On the road to Canadian Nuclear Laboratories in Chalk River, Ont., the country’s premier nuclear research site, there’s a clearing visible through the trees with an eight-foot-tall mound at its centre. The mound is no geological feature, but a reminder of the risks and the ingenuity that underlie humanity’s quest to harness the atom.
In the spring of 1953, workers dragged a large aluminum cylinder to the clearing, and raised the earthen mound over it to screen its radioactive emission. Known as a calandria, the cylinder was the damaged heart of what was then Canada’s groundbreaking National Research Experimental (NRX) reactor.
The burial was part of a massive cleanup effort and a push to restore a device that was operating at the frontiers of a new science.
In total, the project involved some 850 staff members of Atomic Energy of Canada Limited who were based in Chalk River. To help reduce individual exposure to radiation, more than 300 Canadian and U.S. servicemen also participated as well as additional contractors.
Among them was James Earl Carter, a 28-year-old naval officer who later would become president of the United States. With Mr. Carter’s announcement last month that he has entered hospice care, the story of the reactor and the mishap that brought him to Canada 70 years ago has recaptured public attention.
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As one of the most powerful devices of its kind in the world, the NRX reactor was primarily used to probe the nuclear properties of matter and help advance reactor technology toward the goal of generating electricity.
In the early days of cancer radiation therapy, it also provided the world’s only ready source of the radioactive isotope Cobalt-60, which Canadian researchers first used to bombard tumours in 1951.
Less public was the use of the reactor by the U.S. Navy to test the uranium oxide fuel it was developing for use in the first nuclear-powered submarines.
But all of that was put in jeopardy in December, 1952, when the NRX reactor was disabled in what would go down in history as the world’s first serious nuclear accident – a combination of human error and mechanical failures that resulted in a breach of the reactor core.
While no deaths resulted from the incident and the worst consequences were averted, it became imperative for Canada’s nuclear program to get the reactor back into service.
The NRX calandria is lowered into a protective bag and driven away to a disposal site in May 1953.Canadian Nuclear Laboratories
Now, 70 years after the cleanup, the largest artefact from the accident is about to see the light of day once again.
The long-planned emergence began last October, when a crew bored into the grassy mound and made contact with the buried calandria – the first time anyone has done so in seven decades.
Over the next several years, the project will require cutting up the calandria and placing its remains into modern storage containers that are built to hold radioactive waste indefinitely. Working from a distance, the team will use cameras and specially designed tools to open up, examine and then carefully dissect the long-buried aluminum structure. “We’re embarking on something that’s never been done before in Canada,” said Alan Taylor, a project manager who leads the reactor segmentation team at Chalk River.
And they will have to do it at least six more times. Over the course of its history, the lab has retired and buried two other calandrias, left two sitting in shutdown reactors on site and two more at other facilities in Ontario and Quebec. All of them are radioactive and in need of modern, long-term storage.
The techniques the team will develop to achieve this will eventually help chart a course for the future disposal of the 19 reactors that are currently providing commercial power in Canada once they reach the end of their operating lifespans.
But it begins at the mound with the most storied Canadian reactor of all – the one that narrowly avoided triggering a disaster but then became the case study for how to bring a nuclear facility back from the brink.
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Chalk River
Canada’s wartime reactor program began in 1942. Initially, the aim was to provide a haven for British and European nuclear researchers who came to work at a temporary facility in Montreal where they teamed up with their Canadian counterparts.
In addition to its military significance, the effort was spurred on by the recognition that the fission of uranium atoms – first achieved in 1938 – could lead to an important energy source in the postwar era.
The group’s scientific focus was developing a reactor moderated by heavy water, a denser version of the standard H₂O molecule in which the hydrogen atoms carry an extra neutron. In a reactor, heavy water can serve to slow down the neutrons released by decaying uranium fuel just enough to keep a controlled chain reaction going.
