WASHINGTON (AP) â¿¿ With workers at the Fukushima Dai-ichi nuclear plant still trying to prevent further radiation leaks, other countries are asking whether the benefits of nuclear power outweigh the risks. Uncertainty about the nuclear industry's future has drawn investors back toward coal and even more into natural gas, domestic energy resources most likely to fill the gap if nuclear production declines.

Driving the concern is an upcoming series of reviews by the Nuclear Regulatory Commission of nuclear facilities seeking to renew their licenses. The eight U.S. plans facing review before 2020 produce 6.7 gigawatts of energy, one analyst pointed out Friday.

Replacing that capacity would require 20 million metric tons of Appalachian coal, or 66 billion cubic feet per day of natural gas, said Dahlman Rose & Co. analyst Daniel Scott. At those levels, output of the fuels would increase by 6 percent and 2 percent, respectively.

The NRC has not rejected a nuclear license renewal in its 35-year history, Scott said. Japan's disaster, the worst since the Chernobyl meltdown in 1986, makes challenges more likely, he said.

"Though it is difficult to determine the eventual outcome of this tide of public opinion, we believe it is reasonable to assume a generally lower level of nuclear energy versus prior expectations in this country in the years ahead," Scott said. "We look for any nuclear generation shortfalls to be made up by a combination of coal- and natural gas-fired baseload replacement power."

Authorities struggled to gain control of the Fukushima plant over the past two weeks after a massive earthquake and tsunami knocked out the reactor's cooling systems. Explosions and fires caused repeated setbacks, stoking fears of a massive release of radiation.

Japanese Prime Minister Naoto Kan said Friday that the situation remains "very grave and serious."

The U.S. nuclear plants currently seeking license extensions "are most vulnerable to post-Fukushima scrutiny by coincidence of timing," Scott said. But several face additional challenges:

â¿¿ The 605 megawatt Vermont Yankee facility, in Vernon, Vt., already received NRC approval for its extension, despite similarities to the design of the Fukushima plant. It still needs state-level approval.

â¿¿ The 1,020MW Indian Point plant in Buchanan, N.Y. is considered dangerous because it is less than 40 miles from Manhattan. By comparison, people living within 20 miles of the Fukushima plant might be forced to evacuate if the situation there worsens, Japanese officials said Friday.

â¿¿ Two California plants lie near fault lines on the Pacific rim, inviting comparisons to Japan's disaster. They are the 2,200MW San Onofre plant, in San Diego County, and the 2,240MW Diablo Canyon station in Avila Beach, near San Luis Obispo, Calif.

Overseas governments also are questioning their reliance on nuclear power. Germany has shuttered temporarily its seven oldest reactors, while China and India have indicated they might reconsider planned expansions, Scott said.

In addition to possible challenges by the NRC, nuclear operators face regulatory hurdles that might dampen the industry's growth.

The Environmental Protection Agency is set to propose new rules this month related to the use of seawater to cool power plants. The changes would apply to about 400 coal-based and nuclear plants. They might force operators to install costly retrofits because of concerns that water intake and outflow can affect fish and other wildlife.

The coal and gas industries also have faced fears of a regulatory squeeze, including limits on mountaintop-removal mining in Appalachia. The threats facing the nuclear industry have overshadowed some of those concerns out of their sheer immediacy. Coal and gas producers will see higher prices and more demand if nuclear output falls.

Most of the companies that produce nuclear reactor units are privately owned. Among those that trade, shares of General Electric Co. rose 10 cents to $19.88 Friday. Babcock & Wilcox Co. jumped 62 cents, or 2 percent, to $32.24.

But nuclear shares have been under pressure.

American depository shares of Hitachi Ltd. skidded $1.89, or 4 percent, to $51.32. The NRC said Thursday that it would seek public comment before allowing use in the U.S. of a reactor made by GE and Hitachi. Many foreign companies listed on U.S. exchanges are traded in ADSs.

Shares of companies that operate the at-risk reactors were nearly flat, in line with broad market indices.

Yet shares of many U.S. coal and natural gas producers showed healthy gains. International Coal Group Inc. added 23 cents, or 2 percent, to $11.10. James River Coal Co. increased 45 cents, or 2 percent, to $24.42. Patriot Coal Corp. gained 36 cents to $25.58.

Alpha Natural Resources rose 60 cents to $60.25. Massey Energy Co. leaped 83 cents to $68.55. Consol Energy Inc. increased 33 cents to $55.82.

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