Complex sentence: Due to seismic risk, the nuclear portion of the Humboldt Bay Nuclear Power Plant was shut down in the 1970s, but no substantial damage occurred to the two fossil-fuel units that were still operational at the facility.
Split into simpler sentences: Due to seismic risk, the nuclear portion of the Humboldt Bay Nuclear Power Plant was shut down in the 1970s. No substantial damage occurred to the two fossil-fuel units that were still operational at the facility.