Nuclear Production of Hydrogen, Fourth Information Exchange ...

HEAT EXCHANGER TEMPERATURE RESPONSE FOR DUTY-CYCLE TRANSIENTS IN THE NGNP/HTE
Figure 11: Ramp of generator load of 3% per minute – IHX temperatures, long term
Step of 10%
Inventory control provides good temperature control as shown above and further high efficiency at
partial load. But in practice its use is limited to slow changing transients. The maximum helium charge
and bleed rates achievable with PCU hardware limit the rate at which inventory can be adjusted to
match generator load rate of change. Turbine bypass provides a means for quickly matching PCU shaft
power with a decrease in generator load. Placement of the bypass valve and line is shown in Figure 12.
Figure 12: Reference interface power conversion unit with bypass
A rapid 10% reduction in generator load with bypass control was simulated. The generator load is
decreased from an initial steady state of 100% power down to 90% power over one second. The
pre-cooler and intercooler water flow rates are also decreased.
The plant response appears in Figures 13, 14 and 15. Figure 13 shows the bypass flow rate
increasing as the bypass flow controller detects a mismatch between shaft speed and set point value
of 60 Hz. The PCU shaft speed response is shown in Figure 14. The oscillations seen in the first ten
seconds are probably too large for the generator to remain connected to the grid. The amplitude can be
reduced by re-tuning the PCU shaft speed controller. The temperatures in the IHX shown in Figure 15
are very nearly constant as was our design objective.
Loss of electric generator load
The HTE hydrogen plant presents largely an electric load to the nuclear plant. Various scenarios can
be envisioned under which the generator load might quickly disconnect from the turbo-machine shaft.
These include an electrical distribution fault in the hydrogen plant, an electrical fault in the generator,
or the need to stop hydrogen production for safety reasons.
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 425