Without being a domain expert, my intuition would be that PCIe is optimized for throughput over latency and there's probably a throughput compromise when you want low-latency access.
The best part about using nuclear for fuel generation is that you get to sidestep the biggest problem with nuclear - when you build a power plant you want to build it near people (who may object on safety grounds), but you can build a DAC fuel generator way out in the middle of nowhere.
Even better, you could build your nuclear DAC fuel generator in an old natural gas field, where there's ready-made transportation infrastructure for your product to where it's needed!