A radioactive spill contaminated the river of a major European capital in a silenced catastrophe
An accident at a nuclear reactor in the heart of Madrid’s University City in 1970 contaminated rivers, crops, and aquifers that continued to be used for human consumption for years.
As unbelievable as it may sound, this story is true. On November 7, 1970, the experimental nuclear reactor at Madrid’s University City suffered an accident, releasing dozens of liters of radioactive liquid into the drainage system. The contaminated water flowed into the city’s sewers, then into the Manzanares River, the Jarama, the Tagus—eventually reaching the sea in Lisbon. Along the way, it contaminated farmlands and irrigation systems. The produce from these fields was sold in markets and consumed without the slightest concern. Many of these vegetables contained radiation levels hundreds of times above the safe threshold for human health.
They left for the weekend
It was a Saturday. Naturally, everyone working at the Nuclear Energy Board (JEN) facilities in Madrid’s University City—just meters from the Moncloa Palace and a short walk from the city center—was eager to finish up and head off for the weekend. At noon, a routine operation began: transferring 185 gallons of radioactive waste from Tank A-1 at the M-I plant, home to the Coral-1 nuclear reactor, to the T-3 waste treatment tank at the CIES facility.
But something went wrong. Some accounts point to a faulty weld; others blame a valve malfunction. Whatever the cause, between 10 and 20 gallons of highly radioactive liquid leaked into the sewer system.
The spill contained dangerous isotopes such as strontium-90, cesium-137, ruthenium-106, and plutonium particles—all of which pose long-term risks to human health and the environment. Five minutes after the transfer began, the facility’s radiation safety officer recommended halting the operation upon detecting the issue. Despite the immediate warning, the transfer and the leak continued until 2:45 p.m., when the workers clocked out and left for the weekend.
Radiation in farmlands and irrigation systems
The contaminated water entered the sewer system through the drainage pipes, flowed into the Manzanares River, then into the Jarama and the Tagus, and elevated radiation levels were detected even at the river’s mouth in the sea near Lisbon. No action was taken until the following Monday.
It was one of the most serious radioactive spills in Spain’s history. It remains unclear whether the public water supply was affected. What is confirmed is that radiation impacted farmlands and irrigation systems along the Manzanares and Jarama rivers. In many areas along the riverbanks, radiation levels exceeded 15,000 counts per second (cps), compared to normal levels of 100 to 120 cps. In Toledo, readings reached 10,000 cps. In some parts of the Jarama and Aranjuez, levels were recorded at up to 75,000 times the legal limit. In certain areas within the JEN facility itself, located in the heart of University City, radiation doses accumulated over a year were measured at up to one million times above the tolerable threshold.
The Franco regime covered up the incident. Authorities secretly purchased contaminated crops from local farmers without offering much explanation. Most of the produce was buried within University City. However, not all the harvest was bought, as the effort was not sustained over time, and farming in the affected areas was never officially banned. Two months later, the JEN’s safety commission issued a report recommending a ban on the consumption of vegetables grown in contaminated plots and a prohibition on using water from polluted rivers and canals for irrigation. But the measures came too late and were only sporadically enforced. For years, vegetables grown in soil tainted with dangerously high levels of radiation were sold in Madrid’s markets—without anyone knowing.
Contamination to this day
In the years that followed, some farmers working the fields along the Manzanares and Jarama rivers developed cancer. However, no studies have been conducted to establish a link between their illnesses and the radioactive spill. Nor are there any investigations clarifying whether the consumption of contaminated produce led to a rise in cancer cases in Madrid or other affected areas. What is documented is that the incident left a radioactive footprint in the soil, rivers, and some aquifers in central Spain. To this day, the riverbanks of the Jarama remain under monitoring by the Nuclear Safety Council, although traces of cesium-137 and strontium-90 no longer reach harmful levels. Radiation levels in University City still exceed those typically found around a nuclear power plant.
But why was there a nuclear reactor in Madrid’s University City in the first place? Coral-1 was a fast research reactor supplied by the United States and installed in 1968. It had the capacity to produce weapons-grade plutonium and was part of “Project Islero,” the Franco regime’s covert attempt to develop a nuclear bomb. The reactor was shut down in 1981 due to international pressure and the risks associated with operating such a facility in a densely populated urban area.
Throughout history, TRIGA reactors have operated—and continue to operate—at universities around the world. Only in two other major cities, Moscow and Buenos Aires, have reactors with military potential ever been installed, and never in a location as central or as densely populated as Madrid.
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