On December 1, 1969, Jersey Central Power & Light initiated fission in the fuel rods of the nation's first boiling-water nuclear reactor—one of 31 ultimately built in the U.S. The first "turnkey" plant, Oyster Creek nuclear generating station in New Jersey was sold for less than $100 million in 1964—a price well below what it would ultimately cost to build the reactor. The point was to prove that a nuclear power facility could be built as cheaply as a coal-fired power plant, and the key to that was a smaller safety system. As the recent meltdown in Fukushima showed, the design of these reactors' systems, such as the donut-shaped "suppression pool" of water meant to cool the reactor in a crisis, showed flaws—flaws identified by regulators decades ago.

"Recent events have highlighted the safety disadvantages of pressure-suppression containments," words that could have been written today but instead appeared in a memo from safety official Stephen Hanauer (pdf) to his fellow workers at the now-defunct U.S. Atomic Energy Commission (AEC) in 1972. "What are the safety advantages of pressure suppression, apart from cost saving?"

Yet, Oyster Creek continues to operate today, churning out electricity for Exelon Corp. Were it not for a requirement that it add cooling towers, Oyster Creek would probably continue to operate for decades—that added expense prompted owner Exelon to announce plans to close the plant in 2019. But on March 21, one of Oyster Creek's sister plants—Entergy Corp.'s Vermont Yankee—received permission to operate for another 20 years, despite a recent history that includes leaks, burst cooling pipes and misplaced fuel rods.

"The acceptance of pressure-suppression containment concepts by all elements of the nuclear field…is firmly embedded in the conventional wisdom," wrote AEC official Joseph Hendrie in response to Hanauer's suggestion. (pdf) "Reversal of this hallowed policy, particularly at this time, could well be the end of nuclear power. It would throw into question the continued operation of licensed plants…and would generally create more turmoil than I can stand thinking about."

The question remains, however: Are such old nuclear reactors safe?

The U.S. has 104 reactors scattered throughout the country, producing 20 percent of the nation's electricity—and 70 percent of our electricity that emits relatively little CO2 pollution, a point emphasized by U.S. Secretary of Energy Steven Chu. The oldest is Oyster Creek; the youngest is the Tennessee Valley Authority's (TVA) Browns Ferry unit No. 1 in Alabama, which first went online in 1974 and underwent a refurbishment that brought it back online four years ago after more than two decades out of commission.

These reactors could face extraordinary challenges, such as the recent twin blows of a magnitude 9.0 earthquake, which knocked out connections to the local power grid, followed by a wall of water that destroyed the fuel tanks for backup diesel generators and flooded critical electrical equipment, crippling the boiling-water reactors at Fukushima Daiichi in Japan. "Our [eight diesel generators] are protected from the seismic and hydrology hazards expected in the area," in addition to being buried in hardened facilities, says TVA spokesman, Terry Johnson, which operates three such boiling-water reactors at Browns Ferry.

All U.S. reactors are in principle designed to withstand the largest earthquake in the local seismological record. "That earthquake becomes the design basis for engineering at that site," says Scott Burnell, a spokesman for the AEC's successor, the U.S. Nuclear Regulatory Commission (NRC). "The reactor must be able to safely shut down even if there is an earthquake of that magnitude."

Boiling-water reactors, such as those at Fukushima Daiichi or Oyster Creek, directly produce the steam that then turns the turbine to make electricity—adding a sheen of radioactivity to the power-generating equipment. Surrounding this steam-producing core is an upside down lightbulb-shaped steel and concrete containment structure that is connected via large pipes to a donut-shaped pool, which is half-filled with cooling water. In the event of an accident hot steam shoots down those pipes into the ringing pool where it is cooled.

But in a meltdown that ring can be prone to cracking or leakage—as may have occurred at Fukushima Daiichi in multiple reactors. Because of this "generic" flaw built into the original plants, a special vent was added after the Three Mile Island accident to reactors in the U.S. and Japan that allows operators to release radioactive steam before pressure gets too high—steam that can also carry even longer-lived radioactive particles, such as iodine 131 or cesium 137, in the event of a meltdown.

"It was made stronger to accept the higher pressures that would be involved during venting," Johnson explains. But the pressures reported at Fukushima—more than seven kilograms per square centimeter at times—more than double the pressures even the hardened vent was designed to handle.

