CHAPTER XVIII. By-Products of Nuclear Reactors

By-products of Nuclear Reactors

Nuclear reactors generate energy with the help of nuclear fission. Every time a fission occurs we are left with radioactive by-products. It is most important to prevent the uncontrolled escape of these fission products from the reactor. Fortunately the dangerous products can be retained in the reactor—if the machine has been constructed and operated with reasonable care.

In the end, however, the burnt or partly burnt uranium charge will have to be removed from the reactor and fresh charge, fresh fuel will have to be added. What will become of the fission products at this time?

During protracted operation of a reactor most of the short-lived fission products decay. Those with longer lives accumulate. The discharge of the reactor is strongly radioactive, and it will remain radioactive for many years. One certainly must not dispose of this radioactive waste in a careless manner. There are, however, many ways in which one can store such waste with reasonable safety.

One can deposit the radioactive material in well-built underground tanks. One can concentrate the activity, imprison it in concrete blocks, and deposit it at the bottom of the ocean. If one is very much worried he might even put the radioactivity in rockets and let it decay harmlessly in outer space. These procedures will cost money and will add to the expense of nuclear energy.

It would be far better if we could find a way in which the radioactive by-products could be made to serve a useful and safe purpose. Some of the by-products can be used and have been used. These uses are connected with some hazards. Furthermore, only a small fraction of the fission products have found good employment up to the present. But the importance of fission products is growing.

We are using them in research. A radioactive isotope imitates the behavior of its non-active brother in all chemical reactions and in all the intricate processes in which matter changes its form inside a living body. Furthermore a radioactive substance can be detected with the greatest ease. It can be found in a concentration which is less than a millionth of a safe radiation dose. What the microscope has been in the exploration of the structure of organisms, the radioactive elements may become in the understanding of the chemical functioning of living matter.

With better understanding there comes the possibility of using radioactive by-products for diagnosis. As with the medical use of X-rays the possible small damage due to radiation exposure should be regarded as the price for the help we can get from early and correct recognition of diseases.

In the treatment of patients, particularly in the case of persons stricken by cancer, radioactive destruction of the diseased tissue is often preferable to the use of the surgeon’s knife. Such radioactive treatment is new. There is much room for improvement. Appropriate use of radioactive substances for this purpose may become a far more powerful tool and much more widespread than it is at present.

But all these applications will use up only a vanishing fraction of the fission products. Moreover, most of the biologically important elements are not produced in the fission of uranium. Many useful activities can be produced by neutron absorption in reactors. But among the fragments of uranium perhaps only radio-iodine has been put so far to direct physiological use.

Industry deals with less sensitive objects than living tissue. Therefore greater amounts of radioactive materials can be used here. And indeed radioactivity has done a great variety of jobs. The penetrating power of X-rays has been used to control the thickness of sheets in an easy and automatic manner. Radioactivity has been incorporated into surfaces which are exposed to mechanical wear or corrosion, to check the rate at which the surface is worn away by the appearance of activity in the lubricant or other fluids which have been in contact with the surface.

By such methods industry has accumulated savings which are rapidly approaching the billion dollar mark. These savings will increase as people learn how to use the new materials. But in all these cases it is important to make sure that the activity will not hurt anyone while it is used and after it has served its purpose.

Possibly the greatest amount of radioactivity will be needed in food sterilization and preservation. One may incorporate the activities into rods which will safely retain the materials but which will allow a considerable fraction of the penetrating gamma rays to escape.

To sterilize food means to destroy all microorganisms. Many of these are radiation-resistant and may have to be exposed to 50,000 or more roentgens—that is one hundred times as much as would kill a mammal. Such massive irradiation begins to affect the foodstuff itself. In some cases sterilization by irradiation changes the food more than would be the case by boiling it or freezing it. In other cases irradiation produces less undesirable side effects than any other methods.

Another way to use radiation is the preservation of agricultural products. This need not be done by the difficult procedure of sterilization. It is enough to control pests and to prevent germination of the seeds which one is trying to preserve. Thus we need here approximately one per cent of the radiation that would be required for sterilization. By so little radiation the food is not altered to a noticeable extent. It is precisely in such processes, where great amounts of materials will have to be irradiated, that a substantial fraction of the fission products might find employment.

In all applications care has to be exercised lest radioactive materials should inadvertently be scattered around. Where great amounts are needed as in food sterilization and preservation, caution has to be redoubled. That trouble may arise has been illustrated by an occurrence in Houston, Texas.

Radioactive iridium¹⁹², which is a beta and a gamma emitter, was being used by a certain industrial concern to take X-ray pictures of metal parts. A shipment of this radioactive material in the form of powder pellets was being opened by remote control when compressed gas in the container exploded and scattered some radioactivity around. The area was shielded but some of the radioactive dust escaped to the rest of the building. The two men who were operating the remote control apparatus became contaminated. They washed themselves and cleaned up the area but did not report the incident.

A few weeks later a standard radiation check showed that the plant was still radioactive. Company officials became worried and called in experts. At this late stage the plant was thoroughly decontaminated. The homes of the two men were also examined and were found to be slightly radioactive. The men and their families were temporarily moved out while their homes were being cleaned up. When they returned, neighbors and friends shunned them. The four year old son of one of the men lost his playmates. People were afraid to enter the houses. One of the houses was put up for sale but no one wanted to buy it.

