I sided with the railroad. I planted the reactor. I spoke with Shaun. I spoke with Tinker Tom who tells me to step into the relay.

Every time I step into the relay the game crashes.

I am highly disappointed and don't know what to do. Can I somehow fast travel to the detonation site?

Fixed it myself.

Apparently during the quest The Nuclear Option there can be issues with Power Armor. Strangely I was not the one wearing it. Cait had found a suit and climbed into it. I took her outside of the relay control room, told her to wait, took back all the power armor pieces and dropped them in another room. Then with Cait still staying where I left here I stepped into the relay and it worked.

I consider myself lucky