A California utility, waiting for "safety lessons" arising from the crisis in Japan, has asked to delay a hearing on extending the operation of one of its nuclear plants by 20 years. The plant lies near a fault that could trigger an earthquake.

The Center reported this morning that, although regulators worried six years ago that nuclear plants in the eastern two-thirds of the country might be more vulnerable to earthquakes than previously realized, the risk assessment spawned by these concerns is unfinished and almost a year past its target completion date.

Nuclear Regulatory Commission spokesman Roger Hannah told the Center that agency officials are assessing whether any plants require retrofits to enhance safety. But, he added, “The currently operating plants are all safe from a seismic standpoint.”

And President Barack Obama asked the commission on Thursday to review the ability of U.S. nuclear plants to weather a natural disaster. Thirty-one nuclear reactors operating in the U.S. have the same design as those in danger of a meltdown in Japan.

In California, the proposed extension of the Diablo Canyon plant’s life from 2025 to 2045 — requested by plant owner and operator Pacific Gas and Electric Company — had prompted concern even before the earthquake in Japan. Company seismic tests, which would be important in determining whether an earthquake could lead to a nuclear meltdown, are not finished.

Some have expressed concern about the plant’s proximity to populated areas. Among them were California Sens. Barbara Boxer and Dianne Feinstein, who wrote a letter to the NRC questioning the safety of the state’s two nuclear plants — Diablo Canyon and another in San Clemente — and asking the commission to inspect both.