Sodium Cooled Fast Reactor for TRU Recycling

1
Sodium Cooled Fast Reactor for TRU
Recycling
Douglas Fynan, Nathan Mar, David
Sirajuddin University of Michigan, Department of
Nuclear Engineering and Radiological Sciences 2007
I. Purpose Stockpiles of plutonium and
minor actinides exist in large quantities from
nuclear weapons programs, civilian reprocessing
programs, and in spent nuclear fuel from light
water reactors. Most of this material is
destined for geological disposal and poses long
term radiological risks. The purpose of the SFR
is to transmute plutonium and minor actinides in
a proliferation resistant closed fuel cycle while
expanding electricity generation, consistent with
the goals of GNEP, AFCI, and GEN IV.

• IV. Fuel Selection
• The SFR core is capable of burning a variety
  of driver fuel compositions. Four driver fuel
  types were modeled in the core based on available
  feedstocks from stockpiles.
• Driver Fuel Selections
• Weapons Grade Plutonium (WGPu) (94 Pu-239, 6
  Pu-240)
• Reactor Grade Plutonium (RGPu) (60 Pu-239,21
  240 Pu, 14 Pu-241)
• Recycled Light Water Spent Fuel (RCLW) (51
  Pu-239, 24 Pu-240,
• 14 Pu-241, 6 Am-241, 4 Np-237)
• Minor Actinide Enriched (MAE) (29 Pu-239, 13
  Pu-240, 28 Am-241, 19 Np237)
• To optimize transmutation of Pu and MAs, thorium
  was chosen over natural
• uranium as the host fuel to prevent breeding of
  Pu during the cycle. However, a thorium
• host fuel breeds fissile U-233 over 95
  enrichment. The proliferation limit for U-233
• enrichment is 12. A 75 Th 25 U host fuel is
  required to denature U-233 below the
• 12 treaty limit at end of cycle.

VI. Burnable Poisons Burnable poisons were
considered as a possible method of reducing the
reactivity swing. However, burnable poisons
increased the reactivity swing. Criticality was
only possible with an increased proportion of
driver fuel with respect to the host fuel.
VII. Safety Analysis Preliminary analyses was
performed to ascertain the potential safety
performance. Doppler, volumetric thermal
expansion, and void coefficients of reactivity
were calculated to illustrate the inherent
safety mechanisms of the SFR design. The
positive void coefficient signifies
overmoderated reactor operation however, this
positive coefficient is offset by both the
Doppler coefficient, and the largely negative
expansion coefficient of the fuel allowing for
safe operation. The SFR design comprises a
passive safety system with layered heat removal
pathways. The reactors response to an accident
is immediate scram, followed by heat
removal Through the reactor coolant system, and
the power cycle heat exchangers. An, emergency
low-capacity heat removal is also provided in the
event of normal power loss. Finally, the SFR
design allows for heat removal through natural
circulation in the case of total power failure.
Void coefficients were further examined in the
inner, middle, and outer regions of the core to
assess the sensitivity of void formation to
reactivity in particular regions.

• II. Core Specifications
• The reference core is a PRISM Moderate Burner
  design with the following characteristics
• - 840 MWt power rating
• - 310 day cycle length assuming 85 capacity
  factor
• - 46 cm active core height
• - 4 m core diameter
• - Variable driver fuel composition

    BOC EOC Units Units
Doppler   -0.017 0.033 pcm / K pcm / K
Void   7.380 6.172 pcm / void pcm / void
Volumetric Expansion Volumetric Expansion -30.77 -18.26 pcm / K pcm / K
           
     
Inner Void   -0.161 -0.033 pcm / void pcm / void
Middle Void Middle Void 8.213 7.373 pcm / void pcm / void
Outer Void Outer Void -0.611 -0.801 pcm / void pcm / void
VII. Thermal Hydraulics REBUS-3 calculates power
density for five axial regions representing the
active core height and five radial regions. The
radial power distribution is relatively flat and
the axial power distribution is a chopped cosine
curve. Pressure drops across a fuel assembly
due to friction and gravity were calculated.
Pressure drop due to form loss was estimated from
values from references. Linear power, fuel
centerline temperature, and clad temperature were
calculated using thermodynamic properties of
liquid sodium and the fuel pin materials.
Coolant flow rate was estimated from references.

• VIII. Economics

The core was found to produce power at nearly
double the projected estimate GNEP for generation
IV reactors. This was primarily a factor of the
high capital cost of constructing a fast reactor,
combined with the relatively high cost of
reprocessing and market thorium prices. The
increased cost of the cores incorporating minor
actinide driver fuels reflects the greater cost
of fabrication for minor actinide fuels.
V. Core Height The effects of core height on
transmutation and reactivity swing were analyzed.
Increasing active core height softened the
neutron spectrum and thereby decreased
transmutation capabilities. The reactivity swing
also decreased with core height. Smaller core
heights increased neutron leakage and possessed
passive safety advantages.
Power Rating (MWe) 288.87
Capacity Factor 0.9
Plant Life (Years) 40
Cycle Length (Days) 310
Overnight Plant Cost () 1.5 Billion
Reprocessing Costs (/kgHM) 1000
Fabrication Costs  
Uranium/Thorium (/kgHM) 250
TRU (/kgHM) 2600
Pu (/kgHM) 1500
Waste Storage Costs (/kgHM) 100
III. Computational Methods - REBUS-3 fuel cycle
code for equilibrium cycle analysis - MC2 for
lattice physics calculations
We would like to thank to Professor John C. Lee
and Nick Touran