Space in the Seventies: The Technological Environment of Mid-1979, Around the Time of Skylab’s Reentry

A nuclear accident that happened in 1979 colored how many viewed Skylab’s impending reentry.

TMI-2 Core End-State Configuration. For more details on numbering, please click here. Image Credit: Nuclear Regulatory Commission

Less than three months before Skylab’s reentry, a nuclear incident of unprecedented proportions unfolded around Harrisburg, Pennsylvania, striking fear into the city’s (and nation’s) populace and effectively ending the United States’ commercial nuclear power industry. Much has been written about the March 28, 1979 incident at the Three Mile Island Nuclear Generating Station. Still, attitudes towards technology — and more precisely, ambivalence and distrust towards technology — affected how some viewed the Skylab space station’s upcoming re-entry. Here is a general explanation detailing the circumstances of the TMI-2 reactor accident, its aftermath, and how it impacted the United States’ culture.

Background of the Three Mile Island Unit 2 Incident

Before TMI-2, reactor accidents in the United States had occurred in the government sector. The Nuclear Navy, headed by legendary Admiral Hyman G. Rickover, boasted (and still boasts) a clean record as far as nuclear accidents are concerned, probably due to the fact that the infamous Naval Nuclear Power School has been described as a “$50,000 education, shoved up your butt one nickel at a time.” However, shortly before Christmas 1960, an Army accident of nightmarish proportions drove home the inherent danger of working with nuclear reactors.

The 3 megawatt (MW) SL-1 (Stationary Low-Power Reactor Number One) reactor in Idaho Falls, Idaho, was serviced on the evening of December 21. For unknown reasons, the reactor’s central control rod — which was meant only to move a distance of 4.2 inches — was moved out 20 inches, causing a rapid addition of reactivity to the core, leading to supercriticality. All three Army operators died, and their remains were exposed to thousands of rem; one had lived long enough to survive the initial blast but later succumbed to his injuries. One operator was rumored to have been impaled to the facility’s ceiling by the control rod.

The remnants of the SL-1 reactor. Image credit: Idaho National Engineering and Environmental Laboratory, INEEL 81–3966

Before March 1979, the commercial nuclear power industry had never suffered a serious incident. But that all changed during the early morning hours of March 28, 1979, when the 906 MW TMI-2 plant began to experience a confusing cascade of caution and warning alarms. This text from the Nuclear Regulatory Commission (NRC) provides a short-form, general explanation of the events that began to unfold:

The accident began about 4 a.m. on Wednesday, March 28, 1979, when the plant experienced a failure in the secondary, non-nuclear section of the plant (one of two reactors on the site). Either a mechanical or electrical failure prevented the main feedwater pumps — component (1) in the animated diagram) — from sending water to the steam generators (2) that remove heat from the reactor core (3). This caused the plant’s turbine-generator (4) and then the reactor itself to automatically shut down. Immediately, the pressure in the primary system (the nuclear piping portion of the plant shown in orange) began to increase. In order to control that pressure, the pilot-operated relief valve (5) opened. It was located at the top of the pressurizer (6). The valve should have closed when the pressure fell to proper levels, but it became stuck open. Instruments in the control room, however, indicated to the plant staff that the valve was closed. As a result, the plant staff was unaware that cooling water in the form of steam was pouring out of the stuck-open valve. As alarms rang and warning lights flashed, the operators did not realize that the plant was experiencing a loss-of-coolant accident.

Other instruments available to plant staff provided inadequate or misleading information. During normal operations, the large pressure vessel (7) that held the reactor core was always filled to the top with water. So there was no need for a water-level instrument to show whether water in the vessel covered the core. As a result, plant staff assumed that as long instruments showed that the pressurizer water level was high enough, the core was properly covered with water too. That wasn’t the case.

