The Russian forces seem to be trying to encircle or assault Kyiv. I think they've taken the nuclear plant because it is a defensible point along their shortest line of advance. They wouldn't want to move past it without controlling the site.
Also, either side would be pretty reluctant to bomb it, or otherwise battle too hard close to it. It's a great position to hold if you can.
It is a great position to hold and fight in, because the area is pretty empty of civilians. And russia must avoid ukranian (russian in their eyes) civilian casualties, to not loose the little popular support they have for this war.
And neither side will be so stupid to directly bomb the remains of the reactor, but I think it would need a serious direct bombing, for radiation to leak out. I don't think there can be still a major uncontrolled chain reaction. The worst that can happen under normal circumstances, is radiation leaking out.
(but all this is from the back of my head knowledge, about documentaries about chernobyl, I might be wrong)