As the goal of building a nuclear reactor came closer to reality, a new location was needed, in part to make the program harder for foreign agents to spy on. The result was the Chalk River Laboratories, a scientific powerhouse that grew out of the wilderness 350 kilometres up the Ottawa Valley. Opened in 1944, the sprawling facility was an early centre of nuclear research and a scientific crossroads that hosted some of the era’s brightest minds.
“The word that comes to mind is exciting,” said Morgan Brown, a retired reactor safety research engineer at Chalk River and president of the Society for the Preservation of Canada’s Nuclear Heritage. “It was new science that they were following.”
In September, 1945, scientists at Chalk River switched on ZEEP, a prototype heavy-water-moderated atomic pile that became Canada’s first nuclear reactor as well as the first outside of the United States. It was an important milestone, and a prelude to the far more powerful device that scientists were envisioning.
Anatomy of a research reactor
Canada's NRX reactor was at the forefront of nuclear science when it began operating in 1947. The reactor consisted of 176 uranium fuel rods that remained in place inside the calandria, while control rods were raised and lowered to adjust the power of the reactor. The heavy water around the rods acted as a moderator to keep nuclear reactions going.
Cooling water
from Ottawa
River goes in
Cooling water
comes out
Pump system circulates and cools the heavy water
Removable
steel deck
Water travels down pipes to cool fuel rods
Concrete
shields
Steel shields
Control rod
Graphite
Cast iron
Fuel rods
Helium
Heavy water
Steel shields
Cross section of a fuel
rod inside the calandria
Uranium
Fuel rod
outer tube
Cooling water
Fixed
calandria
tube
Air stream
Base of calandria
Heavy water
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: ATOMIC ENERGY OF CANADA LIMITED
Anatomy of a research reactor
Canada's NRX reactor was at the forefront of nuclear science when it began operating in 1947. The reactor consisted of 176 uranium fuel rods that remained in place inside the calandria, while control rods were raised and lowered to adjust the power of the reactor. The heavy water around the rods acted as a moderator to keep nuclear reactions going.
Cooling water
from Ottawa
River goes in
Cooling water
comes out
Pump system circulates and cools the heavy water
Removable
steel deck
Water travels down pipes to cool fuel rods
Concrete
shields
Steel shields
Control rod
Graphite
Cast iron
Fuel rods
Helium
Heavy water
Steel shields
Cross section of a fuel
rod inside the calandria
Fuel rod
outer tube
Uranium
Cooling water
Fixed
calandria
tube
Air stream
Base of calandria
Heavy water
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: ATOMIC ENERGY OF CANADA LIMITED
Anatomy of a research reactor
Canada's NRX reactor was at the forefront of nuclear science when it began operating in 1947. The reactor consisted of 176 uranium fuel rods that remained in place inside the calandria, while control rods were raised and lowered to adjust the power of the reactor. The heavy water around the rods acted as a moderator to keep nuclear reactions going.
Cooling water
from Ottawa
River goes in
Removable
steel deck
Water travels down pipes to cool fuel rods
Experimental hole from which beams of neutrons emerge
Control rod
Concrete shields
Calandria
Steel shields
Fuel rods
Cast iron
Helium
An aluminium ball containing material to be irradiated is inserted here
Graphite
Heavy water
Cooling water
comes out
Self-serve unit
places ball at
required distance
Irradiated ball
is retrieved
from here
Steel shields
Pump
Heavy water
cooler
Pump
Pump system circulates and cools the heavy water
Heavy water
storage
Cross section of a fuel
rod inside the calandria
Uranium
Cooling water
Fuel rod outer tube
Air stream
Fixed calandria tube
Heavy water
Base of calandria
MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: ATOMIC ENERGY OF CANADA LIMITED
NRX
Where ZEEP was the nuclear equivalent of a jalopy, the NRX reactor was like a sportscar. Designed with a power output of 10 megawatts, the NRX reactor would vault Chalk River into a world-leading position when it began operations in July, 1947. Writing in the journal Physics Today, Wilfred Bennett Lewis, a Cambridge-trained nuclear physicist who had by then arrived to take charge of the Chalk River lab’s research, extolled the machine’s capabilities, especially its high rate of neutron production.
