Smithsonian - National Museum of American History, Behring Center
Three Mile Island
Unit 2 nuclear power plant
First looks inside the reactor

Three Mile Island: The Inside Story

The Importance of the Sonar Survey

 
This montage makes evident the large impact that the core topography survey, and the topographic model presenting its results, had on conceptions of the real state of affairs within the reactor vessel.

Click to enlarge imageFigure 9.1. This montage makes evident the large impact that the core topography survey, and the topographic model presenting its results, had on conceptions of the real state of affairs within the reactor vessel.

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This importance of the INEEL core topography survey was recognized in several publications in 1985 and 1986, but later reviews made only passing reference to it (ref. 12, ch. 5) or omitted it entirely (ref. 21). Among the factors contributing to this rapid forgetting of the impact of the sonar survey was an over-valuation of—and over-investment in—video inspections of the interior of the reactor vessel. And this was because, in the estimation of the authors of the comprehensive technical history of the TMI cleanup, “Even when accurate predictions of core conditions could be made, engineers and management were reluctant to accept the bad news until it was seen on a video screen. A picture equaled far more than a thousand words.” (Ref. 12, ch. 5, p. 1, which, ironically, itself contributes to this erasure of the sonar survey’s significance.)

The INEEL core topography team recognized this not-til-we’ve-seen-it-with-our-own-eyes bias arising in good part from the not-wanting-to-know-what-we-don’t-want-to-be-so mentality of the reactor’s manufacturer and the utility’s management. And it was in part for that reason that they put so much effort into providing such striking means for visualizing their results. But the large impact of their sonar survey had rather the effect of leading to still larger investments in video in order to see what was so.

Thus although the sonar survey in the summer of 1983 had provided a precise and detailed topography of the cavity at minimal cost—minimal not merely in dollars, but also in personnel-hours of radiation exposure and in hours of cleanup time lost—in April 1984 its results were confirmed by a specially designed video camera and camera manipulation system providing broadcast-quality images and position and orientation data (ref. 5, p. 144). And that was just the beginning. Once the head (top) of the reactor vessel was unbolted and lifted off, still more elaborately complex and expensive video-guided sample retrievals were undertaken—and described with enthusiasm (ref. 21, p. 575):

“. . . it was necessary to develop the tools, procedures, techniques, and proficiencies that would enable a five-member crew to perform as a single individual. The task required a camera operator to continuously position and reposition underwater cameras to provide clear video images of the sampling activities, an operator to position underwater lights to provide the best possible lighting for the camera, an operator to position and operate a heavy-duty cutting tool mounted on a long pole, and an operator to manipulate and position a long-handled grasping tool used to hold the fuel rod sample during cutting. The fifth member of the team was the engineer/task supervisor who supervised the sample activity and coordinated the movements and positioning of the tools by directing the actions of the other team members. Extensive mock-up training and practice were necessary to produce the team proficiency that proved to be essential to the success of the sampling task.”

Under the spell of such extravagant efforts, the historic importance of so quick and cheap an investigation as the ultrasonic survey was bound to be forgotten.