Ecoscience: Lessons of the Three Mile Island Nuclear Accident

This article looks at the sequence of mechanical and operator failures that led to the 1979 Three Mile Island nuclear accident and what the authors feel the accident revealed about the unjustifiable hazards of nuclear power.

| March/April 1980

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Anne and Paul Ehrlich (INSET) concluded the Three Mile Island nuclear accident revealed nuclear power was too unsafe to become a mainstay energy source. 


Paul Ehrlich (Bing Professor of Population Studies and Professor of Biological Sciences, Stanford University) and Anne Ehrlich (Senior Research Associate, Department of Biological Sciences, Stanford) are familiar names to ecologists and environmentalists everywhere. As well they should be. Because it was Paul and Anne who — through their writing and research — gave special meaning to the words "population," "resources," and "environment" in the late 1960's. (They also coined the term coevolution, and did a lot to make ecology the household word it is today.) But while most folks are aware of the Ehrlichs' popular writing in the areas of ecology and overpopulation (most of us — for instance — have read Paul's book The Population Bomb ) . . . far too few people have any idea of how deeply the Ehrlichs are involved in ecological research (research of the type that tends to be published only in technical journals and college textbooks). In this installment of their regular Ecoscience column they discuss the Three Mile Island nuclear accident and what it revealed about the nuclear power industry.

Now that the dust and radioactivity have settled, and the laborious and dangerous cleanup is underway, it's time to take a look at the lessons that can be learned from the near disaster at Three Mile Island.

A Frightening Story

While the details of the complex accident are still not entirely understood, its basic outline is fairly clear. A section of the auxiliary system that was designed to supply cooling water to the reactor core in case of failure of the primary pumping system had been removed from service by the closing of valves so that repairs could be made. However, through human error the valves weren't reopened after the repairs were completed, leaving the backup system cut off from the main system. Before this mistake was discovered, an unrelated breakdown of the primary pump (which is a fairly common occurrence) cut off the flow of cooling water to the reactor core.

The pump of the auxiliary system started up as programmed but could not supply water to the primary system because of the closed valves. Sensors detected the problem and "scrammed" the reactor (in other words, the neutron-absorbing control rods were immediately inserted all the way to stop the chain reaction). This action, however, did nothing to solve the problem of disposing of the residual heat of radioactivity in the reactor core . . . the problem on which the whole subject of emergency core cooling systems (ECCS) is focused.

You may recall from previous columns in MOTHER EARTH NEWS that the heat present in a scrammed reactor core is, under most circumstances, capable of building in less than a minute to the point where the core starts to melt . . . after which a complete meltdown is probably inevitable. The mass of molten fuel then would melt through the floor of the containment building and could, under some conditions, release an enormous inventory of radioactivity above ground. The result would be the kind of accident that, under the worst conditions, is potentially capable of killing thousands of people immediately and hundreds of thousands more by delayed cancers, while making state-sized areas uninhabitable.

After the TMI reactor scrammed, mechanical failures exacerbated the problem initiated by the original human error (the failure to reopen the valves on the secondary system . . . which was not corrected until a full eight minutes after the start of the accident): A pressure-release valve stuck open, and a gauge that was supposed to register the level of water around the core malfunctioned. . . showing more water than was actually present (a condition astonishingly similar to that portrayed in the movie The China Syndrome ).

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