"The NRC's actions in the 1980s and 1990s regarding Mark I [model boiling-water reactor] containment issues significantly improved the Mark I's ability to deal with accident conditions," Burnell says. "The agency continues to conclude the Mark I containment design provides appropriate protection of public health and safety."

These reactors also face a more insidious threat: age. Concrete, pumps, pipes and wiring face a daily load of some combination of high temperatures and pressures, vibration and—unique to nuclear infrastructure—bombardment with the neutrons thrown off by splitting atoms. Thick steel walls become brittle over time when exposed to a reactor's extreme temperatures, pressures and radiation. In fact, the NRC has shown that the stainless steel surrounding the reactor cores in boiling-water reactors degrades over time. Cracks also form at welds or joints.

Of course, it's not just the old General Electric boiling-water reactors aging in place. Pressurized-water reactors designed by Westinghouse—such those that employ pressurized water and heat exchangers to produce power, unlike the boiling-water variety—face similar challenges. In the 1990s the two pressurized-water reactors at the Salem nuclear facility in New Jersey were shut down for two years due to leaks, faulty reactor controls, poor maintenance and other serious issues.

Plus, parts fail: In the 1970s and 1980s, nuclear power plants endured a rash of steam-filled tubes bursting as a result of a faulty alloy—Inconel 600—used in their construction. Patches held the vital component together but, ultimately, entire steam generators had to be replaced as a result. Leaks have released radioactive hydrogen—tritium—into the environment at reactors from Vermont to Illinois.

And then there's the human element: The accident at Three Mile Island was made worse by operators reading a lack of cooling water as too much water in the reactor. And, in 1990, Plant Vogtle in Georgia lost all externally supplied electric power—just like Fukushima Daiichi's reactors—when a truck backed into a transmission line and the backup diesel generator failed, forcing it to rely on its last power source: batteries with an eight-hour life.

The U.S. has endured a slew of "near misses" in recent years: a 0.48-centimeter thick stainless steel lining is all that stood between Davis–Besse nuclear power plant in Ohio and a meltdown in 2002. And in 2010, alone, the NRC launched 14 investigations into safety-related issues at U.S. nuclear plants. "Many of these significant events occurred because reactor owners, and often the NRC, tolerated known safety problems," wrote David Lochbaum a nuclear engineer with the Union of Concerned Scientists in a report examining the 2010 track record. According to Lochbaum, the NRC overlooks some safety problems, such as a refueling-cavity liner leaking at the Indian Point facility in New York State since 1993. "By allowing this reactor to continue operating with equipment that cannot perform its only safety function, the NRC is putting people living around Indian Point at elevated and undue risk," Lochbaum writes.

The nuclear industry certainly has a history of ignoring potential problems until they become critical. Flaws in the boiling-water reactor safety system at Fukushima Daiichi (as well as Oyster Creek and Vermont Yankee) had been known since 1972. The potential for Inconel 600 to crack under pressure was first identified in the 1950s. A new report from the NRC Inspector General notes that nuclear power plant operators have consistently failed to report equipment defects. And the U.S. National Academy of Sciences in 2006 suggested the practice of overcrowding pools for the storage of spent nuclear fuel rods—that has caused fires and explosions at Fukushima Daiichi, which stores far less used fuel than typical U.S. plants—could prove dangerous.

This problem continues to grow because there remains no place for used nuclear fuel rod storage other than such pools or massive dry casks—both located on nuclear facility grounds. Yet, since 2000 more than half of the U.S. fleet of nuclear reactors have received 20-year operating extensions, piling yet more (thermally and radioactively) hot nuclear rods into their spent-fuel cooling pools.

Regardless of those extensions, all U.S. nuclear power plants currently in operation most likely will be decommissioned by 2050. Replacing them, however, may prove more difficult than extending their useful lives. Simply swapping old for new would require starting construction on a new reactor every six months for the next 40 years. As it stands, there are four new reactors under construction in the U.S.—and applications for another 16.

And that's why the U.S. Department of Energy, the NRC and industry are currently assessing whether the first-generation plants could operate another 20 years—thereby lengthening the life span of a given reactor to 80 years. "The NRC is a full participant into the ongoing research examining whether it's technically feasible to consider 'second' renewals to extend reactor operating life," Burnell says. "The matter has yet to be decided."

Editor's Note: David Biello is the host of a forthcoming series on PBS this April, titled "Beyond the Light Switch." The series, produced by Detroit Public Television, will explore how transformation is coming to how we use and produce electricity, impacting the environment, national security and the economy.