1. Alternate VHTR/HTE Interface for Mitigating Tritium Transport and Structure Creep
R. B. Vilim
Argonne National Laboratory
Fourth Information Exchange Meeting – Nuclear Production of Hydrogen
Chicago, Illinois
April 16, 2009

2. Background
Elevated Service Conditions at Interface between the Nuclear and Chemical Plant
Temperature of 850 C and pressure of 2-5 MPa
Two Technical Challenges Arise at the Interface
Creep of structures
Migration of tritium from reactor to chemical plant
Possible Solutions
Ceramic structures – In the development stage
Lower the interface temperature without adversely effecting coupled-plant efficiency – This work

3. Outline Objectives Reference Interface Alternate Interface
Full Power Operation
Partial Power Operation
Assessment
Conclusion

4. Objectives To Investigate an Alternate Interface
Very-High Temperature Reactor (VHTR) coupled to High-Temperature Electrolysis (HTE)
Based on heat pump
Design to
Lower interface temperature
Better match VHTR heat quality with HTE heat requirements
Assess Performance by Comparing to Reference Interface
Structure creep, tritium migration rate, and efficiency

5. Reference Interface Heat Addition to HTE Plant
Low range heat Qlow = 43 MWt boils water at 265 C
High range heat Qhigh = 6 MWt raises water vapor from 750 C to 850 C

6. Alternate Interface
High Temperature Power is a Small Percentage of Total Power
Supplying Qhigh = 6 MWt via electric heaters or H2 combustion would significantly simplify nuclear plant design and improve maintenance and safety by eliminating HTLHX
Low Temperature Heat Boils Water at 265 C
Supplying Qlow = 43 MWt via 130 C plant waste heat with vapor recompression would significantly simplify nuclear plant design and improve maintenance and safety by eliminating HTLHX

7. Alternate Interface
Use Heat Pump to Upgrade and Transport Near-Waste Heat from Nuclear Plant

8. Alternate Interface
Shaded Region Shows Modification to PCU

9. Alternate Interface
Heat Pump Links PCU (Source) to HTE Boiler (Sink)

10. Full Power Operation
Temperature and Pressure Significantly Reduced at Peak Location

11. Partial Power Operation
Goal is Constant Hot-Side Temperatures Over H2 Load
VHTR Control Strategy
Inventory control to maintain power-to-flow ratios (constant ΔT rise and velocity triangles)
HTSE Control Strategy
Flow control to maintain power-to-flow ratio
Cell ohmic heating proportional to load => constant current density => constant cell ΔT
Need to vary cell area so proportional to load (i.e current)

12. Partial Power Operation
Cell Inlet and Outlet Temperature near Constant
Reactor Temperatures HTE Temperatures

13. Coupled Plant Efficiency
Better Heat Matching Improves Efficiency

14. Overall Assessment
Structural Materials – More Economical Steels can be Substituted into the Process Heat Loop
Reliability – Corrosion and Creep Reduced at Lower Temperature
Maintenance – In-Service Inspection and Service Work Simpler at Lower Temperature
Safety – Perhaps Superior since Chemical Plant Process Heat Loop is now Isolated from Reactor Heat Removal Safety Systems – Migration of Tritium from the Reactor through to the Chemical Plant is Reduced by a Factor of Mode than 100
Efficiency – Improves due to Improved Heat Matching

15. Conclusions
Significant Reduction in Operating Conditions in Nuclear Plant Heat Exchanger that Provides Bulk of HTE Process Heat
Temperature of 870 C lowered to 230 C
Pressure of 5 MPa lowered to 2.5 MPa
Effective Temperature Barrier Reduces Rate of Tritium Transport to Chemical Plant
Coupled-Plant Efficiency Increases from 0.44 to 0.45
Safety Improved, Maintenance Cost Reduced, Capital Cost Reduced