In the early 1980s, deep in the pine-covered hills of Da Lat, Vietnamese physicist Professor Phạm Duy Hiển led a daring mission: to resurrect a long-abandoned nuclear reactor built by the United States in the 1960s, stripped of its core and left to decay after the war. With the help of Soviet scientists, Hiển and his team brought the reactor back to life, creating what he later called “an American shell with a Russian soul.”
From Abandonment to Ambition
The story began in 1961, when the United States constructed Vietnam’s first research reactor as part of its “Atoms for Peace” program. It went operational in 1963, symbolizing the promise of modern science in the nascent Republic of Vietnam.
But by March 1975, as the war neared its end, American personnel evacuated Da Lat, removing all the uranium fuel rods, the “heart” of the reactor, and shipping them home. The facility was left silent, its dome glinting in the mist above the empty town.
Months after reunification, in late 1975, the Vietnamese government resolved to restore the reactor. The Soviet Union, Vietnam’s new ally, agreed to assist. The task fell to 38-year-old Phạm Duy Hiển, a Lomonosov-trained nuclear physicist then working at the Institute of Physics in Hanoi.
Appointed personally by General Võ Nguyên Giáp, Vietnam’s revered military hero and then Deputy Prime Minister, Hiển was told bluntly:
“The most urgent task for our scientists now is to restore the Da Lat reactor. You must make this your mission.”
Hiển accepted, though, as he later admitted, “it felt like stepping into the unknown.”
A Reactor with Two Souls
In 1976, the Da Lat Nuclear Research Institute was officially founded. Its mission: to rebuild a reactor out of incompatible parts - an American-designed structure powered by Soviet technology. It was, in every sense, a world first.
The challenge was enormous. American reactors of the period used a homogeneous core, with uranium blended into zirconium hydride, ensuring inherent safety and stability. Soviet designs, by contrast, relied on a heterogeneous configuration, with separate fuel and moderator elements, allowing greater output, but demanding more complex safety systems.
Reconciling these two philosophies required ingenious engineering and dogged persistence. Over nearly a decade, teams of Soviet specialists worked side-by-side with Vietnamese engineers, often improvising solutions on the spot.
By 1984, the hybrid reactor, a Soviet heart beating inside an American body, reached full operation at 500 kilowatts, double its original power. It became not only a symbol of scientific resilience but the cornerstone of Vietnam’s nascent nuclear science program.
Challenges, Storms, and Soviet Patience
Progress, however, was never smooth. Hiển recalls arriving in Da Lat after a tropical storm to find the facility littered with fallen trees and dirty cooling water. He halted operations for several days to clean the reactor basin - a move that irked the Soviet delegation but likely prevented long-term damage.
Later, a strange discoloration appeared on a fuel rod, turning its shiny metal surface dull gray. Alarmed, the team halted power-up and sent samples back to Moscow for analysis. The delay pushed the inauguration back by three months, but the decision preserved the project’s integrity. Soviet engineers eventually confirmed the discoloration was harmless - an unexplained but non-critical electrochemical effect.
When the reactor finally went live in March 1984, it did so safely and has remained so ever since.
Science Amid Scarcity
Rebuilding a nuclear reactor in postwar Vietnam meant operating under extreme scarcity. Researchers lived on food rations; rice was measured out by coupons. During the early years, team members sometimes supplemented their meals with bo bo, a coarse grain substitute for rice.
When supplies ran out, Hiển personally visited General Giáp in Hanoi to request additional provisions. The general, ever the wry soldier, reportedly smiled and said, “So they say, ‘a loving wife makes porridge with bo bo’, but let’s get you some proper rice.”
Giap immediately ordered food shipments from the central government. Prime Minister Phạm Văn Đồng later arranged weekly deliveries of fresh fish from Phan Rang. “No one in Da Lat was richer than the people at the Nuclear Institute,” Hiển joked years later.
Radiation and Research
Once operational, the Da Lat reactor became the beating heart of Vietnam’s applied nuclear science. The institute began producing radioisotopes for medical use, sterilizing plastic surgical tools through gamma irradiation, and even helping solve environmental and industrial problems.
One celebrated project involved tracking sediment in Haiphong Harbor using radioactive markers to understand how silt moved through the shipping channels. The findings later informed Japanese engineers when redesigning the port’s waterways.
After Chernobyl: Fear and Conviction
Two years after Da Lat’s revival, the Chernobyl disaster sent shockwaves across the world. In Vietnam, public anxiety surged. Even local officials grew wary of any project involving radiation. One coastal province initially refused to approve the sediment-tracing experiment, fearing it could “turn into another Chernobyl.” Permission came only after ten days of persuasion.
International scrutiny followed. Visiting experts from the International Atomic Energy Agency (IAEA) once claimed the reactor vessel might corrode and rupture within two years - a charge Hiển vehemently denied. Summoned to Hanoi to defend his work, he produced years of records proving the corrosion was long-stable and non-threatening.
When he considered resigning from the stress, General Giáp rebuked him: “If you quit, that means you surrender. And you know what the penalty for surrender is, don’t you?”
Hiển stayed. The reactor endured.
Today, more than 40 years later, the Da Lat reactor still operates safely, serving as the core of Vietnam’s nuclear research infrastructure. During his 1991 visit, IAEA Director-General Hans Blix praised it as “one of the most effective uses of IAEA technical cooperation in the world.”
Legacy of Quiet Brilliance
Professor Phạm Duy Hiển retired in 1991, later joining the IAEA as a senior expert for Asia–Pacific cooperation. But his legacy and that of his Soviet colleagues lives on in Da Lat’s humming reactor, where young Vietnamese scientists still train today.
What began as a derelict symbol of a divided era became a testament to resilience, ingenuity, and the unyielding curiosity that drives science forward, even amid scarcity and fear.
In the words of the man who rebuilt it:
“We turned an abandoned reactor into a living heart. And it still beats for Vietnam.”