U.S. to Breed Own Atoms, June 1949 Popular Science

In the aftermath of World War II, the entire world had become suddenly aware of and interested in the power of nuclear reactions. As with so many technical innovations, the necessities of winning and ending a battle produced knowledge and means to exploit the energy released in both nuclear fission (uranium and plutonium) and nuclear fusion (hydrogen). The remaining issue was learning to safely contain and control reactions so that electric power could be generated by it. The world's first commercial nuclear power generation facility, Calder Hall Nuclear Power Station, located at the Sellafield site in Cumbria, England, was commissioned by the United Kingdom Atomic Energy Authority (UKAEA) on October 17, 1956 (7 years after this 1949 Popular Science magazine article). The station's initial generation capacity was around 50 MW, utilizing a Magnox reactor, a type of gas-cooled nuclear reactor that used natural uranium as fuel and carbon dioxide as a coolant. The first commercial nuclear power facility in the U.S. was the Shippingport Atomic Power Station, located in Shippingport, Pennsylvania, on the Ohio River, was dedicated on December 2, 1957.

U.S. to Breed Own Atoms

Only three fissionable materials, or fuel for atomic power (symbolized by eggs in picture above), have so far been discovered. And only one can be dug from a mine. The other two must be manufactured in an atomic pile from naturally occurring fertile atoms (balls).

"Operation Bootstrap" is an attempt to build an atomic power plant that will manufacture more fuel than it consumes. This would be like heating your home with a furnace that turned water into oil so readily that you never had to buy oil, either for the furnace or your car.

This sounds as crazy as eating your cake while baking it. But it is now theoretically possible for a nation to multiply its supply of fuel while using it.

The Atomic Energy Commission has started Operation Bootstrap by ordering two "breeders" built. They will be nuclear reactors that, if successful, will produce simultaneously:

These breeders will be test models, representing only two steps toward the development of power plants capable of generating millions of kilowatts while manufacturing fuel for ships, airplanes, and rockets. There is no more reason to doubt now that such plants can be built than there was in 1940 to doubt that an atomic bomb could be made. But questions about the best way to do it, the hazards and costs, cannot be answered yet. These breeders will be built to end those misgivings.

Nuclear reactors are called fast, slow, or intermediate, according to the velocities at which neutrons generally are used in them to split atoms. A slow neutron is one that is only going about as fast as the fastest airplanes ever built; a fast neutron is one that is traveling a million or so miles an hour. The piles that you have seen pictured in Popular Science are slow reactors, "How to Run an Atomic Power Plant," Feb. '48, p. 128; "U. S. Lights New Atomic Pile for Peace," April '49, p. 121).

The first breeder tried will be an intermediate-speed reactor, and the second one will be a fast reactor. Construction of the intermediate-speed device is scheduled to begin this year. General Electric will build it near Schenectady, N. Y., for the Knolls Atomic Power Laboratory. It is expected to cost $18,000,000, and completing it will take about two years. It will be the first intermediate-speed reactor ever erected.

Fertile atom can be changed into fissionable atom by neutron (represented here by tiny car) of right speed. The neutron is absorbed by the atom's nucleus. Fertile atom then undergoes radioactive changes - wheels indicate emission of beta particles - and becomes fissionable.

Building the second, faster breeder may take at least a year longer. Designers at the Argonne National Laboratory near Chicago have been working on plans for it for about two years. A fast reactor that will not explode has been running for some time at Los Alamos, but it is such a little thing, as reactors go, that it has been called a watch-fob model of a future atomic engine. The big fast reactor that the AEC now has ordered will probably be placed in the new reactor-testing station about to be established in Idaho. It will be a source of both power and more fuel.

Physicists call nuclear fuel "fissionable" material and refer to the stuff from which it can be made as "fertile" material. By fissionable material, they mean something consisting of atoms that will not come apart naturally for a long time but that can be broken by a slow neutron.

These are the three known fissionable materials. Only one of them, Uranium 235, can be dug out of a mine, and it is not only scarce but also difficult to separate from other uranium. The other two nuclear fuels, Plutonium 239 and Uranium 233, have to be manufactured from fertile material.

