Nuclear reactors in the central and eastern U.S. face previously unrecognized threats from big earthquakes, the Nuclear Regulatory Commission said Tuesday. Experts said upgrading the plants to withstand more substantial earth movements would be costly and could force some to close.

The two nuclear power reactors in North Anna, Va., were cooling off Wednesday after being shut down by Tuesday’s earthquake, but the debate about what lessons should be learned for nuclear safety was still simmering.

Scientists have long sought easier ways to make the costly material known as enriched uranium — the fuel of nuclear reactors and bombs. However, activists are concerned that a potential breakthrough using laser enrichment could increase risks of proliferation and nuclear terrorism by making it both easier to accomplish and easier to conceal.

A special inspection of U.S. nuclear plants after the Fukushima disaster in Japan revealed problems with emergency equipment and disaster procedures that are far more pervasive than publicly described by the Nuclear Regulatory Commission, a review of inspection reports by ProPublica shows.

As America's nuclear power plants have aged, the once-rural areas around them have become far more crowded and much more difficult to evacuate. Yet government and industry have paid little heed, even as plants are running at higher power and posing more danger in the event of an accident.

The accident at the Fukushima power plant in Japan has led to much discussion about the future of nuclear power. I believe one important lesson of the accident has been overlooked. Nuclear power is often touted as a solution to climate change, but Fukushima serves as a warning that far from solving the climate problem, nuclear power may be highly vulnerable to it.

Developers have created a crowdsourced radiation map to track the flow of radiation from the failed Fukushima Daiichi nuclear plant, using a mix of government sources and data from amateurs equipped with geiger counters.

Pakistan has begun work on what independent experts say appears to be a fourth plutonium-producing reactor at the country's Khushab nuclear complex, a move that could signal a further escalation in Pakistan's arms race with arch-rival India.

The threat to digital systems at the country's nuclear power plants is considerable, but the sector is better prepared to defend against potentially devastating cyber attacks than most other utilities, according to government and industry officials and experts

China is preparing to build three times as many nuclear power plants in the coming decade as the rest of the world combined, a breakneck pace with the potential to help slow global warming. Yet inside and outside the country, the speed of the construction program has raised safety concerns. China has asked for international help in training a force of nuclear inspectors.