12 criticality analysis methodology development to support direct disposal of currently loaded dual purpose banerjee ornl

Spent Fuel and Waste Science and Technology
Criticality Analysis Methodology
Development to Support Direct
Disposal of Currently Loaded
Dual-purpose Canisters
Kaushik Banerjee, Henrik Liljenfeldt, and John
Scaglione
Oak Ridge National Laboratory
SFWST Annual Work Group Meeting
May 24th 2017

Spent Fuel and
Waste Science and
Technology
Agenda
 Overview of the criticality analysis related developments over the
past years to support direct disposal of DPCs (10:10 am– 10.35 am)
 Misload analysis methodology to support as-loaded criticality
analysis approach (10.35 am – 11.05 am)
 Updates to the FY15 direct disposal summary report to capture new
developments in the criticality area (11.05 am– 11.20 am)
 Proposed FY18 and future criticality related activities to complete
method/tool development to support direct disposal of DPCs (11.20
am – 11.35 am)
 Discussion (11.35 am - 12.00 am)
May 24, 2017 SFWST Annual WG Meeting 2

Spent Fuel and
Waste Science and
Technology
May 24, 2017 SWFST Annual WG Meeting 3
past years to support direct disposal of DPCs
am – 11.35 am)

Spent Fuel and
Waste Science and
Technology
Direct disposal of already loaded dual-
purpose canister (DPC)s should be
considered regardless of disposal options
 It has been shown that the direct Disposal of DPC is technically feasible for
majority of the loaded DPCs depending on the repository host geology and
has many potential benefits
- Criticality safety demonstration could be a challenge
- Criticality could only be an issue if internal of a DPC degrades partially or
completely in presence of moderator
 Objective for the criticality analysis is to evaluate available margins, options
and parameters of importance to support the feasibility of direct disposal of
DPCs from criticality perspective
 Substantial progress has been made to support the criticality aspect of the
direct disposal of DPCs over the past years
- As-loaded canister-specific criticality analysis
- As-loaded criticality analysis methodology for boiling water reactors (BWRs)
- Credit for available salt (Cl) in the repository medium
- Impact of filler materials on criticality
- Misload analysis methodology to support as-loaded criticality analysis approach

Spent Fuel and
Waste Science and
Technology
UNF-ST&DARDS - A unique tool is being
developed to analyze each loaded canister
for its suitability for direct disposal
 Used Nuclear Fuel- Storage,
Transportation & Disposal Analysis
Resource and Data System (UNF-
ST&DARDS) is being used for as-
loaded canister-specific analyses
 UNF-ST&DARDS integrates data and
analysis capabilities
– Unified database preserves spent nuclear fuel
(SNF) data for generations
– SCALE and COBRA-SFS are being used for as-
loaded criticality, shielding, and thermal analyses
in an automated fashion
 The objective of UNF-ST&DARDS is to
support SNF analysis from the time it
is discharged from the reactor to the
time it will be disposed of in a
geological repository

Spent Fuel and
Waste Science and
Technology
UNF-ST&DARDS has completed as-
loaded criticality analysis of 554 loaded
DPCs at 23 sites
 UNF-ST&DARDS analysis includes
– 12 DPC types including 24-assembly
baskets (flux trap design), 32-assembly
and 37-assembly baskets, and BWR
canister with 68-assembly and 80-
assembly baskets
 Two degradation scenarios were
considered
– Loss of neutron absorber panels (all
sites)
– loss of carbon steel components and
neutron absorber panels (two sites)
 Representative subcritical limit
– keff <0.98 was used in this study as a
representative acceptance criteria for
as-loaded calculations
With loss of neutron absorber panels for PWR sites
With loss of neutron absorber panels and
carbon steel components for two PWR sites

Spent Fuel and
Waste Science and
Technology
A rule-based BWR as-loaded criticality
analysis approach has been developed
 Rule-base approach has been
developed for certain fuel types
(e.g., 6x6, 7x7, 8x8)
– Justification of the axial burnup profiles
(selected from publicly available
sources)
– Justification for modeling fuel
assemblies with uniform axial and radial
enrichments
– Justification for representing axial void
profile by a single value
 Need additional BWR information
(e.g., GE14 data, GNF2, Atrium, etc.)
to further develop rule based
approach
With loss of neutron absorber
panels for BWR sites

Spent Fuel and
Waste Science and
Technology
What else can be credited?
 Components such as burnable poison rod assemblies (BPRAs)
- Requires component loading maps
 Aqueous species in groundwater such as Chlorine
 Preconditioning with filler materials
8
77% of analyzed DPCs are below the
representative subcritical limit with as-
loaded analysis with fresh water
Description Value
Total DPCs analyzed 554
Total DPCs below subcritical limit with loss of neutron
absorber (design-basis loading)
0 (0%)
absorber (as-loaded)
428 (~77%)
absorber and carbon steel structures (as-loaded)
379 (428 -
49) (~68%)
May 24, 2017 SFWST Annual WG Meeting