Both are comparatively plentiful and less difficult to obtain than Uranium 235. So, whether we want more bombs or more industrial power from atomic energy, we are likely to find it worth while to make much of our nuclear fuel out of these fertile materials. One kind of fissionable material, Plutonium 239, can be made out of Uranium 238; and another kind of nuclear fuel, Uranium 233, can be made out of Thorium 232.

The bomb acts extremely fast, but a fast reactor is not necessarily explosive - any reactor that uses neutrons without slowing them is called fast. In bomb, so many neutrons (tiny cars) are confined in so little space with so many fissionable atoms (eggs) that explosion results.

You can step into your kitchen and see the difference between fissionable and fertile atoms. Let some water splatter into the sink so that big drops cling to the enamel. Then take a medicine dropper and let some droplets fall on a few of those big drops. You will find that your droplets are more likely to break a big drop that is long and narrow than one that is nearly round. In the lingo of physics, the elongated drops are more fissionable than the round ones.

The nuclei of the three fissionable and two fertile materials' atoms resemble those big drops of water. The fissionable atoms' nuclei seem to be more lopsided and less nearly spherical than those of the fertile atoms. This difference in shape explains - as well as any mathematical process that men have been able to devise - why the fissionable atoms usually come apart but the other two usually do not when hit by slow neutrons.

By glancing at the five atoms' names, you can see why they are believed to be shaped differently. The numbers after the names show how many nuclear particles - protons and neutrons - each of these five kinds of atoms contains. All five are large numbers, but, as you may have noticed, the numbers after the fissionable materials' names are odd numbers whereas those after the names of the fertile materials are even numbers. Each of these five kinds of atoms has an even number of protons in it, so the final number means that the fissionable nuclei contain odd numbers of neutrons and the fertile materials' nuclei contain even numbers of neutrons.

The protons see to it that the nucleus is less spherical when the number of neutrons is odd than when it is even. As you've heard many times, no doubt, each proton has a positive electrical charge. These charges make the protons tend to stay as far apart from each other as they can. Some of them get farther apart from some of the others when they are confined in a nucleus with an odd number of neutrons than they can when they are locked in with an even number of neutrons.

To make a fertile atom elongated enough to become fissionable, all you have to do is put another neutron into its nucleus. But how would you go about such a delicate and difficult operation as putting another invisible and only indirectly detectable particle such as a neutron into a nucleus that is satisfied with an even number of neutrons?

Ten years ago two refugees from Germany, O. R. Frisch and Lise Meitner, guessed that hitting an atom of uranium with a neutron would sometimes split it. At a meeting in Washington, Enrico Fermi then guessed that more neutrons would pop out when a uranium atom was split. And that gave scientists the idea of splitting some atoms of uranium to obtain more neutrons to drive into other atoms of uranium that were fertile but not fissionable. This was done, and nuclear fuel made out of fertile material was used in the bomb that was dropped on Nagasaki.

Splitting other atoms is still the only feasible way known of obtaining big batches of free neutrons that can be added to the nuclei of fertile atoms. Suppose you were to smash a pound of fissionable Uranium 235 atoms. You would obtain about one-sixth of an ounce of free neutrons. Most of them would start out extremely fast. Some would hit and break other atoms. Others would bump into sturdier nuclei and such collisions would slow the neutrons down. Many would slip right into other nuclei and stay there.

In a slow reactor, the fast neutrons (racing cars) are slowed down by their collisions with the sturdy atoms of a "moderator" (balls). The slow neutrons (trucks) are then used to split more atoms and thus maintain the chain reaction. All controllable reactors built thus far, except for one at Los Alamos, have been slow, using graphite or heavy water as the moderator.

In a breeder, one of neutrons released by each atom that is smashed will be used to continue the chain reaction, as usual. But other neutrons will be used to convert fertile atoms into fissionable atoms, as indicated below, where two are diverted for breeding purposes while another goes on to continue reaction. Two experimental breeder reactors are planned by AEC.

