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

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

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

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

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

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

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

Alternate Interface Shaded Region Shows Modification to PCU

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

Full Power Operation Temperature and Pressure Significantly Reduced at Peak Location

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)

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

Coupled Plant Efficiency Better Heat Matching Improves Efficiency

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

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