The Nuclear Regulatory Commission on Thursday ordered the owners of nearly a third of all U.S. nuclear reactors to add venting systems to their containment buildings to prevent the pressure-induced explosions that plagued the Fukushima reactors in Japan in 2011.

The order pertains to 31 boiling-water reactors, including Exelon Corp.'s Limerick Generating Station, Peach Bottom Atomic Power Station and Oyster Creek Nuclear Generating Station in New Jersey; PPL Corp.'s Susquehanna Steam Generating Station, and PSEG Nuclear's Hope Creek Generating Station.

According to industry estimates, the venting systems could cost reactor owners up to $20 million per unit.