High Support Ratio Fusion-Fission Hybrid System ~ Fuel Cycles

1
High Support Ratio Fusion-Fission Hybrid System
Fuel Cycles

• Swadesh Mahajan
• for
• The Texas Group
• DOE Fusion-Fission Hybrid
• Workshop
• Sept.30-Oct2, 2009

2
Outline

• Objective provide an overview of FFH-enabled
  high support ratio fuel cycles
• that mitigate the burden placed by the most
  difficult-to-transmute actinides on other thermal
  or fast spectrum transmutation systems.
• Fuel Cycle
• Zero net TRU production Fusion Fission
  Transmutation System (FFTS) concept incorporating
  LWR transmutation
• IMF and Corail based transmutation paths
• Fission Systems- a glimpse with Tritium Breeding
  figures.

3
The Generic High support Ratio Fuel Cycle
Current Practice
TRU Burning in SFR
TRU
LWR Preburn
UOX SF
IMF SF
LWR Uranium Oxide Fuel
Reprocess
Reprocess
SF
FR-FFH
Reprocess
TRU
FP
U, FP
TRU
Maximal Utilization of the LWR consistent with
obvious constraints
TRU Burning in FFTS
4
Hybrid is a part of the FR
family
Obvious
Hybrid is a Sub critical Fast
Reactor
Not so Obvious
Sub criticality, being a mode of FR
operation, is an additional channel
for optimization
5
UT Reference IMF- FF Hybrid
U, FP
TRU
LWR Inert Matrix Fuel
LWR Uranium Oxide Fuel
UOX SF
IMF SF
Reprocess
Reprocess
SF
TRU Burning in FFTS
Fission Fusion Hybrid
Reprocess
TRU/TRU
FP
TRU
With 75 burn in the LWR-IMF step the support
ratio is high 5 thermal burn in the Hybrid.
BUs of more than 50-60 require heterogeneity
enriched U needed to support the reactivity
of IMF fuel. Support ratio is
further boosted by sending Pu242 back to LWR

TRUTRU-Pu242
6
High Support Ratio SFR Based Fuel Cycles
Under this scheme about 75 of the TRU discharged
from the UOX fuel is eventually fissioned in
CORAIL fuel within the LWRs. The remaining 25,
MA from UOX as well as CORAIL fuel, is sent to a
low-fertile FR. This scheme leads to a FR
thermal power share of around 12.
Extensive thermal-spectrum burn is also
compatible with some SFR fuel cycles. One
example uses the CORAIL sustained Pu recycle
scheme to stabilize Pu inventories and passes the
MA recovered from CORAIL fuel to a sodium-cooled
fast reactor.
LWR Uranium Oxide Fuel
CORAIL fuel in LWRs
Spent Fuel
U Pu
Reprocess
Reprocess
Fission products loss
U Pu
Np Am Cm
Sodium Cooled FR, CR 0.5
Geological Repository
Reprocess
U Np Am Cm
Fission Products loss
U Np Am Cm
CorailsHybrid wait Cm out - No U gt run an Am
only Hybrid-send Pu238 back to LWR support ratio
gain 3-4
M. Stillman and R. Hill, Effect of
Thermal-Spectrum Transmuter Deep Burnup of
Transuranics on Fast-Spectrum Transmuter
Performance, Proc. GLOBAL 2003, New Orleans, LA,
2003.
7
Additional Fuel Cycles
1. Double Stratum FR and FFH Transmutation
LWR Uranium Oxide Fuel
FR Sodium Coolant, CR 0.5
Spent Fuel
20 Burn
U Pu
Reprocess
Reprocess
Fission products 0.1 loss
U Pu
Np Am Cm
Up to 50 burn
Fusion Fission Hybrid
Geological Repository
Reprocess
Np Am Cm
Fission Products 0.1 loss
Np Am Cm
2. Am Bypass Cm Partitioning and Decay Storage
Up to 75 burn 1-2 passes
LWR Uranium Oxide Fuel
LWR Inert Matrix Fuel (IMF)
Pu Np
Spent Fuel
Reprocess
Reprocess
Fission products 0.1 loss
Cm
Pu-238,240
Am
Up to 50 burn
Cm Decay Storage
Fusion Fission Hybrid
Pu Np Am
Geological Repository
Reprocess
Pu Np Am
Fission Products 0.1 loss
Cm
8
Fuel Cycles - Additional Comments

• The previous slide showed that Cm decay storage
  could ease the fuel fabrication burden on the
  hybrid and enhance the utilization of IMF. The
  curium isotopes present in spent LWR fuel at
  discharge are predominantly
• Cm-242 (T1/2 163 d) decay to Pu-238 which has
  a favorable effect on the thermal-spectrum
  neutron balance,
• Decay of the strong heat emitter Cm-244 (T1/2
  18.1 yr) to Pu-240
• This plutonium would be harvested and returned to
  the IMF.
• In addition, if Am utilization in LWRs proves to
  be untenable, the Am (predominantly Am-241 at
  that stage) would bypass the IMF recycle step and
  pass directly to the hybrid.
• While fabrication issues tied to volatility
  remain, the Am discharged from IMF is
  overwhelmingly Am-243, a relatively benign(less
  radioactive) isotope from the standpoint of fuel
  handling.

