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A BIT OF TROUBLE IN THE GREAT WHITE NORTH
"A scientist need not be responsible for the entire world. Social irresponsibility might be a reasonable stance.”
—advice given to young physicist Richard Feynman by mathematician Johnny von Neumann
The decade of the nineteen-fifties is often cited as a dull period of time, lacking the excitement and colorful excesses of the following decade, the sixties. The sixties exploded with John Kennedy, the Beatles, recreational pharmaceuticals, space travel, and hippies. What did the fifties give us? Dwight Eisenhower and black-and-white television?
Deeper research indicates that this comparison of two decades is upside down. The utter wildness of the nineteen-fifties, a decade in which 100 new religions were formed, psychedelic drug experimentation was on an industrial scale, and vast scientific experiments outstripped
science fiction, makes the sixties a wind-down.58
Eisenhower, the subdued old Republican who liked to play golf, reversed everything that his predecessor, Harry Democrat Truman, had worked so hard to nail down. He stopped Harry’s Korean War in mid-advance. He played a clever game with the Soviet Union, forcing them to be the first to orbit a satellite that passed over the United States, thus setting the international precedent for down-looking reconnaissance from space. Most surprising, he opened the files of the Manhattan Project, insisting that every document, scientific finding, and gained expertise that did not relate directly to the weapons be declassified and released to the entire world. Truman, seeing this knowledge as proprietary property of the United States government, had denied access to our most trusted allies. Even the British and the Canadians, who had participated in the development work, were allowed no access. Eisenhower wished to give all the world enough knowledge to pursue civilian-owned nuclear power. He railed at the “military — industrial complex,” warning of its desire to make profits from developing new, more advanced weaponry.
Simultaneously, this tranquil administration oversaw the rapid development of the hydrogen bomb, a weapon 1,000 times more powerful than those used to wipe out entire cities in Japan with single drops, and the exotic hardware to deliver it. Nuclear rockets capable of sending a fully equipped colony to Mars in one shot were designed. Most of the nuclear power research effort went into submarine propulsion, with civilian electrical plants a minor sub-topic. Enormous scientific and engineering development efforts, such as the nuclear-powered strategic bomber and earth-moving by atomic bombs, call into question the enthusiasm of this ten-year span. Some projects were so insanely reckless, the public perception of anything nuclear was permanently damaged.
dropped.59
The tritium used in the fusion event was made during the explosion from the lithium component
of the dull gray lithium deuteride powder.60 The light isotope of natural lithium, lithium-6, captures a surplus neutron from the explosion of the RACER trigger device and immediately decays into tritium plus an alpha particle, or a helium-4. This tritium plus the deuterium nucleus in the same molecule fuse, being caught between the severe x-ray pressure front from the
fission explosion and a plutonium “spark plug” in the center of the fusion component.61
The explosive yield of this arrangement was predicted to be 5 megatons, with no possibility of exceeding 6 megatons. It could not be as efficient as the Ivy Mike device using liquid hydrogen isotopes, because the lithium was not all lithium-6. Natural, out-of-the-ground lithium is only 7.5 percent lithium-6; the rest is lithium-7. Lithium-6 has an enormous neutron activation cross section, or probability of capturing a neutron and exploding into tritium plus helium. Lithium-7 has an insignificant cross section and would not participate. With great effort, the bomb makers were only able to enrich the natural lithium to 40 percent lithium-6, and the rest would be inert and wasted.
In the week before the Castle Bravo test, the wind was blowing consistently north. That was good. Any fallout kicked up by the explosion would be blown out over a large Pacific range, empty of islands and inhabitants. Early in the morning of the test, the wind shifted, blowing east. That was bad. From 60 to 160 miles east of ground zero were inhabited islands that could be hit with a load of radioactive debris. Delaying the detonation until the wind direction
The Shrimp was set up on an artificial island on the reef next to Namu Island, and at 6:45 local time it was detonated, becoming the first nuclear accident involving a weapon test. We will never know exactly how powerful the Castle Bravo was, because all the measuring equipment, close-in cameras, and recorders were blown away in the blast, but it is believed to be between 15 and 22 megatons, making it the biggest explosion ever staged by the United States, and much larger than what was planned for. In one second it made a fireball four and a half miles in diameter, visible on Kwajalein Island 250 miles away. The top of the mushroom cloud reached a diameter of 62 miles in ten minutes, expanding at a rate of four miles per minute and spreading radioactive contamination over 7,000 square miles of the Pacific Ocean. Did they do anything like that in the sixties? Not even close.
All hell broke loose. The Rongelap and Rongerik atolls had to be evacuated. Men were trapped in control and observation bunkers, sailors suffered beta burns, and fallout rained down on Navy ships in the area. The bomb had cleaned out a crater 6,500 feet in diameter. The coral in the reef was pulverized and neutron-activated to radioactivity, mixed with radioactive fission debris, and in 16 hours spread into a dense plume, 290 miles long and heading due east in the wind toward inhabited islands. Permanently installed testing facilities at the atoll were knocked down, and radioactive debris fell on Australia, India, and Japan. Circling the world on high — altitude air currents, the dust from the test was detected in England, Europe, and the United States. American citizens were alarmed when warned of milk contaminated with strontium-90, a major product of the uranium-238 fissions in the tamper.
exposure, but he lived on to rise in the ranks at Los Alamos.62 Graves therefore could see no particular problem putting men close to atomic blasts in several experiments, from the Marshall
Islands tests to the above-ground explosions in Nevada.63 This peculiar tendency is similar to the case of Bill Bailey and his Radithor, noticing no ill effects from his elixir while subjecting Eben Byers to a horrible death. Both men, Graves and Bailey, endured later condemnation for exposing so many people to so much radiation.
