
3
 SNL and BAM collaborate in the areas associated with the
back-end of the commercial nuclear fuel cycle; specifically on
packaging, transportation, and storage of spent nuclear fuel.
 A Memorandum of Understanding (MOU) between SNL and
BAM was established by 2012. Bilateral meetings/workshops
take place twice a year.
 Extended interim storage of spent fuel and HLW needs to be
addressed as a major issue in both countries due to delayed
disposal siting procedures.
 Various technical issues concerning degradation effects of
casks and inventories during extended periods of interim
storage have been identified and specific investigations are
being performed.

4. BAM Research Activities
4
 BAM Research Activities related to Extended Interim
Storage Issues
 BAM Seal Investigations
 Metal Seal Systems
 Elastomer Seal Systems
 Polymer Degradation Effects investigated by BAM

5. BAM research activities related to
extended interim storage: General remarks
5
 The need for the extended interim storage of SNF and HLW
casks towards disposal implicates additional challenges for
the nuclear waste management strategy in Germany.
 Improved knowledge and data bases about the long term
performance of casks and their inventories is essential for
future extended storage licenses.
 Recently, governmental research programs have been
adjusted in Germany to address technical and scientific issues
in this area.
 BAM has identified the need for demonstrating the extended
long term performance of seals and polymers used in dual
purpose casks and has already initiated specific R&D
programs. Additional or extended R&D programs are
scheduled.

6. BAM research activities related to
extended interim storage (1)
Long term performance of metal seals, elastomeric seals, and
polymers for neutron shielding purposes
 Preliminary investigations and laboratory tests performed
by BAM for many years
 Project “LaMEP” (Long term investigations on metal seals,
elastomer seals, and polymers) funded by BMWi/GRS for
3 years (2015-2018).
Major Goals are:
 Extension and continuation of initial test series to gain further
systematic material data,
 Development and validation of analytical approaches for the
extrapolation of selected material or component properties to longer
periods of time. 6

7. BAM research activities related to
extended interim storage (2)
Project „New Developments in the Long term Dry Interim
Storage of Spent Nuclear Fuel and Vitrified High-Level Waste“
 Funded by BMUB for 3 years (2015-2018)
Project Lead: GRS Sub-contractors: BAM and Öko-Institut
 Main topics:
1. State of the art and review of national and international developments in
interim storage of spent nuclear fuel and HLW
2. Aging management
3. International activities
4. Non-accessible areas (cask inventories)
5. Organizational and ethical aspects
 BAM key topics:
- National and international regulations and guidance
- Aging Management: technical aspects, integrated approach, gap analyses
- Evaluation of international activities in the area of long term dry interim
storage
7

8. Test Parameters
Temperatures: +20°C +75°C +100°C +125°C +150°C
Holding times since: 02/2009 01/2014 11/2010 01/2014 02/2009
Seal type Al + Ag Al + Ag Al + Ag Al + Ag Al + Ag
BAM laboratory tests with continuous
leakage rate measurement during seal
loading and unloading
Long term performance of Helicoflex® metal seals concerning
seal force, useable resilience and leak tightness
8
BAM metal seal investigations (1)

9. Restoring seal force (Load Fr) reduction depending
on holding time and temperature
0
200
400
600
0,005 0,05 0,5 5 50 500 5000
Load[N/mm]
Holding Time [weeks]
150 C
20 C
100 C
Ag-Seals
40 Years 100 Years
75 C
125 C
58%
85%
0
200
400
600
0,005 0,05 0,5 5 50 500 5000
Load[N/mm]
Holding Time [weeks]
20 C
100 C
150 C
40 years75 C
125 C
50%
79%
100 years
Al - Seals
Computer
tomography scan
of an Al-seal after
3 months at 150°C
9
BAM metal seal investigations (2)
Major outcome so far:
Seal function and leak
tightness are not affected by
seal force reductions

10. Relevance for:
 Auxiliary seals in spent fuel and HLW casks
 Primary seals in LLW/ILW casks
Major topics:
1. Investigation of the low temperature behavior down to -40°C
Results published by Matthias Jaunich, Wolfgang Stark, and Dietmar Wolff:
 Low Temperature Properties of Rubber Seals
Kgk-Kautschuk Gummi Kunststoffe, 2011. 64(3): p. 52-55.
 A new method to evaluate the low temperature function of rubber sealing
materials Polymer Testing, 2010. 29(7): p. 815-823.
 Comparison of low temperature properties of different elastomer
materials investigated by a new method for compression set measurement
Polymer Testing, 2012. 31(8): p. 987-992.
10
BAM elastomer seal investigations (1)

