Faux Pas

Making Nuclear Reactors Safe From Butt-Pinching

Harnessing the power of the atom provides humanity with virtually unlimited power. It also poses devastating consequences if things go poorly. The nuclear disasters at Chernobyl, Fukushima, and Three Mile Island happened through cascading mistakes and failures, all of which could have been avoided through proper planning.

As the United States took its first tentative steps into the nuclear-powered age, many “what if” scenarios had to be played out. If nuclear energy was to be successful, it had to be safe from every imaginable contingency. That is how nuclear reactors were designed to be able to withstand butt-pinching.

Among the first nuclear reactors was the SL-1. It was designed to power the Distance Early Warning (DEW) radar stations throughout Alaska and Canada. The DEW stations kept constant watch against incoming Soviet missiles. Their positions in the unforgiving conditions of the arctic north made them difficult to resupply with fuel for their generators. Nuclear reactors would solve that problem.

SL-1 Reactor schematics. Click image to expand.

The SL-1 could provide heat and electricity for up to three years without refueling. It bore little resemblance to modern reactors. It was designed to be easily disassembled, moved, and reassembled. Easy mobility precluded the use of heavy shielding material. Instead of large concrete structures, the SL-1 used a simple steel building.

There was one big similarity to contemporary reactors. The SL-1 used control rods to control the nuclear reaction. The rods impeded nuclear fission and could be used to slow or shut down the reactor. Removal of the rods altogether is the nuclear reactor equivalent of releasing your car’s brakes while going downhill; the reaction steadily builds until it becomes too intense to contain. In other words, the control rods and the ability to manipulate them are pretty important.

The SL-1 had a wee bit of a design flaw. The control rods were coated with a thin sheet of boron to allow better control of the nuclear reaction. Part of the reaction process converts boron into carbon 14, however. As this happened, flakes of carbon detached from the control rods and caused them to stick and hang up from time to time. Again, using the brake analogy, this would be like driving down a steep hill in a car whose brakes randomly froze in place or failed to engage when needed.

Another design flaw of the SL-1 was that it could go critical with the removal of a single control rod. If the central rod was withdrawn, the fission reaction would go out of control, even though the other rods remained in place. Future models emphasized redundancy, but that was a lesson that had yet to be learned with the SL-1.

The first SL-1 went active in August 1958. Reactor operators received 9 months of training at Fort Belvoir, Virginia, and then went to Idaho for an additional 6 weeks of training at the reactor. The reactor was operated by a three-man team that was rarely switched up.

The crew assigned to the SL-1 in December 1960 consisted of Senior Reactor Operator John A. “Jack” Byrnes, Assistant Operator and shift supervisor Richard C. “Dick” Legg, and trainee Richard L. McKinley. Each of the men completed their training and performed competently up to this point.

Legg had developed a reputation as a prankster. One of his favorite tricks was to quietly shut off the fan that cooled some of the reactor instruments. When the rising temperature caused the system alarms to blare, he laughed hysterically as his crewmates scrambled to avert what they thought was impending doom. Only then would he turn the fan back on and reveal that it was all a joke.

Just the kind of guy you want working with nuclear fission, huh?

On the night of January 3, 1961, the crew was preparing to shut down the reactor for maintenance. Part of the process required the control rods to be disconnected from the rod drive mechanisms. To do this, a C-clamp was used to hold things in place. Once the rod was removed, one of the men would have to lift the 85-pound control rod about two inches off the clamp so another man could remove the clamp. At 9:01 p.m., Byrnes was lifting the control rod. Legg was crouching next to him, prepared to remove the clamp. McKinnley stood nearby, monitoring radiation levels.

Although the procedure called for the rod to be lifted no more than two inches, Byrnes lifted it 20 inches on this fateful night. That resulted in an unexpectedly rapid rise in power levels (a condition known as “prompt criticality”). In less than a second, the fuel melted and produced a massive amount of steam. The steam exploded, sending the layer of cooler water above the reactor core upward to slam into the underside of the reactor vessel head. The reactor vessel jolted, shearing all the piping and instrumentation, dislodging the shield blocks, and slamming into the ceiling of the reactor building. Byrnes and Legg died immediately. McKinnley survived for a short time but was dead before he could be taken to a hospital.

As authorities attempted to figure out what went wrong, they were faced with the problem that the only direct witnesses were deceased. They were forced to speculate about why the control rod was lifted so much beyond specifications. Various theories were proposed, including mechanical failure, improper training, and murder-suicide.

One particularly-troubling theory centered around Dick Legg’s propensity for pranks. What if Legg “goosed” Byrnes while he was lifting the control rod? Could a playful butt pinch have resulted in this deadly disaster?

The SL-1 before the accident. The large cylindrical building holds the nuclear reactor embedded in gravel at the bottom, the main operating area or operating floor in the middle, and the condenser fan room near the top.

With no witnesses available, investigators built a reactor simulator and attempted to recreate the events of that night. Different crews were rotated into the simulator as investigators studied their behavior and the results their actions produced. To test the “goosing” theory, they ran several scenarios in which the control rod operator was given an unexpected jab or pinch in the buttocks, wondering if a nuclear disaster could be triggered by something witnessed in junior high school playgrounds every day.

Let us pause briefly to consider what this must have been like for the person who was lifting the control rod. For the test to be worth anything, the person could not have any idea about what was coming. Highly trained, professional military personnel were sent into the simulator. They have trained and worked together for quite some time and have developed a close comradery. One of them would be given an order to grab his comrade’s backside without warning. The other two members of the crew would have no idea of what was coming. Only after the scenario was completed, could the “gooser” explain that he was just following orders.

We can only speculate about the words that were exchanged (and possibly fists that flew) before everything could be explained.

Anyway, back to the investigation…

After thorough testing, involving an unreported number of pinched bums, the official government findings were that butt-pinching would not result in the control rod being lifted more than a few inches — certainly not the 20 or more than triggered the accident. The official conclusion was that the cause of the accident was undetermined, but it definitely wasn’t caused by anyone’s hand on anyone’s derriere.

The world rested more easily, knowing that the SL-1, flawed though it may be, was butt-pinch proof.


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