A medical study of Marshall Island residents, Project 4.1, was put together hastily to document the radiation injuries. The investigation found that 239 Marshallese and 28 Americans were exposed to significant but non-fatal levels of radiation. The final report was classified
SECRET, “due to possible adverse public reaction.”64
Over-yield of the Castle Bravo device was frightening to many who worked on it, but the real tragedy unfolded far west of the test site, in Japan. It is called the “Lucky Dragon Incident,” and its everlasting effect on the public’s perception of nuclear radiation was outside the control of the test program. It would mark in history the first and last record of a death caused by a United States nuclear weapon test.
The Daigo Fukuryu Maru, or the Lucky Dragon 5, was a wooden 90.7-ton Japanese fishing boat with a 250-horsepower diesel engine and a crew of 23. On March 1, 1951, she was trawling for tuna where the fishing was good and competing with 100 other Japanese fishing boats in the general area of the Marshall Islands. There had been vague warnings from the U. S. earlier that year, defining a rectangular area of hazard around Bikini Atoll and hinting at nuclear weapons tests, but no dates had been specified. The Dragon got as close as it could to the western edge of the rectangle, within 20 miles of the boundary. Tuna liked to swim near the Marshalls.
get the dreaded feeling that they had witnessed a pikodon—Japanese for atomic bomb.65 They had to get out of there fast, but first the moneymaker had to be reeled in. It took several hours to recover and stow the trawling net, with the men wiping the calcium snow out of their eyes. Thirteen days later the Dragon chugged into its home harbor in Yaizu, Japan, filled with radioactive fish.
The crew was suffering from nausea, headaches, burns on the skin, pain in the eyes, and bleeding from the gums—all symptoms of radiation poisoning, and as their boat was unloaded and their catch put on ice the men were sent to the local hospital. Several were obviously sick. For some reason the radio operator, Aikichi Kuboyama, who should have been inside and not on the deck, was in the poorest condition. The men were scrubbed down several times, their hair was shaved off, and their nails were clipped, all to remove the radioactive dust that was ground into their surfaces, but the doctors were stumped when nothing seemed to help.
News of the contaminated crew traveled fast. The entire world became interested, and there was explaining to do. In retrospect, the public relations efforts were dreadful. Lewis Strauss, head of the Atomic Energy Commission, first claimed that the fishermen’s injuries could not have been caused by radiation, they were inside the no-fish zone, and besides that it was a Soviet spy boat that had gathered classified information on the bomb test and simultaneously exposed its entire crew to radiation just to embarrass the United States. Requests from Japan for an inventory of the radioactive species in the fallout so that treatments could be specified were denied, on the grounds that the nature of the bomb could be derived from this
information.66 The extent of contamination was claimed to be trivial, in parallel with the Food and Drug Administration imposing emergency restrictions on tuna imports. The impression given to the people of Japan, still sensitive about atomic bombs, could not have been worse.
A young biophysics professor in the city university in Osaka, Yashushi Nishiwaki, read about the Lucky Dragon in the paper, and he called the health department to see if any tuna had been shipped there from Yaizu. Yes, tons of it. He took his Geiger counter down to the market and waved it over some tuna. To his alarm, the needle on his rate-meter slid off scale. He was counting 60,000 radiation events per minute. The entire catch was heavily contaminated. Even loose scales and paper wrappings of fish that had been bought and eaten by now reeked of fission products. It was headlines in the evening paper, and mass hysteria took the city, then the region, and Japan. First, the Misaki fish market closed. Fish mongers scrambled for Geiger counters so that they could run them over the fish and prove to buyers that there was no radioactivity, but it did not help. People stopped buying fish. Yokohama closed, and then, for the first time since the cholera epidemic of 1935, the Tokyo fish market closed. It was revealed that fish were banned from the Emperor’s diet, and that was it. Prices for tuna crashed, and dealers filed for bankruptcy. It would take years to recover.
Meanwhile, the Lucky Dragon fishermen were recovering, except for Aikichi the radio operator. His liver was failing. His condition worsened and he died on September 23 at the age of 40. “I pray that I am the last victim of an atomic or hydrogen bomb,” were his last words, splashed all over the news. The United States government eventually paid the widow the equivalent of about $2,800 and agreed to pay Japan, with the wrecked fishing industry, $2 million for their trouble. From this donation, each crew member was given $5,000.
Out of the disaster came Nevil Shute’s great novel, On the Beach, later made into a major motion picture starring Gregory Peck, and the entire Japanese monster movie industry, beginning November 3, 1954, with Godzilla, a city-wrecking beast mutated by contaminating radiation. The Lucky Dragon 5 was stripped down, decontaminated, and rebuilt. It was sold to the government for use as a training vessel in the Tokyo Fisheries School, renamed the Hayabusa Maru, or the Dark Falcon. Today, the Lucky Dragon 5 is preserved for all time, lest we forget, in the Tokyo Metropolitan Daigo Fukuryu Maru Exhibition Hall. The other 22 crew
members all recovered with no lingering health effects from the fallout contamination.67 As health physicists always point out, if the men had simply lowered themselves into the water and washed off the gray dust, they would not have suffered any effect from the fallout. It was the fact that it stayed on their skin for so long that caused the trouble. If they had cut loose the nets and headed north at full power, while hosing off the deck, history would be different.
These nuclear shenanigans of the United States in the early 1950s were interesting for how they helped shape the growing public angst, but they were part of a mutant off-shoot of the larger task of taming the atom for use as a power source. The weapons tests were fascinating, almost recreational, but not really helpful from a long-term, scientific perspective. The rest of the world together had a smaller research budget, but progress toward understanding nuclear reactions was being made independently and usually in secret in a few foreign countries. In the beginning, right after the Second World War, England, France, and the Soviet Union were very interested in coming up to speed, but the first nuclear reactor outside the United States was built and tested in the second largest country on Earth: Canada.