11. 2. Aging of elastomer O-rings under thermo-mechanical loads
Investigation program with selected rubbers (HNBR, EPDM and FKM) tested as O-rings
with an inner diameter of 190 mm and a cross sectional diameter of
10 mm since May 2014.
The O-rings are oven-aged at four different temperatures (75 , 100 , 125 , 150 °C).
They are examined after various times between one day and 5 years.
 In order to be able to compare between compressed and relaxed rubber, the
samples are aged in their initial O-ring state (Fig. 1)
 As well as compressed between plates (Fig. 2) with a deformation of 25 %
corresponding to the actual compression during service
 Furthermore, we are aging samples in flanges that allow leakage rate measurements
(Fig. 3).
Fig. 1 Undeformed O-rings
Fig. 2 Half O-rings compressed between plates Fig. 3 O-ring in flange for
leakage measurements 11
BAM elastomer seal investigations (2)

12. 12
BAM elastomer seal investigations (3)
 The test set-up can lead to heterogeneous aging caused by diffusion-limited
oxidation (DLO) effects. These effects depend on material, dimensions, time and
temperature. Heterogeneous aging results in distorted bulk properties such as
compression stress relaxation and compression set (CS) suggesting that HNBR has
better performance than EPDM at 150 °C but which is not the case at 100 °C.
 CS represents the resulting permanent deformation after the load is removed
(CS=100% means no elastic recovery anymore).
 The presence of heterogeneous material properties due to thermo-mechanical
aging was shown by hardness measurements across the seal cross-section.
 If DLO-affected data is excluded, extrapolations of CS data are possible using time-
temperature shifts and Arrhenius graphs.
 According to the extrapolations to 23 °C, exemplary CS values of 50 % and 80 %
would be reached after approx. 10 years and 29 years, respectively for HNBR and
after approx. 400 years and 1100 years, respectively for EPDM.
Selected results from aging investigations of elastomer O-rings
under thermo-mechanical loads
Kömmling A, Jaunich M, Wolff D, Effects of heterogeneous aging in
compressed HNBR and EPDM O-ring seals, Polymer Degradation and
Stability (2016), doi: 10.1016/j.polymdegradstab.2016.01.012.

13. Ultra-High
Molecular Weight
Polyethylene
(U)HMW-PE
for neutron
radiation shielding
CASTOR® HAW28M
cask design by GNS
13
Polymer degradation effects
investigated by BAM (1)
Basic requirement: Sufficient long term neutron
radiation shielding without safety relevant
degradation
Degradation effects to be considered:
 Temperatures (max. 160 °C and decreasing during
storage)
 Thermal expansion
 Structural changes from semi-crystalline to
amorphous
 Gamma radiation (decreasing during storage)
 Structural damages and/or crosslinking
 Hydrogen separation
 Mechanical assembling stresses
 Stress relaxation
 Gamma irradiation tests by BAM (at room temperature)
 Low dose irradiation (60Co source): 0.5 – 60 kGy
 High dose irradiation (conservative max. storage dose): 600 kGy

14. Further gamma irradiation tests with material
blocks of 10*10*50 cm³
0 kGy
50 kGy
100 kGy
200 kGy
400 kGy
600 kGy
UHMW-PEHMW-PE
Exemplary outcomes for UHMW-PE show an increase of the insoluble, crosslinked
fraction after high dose gamma irradiation
Further investigations planned:
 Thermal aging of(U)HMW-PE at elevated
temperatures
 Combination of radiation and thermal aging
 Development of adequate prognostic
methods to allow extrapolation of long term
material performance
14
Polymer degradation effects
investigated by BAM (2)

15.  DOE Program Objectives: Storage and Transportation R&D
 Closing the High Burnup Spent Fuel Cladding Technical Gap
 These activities are funded through the U.S. Department of Energy,
Office of Nuclear Energy. BAM and SNL meet on a regular basis to
collaborate on technical issues, and development and analysis of data
 BAM and SNL are also collaborators on a DOE/Euratom sponsored
International Nuclear Energy Research Initiative (I-NERI) entitled:
Assessing the Integrity of High Burnup Spent Nuclear Fuel
in Long Term Storage and Transportation
15
SNL activities associated with the
BAM/SNL collaboration

16.  Preparing for extended storage and eventual large-scale
transport of spent nuclear fuel (SNF) and high-level waste
(HLW)
 Developing the technical basis for:
 Extended storage of used nuclear fuel
 Fuel retrievability and transportation after extended storage
 Transportation of high burnup used nuclear fuel
16
DOE Program Objectives:
Storage and Transportation R&D

17. What is the fuel cladding issue?
 Reactor operations
• Hydrogen is absorbed into the cladding
• Fission gas build-up increases rod internal
pressures  cladding hoop stress
• Longer operating times and high burnup fuel
(> 45 GWd/MTU) increase these effects
 Dry storage
• The drying cycle creates a thermal spike that
brings H back into solution
• H precipitates preferentially with radial
orientation under subsequent cooling and
cladding hoop stresses
• Degradation of cladding mechanical
properties due to re-oriented hydrides
 Transportation loadings
• Normal conditions of transport induce
cladding stresses due to over-the-road (rail)
loadings
• Cladding integrity during transport needs to
be demonstrated
Billone, “Update on Testing to Evaluate
Radial Hydrides”, U.S. NWTRB Meeting
Presentation, Feb 17, 2016, ANL
Hanson, “DOE R&D in Support of High Burnup
Spent Fuel Dry Storage and Transportation”,
EPRI ESCP Int’l Subcommittee Meeting,
Apr 14, 2016, PNNL
17
Closing the high burnup used fuel technical
gap associated with fuel cladding

