Entergy Corp., the second-largest U.S. nuclear operator, and Duke Energy Corp. said the industry may need to retrofit reactors or bolster safety systems after a pressure-relief system failed in Japan, contributing to the worst nuclear disaster since Chernobyl, Bloomberg said.

Venting systems at Tokyo Electric Power Co.’s Fukushima Dai-Ichi reactors were designed to allow engineers to release pressurized gas into the atmosphere to avoid dangerous hydrogen explosions. The systems were installed in the United States and in Japan after the partial core meltdown at Three Mile Island Unit 2 in Pennsylvania in 1979.

The vents were built into General Electric Co. boiling-water reactors, including the stricken Japanese plant that was rocked by at least two blasts blamed on trapped hydrogen. A conclusion that the vents were at fault may add costs for nuclear-power generators as politicians from Germany to India question the safety of atomic energy.

The hydrogen explosions in Fukushima “call the modification into question,” said Tony Roulstone, who directs the master’s program in nuclear technology at the University of Cambridge in England. “If these vents don’t work, then the design looks wrong. Fixing it will take some design work, but won’t be wildly expensive.”

The U.S. Nuclear Regulatory Commission is “looking at effectiveness of containment venting strategies,” Charlie Miller, head of the post-Fukushima safety review, said at a May 12 agency meeting.

Entergy “fully expects” the U.S. Nuclear Regulatory Commission to order new equipment installed and new procedures to be adopted as a result of the accident in Japan, said Jim Steets, a spokesman for the New Orleans-based company, which owns 11 reactors.