With a population about the size of Metropolitan Los Angeles and a million square miles of uninhabitable permafrost, Canada did not seem to have the makings of a nuclear research hub, which required money, a wide-ranging technical manufacturing base, hundreds of highly specialized scientists and engineers, and yes, still more money. But Canada did have a portion of the scientists involved in the Manhattan Project, the largest and most pure deposit of uranium ore on Earth, and Chalk River.
There were complications. The Cambridge group had actually originated in Paris, and only one of the six senior members was British. To the security-conscious Americans, the initial research staff seemed questionable. It included a Frenchman with jealously guarded patent rights to nuclear systems, a potential defector to the Soviet Union, a possible spy, and a Czechoslovakian. The laboratory director, Hans von Halban, a French physicist of combined Bohemian-Jewish-Austrian-Polish descent and a convinced secularist, lacked certain management skills and tended to irritate the National Research Council of Canada, his sponsor.
interspersed with bags of powdered coke in the corner of a room.68 Performance of this first pile was disappointing, as it seemed to just sit there and not make any attempt to fission. Obviously a much larger stack of bags would be necessary to achieve any sort of success. The group needed a larger working space and more bags.
In March 1943 the lab moved to a new building at the Universite de Montreal, originally intended for a new medical school, and they expanded to a staff of 300, half of whom were Canadians. By June, the level of enthusiasm had reached a low point. Walls and floors of the building were black and filthy with a mixture of uranium and coke powders that had escaped bagging, morale was low, few fission neutrons were produced, and the Canadian government considered closing the project down.
Fatherland since April 1940,— The fear was that they were working on an advanced form of
nuclear reactor, possibly more sophisticated than anything the Americans had come up with.70
On August 19, 1943, an Anglo-Canadian-American understanding had been officially reached. This “Quebec Agreement” was drawn up to ensure that this close, English-speaking component of the Allied forces would be working together on the atomic bomb and not duplicating efforts because of excessive secrecy. From this new sharing of information came news that the Americans had already achieved a successful critical nuclear assembly using graphite back in December 1942, and there was no need to prove it again. The Canadians were encouraged to see what they could do using heavy water as a neutron moderator, trying to duplicate whatever the Germans were doing. They could have all the heavy water being produced in the Trail plant, and they should build an even bigger deuterium-extraction operation somewhere else.
Either graphite or deuterium oxide (heavy water) was a usable moderator for use in building the feeble nuclear reactors of the time. The only known isotope that would fission was U-235, and it was a rare component of mined uranium, being only 0.73 percent of the pure metal. It was possible to build a working reactor using such diluted fuel, but all conditions had to be carefully optimized. The speed of the neutrons that were born in fission, which were necessary to cause subsequent fissions and make the process self-sustaining, was too high. The neutrons have to be slowed way down to “thermal” speed, or the speed of ordinary molecules bouncing around at room temperature. The way to slow them down was to allow them to crash into bits of matter that were standing still, thus transferring all the energy by billiard-ball action. Think of a neutron as the cue ball on a pool table. When the cue ball hits another stationary ball, it stops cold and the ball that was hit takes off at the original speed of the cue. Not only does this action slow the neutron down to fission speed, it also transfers the energy, or the heat, from the frantic neutrons to another medium. The material used to slow down the neutrons and absorb the heat is called the “moderator.”
enthusiastic particle has decreased speed from 2 MeV to 0.025 eV.— A reactor moderated with ordinary tap water would therefore be very compact, not requiring a long chain of repeated contacts to slow down the neutrons. Hit a stationary polo ball with a billiards cue ball, and it does not come to a complete stop with one impact, but only gives a fraction of its energy to the
target.72
Unfortunately, given the natural uranium that was available in the early 1940s, water was not quite good enough. On rare occasion, a neutron would stick to a proton instead of bouncing off it, thus taking a neutron out of the pool of fission-producing particles. The maintenance of criticality, or the ability to produce as many fission neutrons as were lost, is so sensitive to the number of available neutrons, just losing one out of trillions can shut the process down. That is, in fact, why we always call it “criticality.” By capturing a neutron, an ordinary hydrogen atom
instantly becomes deuterium, but the incident is too rare to make any difference in the composition of the moderator.
There was another possible moderating material. Heavy water, the compound made of two atoms of deuterium, the isotope that weighed twice as much as plain hydrogen, plus an oxygen, looked, tasted, and poured just like tap water, and it also had a very low capture probability for neutrons. Each deuterium nucleus was a proton that had already captured a neutron and was unlikely to need another one. Although it lacked the slowing-down power of pure hydrogen water, it had other advantages of water. Uranium held in a matrix and immersed in it would transfer its fission energy to this moderator, and it would be an ideal coolant. Unlike the graphite, it could be pumped into and out of the reactor space, being a mobile material. Graphite was stationary, and energy deposited into it had to be removed by another moving material, such as air, helium gas, or even water pumped through channels in the structure. Heavy water, on the other hand, had the advantage of not absorbing any neutrons, just as graphite, but it was also a mobile energy transfer medium. Perhaps this was why the Germans were so intensely interested in the Norwegian heavy-water plant?
