That's not what this is about. Negative electricity prices are rare, and do not account for the massive difference in utilization between renewables and nuclear. By the way nuclear power output can be ramped up and down by a lot, and in a matter of minutes in case of unplanned problems, even if it can't (really shouldn't) go to dead zero.

The person I responded to claimed that nuclear plants run at close to 100% because they bid low because the marginal cost of their electricity production is low, but the same is true for renewables like wind and solar. Yet these renewables run at much lower utilization rates - because of weather and daylight cycle, not "because they can", except in rare cases of negative prices as you mentioned.