Spent Fuel and
Waste Science and
Technology
 In addition to salt repository
concepts, Cl is also available (in
moderate quantity) in clay*, granite*
and crystalline rock**
– The quantity of Cl varies between the
geological media
 Literature reviews show that Li and B
may also be available in small
quantity in some geological media*
 Other commonly available dissolved
aqueous species may not yield a
significant neutron absorption effect,
but together may provide a
significant moderator displacement
effect (not studied here)
*Y. Wang et. al., “Integrated Tool Development for Used Fuel Disposition Natural System Evaluation – Phase I Report,”
Prepared for U.S. Department of Energy Used Fuel Disposition, FCRD-UFD-2012-000229 SAND2012-7073P, 2012.
**C.F. Jove Colon et. al. “Disposal Systems Evaluations and Tool Development – Engineered Barrier System (EBS)
Evaluation,” Prepared for U.S. Department of Energy Used Fuel Disposition Campaign, SAND2010-8200, 2011.
Cl is expected to present in all the
geological media under consideration and
provides noticeable reactivity reduction
9May 24, 2017

Spent Fuel and
Waste Science and
Technology
A dedicated set of criticality experiments
to validate Cl credit for disposal
applications is needed
 Extensive literature search conducted
in FY15
– Six commercial proprietary experiments
identified but not available for evaluation
– 141 experiments involving Cl (in PVC,
plexiglass, paint coating) were found in
International Handbook of Evaluated
Criticality Safety Benchmark Experiments
(ISCBEP) but only 11 have a similar
chlorine sensitivity profile shape and
magnitude as the application system
(based on S/U analysis)
– Experiment design and small sample set
make validation through traditional
trending analysis (regression) difficult
 IER to perform an experiment at SNL
involving chlorine is being submitted
to the NCSP
– With a good integral experiment that is
sensitive to Cl and relevant to a SNF
application, we can then validate the
performance of Cl
– Long lead time element
– Cofunding will elevate priority in NCSP
experiments list (proposed FY18 activity)
10
Relative uncertainty of the total cross section of 35Cl
May 24, 2017 SFWST Annual WG Meeting

Spent Fuel and
Waste Science and
Technology
Filler materials can also be used to prevent
flooding of the DPCs during the repository
time frames
 The moderator displacement aspect
of the filler materials was
investigated using as-loaded DPCs at
a site (with loss of neutron absorber)
 Aluminum was used as a
representative filler material that only
provides water displacement
 Gibbsite (Al(OH)3), which is a mineral
of aluminum and can potentially form
from aluminum in the presence of
water over the repository
performance period, was also
considered
 58% and 68% volumetric mixtures of
filler materials were considered
 Future study will consider Diaspore
formation from aluminum and
moderator displacement by the
basket corrosion products
Filler Material
Water
Water
Filler Material
11
SFWST Annual WG Meeting

Spent Fuel and
Waste Science and
Technology
Filler materials should occupy substantial
DPC volume to provide criticality control
over repository time frames
 About 34% volume (58% volumetric
mixture) is required to be filled
(uniformly) by aluminum slurry to
maintain keff below 0.98 for all the
DPCs at Site E in the year of 9999
 However, if the aluminum turns into
gibbsite (or other similar materials
that react with water to form a
hydrogenous compound) over the
repository time frames, about 72.5%
volume would be required to be
filled
12May 24, 2017 SFWST Annual WG Meeting

Spent Fuel and
Waste Science and
Technology
Direct disposal of DPCs has many benefits
but criticality related concerns needed to
be addressed
 To address criticality related concerns, criticality analysis is being
performed for the loaded DPCs using as-loaded content
- Reduce uncertainty and quantify realistic criticality margin
- Realistic criticality margin can be used to demonstrate that majority of the
canisters will not be critical over a disposal time frame
 Objective is to preclude criticality of DPCs from the repository
performance analysis
- Criticality consequence analysis could be an option
 If chlorine from the repository environment is in the groundwater,
there may be substantial criticality benefits
– It may be difficult to benchmark this analysis with current criticality experiments
 Preconditioning measures such as adding filler materials to fill the
canister void region and displace the moderator could be another
option to mitigate post-closure criticality
13May 24, 2017 SFWST Annual WG Meeting

Spent Fuel and
Waste Science and
Technology
Criticality analysis roadmap status
at the end of FY16

Spent Fuel and
Waste Science and
Technology
FY17 efforts include development of
misload analysis methodology to support
as-loaded criticality
 M4FT-17OR010305022 - Due 31st May, 2017 (Status: on schedule)
– According to NRC interim staff guidance a misload analysis is needed in absence of burnup
measurement for any burnup credit criticality analysis including as-loaded
– A comprehensive misload analysis methodology has been developed and implemented in
UNF-ST&DARDS
– The misload analysis methodology has been used to analyze three sites to determine impact
on criticality
 M3SF-17OR010305023 – Due 30th June, 2016 (Status: on schedule)
– Update FY15 summary report on feasibility of direct disposal of DPCs to reflect progress
made in the criticality area

