Heavy water: Neutrons, nukes, and Norway

Profiles in Norwegian science

Photo: Michelle Holton / Shutterstock
Heavy water is a variant of water, a molecule of two hydrogen (H) atoms and one oxygen (O) atom, giving the well-known formula H2O.

Ilan Kelman
Agder, Norway

The Norwegian resistance won World War II. In 1943, Operation Gunnerside destroyed the Nazis’ heavy water coming from a plant at Vemork in Telemark, southern Norway. This action denied the atomic bomb to the enemy. Or so the story goes. As always, reality is far more complicated.

Heavy water is a variant of water, a molecule of two hydrogen (H) atoms and one oxygen (O) atom, giving the well-known formula H2O.

Hydrogen comprises one electron orbiting one proton. When a neutron is added to hydrogen, it becomes deuterium (D). Deuterium and hydrogen are isotopes, meaning similar atoms with the same number of protons but different numbers of neutrons.

Neutrons and protons have similar masses, whereas electrons have negligible mass in comparison.

Deuterium, with about twice the mass of hydrogen, is called heavy hydrogen, occurring naturally in small amounts. When it appears in water, H2O becomes D2O, two deuteriums and one oxygen, or heavy water. Water with one hydrogen, one deuterium, and one oxygen is semiheavy water.

Heavy water has applications for many physics, chemistry, and biology experiments. It helps to detect elusive particles called neutrinos, which are key to understanding fundamental physics. Lab techniques called nuclear magnetic resonance and infrared spectroscopy require heavy water to identify some chemicals. Heavy water works well for testing metabolism rates, tracing other substances through a living creature, and increasing the effectiveness of some medications.

Heavy water is also used in nuclear reactors. It absorbs neutrons less efficiently than water, producing different materials than in reactors using water. These isotopes are used for medical treatment and for nuclear bombs.

How important to the Nazi war effort was the heavy water manufactured in Norway? Fictionalizations, such as the 1965 movie The Heroes of Telemark, tell parts of the convoluted tale, which still sports variations and gaps. Other dramatizations, documentaries, and extensive scientific research continue to piece together the full picture.

The United Kingdom attempted a commando assault, but the gliders carrying the soldiers crashed and survivors were killed by the Nazis. Next came the famous Operation Gunnerside. Eleven Norwegians traversed a steep ravine to reach the plant, penetrated inside, and blew up the room producing the heavy water, without loss of life.

Months later, the heavy water plant was back in operation. In October 1943, U.S. Air Force bombings could not put it out of action. The Nazis eventually decided to stop using the plant and to transport the supplies to Germany. In February 1944, the Norwegian resistance sank the ferry SF Hydro carrying the supplies. Setting back the Nazi atomic bomb hunt by months, or even weeks, might easily have made the difference between victory and defeat. Dropping atomic weapons on Allied troops storming Normandy or entering Germany could have transformed the entire war.

Too late to deploy it against the Nazis, the United States detonated the world’s first nuclear weapon in a test two months after Victory in Europe Day.

Photo: Bjørn-Owe Holmberg / VisitNorway
The Vemork heavy water plant near Rjukan, Norway, where Operation Gunnerside took place, is seen in springtime. Today, tourists can come to Vemork to learn about its history.

Yet wars are won and lost through a plethora of factors and events. The Norwegian resistance did much more than sabotage one building and one ferry, with a slew of actions against the Nazis during the occupation years of 1940-1945. Non-violent resistance abounded throughout Norway, from Norwegians pretending to not understand German to teachers refusing to use the Nazi curriculum in their schools.

Was too much put into and is too much ascribed to one operation?

Judging across decades is easy from the comfort of our homes—homes made comfortable by those before us winning World War II. Key is that, given the knowledge at the time, the heavy water from Telemark was a credible threat. Did any option exist except trying to stop it?

The immense courage of those who inhibited the Nazis’ heavy water supply, many sacrificing their lives for it, was part of the victory in World War II. The same is true for many others around Norway and the world. We must continue to thank them for what they did for us.

Also see: The place that changed the world in the July 8, 2022 issue and Heroes on skis in the February 7, 2020 issue of The Norwegian American.

This article originally appeared in the May 2023 issue of The Norwegian American.

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Ilan Kelman

Ilan Kelman is Professor of Disasters and Health at University College London, England, and Professor II at the University of Agder, Norway. His overall research interest is linking disasters and health, including the integration of climate change into disaster research and health research. Follow him at www.ilankelman.org and @ILANKELMAN on Twitter and Instagram.