The fact that the houses had been checked by radiation meters and found to be clean, and the fact that the half-life of iridium¹⁹² is only 75 days so that any trace of activity would disappear in a reasonably short time, did not dispel people’s fears.

It is fortunate that no one was seriously hurt in this incident. But there is an important lesson we can learn from it: Ignorance may hurt more than radioactivity. That a house should lose its value in spite of the fact that its radioactive contamination has been removed, that a little boy should be shunned as though radioactivity were infectious like the plague—these are examples of suffering caused by one of the greatest sources of human misery: unreasoning fear.

The greatest potentialities of fission products for the future might lie in still a different direction. Radioactivity can induce mutations. To what extent this is a danger we have discussed in an earlier chapter. In the hands of a breeder who tries to bring about changes in animals or plants radioactivity could become exceedingly useful.

Of course it is true that most mutations are harmful. It is also true that artificial mutations have been produced for many decades. But now it is possible to place simple and cheap tools in the hands of many more people. Therefore the chances will increase to find among the many wrong mutations the few and decisive changes which lead to improvement.

Do we dare to place dangerous materials in so many hands? We should not do so without making certain that only competent and responsible individuals will get radioactive materials. This can be done. Druggists have dispensed poison; doctors and biologists have bred in their laboratories the multiplying menace of germs. All this was done and is being done with safety and to the great benefit of all people.

The use of radioactivity should be even more safe because this material is easy to detect. If poisons or germs become lost, they may be hard to find. Radioactive materials, however, give unmistakable evidence of their presence. It is, of course, never easy to find a needle in a haystack. But the chance to find it is much better if it is a radioactive needle.

Radioactive by-products need not remain what they seem to be today: dirt and danger to be disposed of and hidden. But in the immediate future we shall incur some expense to keep radioactivity in a safe place.

Some gaseous by-products like the long-lived krypton⁸⁵ (half-life: 10.4 years) might continue to give rise to real difficulties and to considerable expense. The trouble is, of course, that a noble gas like krypton will not be bound to any material by strong bonds. It may be inadvisable to let long-lived gases escape. On the other hand, their adsorption or their storage at low temperature or high pressure may prove to cost a considerable amount of money.

We have been talking about the problem of handling the by-products of nuclear power. This problem will not appear in proper proportion unless we also give some thought to the by-products of the kind of power we are using at present.

That we do not like smoke and smog is obvious. To what extent these residues of incomplete burning can cause cancer or other damage we do not know. Chemistry is more tricky than radiation. Our lack of knowledge about the slow biological effects of chemicals is much greater than our remaining uncertainties about radiation.

In addition to the obvious annoyance and worry caused by the products of incomplete combustion there exists an interesting question connected with the result of complete combustion. The carbon that has been deposited through the geologic ages as coal and as oil is being used up gradually and converted to a colorless, odorless, harmless gas—carbon dioxide. There is always some carbon dioxide in our atmosphere. The amount is approximately 300 parts per million of common air. All the carbon that has been burned since the beginning of the industrial revolution could have increased the carbon dioxide in the atmosphere by ten per cent to the value of 330 parts per million.

This increase could be significant. Carbon dioxide acts like a blanket or a valve for some kinds of radiation. In the daytime we receive energy in the form of visible light from the sun. This form of radiation has no difficulty in penetrating the carbon dioxide gas. However, the incoming radiation is balanced by invisible heat radiation, which flows out from the earth into space day and night. This infrared radiation is quite similar in nature to light, only our eyes are not sensitive to it. Now the carbon dioxide gas acts like a barrier, though only a partially effective barrier, to this outgoing heat radiation. If the carbon dioxide content of our atmosphere were to increase too greatly, it would act like the glass in a greenhouse and our climate would grow warmer.

A ten per cent increase in the carbon dioxide content of the atmosphere should have produced an observable rise in temperature. Such a temperature rise has not, in fact, been observed. The reason is that not all the carbon dioxide which has been generated in the processes of combustion has actually remained in the atmosphere. Most of it has found its way into the great reservoir of our oceans. Some of it is deposited as lime at the bottom of the oceans. However, some time is required for the carbon dioxide to be removed from the atmosphere and to reach the oceans. One would expect, therefore, that there would have been at least a slight increase in the carbon dioxide content of the atmosphere. Measurements show that this is the case and that the increase is about two per cent—which is too small to have changed our climate.

If we continue to consume fuel at an increasing rate, however, it appears probable that the carbon dioxide content of the atmosphere will become high enough to raise the average temperature of the earth by a few degrees. If this were to happen, the ice caps would melt and the general level of the oceans would rise. Coastal cities like New York and Seattle might be inundated.

Thus the industrial revolution using ordinary chemical fuel could be forced to end before the advantages of civilization have spread all over the earth. However, it might still be possible to use nuclear fuel. With nuclear fuel the industrial revolution and its countless benefits for man could continue to every part of the globe. The by-products of the nuclear age are less bulky and therefore are more easily handled than the by-products of our coal- and oil-economy. The main advantage of nuclear energy may yet turn out to be this: With proper care nuclear energy may turn out to be the cleanest among the available sources of power.