The Americans suggested that the Canadians should try the alternate moderation scheme of using heavy water, and the Brits were keen on the idea. It would be excellent for their purposes to have a unique set of reactors working, hidden away in rural, uranium-rich Canada. At that time the purpose of nuclear piles was not seen as a power-generating technique, but as a way to make an alternate fissile isotope. Over 99 percent of mined uranium is uranium-238, which is inert for the purposes of fission but is important for the production of the new, man-made element, plutonium. Uranium-238 captures neutrons and becomes uranium-239, which quickly beta-decays into neptunium-239, which in a few days beta-decays into plutonium-239. Plutonium-239 is fissile and is appropriate for making atomic bombs. Uranium-235 is also a bomb material, but separating it from the uranium-238 as mined is an extremely difficult, time- and-energy-dependent process. The Pu-239 doesn’t have to be isotope-separated from anything, and it is immediately usable. The Canadians took the challenge with enthusiasm.
This commitment to heavy-water moderation became a Canadian trademark, following them for decades and into the next century, starting with a primary agendum, to make plutonium for the Brits. The traditional use of natural uranium in Canadian reactors has its advantage and its disadvantage. The upside is that no expensive U-235 enrichment is required, as it is for all American power reactors. You just use the uranium as it comes out of the ground. The downside is that this natural uranium contains so little usable isotope, you have to constantly remove the expended fuel and load in new fuel, as the reactor is running. This feature becomes complicated and the radiation hazards in a reactor that is open at both ends are considerable, but the fuel juggling is essential.
the plutonium with Pu-240.73
volts at the top electrode. They jointly won the Nobel Prize in physics for this work in 1951 .—
Quebec Agreement.75 Kowarski was put in charge of the small reactor project, with Charles Watson-Munro as second in command. Cockcroft named it the Zero Energy Experimental Pile: ZEEP.
ZEEP was housed in a metal building, about the size and shape of a hay barn, with the enormous, four-story, brick NRX building being built next door. Final approval for construction was given on October 10, 1944. By that time, the Americans had already built the CP-3 heavy — water research reactor at the Argonne Lab in Illinois, and they were glad to unload some advice and a truck filled with graphite bricks. The graphite was used to build a box-shaped neutron reflector in the center of the building, and the cylindrical reactor vessel, made of aluminum, was installed inside. Aluminum-clad fuel rods made of uranium metal were lowered down into the vessel, which would eventually be filled to a depth of 132.8 centimeters with heavy water. The reactor top could be easily removed for access to the fuel, but during operation it was covered with cardboard boxes filled with borated paraffin, another gift from Argonne. The paraffin was there to prevent neutrons from escaping out the top and bouncing into the control room area. In the basement was a large holding tank for heavy water.
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ZEEP was a small experimental reactor, built to test the concept of building a larger reactor using heavy water as the coolant/moderator and natural uranium as the fuel. Cardboard boxes filled with a mixture of paraffin and boric acid were stacked on top of the open reactor vessel, discouraging neutrons from streaming out into the building.
By 1944 one thing that was standard in the nuclear camp was a “scram” system, or an
auxiliary shutdown mode that could kill the neutron flux and quench the fission as quickly as possible to avert a power excursion. For ZEEP, this part of the reactor consisted of heavy plates made of cadmium, known to have a very high neutron absorption cross section, hung over the top of the reactor vessel on cables. The cables were wound onto drums in the ceiling of the reactor building, and in an emergency the drum-shafts would be unlocked electrically, allowing the plates to unwind the cables by gravity and descend into the vessel to stop an energy-climb. As is the case with all scram systems, this one was triggered automatically by a neutron detector located outside the reactor vessel. When the neutron production rate and therefore the reactor power reached a pre-set maximum, the detector’s rate-meter circuit would close a switch, and down would come the cadmium.
Oblivious to this safety measure or because of it, an interesting incident occurred at ZEEP in
the summer of 1950.— The reactor was shut down so that two physicists could insert metal foils into a few fuel rods. These foils would be activated by the neutron flux, and the resulting radiation count at a later time would identify hot spots in the reactor core. They had cleared off the paraffin boxes and were standing directly over the naked reactor core.
thumb, he had jammed a chip of wood into the pump switch so that it would run continuously.77 The phone rang. Unfortunately, the telephone was on the wall at the opposite end of the building. The operator rose from his chair, hustled to the phone, and answered. Getting immersed in the conversation, he forgot about having left the moderator pump running. The water rose slowly in the vessel. After a while, it reached 130 centimeters. The two physicists on top of the core were now down on their knees, fiddling with the foils, and they did not notice as the moderator level slowly crept up. 131 centimeters. The operator was leaning against the
wall, getting stiff from standing so long and talking on the phone.78 132 centimeters. 133 centimeters. Wait for it… .
SNAP! The two busy men froze, then looked up. The scram reels had tripped loose, and they were spinning as the cadmium plates slithered down and into the core. Uh oh. Both physicists, who had left their lab coats downstairs with their radiation dosimeters clipped to the pockets, were being painted with a blast of broad-spectrum fission radiation as ZEEP went supercritical. Although the power threshold was set at three watts, there was no telling how the power was still climbing as the cables unwound. Next door at the very large NRX reactor, another snap, and the entire staff jumped. The gamma radiation beaming from the top of ZEEP went through the physicists, through the roof, reflected off the cloud cover, and back through the ceiling at NRX. Its scram system, ever vigilant, interpreted the sudden radiation increase as a fission runaway and slammed in the emergency controls. The world’s first power excursion had scrammed two reactors at once. The staff at ZEEP was far too embarrassed to admit that they had done anything so careless, so this historic incident went unreported, and the NRX staff was at a loss to explain why their reactor had scrammed. With nothing reported, the only lesson learned was the importance of not saying anything about it. The magnitude of the dosage received by the scientists and how they expressed their disappointment with the operator’s performance are unknown. The ZEEP continued on for a distinguished and uneventful career and was decommissioned in 1973. It is now on static display at the Canada Science and Technology Museum in Ottawa.