At the core of the reactor, 176 uranium fuel rods, cooled by a continuous flow of water and air, shed neutrons that penetrated the fuel’s surrounding metal tubes and then passed into the three-metre-tall calandria filled with heavy water. There were also control rods that could be lowered down into the calandria to absorb neutrons and precisely set the rate of fission reactions. The calandria was surrounded by graphite, which reflected escaping neutrons back into the reactor, and a thick concrete wall. Heavy steel plates provided radiation shielding above and below the calandria.
The designed included multiple access points where measuring devices could be inserted or materials irradiated as part of various studies. The versatile set up ensured the reactor was both productive and easy work with.
“Scientists, engineers and other staff go about their operational duties or research work dressed in ordinary clothes or in white coveralls – no gas masks nor ‘space suits,’” according to a promotional description of NRX reactor operations published by Atomic Energy of Canada Limited.
The Globe and Mail's front page from Dec. 13, 1952, reports on the evacuation of Chalk River workers due to 'an abnormal amount of radioactive particles.'The Globe and Mail
The accident
The image of a smooth and technically sophisticated operation was shattered on Dec. 12, 1952. On that day, the reactor was set at low power with a number of tubes disconnected from the coolant system as part of a test.
The accident began when an operator working in a basement room beneath the reactor mistakenly opened some of the valves controlling the air system. The change in pressure caused some of the control rods to rise out of the calandria, increasing the rate of nuclear reactions. A supervisor saw the problem and went down to shut off the valves. The displaced control rods dropped back down but not entirely into their correct position.
At that point the supervisor called up to the control room and instructed an assistant to press two numbered buttons that would seal the tubes and increase pressure to push the rods down. But in the urgency of the moment he called out the wrong pair of numbers on the buttons.
According to Dr. Lewis’s official report of the incident, the supervisor immediately realized his mistake and shouted the correction but it was too late. The assistant had put down the phone and done as he was told.
The power of the reactor began to double about every two seconds. Within 20 seconds, those in the control room realized there was still a problem. A manual trip switch was hit, but only one control rod descended instead of the expected four and power continued to increase.
Within 44 seconds of the assistant hitting the wrong buttons, at least two people realized that, as a last resort, the heavy-water moderator should be dumped from the calandria, which would cut off the chain reaction. They raced to hit the switch but the measure had come too late to avert serious damage.
“At the increased power, some of the aluminum sheathing the uranium melted,” Dr. Lewis wrote. “At least one rod blew itself apart and molten uranium poured out.”
Down below, the basement was flooded with water carrying radioactive materials from ruptured fuel rods. Meanwhile, air had leaked into the reactor, triggering an explosion that released some airborne radiation. As alarm bells sounded, the facility was evacuated.
Using geiger counters, specialists from the Royal Canadian Engineers check for radiation in December, 1952.The Canadian Press/Dept. of National Defence
W.B. Lewis, the British-born head of research and development at the Chalk River lab, wrote the official report into the cause of the accident.Courtesy of Atomic Energy of Canada Ltd.
The cleanup
Fortunately, the accident produced no harmful effects for those at Chalk River. It could have been worse. An analysis published one year later found that the difference of a single shut-off rod left up or partially up could have led to an even steeper rise in power with “dire consequences locally.”
In the aftermath, Dr. Lewis understood that the future of the laboratory depended on bringing the reactor back to life. The recovery effort began with pumping out the water that had accumulated in the basement to a depth of about one metre. To dispose of it – an approach that would have been unthinkable in a more populated area – the water was run through two kilometres of piping and then simply poured into the ground.
“It was a rapid solution at the time,” said Mr. Brown, who said that the location of the discharge along with its slowly decaying fission products has been tracked ever since, providing an unintended study of the movement of contaminated water.
“It’s actually provided quite a bit of experimental knowledge over the years,” he added. “But it’s not the way you would want to go about doing it.”
The bigger challenge of removing damaged and irradiated components would begin in the new year. It’s at this point that Mr. Carter’s story intersects with that of the disabled NRX reactor.
