I like real-life mysteries. As I've pointed out before in this column, some of the most interesting are just too graphic for a column such as this. In this month's column, I'm going to discuss a mystery on the borderline, which I've wanted to write about for some time. I'm going to leave out many details - this is a very detailed story, and I also wish to avoid the forensic details that some readers would not appreciate.
At 9:01 pm on January 3, 1961, the SL-1, an experimental military nuclear power reactor located forty miles from Idaho Falls, Idaho went "prompt critical." In four milliseconds, the heat generated by the resulting enormous power surge caused water surrounding the core to explosively vaporize, killing three military personnel who were supervising maintenance operations as preparations were being made to restart the reactor.
Heat sensors above the reactor set off alarms at the central security facility. The first emergency crew, composed of firemen, was on site within nine minutes, At first, nothing appeared out of the ordinary. The small amount of steam rising above the reactor building seemed normal in the intense cold (about -20 F) of the evening. There was no sign of the three workers at the reactor.
Entering the control building, the crew found nothing obviously wrong, but there was still no sign of anyone. As they neared the entryway to the reactor building, however, the radiation indicators jumped sharply, causing the crew to withdraw.
By 9:17 pm, the first health physicist arrived with better equipment. He and a fireman got part way up the stairs to the reactor building before the radiation level prompted them to leave. Communications with central security and inspection of other site buildings led the crew to the conclusion that the three men must be in the silent, and apparently highly radioactive, reactor building.
As the minutes passed, more health physicists arrived with better radiation detectors. Previous devices had upper ranges which were too low to be able to assess the radiation levels, which were by then known to be extremely high. The new devices got the crew into the reactor building, barely, before being pegged at an incredible 500 R / hr, a lethal radiation level for prolonged periods. The reactor room, from their vantage point, was observed to have sustained damage, but the health physicists ordered withdrawal before any further assessment could be made.
By 10:30 pm, sufficient equipment and manpower had arrived to allow the reactor room to be explored. No one was allowed to enter the reactor room for more than one minute, and no one could enter more than once. A crew with a stretcher found one man obviously dead, but another who was still breathing. He never regained consciousness, however, and died about 11 pm. He was shockingly contaminated with radioactive material, emitting about 500 R / hr, even after his clothing was removed. The third man was not found for several days, being lost in the incredible damage to the reactor room. He had been killed instantly.
It took years of research to figure out precisely what had happened. The men had been performing standard maintenance to the control rod mechanisms of the reactor, which control the nuclear reactions in the core. In those days, manual lifting of the control rods was an approved maintenance procedure, and they had apparently lifted the main control rod too high. The standard withdrawal distance, three inches, would not have induced a chain reaction, and would be a (relatively) safe procedure. Instead, it is estimated that the rod was removed about 20 inches. This caused an enormous increase in power, which resulted in the steam explosion that destroyed the core and killed the men.
There was little contamination outside of the reactor building, which was not designed as a containment structure, since this type of accident was inconceivable at the time. Cleaning up the mess was a nightmare due to the huge radiation levels in the building, but eventually the entire facility was decommissioned. Those parts that couldn't be cleaned up were buried near the original site of the reactor (see terraserver.homeadvisor.msn.com/image.asp?S=10&T=1&X=1765&Y=24101&Z=12&W=2 for what I believe to be the burial site).
What caused the men to remove the main control rod so far? The military and some of the media favored a murder/suicide scenerio - that one of the men wanted to die and take his fellow workers with him. A letter by Martin J. Daly, one of technicians who was trained at the time, seems to refute this possibility. Workers were trained that this kind of accident was not possible; withdrawal of any one rod, even the main control rod, could not cause an accident. No technician would try to commit suicide this way, because he would have been trained to believe that nothing of this sort would happen.
Another theory was that a sticky control rod was pulled out too far. Sticking of the control rods had become a common occurrence in previous months at the SL-1. When the mechanical systems were in place, there was no danger of sudden release of the rod, but a person tugging on the rod might well pull a sticky rod out too far. The fact that the reactor had been shut down for several weeks in very cold weather might have contributed to the stickiness. Many people have trouble believing that a three-inch withdrawal accidentally became a 20-inch withdrawal, even with sticking control rods.
A third possibility was that the crew was trying to improve the stickiness problem by "exercising" the rods, unaware that the reactor could explode upon extreme withdrawal of just one control rod. I think this is most plausible. A consciencious crew was trying to fix a problem, unaware of the disaster such a procedure would lead to.
The real mystery, in my opinion, is that this accident is so poorly known by the general public. I don't believe that the government took great pains to keep it secret, since I knew about it in college, in the mid-1970's. Certainly, after "The China Syndrome," Three Mile Island and Chernobyl, I would have expected it to enter the public consciousness. But it remains, over 40 year later, almost unknown.
Please be warned that if you search for SL-1 information, that many of the descriptions of the accident are very detailed - some readers will find these sites disturbing. There are lots of web sites that talk about the SL-1, but SL-1 is a popular acronym for other things, so if you search, you might want to qualify your search with "Idaho" or other limiting terms. One of the best sites is the Idaho National Engineering and Environmental Laboratory history site, "Proving the Principle" at www.inel.gov/proving-the-principle/default.shtml. Much of the material for this article comes from this site. Chapters 15 and 16 deal with the SL-1 accident and its aftermath. The rest of the document is very interesting, too, for those interested in nuclear history. Very enlightening, but very explicit, is the DOE Openness: Human Radiation Experiments (Oral Histories) page at tis.eh.doe.gov/ohre/roadmap/histories/index.html. Dr. George Voelz was a physician who was involved with post-accident decontamination of the victims, so that the bodies of the dead could be returned to their families for burial. You can see the Arlington National Cemetery website of one of the victims, Richard McKinley, at www.arlingtoncemetery.net/rlmckinl.htm.
The site where I read the technician's letter is www.nikemissile.net/~nikenuke/nuke/text/sl-1.html. It includes a good picture of the reactor building. This site does not include explicit details of the accident itself. Another site with little explicit detail is ANL-W History - Reactors (ALPR) at www.anlw.anl.gov/anlw_history/reactors/alpr.html. ALPR is an older name of the SL-1. This site includes a small and large color picture of the reactor building and includes some technical details of the reactor, but no information on the accident, other than the date of destruction of the reactor.
One final, very useful site is the July 1996 issue of Atomic Energy Insights, available online at www.ans.neep.wisc.edu/~ans/point_source/AEI/jul96/AEI_Jul96.html. The entire issue is devoted to the SL-1 accident. While some discussion of the victims is included, it is probably as modest a treatment of the details as has been made in any resource I've seen.
CATBAR - Brain Candy #59 - The SL-1 Accident / Brian Rock / Jul 3 2002