Was D66 as a whole previously anti-nuclear energy or was this just Jetten's position?
What is written above is not entirely correct.
Jetten's position was much more nuanced than just being against nuclear energy, as is D66's position. To claim Jetten will be responsible for 'building two nuclear power plants' is also a stretch. The coalition agreed to take the 'necessary steps to build two nuclear plants', which includes facilitating nuclear initiatives and looking into a financial contribution (subsidy) from the government. Of course everything hinges on the last and there is bound to be discussion over it. That doesn't mean that there won't be nuclear plants but it is a long way still.
Essentially the new policy should come as no surprise. There are two parties in government which want nuclear energy and two which don't take a strong position either way. Of course things would have been different had Groenlinks and PvdA been in government.