Lieutenant James Earl Carter, second from left, looks at instruments in the control room of the submarine USS K-1 in 1952.Courtesy of Naval History and Heritage Command
The lieutenant
Long before his political career, Mr. Carter was a U.S. Naval Academy graduate with a burning ambition to work on the Navy’s first nuclear-powered submarines as an engineering officer. His dream was aided when he was hired by Captain (later Admiral) Hyman Rickover, a driving administrator who led the nuclear submarine program.
But when the accident occurred at Chalk River, the submarine program faced a potential setback. “The American interest was in getting that reactor back up and operating as soon as possible,” said James Ungrin, a society member.
In a speech delivered years later, Adm. Rickover said that he asked the Canadian government for permission to send a team to Chalk River to help. The goal was to learn as much as to assist. What had happened to the NRX reactor was unprecedented and it offered an opportunity to gain practical experience at dealing with a real life nuclear accident.
Mr. Carter on a Toronto book tour in 1988.Jeff Wasserman / The Globe and Mail
According to his memoirs, Mr. Carter was by then based in Schenectady, New York, where he was part of a team helping workers at General Electric to construct a prototype power plant. He was also taking courses in reactor technology and nuclear physics at nearby Union College and teaching enlisted men.
“We went to Canada on a train,” Mr. Carter recalled in 2011 at the launch of a book covering his various links to Canada by author Arthur Milnes. “Nobody in the United States knew we were going, nobody in Canada knew we were coming.”
Documents that have emerged since then suggest that Mr. Carter led a team of 12 men that were present at Chalk River from Feb. 9 to March 2, 1953, alongside other U.S. personnel. The task that his team faced was the removal of the headers, the piping atop the reactor. The men worked in small groups and used a mock-up to practice disassembling the reactor to be sure they could accomplish the job swiftly and minimize their exposure to harmful radiation.
“Finally, outfitted with white protective clothes, we descended into the reactor and worked frantically for our allotted time,” Mr. Carter wrote in his 1975 book Why Not the Best?
Gauges at the Chalk River control room in 2007, the year before the Department of National Defence would compensate military personnel who helped clean up the NRX leak in the 1950s.Fred Chartrand/The Canadian Press
The burial mound of the NRX calandria, as seen earlier this month. Later this spring, a project team will resume work on excavating and then cutting up the calandria for longer term storage.Canadian Nuclear Laboratories/Supplied
The legacy
Those who took part in the cleanup faced a carefully calibrated risk at a time when less was known about the long-term consequences of radiation. Mr. Carter wrote that for several months afterward he and other navy men had their urine and feces samples tested for radioactivity, though he experienced no ill effects.
Mr. Carter’s naval career ended soon afterwards when his father died and he took over the family farm in Georgia. He became a state senator in 1963.
Follow-up reports on the health of Chalk River workers who participated in the cleanup showed no increased mortality, a result that is consistent with the radiation doses that were recorded at the time.
Even so, in recognition of the risk, the Department of National Defence compensated Canadian military personnel who were involved in the NRX cleanup or in one that followed an accident with the larger NRU reactor that came later. After a long battle, retired Chalk River employees won similar compensation from Ottawa only last year.
The recovery of the NRX reactor carried on long after Mr. Carter returned home. By May, 1953, it was finally possible to extract the damaged calandria and drag it to a waste site for burial. Several changes were instituted to the reactor’s control system to prevent a future accident.
After the reactor resumed operations in February, 1954, John Robson, a nuclear scientist at the lab, wrote that in a future where more reactors and, inevitably, more accidents were likely, the incident showed that such breakdowns “though more serious than in normal non-radioactive equipment, can be handled, and the damaged reactors can be repaired.”
The NRX reactor was retired in 1993. The following year, McMaster University professor Bertram Brockhouse shared the Nobel Prize in Physics for his research conducted in the 1950s using neutrons from the NRX and later the NRU reactors to discern the properties of molecules.
Seventy years later, the mound at Chalk River slumbers under a thick blanket of snow, awaiting the spring runoff that will herald its next act.