None of the commercially available (Western) reactor designs today are fast load followers, so you are dependent on having gas or hydro when you project for new

None of the commercially available (Western) reactor designs today are fast load followers, so you are dependent on having gas or hydro when you project for new nuclear power plants. That's one part of the reason why this stuff is politically charged. From what I understand it's not a theoretical constraint, but mostly a lack of enough commercial interest for any other design. But it is what it is.