The reactor vessel was a cylindrical aluminum tank, named the calandria, about three meters tall and eight meters in diameter. Inserted into the top of the calandria in a hexagonal lattice were 175 aluminum tubes filled with uranium metal, and around each fuel tube was a larger aluminum cooling tube, filled with ordinary water. The moderator was 14,000 liters of pure heavy water, with the depth adjustable as a means of controlling the fission reaction. In 1952 the power level had been increased to 30 megawatts, which was carried away by 250 liters of water per second from the Ottawa River flowing through the cooling tubes. The versatility of the NRX was increased by allowing any cooling tube to be blown clear of water, using outside air as the coolant instead.
A blanket of inert helium gas was kept on top of the heavy water to prevent corrosion, and it was kept at a pressure of about 3 kilopascals above atmospheric pressure. The top of the calandria was sealed and connected by a pipe to an external tank holding about 40 cubic meters of helium. As the level of heavy water in the calandria changed, the top of the helium tank was free to move up and down on greased tracks, maintaining a constant pressure.
In retrospect, the controls for the NRX may have been overly complex, or, as W. B. Lewis, Director of Research at Chalk River, put it, there were 900 ways to keep the reactor from operating and only one to make it work. Twelve of the 175 rods stuck in the calandria, called “shut-off rods,” were filled not with uranium but with boron carbide, meant to absorb neutrons
and not release them.79 If as few as seven of these tubes were fully inserted into the reactor core, then no self-sustaining fission reaction could occur. Normally during operation these rods were kept out of the reactor, locked in position by active electromagnets. If everything failed, including the electrical power in the control room, then the electromagnets would lose their grip and the shut-off rods, each weighing 29 pounds, would simply fall by gravity into the core and kill the power production. There were also controls that would put compressed air into the top or the bottom of the shut-off rod tubes, forcibly running them into or out of the reactor core. With compressed air on top, you could drive the rods halfway down the 10-foot run in half a second. With only gravity, it would take as long as five seconds.
Operation of these shut-off rods was the subject of a complex set of startup rules and safeguards. The 12 rods were arranged in six banks, with Bank 1, the “safeguard” bank, consisting of four rods. There were four important push buttons on the control desk. Push button 1 raised the safeguard bank out of the core. Push button 2 raised the remaining eight rods in an automatic sequence. Push button 3 temporarily increased the current in the electromagnets to make sure that the rods were held tightly at the top of travel. Push button 4, mounted on the wall separately from 1, 2, and 3, put compressed air on top of all the rods and drove them in. Although it is not entirely clear why, when you pushed button 3, you had to be pushing buttons 1, 2, and 4 also, and this was awkward. The full-up position of each rod was indicated by a red light on the control panel. With all the shutdown rods fully withdrawn from the reactor, there was no “neutron poison” to prevent fission in the core.
On Friday afternoon, December 2, 1952, most of the senior staff at Chalk River had gone home, and the last experiment of the day was to find the reactivity of a newly installed aircooled fuel rod with the reactor running at low power. To make it easier to shuffle some fuel rods for test purposes, several were disconnected from the main cooling water circuit and instead were connected to flexible hoses. The reactor was going to be operated at very low power for this experiment, so the quality of the cooling was not a concern.
Arriving quickly, he was horrified to find that the operator had applied compressed air to the underside of four shutdown rods, blowing them clean out of the core. Fortunately, someone had removed the handles from the other valves, so the reactor had not gone supercritical. The supervisor returned the four valves to their correct positions, letting the rods drop back to full-in position by gravity, and received word over the phone that the red lights had indeed gone out. Unfortunately, only one of the rods had actually gone back into the core, and the other three had fallen just far enough to clear the light switches and were hung in the tubes.
Still on the phone, the supervisor then told his assistant at the control desk to press buttons 4 and 1, just to make certain that the shutdown rods were firmly seated in the full-in positions. The assistant immediately proceeded to carry out this instruction, but to do so he had to put down the phone and use both hands. The supervisor, realizing almost instantly that he had meant to say push 4 and 3, tried screaming his correction into the phone receiver. He could not be heard with the control room phone sitting on the desk. By pushing button 1, the assistant had pulled the entire safeguard bank out of the reactor, overriding button 4. With three other rods stuck in the out position and the core full of heavy water, the reactor was now supercritical, with power doubling every 2 seconds. It was 3:07 P. M.
Reactor power was indicated by a Leeds and Northrup Micromax galvanometer recorder with a lighted spot moving across a scale, and it seemed to indicate that power was still rising. The power level was now 17 megawatts. The reactor had been set up for very low-power operation, and the rubber hoses could not run water through the cooling tubes fast enough to handle the megawatts of heat. The water boiled furiously.
took off too fast for the power recorder to follow it. The instruments ran off scale.80
for the dump switch.81 It was 44 seconds since the assistant had pushed button 1, and it took five seconds for the dump valve to fully open.
As the heavy water drained, it occurred to the men that the helium tank would not be able to keep up with the sudden loss of heavy water, and the suction could implode the aluminum calandria. The helium pressure gauge went off scale low, confirming a possible problem, and the superintendent reached for the dump switch and turned it off. Unexpectedly, the domed lid on the helium holding tank continued to go down, indicating… what? After thinking about it for a few seconds, he turned the dump valve back on. To everyone’s relief, the power level dropped to zero and all the instruments returned to scale. The assistant superintendent declared the reactor power excursion over, having run out of control for about 62 seconds, and he left the control room to tell his boss, the reactor superintendent, the bad news and then the good news.
