Later on the same shift, they discovered a substance technically designated “black goo” collecting at the end of the line where uranium was supposed to be coming out. The next day, the line had to be shut down, and everything had to be taken apart and cleaned, and the labeling conventions got a little scrambled as parts and wet rags and bottles were scattered around.
Most of chemical engineering practice had been fully automated by 1964, but this part of nuclear engineering, which was actually similar to other parts of nuclear engineering, seemed based in the nineteenth century. Processing nuclear fuel at this level was an astonishingly manual operation, requiring human beings to carry bottles of liquid material by hand and empty them into vats, tanks, or funnels at the tops of vertical pipes. The system was mostly gravity-driven, with liquid flowing naturally from the top floor to the ground floor in the plant. Somehow it seemed safer to have men carry around batches of uranium in small quantities, knowing exactly where and when it was to be transferred, than letting uncaring machinery do it.
The basic transfer units were specially built bottles, made of polyethylene, four feet tall and five inches in diameter, with plastic screw-on tops. Being tall and skinny, they discouraged a critical mass. No matter how concentrated was the uranium solution, it was impossible to get enough into one bottle to cause a chain reaction. However, it would be possible to stack them together in a corner and make a working nuclear reactor out of filled bottles, as stray neutrons flying back and forth from bottle to bottle would cross-connect them. That possibility was eliminated by having the anti-criticality bottles rolled around from place to place in “safe carts.” Each cart was built to hold the bottle vertically at the center of an open-framed, three-by-three-foot cube, made of angle irons and fitted with four casters at the bottom so it would roll. There was no way that all the bottles in the plant filled with highly enriched uranium solution could go critical as long as they were sitting in safe carts. The bottles were always separated by at least three feet of open space.
The problem with the polyethylene bottles was labeling them to identify the contents. Paper labels stuck on with Scotch tape would come off easily, because the bottles were frequently covered with slippery kerosene residue. The only way to get a label to stick was to hold it on with two rubber bands. On Thursday, the day shift was cleaning out the black goo in the system, and they found a plug of uranium nitrate crystals clogging a pipe. They cleaned it out with steam and drained the highly concentrated, bright yellow solution into polyethylene anti-criticality bottles. Paper labels were attached with rubber bands identifying them as containing a great deal of highly enriched uranium.
Five people at any one time ran the entire plant. On the night shift it was three young technicians, Peabody, George Spencer, and Robert Mastriani, the supervisor, a 30-year-old chemist named Clifford Smith, and the security guard. The plant superintendent, Richard Holthaus, was usually there during the day.
The back-breaking task of the evening was to clean the TCE, which had been used to wash the kerosene out of the uranium concentrate. It was expensive stuff, and it had to be recycled back into the process, but it always picked up a little uranium oxide when washing out the oil. The uranium was separated out of the TCE by adding some sodium carbonate and precipitating it to the bottom of the vessel. This process, like others in the plant, was carried out in small batches, and a shift-load of bottles loaded with dirty TCE was bunched up in safe carts. Peabody was expected to pick up each 35-pound bottle of solution, pour in some carbonate, and shake it for 20 minutes to ensure mixing. There had to be a better way.
Another way of agitating the TCE had been worked out in a previous shift. Weary of manipulating the heavy bottles, a technician had noticed that on the third floor was a perfectly good mixing bowl with a motorized stirrer, and why couldn’t we use that to slosh the TCE? It is not recorded, but I am sure he got the standard nuclear-work answer from the supervisor: “No! Give me a few minutes, and I will think of why you can’t do that.” Technicians could not be allowed to improve operating procedures on a whim. Eventually, the technician was able to wear down the supervisor, and word of an undocumented labor-saving procedure traveled through the plant with the speed of sound. The vessel in question, the carbonate make-up mixer, was about 18 inches in diameter and 26 inches tall, or the size and shape of a very efficient submarine reactor core. It was okay to use it, as long as the uranium content in what it was mixing was less than 800 parts per million, or very, very dilute.
It was nearly 6:00 P.M. Peabody rolled the safe cart with the first bottle in the cluster of what he assumed were bottles of TCE to be cleaned to the base of the stairs. The cart would not make it up the stairs, so he hefted the bottle to his shoulder. The label slipped out of the rubber bands and fluttered to the floor. The contents of this bottle looked about like the stuff in all the bottles. It was yellow, due to the extreme fluorescence of uranium salt, but this was not a bottle of contaminated TCE: it was uranium nitrate dissolved in water, from the black goo cleanout.
It was about as much work to get it up the stairs as it would be to shake the bottle, but Peabody arrived on the third floor, dragged the bottle over to the mixer, and unscrewed the top. The mixer was against the north wall of the room, held a couple of feet off the floor by metal legs, making the rim five feet high. The stirrer motor was hanging over the open top. Workers were protected from falling off the third floor and to the ground floor by a railing on either side of the narrow platform. Leaned against the railing on the right side, very near the mixer, was a folded two-section ladder, lying on its side.
The mixer already had 41 liters of sodium carbonate in it, and the motor was running. Peabody, who was only six inches taller than the lip of the vessel, stepped up on the sideways ladder and tilted the bottle into the mixer. Glug, glug, glug. As the last dregs emptied into the mixer, there was a bright blue flash and the sound of an enormous water balloon being slammed against the wall. As the geometry improved from long and thin to short and round, 6.2 pounds of nearly pure U-235 homogeneously mixed with water went prompt critical. Instantly, the contents of the mixer boiled violently, sending a vertical geyser hitting the ceiling, the walls, and thoroughly soaking Peabody with the products of 1 3 1017 fissions. He fell backwards off the ladder, jumped to his feet, and lunged for the stair well, screaming “Oh, my God!” The criticality alarm went off, and this time it meant it.
Peabody ran full tilt down the stairs, out the door, and was quickly making for the emergency shack, 450 feet away. His fellow workers were right behind him, fleeing the criticality alarm and watching Peabody tear his clothes off. He almost made it, but he fell to the ground naked, vomiting, and bleeding from the mouth and ears. Smith, the supervisor, ran to call Holthaus while Spencer and Mastriani grabbed a blanket from the shack and tried to wrap the injured man on the ground. He got up twice and tried to walk around, but he sank back to the ground with severe stomach cramps.
Soon the company officials and the police were backed up at the gate, and Peabody was loaded into the ambulance. His wife and eldest son, Charles “Chickie” Peabody, were found by a police officer. “There’s been an accident,” he began. “We’ll take you to the hospital.”
At 7:15 P.M., Richard Holthaus arrived at the plant, waving a radiation counter. Peabody had been the only person anywhere near the criticality, and he was the only one affected by the radiation burst. There was no radiation evidence on the ground floor that anything had happened, but nobody had turned off the criticality alarm, and the klaxon was still screaming. At 7:45 Smith joined him, and they cautiously climbed the staircase to the third floor, radiation probe held in front. There was no hint of a continuing criticality. Clearly, enough material had immediately boiled out to stop the chain reaction, but the walls, floor, and mixer showed fission-product contamination and were painted a brightly fluorescent yellow. Peabody’s bottle was still upended in the mixer. Holthaus went over to the mixer, removed the bottle, flipped the switch to turn off the stirrer, and quickly turned to go out the door. Smith took one last look and was right behind him. They had to quickly go downstairs and drain the contents of the mixer into anti-criticality bottles.