Sodium Cooled Fast Reactor for TRU Recycling
Douglas Fynan, Nathan Mar, David Sirajuddin
University of Michigan, Department of Nuclear Engineering and Radiological Sciences 2007
IV. Fuel Selection
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.
VI. Burnable Poisons
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.
VII. Safety Analysis
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.
Driver Fuel Selections:
Effect of Hafnium Burnable Poison on Reactivity
– 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)
8.00%
7.00%
The reference core is a PRISM Moderate Burner design with the following characteristics:
- 310 day cycle length assuming 85% capacity factor
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
- 46 cm active core height
12% treaty limit at end of cycle.
- 840 MWt power rating
The SFR design comprises a passive safety system with layered heat removal pathways.
The reactor’s 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.
9.00%
Reactivity Swing
II. Core Specifications
10.00%
6.00%
WGPu
5.00%
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.
10% Hafnium BP
4.00%
3.00%
BOC
EOC
Units
Doppler
-0.017
0.033
pcm / K
Void
7.380
6.172
pcm / %void
Volumetric Expansion
-30.77
-18.26
pcm / K
Inner Void
-0.161
-0.033
pcm / %void
Middle Void
8.213
7.373
pcm / %void
Outer Void
-0.611
-0.801
pcm / %void
2.00%
1.00%
0.00%
1
- 4 m core diameter
- Variable driver fuel composition
VII. Thermal Hydraulics
Transmutation Characteristics for Driver Fuels with Th-U Host
Mass Destroyed per Equilibrium Cycle (kg)
250
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.
200
150
WGPu
100
RCLW
RGPu
50
MAE
0
NP237
PU238
PU239
PU240
PU241
PU242
AM (All)
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.
VIII. Economics
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.
CM (All)
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.
-50
-100
Nuclide
Core Power WGPu Driver BOC
250
Linear Power per Rod Axial Section (W/cm)
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.
Capacity Factor
Plant Life (Years)
150
0 to 9.2 cm
9.2 to 18.4 cm
18.4 to 27.6 cm
27.6 cm to 36.8 cm
36. 8 to 46 cm
100
Cycle Length (Days)
Overnight Plant Cost ($)
Reprocessing Costs ($/kgHM)
Uranium/Thorium ($/kgHM)
Reactivity Swing in a RCLW Core for Various Core
Heights
Center
0.07
250
0.06
200
25cm
46cm
150
55cm
85cm
100
50
- MC2 for lattice physics calculations
Net TRU Destruction
310
1.5
Billion
1000
250
TRU ($/kgHM)
2600
Outer
Pu ($/kgHM)
1500
Waste Storage Costs ($/kgHM)
100
30
25
20
15
10
5
0
GNEP Target
WGPu
RGPu
RCLW
0.05
25cm
0.04
46cm
55cm
0.03
85cm
0.02
0.01
0
0
- REBUS-3 fuel cycle code for equilibrium cycle analysis
Reactivity Swing in percent keff
III. Computational Methods
Transuranics destroyed (kg)
Radial Position
300
40
0
Outer
Fuel Costs to Electrical Energy Generation for Varied Driver Fuels
0.9
Fabrication Costs
50
Net TRU Destruction in a RCLW Core for Various Core
Heights
288.87
Premium Added to Electrical Energy Generation
(mill/kWh)
V. Core Height
Power Rating (MWe)
200
Reactivity Swing
We would like to thank to
Professor John C. Lee and
Nick Touran
EMA