The incident was not quite over. The moving top of the helium tank, having lost all its gas, fell to its lowest possible position, cocked slightly, and jammed in place. In the basement, the door to the base of the reactor had been left open, and an operator could see water gushing down a wall and rolling through the doorway. It was radioactive. The metallic uranium fuel, deprived of cooling water, had melted, burning through the aluminum tubes which defined the fuel rods and the surrounding water-cooling jackets. The entire coolant inventory was draining into the basement, taking with it whatever fission products in the molten fuel could be dissolved out.
to the top of the reactor.82 Opening the door made the detector jump to 200 mr/hr. None of this was normal, by any stretch. The phone rang. It was the chemical extraction plant next door. Their air activity monitor had gone off scale, and they wanted to know what was going on. Sirens started going off all over Chalk River, and plant evacuation was called for.
radioactive fission products.83
This accident was small, but it was a harbinger of things to come, being the world’s first core
meltdown and the first hydrogen explosion in a nuclear reactor.84 These events would happen again, perhaps on a larger and even more dangerous scale, but in numerous ways the NRX accident was typical of nuclear disasters. Not one person was harmed, and the medical histories of personnel involved were studied for decades afterward, looking for health issues that could be attributed to having worked at Chalk River in 1952. The reactor itself was a total loss, and the world’s first nuclear accident cleanup would begin shortly.
What did the scientific community learn from this accident? Very little, I am sorry to say, although there were lessons aplenty to glean. The problems at NRX that led to the accidental series of events were operators trying to out-think the system, woefully inadequate instrumentation, and the use of tap water to cool a reactor having a separate, highly efficient moderator. Through the remaining years of the 20th century and into the next, these fundamental problems would destroy nuclear reactors.
The most difficult problem to handle is that the reactor operator, highly trained and educated with an active and disciplined mind, is liable to think beyond the rote procedures and carefully scheduled tasks. The operator is not a computer, and he or she cannot think like a machine. When the operator at NRX saw some untidy valve handles in the basement, he stepped outside the procedures and straightened them out, so that they were all facing the same way. They should not have been manipulated, but why did the valve handles exist if they were never to be touched? Someone in the past had started to correct this by removing the valve handles, but he had stopped with four handles left. They were poorly labeled, if at all. Inadequate labeling of controls is a disaster setup, given that a non-computer mind can try to think around it. The supervisor corrected the operator’s error, as he should have, but then he thought beyond the simple repositioning of the valve handles. He stepped outside the problem, wanting to improve the situation even further with an extra effort. He called up to the control room and made a simple error in his instruction to the junior man, who, unfortunately in this case, did not think beyond what he was told to do and, like a computer, did exactly as he was told. The telephone as a communication link failed at this time, due to its position on the console, and this was similar to the telephone problem at ZEEP. The assistant did not receive the counter-instruction.
At this point in the NRX accident, the inadequate instrumentation was the problem. The red lights were supposed to indicate that the shutdown rods were in the up position, completely out of the core. One was to assume that if the rods were not out of the core, then they were in the core. In reality, these lights did not give a clue as to the position of the control rods. The best one could surmise was that the rods were not touching the switches at the top of travel when the lights extinguished. This lack of position information from a very important mechanism combined with an operator’s out-thinking the system would cause another meltdown 27 years later at the Three Mile Island power plant in Pennsylvania.
Cooling a heavy-water — or graphite-moderated reactor with tap water because it is inexpensive remains in effect today, even though when the water goes absent the reactor goes supercritical. Canadian CANDU reactors, still using heavy-water moderation, are in use all over the world, and the latest designs use tap-water cooling in the core. Certain Soviet-era Russian reactors, such as the infamous RBMK-1000 at Chernobyl in the Ukraine, are graphitemoderated with in-core tap-water cooling, and this feature, the “positive void coefficient,” helped lead to the worst nuclear reactor disaster in history in 1986. There are 11 of these plants still running.
It took two years to get the radiation spill cleaned up and the NRX back to working condition. The reactor was pulled out of the building and buried somewhere in the yard outside. The remaining water in the coolant tank was emptied into the Ottawa River, and the basement water was pumped into the tank for temporary storage. Chalk River now had a basement with every square inch contaminated with fission products, a tank full of radioactive water, and an empty space where the pile used to be.
There was one in Canada, NRX.85 Although it was technically forbidden by federal law to ship enriched uranium out of the country, Rickover did it anyway, flattering the Chalk River Laboratory with praise and talking them into allowing him reactor time. He shipped a model fuel assembly over the border under guard, labeled “materials test.” The time spent in NRX gave valuable results. A black crud built up on the fuel, apparently iron, nickel, and cobalt oxides
coming from dissolving stainless steel.86
Shortly after the Mark I fuel element was shipped back from Canada, NRX melted, and Rickover in his optimistic mode saw this as a bonanza. The United States had a great deal of nuclear expertise, more than all other nations of the world combined, but we had no hard experience cleaning up a major nuclear radiation spill. In 1952 we had not actually spilled anything of significance, and this would be a terrific opportunity to discover the gritty details of what it would take to decontaminate an accident site. He generously volunteered 150 nuclear workers, all security cleared, to Canada to assist with the cleanup. He wanted 50 from the
Bettis Lab, 50 from General Electric, and 50 from Electric Boat.87 Naval officer James Earl Carter, the eventual President of the United States, would lead the Navy personnel.
