Nuclear waste and enriched uranium cannot be transferred between two parts, nor can they interact with components from other mods that have the same resources.

[toobigtou]

Full log:log:

the mod list：
modlist.txt

To reproduce the issue, it’s very easy. Just use it as intended, and when you reach the point where there should be a functional button, there’s nothing there----

[ChrisAdderley]

This seems to be working as intended in the latest releases of NFE, System Heat and the SystemHeatReactors plugin, which is the same core setup as your logfile and modlist.

Here is a ship with a reactor, fuel container and NO level 3 engineers (she's standing on the ladder). Note that the fuel transfer In/Out don't appear when both the reactor and fuel container are selected

The engineer has boarded the ship and you can see the IN/OUT controls are there

I see you have TweakScale and its companion KSP-Recall installed - those are known to cause some issues and I don't support them. You could try removing them.

[Ryan-Gorley]

This issue seems to be a result of the "Resource Transfer Obeys Crossfeed Rules" setting. If it is enabled, the transfer buttons for enriched uranium and depleted fuel will not appear.

Modlist I used when testing this:
fueltransfermodlist.txt

[ChrisAdderley]

Spent 4 hours on this, because of the way Squad built this it's very difficult to fix. Disable that KSP setting or disable fuel transfer rules in settings