TMI Operators Took Actions They Were Trained to Take

Editor’s note. This post has a deep background story. The author, Mike Derivan, was the shift supervisor at the Davis Besse Nuclear Power Plant (DBNPP) on September 24, 1977 when it experienced an event that started out almost exactly like the event at Three Mile Island on March 28, 1979.

The event began with a loss of feed water to the steam generator. The rapid halt of heat removal resulted in a primary loop temperature increase, primary coolant expansion and primary system pressure exceeding the set point for a pilot operated relieve valve in the steam space of the pressurizer. As at TMI, that relief valve stayed open after system pressure was lowered, resulting in a continuing loss of coolant. For the first twenty minutes, the plant and operator response at Davis Besse were virtually identical to those at TMI.

After that initial similarity, Derivan had an ah-ha moment and took actions that made the event at Davis Besse turn into an historical footnote instead of a multi-billion dollar accident.

When Three Mile Island happened and details of the event emerged from the fog of initial coverage, Mike was more personally struck than almost anyone else. He has spent a good deal of time during the past 35 years trying to answer questions about the event, some that nagged and others that burned more intensely.

In order to more fully understand the below narrative, please review Derivan’s presentation describing the events at Davis Besse, complete with annotated system drawings to show how the event progressed.

Warning – this story is a little longer and more technical than most of the posts on Atomic Insights. It is intended to be a significant contribution to historical understanding of an important event from a man with a unique perspective on that event. If you are intensely curious about nuclear energy and its history, this story is worth the effort it requires. Mike Derivan (mjd) will participate in the discussion, so please ask for clarification if you still have questions after you have read the story and the background material.

The rest of this post is his story and his analysis, told in his own words.

By Mike Derivan

My first real introduction to the Three Mile Island (TMI) accident happened on Saturday March 31, 1979. At Davis Besse Nuclear Power Plant (DBNPP) in Ohio we heard something serious had happened as early as the day of the event, March 28, and interest was high as it was a sister plant.

Actual details were sketchy for the next couple of days, and mainly by watching the nightly TV news it became clear to me that something serious was going on. It was clear from watching the TV news reports that conflicting information was being reported. Some reports indicated there had been radiation releases and also reports by the utility, Metropolitan Edison the owner of TMI, of no radiation releases.

I even remember hearing the words “core damage” first mentioned. It was that Saturday on a TV news report I saw the first explanation using pictures of the system to the suspected sequence of events and it became clear to me the Pilot Operated Relief Valve (PORV) had stuck open.

My reaction was gut-wrenching and I was also in disbelief that TMI did not know what had happened at Davis Besse. That evening I watched the Walter Cronkite news report. I sat there with total disbelief as he discussed potential core meltdown. Disbelief because if you were a trained Operator in those days it was pretty much embedded in your head that a core meltdown was not even possible; and here that possibility was staring me right in the face.
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