A free neutron's chances of slipping into a fertile atom's nucleus depend mainly on its speed. The neutron may break the fertile atom, rather than slip in, but this is not likely enough to happen to permit fertile materials to be used as fuel for a chain reaction. The neutron also may recoil from the fertile atom, the way a rubber ball bounces back from a wall. But if the neutron hits the fertile atom at a certain speed, it is likely to be absorbed by the atom and become a part of its nucleus.

This speed is called the "resonance" speed. It is one at which the neutron can get into step with the vibrations of the fertile atom's heart. Several different speeds may be resonant, but the neutron must be moving at one of them to enter the atom's nucleus. If the neutron is too fast or too slow, it will not get in. But whenever a neutron hits a fertile atom at a speed that is resonant for that atom it is absorbed by the fertile atom's nucleus.

Quite literally, the result is a dance of death. Absorption of a neutron by an atom of Uranium 238 makes it an atom of Uranium 239. Before Uranium 239 is many minutes old, it becomes Neptunium 239 and within a few days this decays into Plutonium 239, which is a fissionable material. Thorium meets a similar fate when it admits a neutron to its heart. First it becomes Thorium 233, then Protoactinium 233, and finally Uranium 233. This aging process in thorium, however, takes about ten times as long as in uranium.

The names change while the fertile atoms are growing older and becoming fissionable material because their radioactivity changes the number of protons in them, but the final figures remain odd numbers. So, in each case, the result is the transformation of an atom that previously could not be used as nuclear fuel into one that is elongated enough to serve as fuel for either atomic bombs or atomic power plants.

Two discoveries during the war surprised the scientists. They were surprised to find how easy it was to establish a nuclear chain reaction, and how easy it was to turn Uranium 238 into Plutonium 239.

Plutonium 239 was made in the big plants at Hanford from material that contained both Uranium 235 and Uranium 238. The Hanford reactors transferred neutrons from the odd-numbered fissionable atoms to the even-numbered fertile atoms. Thus they made one kind of nuclear fuel out of another kind-and enabled the United States to load its bombs with either one of two of the three known fissionable materials.

But the Hanford plants were not breeders because they did not produce any more pounds of Plutonium 239 than they consumed of Uranium 235. The breeders are expected to turn out greater quantities of fissionable material than are needed to keep them running. And whereas the heat from the Hanford plants is lost, the heat from the breeders is to be used to generate electricity.

If you neither lost nor wasted any neutrons, you would need only one neutron per atom to split every atom in a pound of fissionable material. You then might have at least twice as many neutrons to work with as you would need-assuming that you were fantastically super-duper at the job - to split a second pound of atoms. So you could use the extra neutrons to do something else. That's the big idea in a nutshell.

In both of the breeders to be built for Operation Bootstrap, some of the neutrons freed when atoms are split will be used to split more atoms. Others will be employed to elongate fertile atoms. This is to be done by controlling the neutron traffic more efficiently than the builders of the Hanford piles tried to control it.

This neutron traffic problem, however, is much bigger and more complex than the one posed by the cars in New York City's streets. It entails the control of far more neutrons than any city has cars, going much faster, and headed every which way.

The makers of the bomb deliberately designed a reactor in which the worst possible neutron congestion would occur in the least possible time and space. They did this so well that their bombs splattered nuclear energy all over the countryside.

In other nuclear reactors, however, the neutron traffic has been firmly controlled. This usually has been done both by slowing down the neutrons and by keeping them from becoming too numerous. Their speed has been reduced by placing "moderators," which function like a maze of traffic circles, in their paths. The neutrons bounce around amidst the atoms of these moderators until they lose much of their energy. And the volume of the neutron traffic has been curtailed by inserting materials that soak up neutrons as readily as a sponge absorbs water.

Three products from one reactor.

Plants like this - one of the original chemical - separation buildings at the Hanford plutonium works - will be needed to get fissionable material out after it is manufactured in the breeder.

In the breeders the number of neutrons will be kept small enough to avoid trouble, but they will not be slowed down as much as in the first reactors built. And the traffic problem is to be dealt with in a way that also may make it easy to utilize the heat from the nuclear chain reaction to produce power.