9
Maximal Thermal Spectrum Transmutation Synergies
with the FFTS

• Because of their non-fertile matrices, inert
  matrix fuels (IMFs) enable light water reactors
  (LWRs) to meaningfully reduce transuranic (TRU)
  inventories.
• Very deep (gt 50) burn up in the IMF- LWR step (
  additional flourishes like waiting Cm out
  (sending Pu240 to LWR), running only an Am
  reactor in the second step)may preclude fuel
  cycle closure using unaided FRs because of the
  high minor actinide (MA) content of the residual
  TRU safety and stability issues.
• Million dollar questions- how bad does the fuel
  have to be that the best optimization may be
  attained through a sub-critical assembly? Does
  making such bad fuels (that go into FR) bring
  enough advantages?

10
Inert Matrix Fuel Forms

• This is Jim Tulenkos subject. Yttrium stabilized
  ZrO2 (YSZ) and SiCO2 are typical ,
• Fabrication techniques are similar to those used
  for MOX and UOX dry milling of constituent
  oxides or co-precipitation to form a solid
  solution, followed by compaction and sintering of
  resulting grains.
• Mechanical and thermal properties of YSZ based
  IMF have been reported in several studies as has
  durability under irradiation.
• Initial results from in-pile testing at Halden
  (57 burnup to update models for fission gas
  release, thermal conductivity and fuel swelling)
  have been published.
• Fission gas release issues have been noted
• Magnesia-zirconia may offer superior performance

11
What Can be Accomplished in a Thermal Spectrum?

• Most IMF single-pass deep burn studies (e.g.
  Herring, Nucl. Tech., 2004) attain IMF burnups of
  up to 55-60
• Achievable in contemporary PWRs with minimal
  modifications (e.g. heterogeneous assemblies with
  1/9 IMF pins, remainder 4.95 enriched UOX)
• CONFU and CONFU-B assembly designs investigated
  at MIT have the potential to ultimately attain
  near-complete TRU burn-down via multi recycle in
  PWRs
• Challenges related to high IMF loading (power
  peaking, DNBR)
• Certain species (242Pu, 243Am, 244Cm) transmute
  exceptionally slowly in a thermal spectrum, so
  that a practical limit upon what can be
  accomplished in a thermal spectrum may exist

12
A Practical Burnup Limit
Burnup in a thermal spectrum is limited
because an inflection point occurs near 75
burnup . Additional incineration requires large
residence times because the remaining actinide
isotopes are relatively transparent to thermal
neutrons.
Figure. IMF Burnup versus Fluence
13
Residual TRU Following IMF Burn

• It may be plausible to achieve 75 TRU burnup in
  a single IMF pass given perturbations from
  existing single pass schemes (e.g. increased 235U
  enrichment, 4/3 IMF-bearing / all-UOX assembly
  cycle reload pattern)
• The more transmutation that is accomplished in
  LWRs, the fewer fast spectrum systems that will
  be required.
• The isotopic content (a/o) of the residual TRU
  after 75 burn is shown in the table at right.
  This is the feed to the FFTS.

14
Thermal Power Split ()TRU production kg TRU
produced / kg TRU produced in UOX
IMF/FFTS IMF/FFTS with Cm decay storage 3 Pass MOX Pu-Np-Am/ FFTS Double Stratum FR FFTS
LWR - UOX 77.7 1.0 77.7 1.0 76.9 1.0 73.1 1.0
Thermal Recycle 17.0 -0.75 18.5 -0.81 10.3 -0.28
Fast Reactor 21.1 -0.68
FFTS 5.3 -0.25 3.8 -0.19 12.8 -0.72 5.8 -0.32
CORAILHybrid is very similar to IMF/FFTS Mixing
CORAIL philosophy (Send all Pu back to LWR) works
wonders for the support ratio.
15
Multi-Pass IMF CONFU

