1. Impact of Technology Characteristics on Transition to a Fast Reactor Fleet
drhgfdjhngngfmhgmghmghjmghfmf
20 min total
EDWARD Hoffman
Bo Feng
Ben Betzler, Eva Davidson, & Andy WOrrall
Argonne National Laboratory
Technical Lead for Transition Analysis Studies for the Systems Analysis and Integration Campaign
Argonne National Laboratory
Oak Ridge National Laboratory
3rd Technical Workshop on Fuel Cycle Simulation
Paris, France, July 9-11, 2018

2. Overview Introduction Study objective
Representative SFR and MSR systems
Modeling Methodology
Describe simplified modeling approach
Results

3. Study Objective
The focus of this study is on technology characteristics that are likely to be impacted by the choice of SFR or MSR
Specifically those characteristics that will have the biggest impact on the supply of and demand for fissile material
Inform R&D and design choices to enable a more efficient deployment of a large fleet of fast reactors under different scenarios
Inform on the characteristics that will lead one technology to perform better than another and not try and predict which technology will ultimately perform better
Assess our current understanding in this area

4. Fuel Cycle choice
Fast Breeder Reactors Continuously Recycling U/TRU (EG24)
Low enriched uranium (LEU) used as need
Recycled fast reactor material utilized as soon as available
Assume only constraint is a minimum recycle time (theoretical performance)
Fast Reactors
Liquid-Fueled Molten Salt Reactor (MSR)
Solid-Fueled Sodium-Cooled Reactor (SFR)
Recycle Time
MSR - ~0 (longer times will look like SFRs)
SFR – collocated (2-3 yrs) or centralized (7+ years)
Breeding – Breakeven through maximum practical
Discharged
Recycle
As Needed
Fast Reactor Fleet
LEU
Recycled

5. Modeling and Performance Measures
Because the study is focused on the impact of differences in technology characteristics and not detailed dynamic behavior of a specific scenario about the future, the modeling can be simplified
Used the DYMOND code to model a few scenarios
Acted as benchmark for a spreadsheet model used for rapidly modeling many scenarios
Both were useful in calibrating user input for the other model
The performance measure chosen was how much natural uranium (NU) and enrichment (SWU) is required
No cost info, both should have similar waste without detailed designs, etc.

6. Spreadsheet Modeling
MSR and SFR deployed with required startup inventory (fissile material needed at or very near deployment of new capacity)
Initially only source of fissile material is LEU
MSR and SFR breeding ratio is minimum to be reactivity breakeven or higher
No additional fissile required after first fuel is recycled
Breeding accounts for fissile quality difference: U-235 vs TRU (Pu-239)
For the SFR, operating under the same conditions approximately 1.3 – 1.4 atoms of U-235 is equivalent to 1.0 atoms of Pu-239
The LEU system can have a fissile breeding ratio well below 1.0, but produce sufficient Pu-239 to have the same reactivity in the recycled fuel
The LEU fuel will have significantly higher fissile (U-235) concentration than the steady-state fissile (primarily Pu-239) concentration
Material is recycled as soon as assumed possible
MSR is self-sufficient immediately (zero recycle time)
SFR requires additional fuel reloads determined by the minimum recycle time
For excess breeding scenarios, the system automatically balances once no more LEU is required
Pu equivalence needed to estimate startup when there is no LEU case and the maximum equivalent breeding ratio. LEU fuel will have a much lower fissile breeding ratio, but in terms of reactivity of the recycled fuel, it can get near that of Pu because it needs to produce less.

7. Spreadsheet Modeling Single Unit Examples
In order to explain the underlying behavior during transition, several examples of the fissile material flow are show for single units operating independently
IFR: SFR with a 2 year recycle time such as an Integral Fast Reactor
SFR - Central: SFR with a 7 year recycle time such as a system with centralized recycling
MSR (y.yx): MSR that requires y.y times as much inventory at startup as and SFR
Examples include 1.5, 2.5, and 3.5. Further study suggest that this range for well-designed commercial MSRs and SFRs ranges from 0.4 to 2.2
The spreadsheet integrates this behavior into a single system to calculate the equivalent fissile mass balance
For reactivity breakeven systems with no constraints on recycling other than the minimum recycle time, this gives the exact answer since they are all effectively independent units (no net flow of fissile between units)

8. Basic Fissile Material Flow
Pu-239 eq fissile (t/GWe)
Pu-239 eq fissile (t/GWe)
Note scale differences. Explain that for breeders the discharge will be greater than demand.
Pu-239 eq fissile (t/GWe)
Pu-239 eq fissile (t/GWe)

9. Integral Demand for a Single Unit
For breakeven systems,
MSR: all fissile demand filled at startup
SFR: additional fissile demand filled for reloads based on minimum recycle time
For breeder systems,
MSR: Excess available immediately
SFR: No excess available until minimum recycle time
Simple constraints applied so there is no need for complex dynamic modeling
Also no interest in cycle by cycle or other dynamic behavior, but approximate integral behavior
Pu-239 eq fissile (t/GWe)
Breakeven
Explain Lines
Pu-239 eq fissile (t/GWe)
Breeder

10. Results
These parametric calculations revealed 3 key technology characteristics that impact front-end requirements
Startup fissile inventory, which includes all the fissile material in and out of the core for the MSR systems
Recycle time, which determines the amount of material and timing for the SFR systems with the MSR effectively being a zero recycle time system
Net breeding rate of fissile material, which account for system losses, isotopic evolution, etc. on a reactivity equivalent basis
Each of these have many important underlying design characteristic such as power density, thermal efficiency, and others that combine to produce these key characteristics
Given these uncertainties in the key characteristics that affect transition performance, it would be misleading to draw any general conclusions from the direct comparison of a few examples of specific SFR and MSR designs
Additionally, the performance is sensitive to the assumptions about the future used in the particular transition scenario
The approach to inform on this was to calculate the Equal Performance Line (EPL) for a range of scenarios
Above the EPL, the SFR performs better and below the MSR does

11. Equal Performance Line
SFR and MSR both breakeven, expand to 100 GWe in 20 years

12. Equal Performance Line
SFR and MSR both breakeven, expand to 100 GWe in 20 years

13. Equal Performance Line
Three cases: SFR and MSR both breakeven, SFR and MSR max Breeding, and SFR max breeding/MSR moderate breeding

14. Summary
By using the dynamic systems tools as a benchmark, developed a simplified spreadsheet to run a large number of cases to study a very large design space efficiently
Identified the most important features under a wide range of conditions
Identified where uncertainty in the current designs is most important to front end requirements to transition to a large fleet
The current range of designs being considered for MSRs and SFRs leads to a wide band of uncertainty in relative performance
SFR systems with high power densities, high breeding rates, and short recycle times are needed to minimize front end requirements for transition
MSR systems with high power densities, high breeding rates, and small fissile inventories outside of the core are needed to minimize front end requirements for transition
A simple method was developed to generate a series of curves that can compare the relative performance of MSR and SFR systems
Easily expandable to systems with more complex constraints
Requires significantly more time to model and calculate EPL
Note that when considering recycle of LWR UNF, it becomes far more complex. How much LWR UNF will you have available and how quickly and how large you grow your fast reactor fleet may lead to a large excess of LWR UNF or a large shortfall.

15. Thank you for your attention!

16. Equal Performance Line
Three cases: 40 year transition

17. Equal Performance Line
Three cases: 40 year transition with 2% sustained growth

18. Equal Performance Line
Three cases: 20 year transition with high burnup SFR fuel