When an atom is split, the things in it fly apart with tremendous velocity. They hit other things. This turmoil yields what we call heat. The velocities of a smashed atom's parts correspond to billions of degrees of heat, and this heat must be let out to keep the whole apparatus in which such things happen from melting. The more efficiently the heat can be removed, the more efficiently the neutrons in the reactor can be employed. And if the heat can be taken out fast and safely, it can be turned into electricity.

There are many ways of removing heat. At Hanford the Columbia River was used and care was taken not to raise its temperature enough to bother the fish. In both of the breeders now in the works, liquid metal will be used as a coolant.

A metal, bismuth, was considered while the Hanford plants were being built, but water was chosen instead to save time. Since bismuth "freezes" at 520° F., it would have to flow in at a higher temperature and come out even hotter to serve as a coolant. Whatever the liquid used to cool these piles is-and considerable work has been done on this aspect of the problem - it is likely to come out at temperatures more suitable for the generation of power than that of the water now coming out at Hanford.

Suppose that you had a gasoline engine that ran best when it was so hot that you had to use a liquid metal instead of water to "cool" it. The hot liquid metal coming out of the engine would have to be cooled before it went back in. What better way would there be to reduce its temperature than to let it heat water? And why shouldn't you use the steam from the water to do something else?

Temperatures of the sort you would be dealing with in that imaginary gasoline engine are desired to breed nuclear fuel, and if they can be maintained and controlled in the breeders, the way to use atomic energy to produce steam to produce electricity may be found simultaneously.

Anything used either in the coolant or the structure of the reactor is liable to soak up some neutrons and thus prevent them from being used either to elongate fertile atoms or to continue the chain reaction. Hence, some neutrons will continue to be wasted, but the breeders have been designed to reduce the losses.

Both the intermediate-speed and the fast reactor may be less wasteful than those built in wartime, but doubt as to which type will be the best breeder will persist until both have been built and operated. And although both are likely to produce useful amounts of electricity, the AEC will be surprised if those amounts are tremendous in either case.

If nuclear reactors, their products, and their debris were as safe and easy to handle as ordinary furnaces, coal, and ashes, atomic power might be available for many purposes fairly soon. But the hazards are so great that the engineers and mechanics cannot tinker much with nuclear reactors.

Soon after the breeders are started, they will become so thoroughly infected with residual radioactivity that it will be extremely difficult to take them apart and remodel or repair them. Very little maintenance work will be possible. And no one know for sure how long even a successful reactor is likely to last.

"Bugs" are liable to be found in the first breeders - as they have been in other inventions - and the designers may have to eliminate many of them before breeder-power plants can compete with ordinary steam plants and hydroelectric dams. Troubles resulting from corrosion and violent differences and changes in temperature have be-come so acute since the war in some of the plants built during the war that the AEC has had to do a lot of work to keep them running.

The extra dividend of radioactive isotopes - valuable for scientific research - that will come out of the breeders along with nuclear fuel and power may prove troublesome, too. These unstable materials will have to be separated from the fresh nuclear fuel that is bred in the piles, by mechanisms and processes isolated from human beings by heavy shielding.

So, even though breeders are now scheduled to be running within three years, the men who know most about the problem believe it will take from eight to ten years to find out whether it will be economically wise to build enormous breeders as the furnaces for electrical generating stations. Different procedures will be necessary to breed nuclear fuel from Thorium 232 than those needed to breed it [rom Uranium 238. And to breed enough fissionable material to make it truly plentiful will take many years.

The best guess now is that from 20 to 30 years will elapse before atomic power replaces other sources of power extensively. Military necessities and security restrictions may postpone even longer the day when people will be better served by atomic energy.

Operation Bootstrap, however, will reveal how skillfully the engineers now can handle hordes of neutrons. Until 17 years ago, no one even knew that neutrons existed. Already, they have been used in both slow and fast reactors. Pretty soon, you may hear more about what can be done with them.

U.S. to Breed Own AtomsJune 1949 Popular Science

U.S. to Breed Own Atoms

U.S. to Breed Own Atoms
June 1949 Popular Science