• Looking again at multi-pass IMF in a CONFU-type
  strategy,
• Blending with fresh TRU is needed to support
  reactivity
• A mass flow diagram for one two-pass blending
  strategy utilizing homogeneous (TRU-Zr)O2
  assemblies is shown below
• Full-core loading of homogeneous IMF assemblies
  may not be feasible (core physics / safety
  constraints)

First IMF Pass 60 TRU Burnup
Masses in kg TRU
To fission fusion hybrid or continued IMF
burn-down
Figure source Taiwo, T. and R. Hill,
Comprehensive Summary of AAA and AFCI
Transmutation Analysis Studies, ANL-AFCI-198,
2007.
16
Conclusions

• A small number of fusion-fission transmuters can
  reduce the burden placed upon other thermal or
  fast spectrum systems by the most
  difficult-to-transmute species
• This talk is by, no means, comprehensive
• We think the main challenges facing the proposed
  fuel cycle are
• Maturity of LWR transmutation technologies
• High-efficiency separation of advanced fuels
• Fabrication of high TRU content fuels for
  high-fluence irradiation
• Materials durability magnets, cladding,
  structural materials
• Semi infinite number of research and development
  issues need to be investigated- some of these
  being studied by UTcollaborators

17
Fission Systems
18
FFTS Geometry
Pb
80Al- 20D2O
6Li2TiO3
3 m
90Cu- 10D2O
Graphite
Fission Blanket
19
Alternate Configuration Tank-type Design
Na
Pb
80Al- 20D2O
0.85 m
6Li2TiO3
90Cu- 10D2O
Graphite
Fission Blanket
20
3H Breeding Central Coil and Divertor Region

• Tritium self-sufficiency can be reached by
  placing Li2TiO3 blankets in two locations where
  shielding of sensitive components is required
• the vicinity of the upper and lower divertor
  plates
• surrounding the central coil.
• Additional breeding (20) is obtained when the
  lithium titanate is backed by a graphite
  moderator.
• 3H production rate, atoms/sec ( of consumption
  rate)

Note divertor plate DPA rate is 2.3 dpa/fpy in
this configuration. Replacement of a portion of
the Li2TiO3 with B4C can reduce the damage rate
to as low as 0.38 dpa/fpy.
Divertor Blankets Central Blanket Total
2.46E19 (69) 1.86E19 (52) 4.32E19 (121)
21
Limitations Imposed by TRU Isotopics

• In the full TRU recycle strategy, the metal fuel
  TRU fraction is limited by the decay power of
  244Cm to 25
• This limitation is imposed to avoid the need for
  active cooling of fuel assemblies during
  fabrication
• In most strategies considered by AFCI, 241Am
  rather than 244Cm constrains TRU loading
• The low TRU fraction may support extended burnup
  but results in a large total TRU inventory and
  lower-than-optimal power density
• lattice pitch can be adjusted, but this pushes
  fuel geometry into regimes where little previous
  work has been done an investigation is ongoing
• An option that avoids this issue and utilizes the
  thermal spectrum more effectively is
  post-reprocessing Cm storage
• Under this strategy, stored Cm is milked for Pu
  (overwhelmingly 240Pu) which is returned to the
  IMF feed
• Limited by ability to partition Am and Cm a
  focus for AFCI in the coming year

22
Neutron Balance

• An aggressive fission / fusion thermal power
  ratio of 30 may be attainable
• To maintain this ratio, keff must remain between
  0.91 and 0.93 (upper limit tied to void
  reactivity coefficient)
• The burnup reactivity behavior of the 242Pu,
  243Am and 244Cm rich fuel makes this possible, so
  that with 3 batch shuffling there is no neutronic
  obstacle to achieving 50 burnup at this power
  ratio
• Material constraints will be limiting unless the
  state of the art improves
• fuel performance at high burnup fraction (note
  that AFCI test metal fuel has exceeded 30 burnup
  in ATR)
• Structural damage imposing a nominal fast fluence
  limit of 4x1023 n/cm2 (limiting burnup to 20
  this constraint is also limiting in present-day
  FR designs)

23
Global Neutron Balance
Normalized to one fusion neutron.
Gains Losses Net
Source 1.000 0 1.000
(n,Xn) (mostly in Pb) 1.500 0.733 0.767
fission N/A 0.217 -0.217
Capture in nonactinide fission blanket components 0 0.039 -0.039
Capture in actinides 0 0.613 -0.613
Capture in Li2TiO3 0 0.348 -0.348
Other captures 0 0.473 -0.473
escape 0 0.062 -0.062
Total 2.500 2.500 0
fission neutron production turned off only
fusion and (n,Xn) neutrons included.