18. Mechanical testing on high burnup fuel cladding:
 Ring compression testing at Argonne National Laboratory
Determines Ductile-to-Brittle Transition Temperature
(DBTT) of cladding, an indicator of material brittleness
• Highly dependent on internal rod pressure
• Dependent on maximum temperatures seen during
drying
Billone, “Update on Testing to Evaluate Radial
Hydrides”, U.S. NWTRB Meeting, Presentation,
Feb 17, 2016, ANL
18
Closing the high burnup used fuel technical
gap associated with fuel cladding

19. Mechanical testing on high burnup spent fuel:
 Cyclic Integrated Reversible-Bending Fatigue Tester (CIRFT)
at Oak Ridge National Laboratory
• Determines the flexural stiffness of the cladding/fuel “system”
• Stiffness provides a measure of fuel/cladding strength
under mechanical loads
• CIRFT testing provides valuable insights regarding
• Pellet-Clad interactions
• Pellet-Pellet interactions
• CIRFT testing provides a good measure of fatigue strength
All figures and picture: Wang, et al., “CIRFT Testing of High-
Burnup Used Nuclear Fuel from PWRs and BWRs”,
U.S. NWTRB Meeting, Presentation, Feb 17, 2016,
Oak Ridge National Laboratory
19
Closing the high burnup used fuel technical
gap associated with fuel cladding

20. Thermal analyses on high burnup spent fuel in storage:
 Thermal analyses on the DOE/EPRI Confirmatory Demonstration Project cask
loading with high burnup fuel:
• Best estimate given fuel vendor data and current drying processes
• Regulatory thermal analyses penalty factors removed
• Best estimate maximum cladding surface temperatures are much less than
the regulatory limit of 400 °C
• Indicating:
• Less Hydrogen going into solution that can re-precipitate in a radial orientation
• Lower internal rod pressures that effect H radial hydride reorientation (PV=nRT)
Hanson, “DOE R&D in Support of High
Burnup Spent Fuel Dry Storage and
Transportation”, EPRI ESCP International
Subcommittee Meeting, Apr 14,
2016, PNNL.
Maximum cladding surface temperature for each assembly in the demo cask 20
Closing the high burnup used fuel technical
gap associated with fuel cladding

21. Normal Conditions of Transport (NCT) Loadings:
 Shaker table and Over-the-Road Truck and Rail (shaker table only) tests were conducted
on a surrogate PWR assembly to estimate realistic loadings that a spent fuel assembly
may see during transport.
• Accelerations and strains were obtained on both the surrogate assembly and the conveyance
• Placement of instrumentation was informed by analyses
McConnell, “Sandia Shaker Table and Over-
the-Road Vibrations Studies”, US NWTRB
Meeting, Feb 17, 2016, SNL.
 Large margin of safety relative to either elastic or fatigue failure criteria
21
Closing the high burnup used fuel technical
gap associated with fuel cladding

22. FY16 Activities:
 Ring Compression Tests: Conduct additional RCTs
to better understand DBTT Zirlo results at 350 °C:
• Higher H content?
• Lack of radiation-hardening annealing at 350 °C?
 CIRFT Tests:
• Tests on TMI (low Sn Zirc) and Surry (Zirc) samples
• Tests on lower sections of fuel rod
 Thermal Analyses:
• Conduct best estimate analyses of other licensed storage
designs
 Thermal Tests:
• Conduct thermal benchmark test to obtain maximum cladding
surface temperatures using higher design temperatures/pressures
 Transportation NCT:
• Plans are underway to conduct a full-scale ENSA ENUN-32P rail
cask with surrogate assemblies to obtain over-the-rail loading
data
22
Closing the high burnup used fuel technical
gap associated with fuel cladding

23.  SNL and BAM collaboration addresses various technical issues regarding
aging effects on spent fuel storage systems and regular workshops are
held to share information.
 BAM investigations on aging effects of metal seals, elastomer seals and
polymers don’t indicate a major safety issue regarding the long term
performance of such materials and components so far. Investigations are
going to be continued and expanded.
 SNL focusses on the technical gap associated with fuel cladding:
 Further testing will focus on cladding response and performance under
realistic temperatures, hoop stresses, and external stresses,
 Indications are that cladding, including for high burnup fuel, will continue to
perform its safety functions during extended storage and normal conditions
of transport.
23
Summary