1. Heat Exchanger Temperature Response for Duty-Cycle Transients in the NGNP/HTE
R. B. Vilim
Argonne National Laboratory
Fourth Information Exchange Meeting – Nuclear Production of Hydrogen
Chicago, Illinois
April 16, 2009

2. Background
Need to Meet Operational and Safety Goals while Achieving a 40 Year Plant Lifetime
Intermediate Heat Exchanger is a Limiting Component
Elevated service conditions : 850 C inlet temperature and 2-5 MPa pressure differential
Temperature transients induce thermal stresses
Important to Limit Thermally Induced Damage to IHX
Need a Control System that minimizes temperature changes in the IHX for Duty Cycle transients

3. Outline Objectives Plant Description Duty-Cycle Event List
Plant Control System
Load Schedule
Step Load Change and Loss of Load
Conclusions

4. Objectives
Develop Requirements for Control and Protection Systems to Operate the NGNP as a Producer of Hydrogen
Design Plant Control System to Minimize Temperature Transients
Perform Transient Simulations to Obtain IHX Temperature Response for Duty Cycle Events
Characterize IHX Temperature Response

5. Plant Description
Primary System Power Conversion Unit

6. Plant Description
High Temperature Electrolysis (HTE) Unit

7. Duty-Cycle Event List
Defines Types and Frequency of Transients that Form the Plant Design Basis
Temperature Time History Calculated to Generate the Corresponding Thermally-Induced Stresses
Damage Plant Components will Sustain over a 40 Life is Estimated from this Data
Simplifying Observation: Over 85 percent of the Useful Reactor Power ends up being Communicated to the Chemical Plant as Electric Power through the NGNP/HTE Interface
Thus transients in the chemical plant act on the reactor through changed electric power load and therefore from the standpoint of the nuclear plant are classic electric-load transients

8. Plant Control System Primary System
Reactor Outlet Temperature Setpoint via Reactor Power
IHX Flow Differential Setpoint via Primary System Inventory
Primary System Comp Speed
Power Conversion Unit
PCU Shaft Speed via PCU Inventory
Precooler Powers via Cold Side Water Flowrate
High Temperature Electrolysis Unit
Constant current density setpoint via Cell Area
Mass flowrates proportional to hydrogen production rate
Supervisory Control System
Coordinates above setpoints specific to particular transient

9. Load Schedule
He Hot-Side Temperatures HTE Temperatures He Cold-Side Temperatures

10. Step Change in Hydrogen-Production Load
Able to Maintain Essentially Constant IHX Hot-End Temperatures
PCU Shaft Speed IHX Temperatures

11. Loss of Hydrogen-Production Load: Protected
Short-Term Transient is Does not Present Significant Temperature Changes
PCU Shaft Speed IHX Temperatures

12. Loss of Hydrogen-Production Load: UnProtected
IHX Hot-End Temperature Change Limited to ~1 C/s
PCU Shaft Speed IHX Temperatures

13. Conclusions
Near-Constant Temperatures can be Achieved over the Load Schedule
IHX Differential Flow Controller is Effective in Maintaining Constant Hot-End Temperature Gradients in the IHX during Transients
Partial Load Plant Efficiency is Maintained via Inventory Control
In Rapid Transients Turbine Bypass Control Limits Shaft Over-speed
In General Hot-End Temperature Changes in the IHX were Limited to ~1 C/s
Stability of Closed Loop Brayton Cycle was Found to be Sensitive to Operating Point on Turbo-Machine Curves
More stable operating point has reduced efficiency