The 862 staff members at the Chalk River Lab participated in the cleanup, as well as 170 Canadian military personnel and 20 construction workers who were in charge of cranes and digging machines. A pipeline was constructed, leading to a flat, sandy area about a mile from the plant, and the heavily contaminated coolant out of the basement was pumped there and allowed to seep into the ground, where it apparently disappeared. Fission product contamination would not be disposed of in this way now, of course, but this was early in the evolution of nuclear power. Carter and his men spent time scrubbing the floors and walls in the basement, dressed out in full rubber suits and respirators, trying to erase all evidence of an accident. A new calandria was installed, and the improved NRX, having a new set of operating procedures, was up and running for the next 40 years, finally decommissioned in 1992. Officer Carter’s impression of stationary nuclear reactors would remain somewhat warped forevermore.
very expensive heavy water.88 Each fuel rod was 10 feet long, consisting of a stack of metallic uranium cylinders sealed against moisture and air in a welded aluminum sheath. Its first full startup was on November 3, 1957, and the reactor would be put to use testing materials and techniques for use in the CANDU commercial power reactors. In 1964 NRU was converted to use highly enriched uranium as the fuel, eliminating the need for regular refueling, and the power was dialed back to 60 megawatts. In 1991 it was modified again to use less-expensive low-enriched fuel, and the maximum licensed power was increased to 135 megawatts. NRU is still running. It is the primary source for medical isotopes in the Western Hemisphere, and it supplies these critical diagnostic and treatment materials for 200 million people per year in 80 countries. Eighty percent of all nuclear medical procedures use technetium-99m, and two thirds of the world’s supply of this material comes from NRU, the now-antique research reactor at Chalk River.
Although there were advantages to using natural uranium fuel in Canadian reactors in 1958, there remained problems. The fissile content of the natural fuel is so marginal, the fuel can stand no contaminants or dilution, and therefore it has to be pure uranium metal. Unfortunately, in its metallic form uranium will catch fire in air and burn like gasoline. For this reason, most nuclear reactors use uranium oxide fuel. Uranium oxide is already burned, and it cannot possibly burst into flame. Uranium oxide also has a much higher melting point, 5,189°F, than uranium metal, 2,070°F, and it will be the last material to melt in a power excursion.
For a modest research reactor, running at say one kilowatt thermal, the residual heat after shutdown from a long run is about 10 watts, or the heat from a Christmas tree light spread out across the entire machine. For a commercial power reactor running at a billion watts, the heat after shutdown is about 10 megawatts. To put this in perspective, the Nautilus nuclear submarine running at full speed used about 10 megawatts. The higher the reactor’s operating power is, the higher is the latent heat being generated after shutdown. This inescapable problem would plague nuclear reactors from the beginning of the art, and much engineering has gone into its solution. This, and the fact that uranium metal burns, would work together to form the third great nuclear accident at Chalk River. It was late in the day on Saturday, May 24, 1958, and the refueling crane was busy.
Running on natural uranium, the NRU in 1958 is refueled often, using a semi-robotic traveling
crane running on rails above the reactor.89 To extract a fuel rod, the crane operator punches in an address, like M-25, on a keyboard, and the crossed crane-arms move with electric motors in or out, left or right, to find the correct location and position the fuel flask over the indicated rod.
The fuel flask is a big metal cylinder, tall enough to contain a fuel rod and filled with heavy water so that the rod, still hot from fissioning, remains below melting temperature after being extracted. To grab the rod and haul it from the reactor core, a cylindrical tool, small enough to fit in the aluminum tube containing the fuel rod, lowers down until it has the fuel rod in its grasp, clamps down on it, and then gently pulls it up into the flask. The crane then moves over an open pit filled with cooling water, slowly lowers the entire flask assembly into it, releases the fuel rod, and returns the flask to its high position. The crane mechanism is electrically interlocked against any action that it does not consider appropriate, so the operator is blocked from doing anything unusual.
The day before, on Friday, NRU was feeling fatigued after having run full tilt for a week, and the instruments that monitor the fuel were acting erratic. The fission products were building up in the fuel, and the heavy water was becoming polluted with stray radioactive debris. With no further warning, NRU called it quits, scramming itself and blowing all the control rods down into the core with a loud clap and a shudder of the concrete floor. Something in the long list of reasons to scram had irritated the system. With a cursory look, the weary operations staff could find nothing obviously wrong, so they restarted the reactor. WHAP! In went the controls a second time. It really did not want to be started. Loud, rude alarms started going off.
Taking it seriously this time, the operators determined that three fuel locations were extremely radioactive, and this indicated that the aluminum fuel rods had broken open. Fission products were leaking out, at least. They would have to deal with it tomorrow.
Starting Saturday morning, the crane operator went after the first fuel rod thought to be having trouble. He positioned the crane over the hole, sent the tool down, grabbed the rod, pulled it up into the flask, trucked it over to the spent-fuel pool, lowered it down, and released it. It took all morning, but the operation went smoothly. Next on the list was the fuel rod in hole J-18. This one seemed to be not feeling well. It was swollen up like a poisoned dog, and the extraction tool would not fit over the top of it. The crane operator called for a larger tip. It was a pain to change tips, and two workers spent hours installing the larger sized unit. They were so focused on the task at hand, neither of them noticed that a valve had failed open on the flask and all the heavy water had drained out. The fuel flask was dry, without a drop of coolant inside.
With the new tip installed, the operator punched in J-18 and watched as the crane moved over the hole, lowered the tool, and successfully clamped onto the damaged rod. Up she came, easily this time, but just then the operators noticed that the flask was innocent of cooling water. Desperate, they tried to turn on a pump and get some water flowing, but the interlock system prevented one from starting a pump when there was no water. The crane operator tried to reinsert the fuel rod back into the core. It would not go in. It cocked sideways and jammed.
Some of the crew were already decked out in rubber suits and respirators, and at this point they jumped to it, pulling hoses over the top of the reactor to try to hit the fuel rod with cooling water. By this time, the fuel with its aluminum sheath cracked open had been without coolant for nearly 10 minutes. The crane operator reversed the insertion tool to pull the damaged rod back up into the flask. The motor groaned. Something snapped. The operator pulled the flask off the reactor face, and it came up with half the fuel rod still jammed in the core and half of it held by the crane. The fuel in the dry flask caught fire.
