Heavy water, light water, and the new race for nuclear energy

The hydrogen that makes heavy water heavy: deuterium, or hydrogen-2. About one in every 5000 water molecules (0.0145 percent, or roughly 200 parts per million) contains this isotope.

It is always interesting to look at the technological world of today from the point of view of a future historian. In what era would that future historian place us? Were (are) we in the beginning, middle, or end of that era? What technological disruptions had (have) occurred or were (are) about to occur? Did (do) we recognized them as disruptions? Per F. Dahl, in his brilliant and fascinating book Heavy Water and the Wartime Race for Nuclear Energy, describes the highly disruptive developments that followed Harold Urey’s discovery in 1931 that the element hydrogen has a heavy isotope. Among these disruptive developments was James Chadwick’s 1932 discovery of the neutron, and, most stunning of all, Lise Meitner’s discovery in 1939 of nuclear fission and her realization, from Einstein’s E = mc², that fission releases unimaginable amounts of energy.

As Dahl describes, Urey’s discovery of heavy hydrogen proved hugely important when, eight years later, scientists scrambled to find a way to run a self-sustaining nuclear fission chain reaction in uranium. Hitler was on the move in Europe and the discovery of fission only months before had suggested to physicists everywhere that the phenomenon could, if mastered, prove decisive in the new war. The challenge facing researchers in the dark days of 1939 was to slow speeding neutrons down sufficiently so as to improve their chances of fissioning (splitting) a certain type of uranium atom—without absorbing too many of the neutrons released by the fissions.

French researchers had through trial and error realized that while ordinary hydrogen, in the convenient and widely available form of ordinary water (¹H₂O), could slow down neutrons to the right speed to promote fission in natural uranium, it absorbed too many of the freshly released neutrons to allow a chain reaction. But heavy hydrogen, in the similarly convenient but vastly rarer form of heavy water (²H₂O), might be just right. So might beryllium; so might carbon. The researchers just needed to test these materials. They got some tantalizing results with heavy water, but needed more of the stuff to run more comprehensive experiments to be sure. Before they could get it, the Germans conquered France. Nuclear researchers in France were driven underground, and French nuclear research essentially stopped for the rest of the war.

But research did not stop elsewhere. The Germans also recognized heavy hydrogen as a strong candidate, and spent the next six years in a failed effort to obtain enough heavy water to do meaningful research. The Allies, working mostly in America but also in Canada and the United Kingdom, realized very soon that carbon in the form of pure graphite was far more easily obtained. In 1942 they finally succeeded in running a nuclear fission chain reaction, in the “Chicago Pile,” a graphite-uranium reactor built at the University of Chicago. Three years after that, the world’s first atom bomb exploded in the New Mexico desert. Nuclear strikes on Japan followed less than a month later, and the Second World War ended.

Casual readers might infer from this brief summary that because ordinary (“light”) water proved inadequate, and because the fixation on heavy water spelled the failure of the German effort and cost Germany the war, that water in any form, light or heavy, is an inferior nuclear material.

Water may have indeed failed to fit the bill in the desperate early wartime circumstances in which it was initially considered. But both light and heavy water soon after the war became central to another hugely disruptive technology: the nuclear heat engine. The U.S. Navy, already in a class by itself at the end of the war, took a quantum leap in its mastery of the oceans by converting its submarines and aircraft carriers from diesel-powered propulsion to nuclear power, thereby cutting refueling requirements from once a week to less than once a year. The basis of naval nuclear propulsion, in the U.S. navy anyway, is light water.

A less recognized but equally disruptive development occurred hard on the heels of the nuclearization of the U.S. Navy. That was the entry of nuclear power into civilian electricity grids. Today, water reactors predominate in the nuclear power generation field: almost all power reactors in the world today are run with either light or heavy water. In my home province of Ontario, heavy water reactors are providing 100 percent of the output in the “nuclear” fuel category in Table A1 up on the left. Table A1 gives a near realtime view of electric power generation in Ontario.

In Ontario, nuclear power was enormously disruptive from the get-go. It was disruptive because within about twenty short years it had supplanted hydropower and fossil-fired power combined as the main way of making electricity in this province. This nearly unqualified success caused major problems inside Ontario Hydro, the provincial electric utility. Hydro, supplemented by fossil power, had been for more than half a century the backbone of one of the most innovative electricity systems in the world. Suddenly they were superseded by a technology that had been literally unknown only three decades before. They were now junior divisions inside a giant nuclear utility.

Today nuclear energy is playing a pivotal role in a new war, a war unlike any other that we humans have ever fought: the war against climate change. In a way, it is a war against the very substances, fossil fuels, that took us out of the dark ages in the first place. It is an economic war: fossil fuels begat huge industries, industries that, in reach and revenue and all the attendant political clout, dwarf the nuclear industry like a ton of coal dwarfs a single uranium fuel pellet.

Rod Adams, former U.S. navy nuke and currently publisher of Atomic Insights, holds something the size of a uranium fuel pellet. Not even Rod could hold that pellet’s energy equivalent in coal, which is close to a ton.

And it is a war we must win. As you can see in Item A1 in the upper left, atmospheric concentrations of carbon dioxide (CO₂), are close to 400 parts per million. They were around 275 ppm before the industrial Revolution, which saw the advent of the fossil fueled heat engine. That we humans have through our use of fossil fueled heat engines added roughly 125 ppm since the Industrial Revolution is simply beyond dispute. So is the warming of the climate system. And so is the role that man-made CO₂ plays in that warming.

Every year, fossil-fueled heat engines put nearly 30 billion tons of CO₂ into the atmosphere. Nuclear powered heat engines put zero CO₂ into it.

We will win this war not by stopping our use of heat engines. We will win it by stopping running them with fossil fuels. The nuclear powered heat engine, especially in the power generation sector, will be the vanguard in this victory.

But, just as in the first war in which nuclear technology played a decisive role, the question is: what will enable the chain reaction in the nuclear heat engines that will power societies with no carbon emissions? Will it be light water or heavy water?

This question is now urgent. Today, light water predominates. Only a few countries—Canada, India, China, South Korea, Argentina, Romania, and Pakistan—have heavy water reactors. But the most successful heavy water model, the CANDU 6, has, in addition to an excellent in-service record, the best record in the world for speed in construction. The most recent one built in China took 54 months. In the war against climate change, time is of the essence. That could prove decisive in countries that need lots of reliable CO₂-free electricity, fast. And that could make the CANDU a disruptive technology in this new war.