Unaware of the stuck-open relief valve and unable to tell if the core was covered with cooling water, the staff took a series of actions that uncovered the core. The stuck valve reduced primary system pressure so much that the reactor coolant pumps (8) started to vibrate and were turned off. The emergency cooling water being pumped into the primary system threatened to fill up the pressurizer completely — an undesirable condition — and they cut back on the flow of water. Without the reactor coolant pumps circulating water and with the primary system starved of emergency cooling water, the water level in the pressure vessel dropped and the core overheated.

The devastation to the TMI-2’s reactor core — in service for only three months — was done in a little over two hours. Due to the core being uncovered for this period, the uranium fuel at the top of the reactor began to melt, releasing large quantities of radiation. While the melted fuel rods were isolated within a shielded containment vessel, several plant personnel monitoring the incident were exposed as they attempted to gauge the condition of the reactor.

Later that afternoon, operators noted a transient pressure spike. The building — including the control room —briefly shook from what is believed to have been an explosion from a buildup of hydrogen in the reactor’s containment vessel. As further developments revealed the severity of the incident during the following days, residents of neighboring populated areas were encouraged to evacuate. Several residents claimed to suffer from sudden mysterious illnesses and observed dead fish clogging the Susquehanna River, where the Three Mile Island nuclear facility had been situated.

Aftereffects of TMI-2

It would take years for the true breadth of the TMI-2 incident to unfold. While the NRC emphasized that “The approximately 2 million people around TMI-2 during the accident are estimated to have received an average radiation dose of only about one millirem above the usual background dose…The accident’s maximum dose to a person at the site boundary would have been less than 100 millirem above background,” many radiation workers and former Harrisburg residents have noted high incidences of cancer and other health issues possibly related to TMI-2. (One can find a primer on acceptable exposure to civilians by clicking on this NRC link.) In addition, reactor cleanup took years to complete.

By 1984, a polar crane — the source of much understandable concern among those doing cleanup due to concerns its failure could lead to uncontrolled reactor transients — removed the reactor vessel head so defueling and further cleanup could occur. The entire decommissioning process for TMI-2 took 14 years following the initial accident. The newly-released Netflix documentary Meltdown: Three Mile Island has more information about the accident, its aftermath, and the sometimes controversial cleanup process.

How is Any of this Related to Skylab?

When it became clear to the general public that Skylab would be deorbited and there was a chance — however infinitesimal — that it could come apart over populated areas, the recent TMI-2 accident undoubtedly contributed to a particular zeitgeist of the time: that government agencies weren’t necessarily transparent, and people were often at the mercy of technological innovations. The NRC had minimized the TMI-2 incident, likely in a feeble attempt to not cause any undue alarm in Pennsylvania residents. This tactic, however, didn’t work. Now, NASA’s attempts to minimize the possible impact of Skylab’s reentry on people fell upon deaf ears.

“This image is an artist’s concept of the Skylab in orbit with callouts of its major components.” 1974 NASA image

While it’s estimated that the chance of being directly hit by satellite debris is less than one in one trillion, distrust in technology circa mid-1979 certainly contributed to the feeling that it wasn’t something completely off-limits. Companies began marketing Skylab reentry “kits” complete with hardhats, pointy cardboard hats, and commemorative “Skylab target” T-shirts to poke fun at NASA’s errant space station. Even Saturday Night Live star John Belushi got into the act, supposing Skylab would somehow be aimed directly for his apartment. But as we all know, there’s some truth — and fear — behind jokes.

In the end, Skylab did fall over parts of Western Australia, ironically in an attempt to steer it away from populated areas. Thankfully no one was injured, but no one could easily buff out the dings made in the United States’ reputation of being the leader in predictive technology following mid-1979. In less than a decade, the Soviet Union would experience its own nuclear accident — but that’s another story for another day.


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Emily Carney is a writer, space enthusiast, and creator of the This Space Available space blog, published since 2010.

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Emily Carney

Emily Carney

Space historian and podcaster. Space Hipster. Named one of the Top Ten Space Influencers by the National Space Society. Co-host of Space and Things podcast.

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