Seeing a need to work quickly, the operator tried to send the flask over to where the crew was standing by with the hoses. It would not move. The interlock system had detected something wrong in the flask, and under this condition it would not allow crane motion. Radiation alarms in the building started going off, blaring loudly as the men flipped switches and turned valves, trying to get something to work. Smoke was streaming out the end of the insertion tool. The crane was completely locked up, and the intricate safety system that had been designed to prevent accidents was working against them.
fell out the end of the tool and hit the floor with a shower of sparks.90 At that instant, the problem with the stuck fuel rod became a major accident. The entire reactor building was now being contaminated with radioactive fission products boiling off a cylinder of partly fissioned metallic uranium, flaming freely in the air. Directly over the pit, the radiation level was over 1,000 rem/hr, which could mean death for anyone lingering there, looking down at the burning metal. Something had to be done to put out that fire, and spraying it with water was not going to work. They would have to cover it with sand. Quickly.
The steadfast rule of working in a high radiation field still applied: use a large force of men with each individual given a small slice of time under hazard. Everybody in the building was suited up. Bookkeepers, janitors, geeks, forklift drivers, directors—all were given the three-
minute instruction on how to breathe through a full-face Scott respirator and lined up along the wall. Each would have to climb an open steel stairway to a catwalk, walk quickly across until the burning fuel was straight below, empty a bucket of sand, and then continue moving and exit out the other side of the building.
The first up was an accountant. He climbed the dizzying stairs, not looking down, trotted to the point specified, dumped the load, and exited in haste. In those few minutes, he absorbed his entire radiation dose allowed for one year working at Chalk River. Everyone working at the lab site had an assigned dosimeter always attached to his clothing, and his cumulative dose had been tabulated daily. In 15 minutes of sanding, the fire was out and the source of radioactive vapor was covered. The entire building was contaminated, because the ventilation system had been jammed in the open condition, and the air in the highbay had circulated all over, even soaking the outside. It was just before midnight, and the cleanup operation started immediately. It would take three months of round-the-clock work by more than 600 men to restore the NRU
to operation. They were careful, and nobody was injured by radiation exposure.91
What was learned from this accident? This was a case that argued against the danger of having operators trying to outthink the system. The operators found the fuel-handling equipment locked up and unable to move because of the safety rules rigidly wired into the electrical circuits. They reasoned their way out of this predicament, modifying the system as wired and making the crane do something that it was never allowed to do, moving a broken fuel rod. Without the ability of men to think beyond the designed parameters, this accident could have been a disaster.
These examples of technical adventures in the 1950s, a period that gave us thermonuclear weapons, Scientology, and the Urantia Book, would not be repeated in exactly these ways, but the pioneering accidents in Canada would outline fundamental problems that would continue to bug the nuclear power industry. By the end of the decade, the art of fissioning uranium to make heat was in its adolescence, only 18 years old, and the release of mayhem had only begun.
enthusiastically administered by the Central Intelligence Agency beginning in 1953. Experiments were performed at 44 universities and 36 other venues, including hospitals, prisons, and pharmaceutical companies. Citizens were subjected to drugs, hypnosis, sensory deprivation, torture, and abusive language. Today, they would not let us do any of this to a goat. (Don’t ask me how I know.) Records of this project were declassified in 2001.
62 Alvin C. Graves, Ph. D. physics, became head of the Test Division at the Los Alamos National Laboratory. The accident with Slotin made him temporarily sterile, and his eyesight was never the same. He appeared in the documentary motion picture Operation Cue. Graves died of a heart attack in 1965 at the age of 56.
65 Literally “flash-boom.” First comes the flash and then the boom.
75 Much as one would like to think that Britain and Canada were managing their own plunge into nuclear science and engineering, they were not. Control of everything, including the work of these friends of the United States, was ultimately under one man, General Leslie Groves of the Manhattan Engineer District. When Groves formed the vaguest suspicion that this Frenchman had spilled some information, he was jerked out of the project immediately and was unable to travel or find work until the war was over. A bit of nuclear apocrypha has General Groves holding forth to Robert Oppenheimer in a hallway when in mid-breath he peeled off his tunic and handed it to the colonel standing next to him with instructions to have it dry-cleaned. Without batting an eye, Oppenheimer turned to the physicist by his side, pointed to a mustard stain on the cuff of his jacket, and asked him to lick it off.
76 The official word in “A Review of Criticality Accidents” from Los Alamos says that this event occurred “late 1940s or early 1950s.” The date is unknown, because this accident was never reported, and it was a dark secret until 1992, when the participants were interviewed for Nuclear Chain Reaction: The First50 Years, a book published by ANS. They couldn’t remember what year it was. By back-tracing the operating log summaries of the ZEEP and the NRX, I was able to pin it down. The excursion caused a scram in the NRX next door, so it had to be running, and NRX was first started in 1947, at which time ZEEP was down, because its heavy water load was needed for NRX. ZEEP was brought back online in April 1950, and it was busy with experiments until August.
82 “mr/hr” means millirems per hour, or the rate at which a man is absorbing radiation. “rem” means roentgen equivalent man, or a roentgen of absorbed radiation corrected for the sensitivity of an adult male, and a millirem is 1/1,000 of a rem. One roentgen is 0.01 joules of energy from radiation absorbed per kilogram of body mass. To put this all in perspective, to exhibit any clinical effects of radiation poisoning, a man would have to be exposed to over 25,000 mr/hr for an hour. Being exposed to 25 mr/hr for 1,000 hrs for some reason does not necessarily give the same effect.
Chapter 4