It was thirty years ago this week that the Unit 2 reactor of the Three Mile Island (TMI) nuclear power plant began a partial meltdown. As its fuel rods began to burn out of control, a hydrogen bubble formed, causing a small explosion.

During the accident, plant operators were myopically glued to their instruments, which were incorrectly indicating that a crucial pressure valve was closed. In fact, it was open and draining coolant from the plant’s core, thus causing it to burn out of control. When the shift changed, someone on the new crew had the presence of mind to check the temperature on the reactor’s effluent pipe. It was way too hot. That meant the crucial pressure valve–which read “closed” on the monitors–was actually wide open.

The crisis was eventually brought under control. How narrow the margin of error. That accident was bad–43,000 curies of krypton radiation were released–but it could have been catastrophic.

One reason more radiation was not released was because “paranoid” anti-nuke activists worried that the plant, built directly in the flight path of the Harrisburg airport, could be hit by a jet. They demanded a very strong containment shell be built over the reactor. As a result, TMI had one of the strongest such protective seals in the country. Had the meltdown not been caught when it was and had there not been a containment shell, the whole Northeast could have become a fallout zone for 10,000 years thereafter. It would have been like those Chernobyl fallout zones: a radioactive wilderness; a national sacrifice zone; devastation akin to Sherman’s March, except permanent. America would have been reduced to a rump version of itself.

It is fitting to reflect on the TMI accident because in the face of climate change there is still much unhinged talk about a nuclear renaissance. During the 2008 presidential campaign, John McCain called for forty-five new nuke plants to be built. Barack Obama, while less specific, also pledged federal subsidies to help build atomic power plants.

As I have reported in these pages, this second wave of state-of-the-art atomic power plant construction is pure fantasy. No one wants to invest in nukes, despite government guarantees to cover 80 percent of the costs if the projects default. No one will insure them. They will not be built. However, underneath this nuclear renaissance discourse lurks the real danger: while we debate the fantasy qualities of a new fleet of plants that will never be built, a handful of companies that own the existing fleet of decrepit old zombie plants are quietly pushing these reactors to the very edge of their capacity and beyond.

There are 103 reactors in sixty-four locations across the United States. None of these reactors were designed to last more than forty years. We are reaching that deadline. But companies like Entergy and Exelon have been demanding and receiving dangerous license extensions and so-called power “uprates”. These companies are insisting that the plants be allowed to run for sixty years rather than forty, and that they be allowed to run the plants at 120 percent of their designed capacity. The companies are doing this to extract every last penny of profit from the old reactors. During the Bush years, the NRC relicensed forty of the country’s reactors. In those eight years, the NRC did not deny a single renewal request. This is unconscionably reckless behavior. The regulators of this industry would appear to be somnambulant hostages to the nuke operators.

President Obama has an opportunity to address this gathering crisis. Though he supported atomic power subsidies during his campaign, he has not come out in support of relicensing old plants–this, after all, is the crucial issue. Subsidies don’t matter because no one is going to build new plants. Relicensing, on the other hand, is a real and present danger. There are two positions open on the Nuclear Regulatory Commission, and President Obama has yet to make any appointments. For the sake of sanity and safety he must use his NRC appointments to oppose relicensing. And at the top of the NRC’s agenda should be shutting and decommissioning the nation’s remaining fleet of Three Mile Island-era nuke plants.