Large scale nuclear accidents like those at Chernobyl and Fukushima are environmental disasters which grab the headlines. But lesser accidents do occur, just as in any industrial facility. I was involved in one such incident.
From the mid-sixties to the mid-nineties, Georgia Tech had a research reactor which served a multitude of research purposes. It also gave Nuclear Engineering students a hands-on experience with a working nuclear reactor.
The Frank H. Neely Nuclear Research Center, contained a 5-megawatt heavy-water (D2O) cooled reactor located on the Georgia Tech campus.
In the late 60s, I was a graduate student in the Georgia Tech Department of Biology. I was working for a professor who had an interest in manganese and bacteria. One of his projects was using neutron activation of the manganese ions found in Atlanta’s drinking water supply, Lake Lanier. Elevated manganese levels in water is an indicator of pollution.
After driving to Lake Lanier and launching a small boat, another graduate student and I would pump lake water from 100-feet down up into water sampling jugs on the boat. Our most important sampling site was just offshore a water treatment plant, the currently named Shoal Creek Filter Plant. That plant was less than two miles from the Buford Dam, so the water was reliably deep.
One day, the 100-foot-long sampling line disconnected from its reel and disappeared overboard. Without thinking, I dived over the side of the boat with my glasses and billfold, and swam down after the disappearing line. The yellow-green light was getting dimmer every foot I descended.
I was probably twenty feet down when I caught a blurry sight of the barely visible line sinking rapidly through the water.
As I rose back to the boat with the line in my grasp, my crewmate gave me a look of “What the (expletive deleted) just happened?” He had been looking away when I dived overboard, severely rocking the boat. One second, I was there, and the next second I was gone, almost throwing him into the lake in the process.
That was not the last time he would be surprised, as you will read shortly.
Miraculously, I did not lose my glasses, but all my billfold photos were a total loss. But I had saved the research equipment!
Back at the Frank H. Neely Nuclear Research Center, my crewmate and I would send aliquots of the water into the core of the reactor using an air-driven pneumatic system called a “rabbit.” Once in the reactor core, the water sample was bombarded by a dense neutron flux, for a predetermined amount of time.
Once the rabbit system pulled the sample out of the core, the sample was measured by Geiger counter to determine if it was safe to approach.
Neutron bombardment produced radioactive isotopes of manganese, converting Mn55 into Mn56. Mn56 has an ideal half-life of 2.6 hours and emits gamma rays at 846.8 keV. Manganese is easy to detect with gamma spectroscopy.
Due to the low level of manganese in the fresh water samples, the Geiger counter never indicated the sample was “hot” after its trip to nuclear hell.
We prepared the lake water samples in a clean room environment. That is also where we returned the newly radioactive sample, transferring it to a sample cell placed in the lead-lined spectrometer. Of course, we always wore full isotope protection (disposable gloves, gowns and masks.)
After gamma ray measurements were taken, the radioactive samples were placed in lead-lined cavities for disposal by reactor staff.
Our work progressed without incident until the professor asked us to activate a sample of saltwater. Neutron activation of Cl35, the natural form of chlorine, produces Cl36, with a half-life of 301,000 years.
We noted that as the rabbit returned with its sample of saltwater from its trip into the reactor core, the sample was extremely hot (radioactive), due no doubt to the high concentration of chlorine in salt water. After letting it cool a bit (some chlorine isotopes decay quickly), we performed our usual sample transfer and measurements.
Cl36 is a weak gamma emitter, but we had a hot enough dose to pick it up on the gamma spectrometer. The primary decay mechanism for Cl36 is through low-energy beta particles.
The radiation doses and half-lives had always been low and short for the manganese fresh water samples, and thus we were not in the habit of placing our hands and feet through a radiation detector prior to leaving the reactor research building. That dosimeter was intended for “hot” work.
As usual, it was late in the day when we finished our work, and few people remained in the building. Before exiting the building after our seawater work, we passed by the usually ignored detector.
But that day, I turned around and said, “Let’s check ourselves, just to be sure.”
I was clean, as I had expected. But as my colleague put his hands and feet into the device, screeching alarms and flashing red lights stunned us. As we southerners say, it caused a commotion.
I had heard that nuclear danger alarm only once before, without knowing the cause of it. But now, we were the center of attention. The few people remaining in the building surrounded us within seconds, or so it seemed. Apparently, running towards danger is for all kinds of first responders.
After the staff carefully examined our discarded gloves, masks and garments, they discovered that one of the gloves had a small tear in the right-hand thumb. That small tear was all it took to contaminate my friend.
It was late at night before we were cleared to leave, and then only with extensive washing of my colleague’s right hand. The radiation safety officer wrapped a thick layer of gauze around the offending thumb, and securely taped it. And then he got to work on a lot of paperwork.
Unlike the Mn isotopes we normally worked with, the Cl36 isotope would not decay for many human lifetimes. So, scrubbing and dilution was the only solution.
The thumb was heavily bandaged because the only risk was to the student’s new baby. Beta particles, essentially electrons, cannot penetrate deeply to vital organs, so Cl36 residue was not as much of a concern as would be gamma emitters. However, if the baby had sucked on the father’s thumb, the way teething babies do, the Cl36 isotope would have been ingested. And beta radiation occurring internally can be a health risk.
And to think, we almost let my friend go straight home to take over baby duty.
My fellow student was warned to keep his distance from his baby, and wash his hands thoroughly several times a day, rewrapping his thumb with fresh gauze after every wash. After a week of that repetitive washing routine, it would likely be safe for him to cuddle his baby girl once again, after one last Geiger Counter check.
In the meantime, he was excused from diaper duty!
This type of contamination incident may be more common than you think. Fortunately, it did not equate to a calamity. But it could have been a calamity for that little girl and her family had she ingested radioactive chlorine atoms.
Those dealing with radioactive materials, high pressure, dangerous chemicals, fires, and carrier flight decks, to name just a few hazards, know that personal disaster is only a misstep away. In spite of training, humans do make mistakes. But fortunately, this mistake was caught in the nick of time.
Radioisotope image credit: Foro Nuclear