Spent Fuel and
Waste Science and
Technology
analysis approach
am – 11.35 am)

Spent Fuel and
Waste Science and
Technology
May 24, 2017 SFWST Annual Work Group Meeting 17
Misload overview
 What is a misload and why do we care?
 Differences between as-loaded and design basis misloads
 As-loaded misload methodology for direct disposal of DPCs
 Results for Site A, MPC-32
 Results for Site B, MPC-68
 Results for Site C, TSC-37

Spent Fuel and
Waste Science and
Technology
Misload is either selection of wrong set of
assemblies from the pool or placing assemblies
at unintended locations inside a cask
 NUREG-6998 mentions two different types of misloads
1. The right assembly is selected but placed in the wrong position, and
2. The wrong assembly is selected but placed in the intended position.
 In a direct disposal scenario type 1 (placing assemblies in the wrong position
inside the cask) is more likely to remain undetected as type 2 misload (selection
of wrong assemblies) should be discovered during subsequent canister
loadings

Spent Fuel and
Waste Science and
Technology
Interim Staff Guidance (ISG) – 8, rev 3
requires misload analysis in absence of
burnup measurement
 Nuclear Regulatory Commission Interim Staff Guidance on “Burnup credit in the
criticality safety analyses of PWR spent fuel in transportation and storage
casks” (ISG-8 rev. 3) states:
– “Misload analyses may be performed in lieu of a burnup measurement. A misload analysis
should address potential events involving the placement of assemblies into a SNF storage or
transportation system that do not meet the proposed loading criteria.”
– “A misload analysis should consider:
• misloading of a single severely underburned assembly and,
• misloading of multiple moderately underburned assemblies.”
– “The misload analysis should also consider the effects of placing the underburned assemblies
in the most reactive positions within the loaded system (e.g., middle of the fuel basket)”
 Burnup measurement before loading of assemblies in dry cask is not practiced
in the United States

Spent Fuel and
Waste Science and
Technology
Design Basis analysis used for cask
certification is bounding in nature to
accommodate diverse fuel types
 Design Basis: Goal is to certify the system
for diverse fuel type and SNF inventory
– Bounding fuel type(s) is determined
– Analysis is performed with the bounding fuel
type and with highest possible enrichment
– Burnup is not credited for storage
certification/licensing
– Burnup credit has been used for transportation
licensing for some systems
• Goal is to apply minimum burnup credit to avoid
complicated analysis process
 Basket degradation needs to be
considered for criticality analysis over
disposal time period
 Design basis analysis approach for high
capacity system with basket degradation
falsely shows that all the canisters are
above critical, whereas in reality they are
not
IE /
BU
5.0 /
30
5.0 /
30
5.0 /
30
4.2 /
15
4.2 /
15
5.0 /
30
5.0 /
30
4.2 /
15
3.8 /
0
3.8 /
0
4.2 /
15
5.0 /
30
5.0 /
30
4.2 /
15
3.8 /
0
3.8 /
0
4.2 /
15
5.0 /
30
5.0 /
30
4.2 /
15
4.2 /
15
5.0 /
30
5.0 /
30
5.0 /
30

Spent Fuel and
Waste Science and
Technology
As-loaded analysis approach using the
actual content of a canister is being
used to show available margin
 As-loaded: Use actual loading maps and individual assembly information
IE /
BU
3.74 /
35.7
3.28 /
38.2
3.72 /
33.5
4.21 /
49.1
2.21 /
21.6
3.21 /
33.1
3.21 /
37.1
2.89 /
28.5
3.79 /
32.3
3.97 /
37.6
3.72 /
31.5
4.51 /
51.8
3.87/
33.8
4.01 /
37.7
2.21 /
19.6
4.17 /
48.6
4.27 /
47.5
2.89 /
30.8
3.79 /
29.5
3.72 /
31.5
3.87/
35.6
4.12 /
46.5
4.16 /
38.7
3.52 /
35.2
– Full burnup credit (actinides + fission
products)
– Most of the analyzed canisters are
subcritical even without the presence
of basket’s neutron absorber
– Requires burnup measurements or
misload analysis according to ISG 8,
rev.3
– Canisters are being loaded without
burnup measurement

Spent Fuel and
Waste Science and
Technology
Misload analysis methodology for as-
loaded DPCs has been implemented
within UNF-ST&DARDS
 Misload analysis steps:
1. Select a canister for misload
• MPC-32, TSC-37, MPC-68, etc.
2. Select the misload type
• Single severely underburned assembly (According to ISG-8)
• Multiple moderately underburned assemblies (According to ISG-8)
• Other…
3. Find the assembly/assemblies in the pool that will be used in the misload
analysis
4. Find the position/positions in the canister to place the assembly/assemblies for
misload analysis
5. Run a criticality calculation using the misloaded loading map of the canister