Comment by sbaiddn

Not a nuclear engineer, but Im curious to know how they do it - throttling nuke is hard. I only know the stream "dumping" method.

There's good reason why they are hard to throttle. For starters thermal contraction shortened lifespan; but also because the nuclear cycle itself doesn't lend itself to throttling safely - nuclear products create "retarded (?) neutrons" which are the cornerstone of a stable control system (as opposed to prompt neutrons) and also significant amounts of neutrons poisons which are normally "burned" at equilibrium steady state power levels but which accumulate if you throttle down (therefore be needing even more prompt neutrons).

My understanding is that the more you need to rely on prompt neutrons for your neutron balance the more unstable your reactor (starting them up, therefore, is delicate). Throttling the power upsets this balance by at least two different mechanism.