Idaho Falls Nuclear Reactor Accident

For some reason, this particular industrial accident has haunted my thoughts quite often. I've left out the most disturbing bits, but those of you who are squeamish might want to ignore this post. I first came across this accident in the book "Set Phasers on Stun". (I can recommend the book, incidentally, a quick, but thought-provoking read about poor equipment usability causing accidents and death. It also is definitely not for the squeamish).

Back in the 50s, the US were developing a fairly small portable nuclear reactor that could be used to power things like remote satellite dishes or radar stations. It was small (i.e. taking up the space of a large garage or shed), and designed to be long lasting. The reactor was undergoing testing at the National Reactor Testing Station at Idaho Falls.

The reactor itself was basically drum shaped with five separate fuel assemblies. Each fuel assembly contained fairly highly enriched uranium and a single control rod with blades that essentially had the profile of a cross. The control rods were attached to a drive mechanism at the top of the reactor which allowed them to be controlled by lowering and raising them, thereby controlling the amount of nuclear reaction that was occurring, and hence the heat output of the reactor.

There were three technicians performing some routine maintenance, re-connecting the control rods to the drive mechanism above. To do this, according to the manual, they have to go into the reactor room, basically stand on top of the nuclear reactor, and manually pull the control rod out roughly 10 centimetres and clamp it in that position while they reconnect the drive mechanism.

Now, the idea of standing on top of a nuclear reactor just gives me the creeps, never mind pulling control rods out of it. However, if you were a trained nuclear technician back in 1961, you would know that it is fairly safe to pull out one control rod. There are usually plenty, and it takes the removal of more than one for the reactor to start going critical or anything. However, with this new design of reactor, with its single bladed control rod per fuel assembly, it turns out that removing just one control rod just 20cm causes the reactor to go critical.

No one knows exactly why the technicians pulled the rod out too far. No one will ever know for sure. Some reconstructions indicated that they actually had to pull it out more than 10 cm to do the maintenance, because they just couldn't reach the bolts to tighten them otherwise. The control rods had also had quite a history of sticking, so perhaps when they tried to lower them back down, it was stuck, and they tugged it to free it and it popped out a bit too far.

What is known, however, is that the reactor went critical, melting the fuel assemblies and almost immediately reaching a temperature of over 3000 degrees. The reactor basically exploded out of its container, hit the roof and then fell back into place, with the explosion dispersing the fuel so that it was no longer critical. Two of the technicians were killed instantly, one died a few hours later.

Rescuers went into a nearly 1000 REM per hour radiation field (fatal dose of radiation in minutes even with protective suits) to retrieve their bodies. Their bodies were so radioactive (over 500 REM per hour) they had to be buried in lead coffins encased in concrete.

And yet, it is common to find claims about the safety of nuclear power like this one by the Uranium Information Centre: "Apart from Chernobyl, no nuclear workers or members of the public have ever died as a result of exposure to radiation due to a commercial nuclear reactor incident" (source). They can say this because, being a military prototype, the Idaho Falls reactor wasn't yet "commercial".

I've never actually been opposed to nuclear power. I'm sure that even if you count indirect deaths from nuclear power generation, it still has fewer casualties that other means of energy generation. I suppose what bothers me is the same things that make me uneasy about biological weapons: you can't see it coming so you can't really protect yourself, and the potential to affect thousands or millions of people at the same time. Even a tiny risk can be too high if the potential damage is severe enough.