1. Transient modeling of sulfur iodine cycle thermo-chemical hydrogen generation coupled to pebble bed modular reactor
Nicholas Brown, Volkan Seker, Seungmin Oh, Shripad Revankar, Thomas Downar, Cheikhou Kane
Purdue University
West Lafayette, IN
Apr. 16, 2009
Research supported by:
DOE NERI Project
U.S. Department of Homeland Security Fellowship Program

2. Outline Hydrogen production Thermo-chemical hydrogen production cycles
Sulfur-Iodine cycle (SI)
Pebble Bed Modular Reactor (PBMR 268)
Purdue hydrogen cycle models
Point kinetics model
Model coupling scheme
Transient results

3. Energy demand in 21st century
Global energy demand – met by fossil fuels
It is almost universally accepted that peak oil production will occur before 20201
Sustainable, CO2 free energy sources are required:
Nuclear
Renewables
Biomass
Hydrogen is widely recognized as a promising energy carrier for the 21st century
1 – “Strategic Significance of America’s Oil Shale Resource. Volume I”
U.S. Department of Energy, March 2004

4. Sulfur-Iodine (SI) Cycle
Section 1: SO2+I2+2H2O H2SO4 + 2HI
(Bunsen Reaction, 120 oC, exothermic)
Section 2: H2SO ½ O2 + SO2 + H2O
(Sulfuric Acid Decomposition, 900 oC, endothermic)
Section 3: 2HI I2 + H2
(Hydrogen Iodide Decomposition, 450 oC, endothermic)

5. Transient cycle modeling
1st priority in nuclear system:
Safety
Important to understand coupled nuclear reactor - chemical plant behavior
Methodology
Treat each chemical reactor as a closed system and a control volume,
Perform a chemical kinetics analysis of each chemical reactor,
Heat/mass balance of each chemical reactor,
Couple model to THERMIX-DIREKT nuclear reactor thermal code and point kinetics model

6. SI cycle simplified schematic

7. SI cycle kinetic behavior
HI decomposition (Section III) dominates chemical plant behavior, since it has very slow response time 7

8. Reaction chamber model
Mass balance:
Energy balance:
Intermediate heat exchanger:

9. Helium (or helium-xenon) cooled with graphite moderator
PBMR-268
Pebble bed type high temperature gas cooled reactor with a power of 268 MWth
Helium (or helium-xenon) cooled with graphite moderator
Inner reflector is dynamic and composed of graphite spheres
Figure reproduced from:
Matzner, Dieter. “PBMR Project Status and the Way Ahead.” Proc. Of 2nd International Topical Meeting on HIGH TEMPERATURE REACTOR TECHNOLOGY Beijing, China, September22-24,2004.

10. PBMR-268 model simplifications
THERMIX PBMR-268 model:
Flattening of the pebble bed’s upper surface
Flat bottom reflector
Flow channels are parallel, equal speed
Constant central column and mixing zone width
Control rods in the side reflector are assumed as a cylindrical skirt with a given B-10 concentration
Point kinetics model
Flux profile does not change, is treated as a single point and scaled up or down based on feedback
Six delayed neutron groups are used
Doppler feedback coefficient is

11. Model integration and coupling
Three codes integrated:
THERMIX PBMR-268 model
Point kinetic model
Purdue SI-cycle models
Relevant calculations are performed each timestep (0.1 sec)
Transfer between codes occurs via thermal conditions at Intermediate Heat eXchanger (IHX)
GA flowsheet scaled to a thermal power input of 268MW
Steady state hydrogen generation rate of ~ 1.4 kmol/sec
Power distribution: 26% in Section 2, 74% in Section 3

12. Model integration flowsheet

13. Reactor initiated transients/accidents
Examples of PBMR-268 reactor transients or accidents:
Control rod insertion or withdrawal
Depressurized Loss of Forced Cooling with or without SCRAM
Pressurized Loss of Forced Cooling with or without SCRAM
Load following accidents
Control rod ejection
Results shown here: insertion and removal of $0.25 of reactivity via control rod

14. Reactivity insertion +$0.25

15. Reactor power +$0.25

16. IHX Temperatures +$0.25

17. Reactivity insertion -$0.25

18. Reactor power -$0.25

19. IHX Temperatures -$0.25

20. Conclusions
HI decomposition section is rate limiting step of the SI cycle
Preliminary scaling of GA flowsheet yields an energy distribution of 25% in Section 2, 75% in Section 3
Hydrogen generation rate of SI plant coupled to PBMR is 1.4 kmol/sec