Living Near Nuclear Power Plants

To hear the power companies and government agencies tell it, a nuclear plant poses no more danger to a community than a new playground, and the answer to the last question should be “no”. If you’re like us, however, you may start to get somewhat suspicious whenever Big Business and Big Government team up to tell you that something is good for you. And in this case, you would be justified in feeling apprehensive . . . because one of nuclear power’s major unresolved technical problems is that of reactor safety.

The reactor safety issue involves two basic questions: [1] What are the chances of a serious malfunction of the nuclear plant? And [2] what would the consequences of such a malfunction be? Before we can answer these questions, however, we need to talk first about what a nuclear generating station is and how it functions under normal circumstances.

The basic idea behind an atomic power plant is not terribly different from that of a fossil-fuel-fired power plant: In both, heat is generated to make steam . . . the steam is used to spin turbines . . . and the kinetic energy of the spinning turbine shaft is converted to electrical energy in a generator. The only difference is in the source of the heat that’s used to make the steam.

In a nuclear power plant, this heat source is a chain reaction in which the nuclei of heavy atoms — primarily uranium 235 (or U-235, for short) — are split apart (or undergo fission). During the fission process, fast-moving particles called neutrons (among other fission products) are produced. These neutrons — which are spewed out by disintegrating U-235 atoms — have interesting properties. For instance: If a neutron collides with another U-235 nucleus at the proper speed, it can induce the U-235 nucleus to split apart . . . sending out still more neutrons.

The basic trick in a nuclear reactor is to arrange the U-235 so that a chain reaction occurs in which the splitting of one nucleus leads — on the average — to the splitting of one more. When this happens, a great deal of heat is generated, because as each nucleus splits, a very tiny amount of its mass is converted into energy (according to Einstein’s famous formula, E = mc 2 ) . . . and some of this energy — in turn — is given off as heat. Since a very little mass converts into a lot of energy (remember, energy equals mass times the speed of light squared), a rather small amount of uranium can produce a large amount of heat.

A few kilograms (one kilogram = 2.2 pounds) of U-235 can also be arranged in such a way that the splitting of one nucleus leads to the disintegration of more than one other nucleus. In this case, a rapidly escalating chain reaction is set up . . . and those few kilos of U-235 can quickly generate the awesome heat and associated shock waves of an atomic bomb.

All right. With this somewhat simplified background information out of the way, we can immediately reassure you on one point: In the standard nuclear reactor deployed in the U.S. today, the arrangement of the radioactive “fuel” is such that an atomic-bomb-type explosion is impossible. (The fuel simply is not “weapons grade”, for one thing.) “Why, then, should anyone be worried about ‘malfunctions’ in nuclear power plants?” you might ask. To see why, we must look a little more closely at the design of the beast.

In a nuclear plant, the fissile material (the radioactive fuel) is contained in long, thin, hollow rods. Inserted between these rods are other rods containing a substance (often boron) that has the property of being able to “soak up” neutrons. When the neutron-absorbing “control” rods are in place, the high-speed neutrons being spewed out by spontaneously fissioning U-235 nuclei can’t reach enough other U-235 nuclei to sustain a chain reaction. In this situation, the reactor is said to be “subcritical”.

When the control rods are slowly withdrawn, however, the situation changes: More and more U-235 nuclei are exposed to the fast-flying neutrons . . . and — as a result — more neutron/U235 collisions take place, leading to the disintegration of additional nuclei (and the liberation of still more high-speed neutrons). Eventually, a self-sustaining chain reaction occurs, at which point the reactor is said to “go critical” and the power plant can be switched into operation.

In the most common form of U.S. reactor, the entire assembly of fuel rods and control rods is bathed in a flow of water. This water serves two important functions. First of all, it carries off the heat of fission to heat exchangers, where it is converted into steam to run the turbines. Second, the water serves as a “moderator” . . . that is, a substance that slows down high-speed neutrons and makes them more susceptible to “capture” by U-235 nuclei. (Note: Since some reactors employ heavy water — or deuterium oxide, D₂O — as the moderator, those that use ordinary H₂O as the moderator are often called light-water reactors.)

Now, where is the danger in all this? Well, the primary danger is that the highly radioactive fission products which are continuously building up inside the fuel rods might somehow escape into the environment. (The quantity of long-lived fission products inside a 1,000-megawatt nuclear power plant that’s been “on line” for a year is roughly equivalent to the amount produced by 1,000 Hiroshima-sized bombs.)

Obviously, the escape of a significant portion of these highly toxic and persistent wastes would be a disaster . . . and the nuclear industry knows this (as does Uncle Sam). Hence, the designers of nuclear power plants have taken numerous precautions to reduce the chance that a “breach of containment” accident can occur. The primary safety precaution has been to encase the entire reactor mechanism in a massive, reinforced-concrete”containment structure”. There are also various safety systems for shutting the reactor down — and seeing that it stays shut down — in case of emergency.

In short, a great amount of effort (and no small amount of money) has been spent to reduce to virtually zero the chance that the gigantic inventory of radioactive poisons contained in every nuclear reactor might accidentally be released. Unfortunately, however, there are many reasons to believe that the safety systems now being built into atomic power plants are hopelessly inadequate to do the job for which they were designed.

Let us consider, for example, what many experts say is the kind of accident most likely to befall a light-water reactor: the so-called LOCA (Loss of Coolant Accident). In such a mishap, one of the huge pipes that conducts water to the reactor vessel and carries it away breaks (either for reasons of bad design or because it is blown apart by terrorists) and the boiling-hot cooling water comes gushing out. When this happens, the reactor is “scrammed”: The neutron-absorbing control rods are immediately inserted all the way to stop the chain reaction, and everybody gets the hell out.

The word” scram” comes quite literally from what every smart person would do in case of a LOCA . . . because simply inserting the control rods does not end the reactor’s problems. The accumulated radioactivity in a reactor that’s been running for a while itself generates terrific heat, even if the chain reaction is stopped. In the absence of cooling water, this accumulated radioactivity can produce enough heat to initiate irreversible melting in the reactor core within one minute or less!

Such a situation is known as a meltdown . . . and — as you can well appreciate — it’s the most feared phenomenon in the nuclear business. Imagine (if you can) more than 100 tons of molten steel, uranium, boron, and exotic alloys (such as are used to make the fuel rods) — all spiced with a mix of deadly radioactive isotopes — slumping through the bottom of the reactor vessel at a temperature of 5,000 degrees Fahrenheit!

Such a molten mass could quickly melt its way through the bottom of the containment vessel. And, once it did, substantial amounts of radioactive materials would immediately be released to the atmosphere. This is the start of the “China syndrome” (so called because the super-hot mass of material would continue to melt into the earth for a considerable distance . . . all the way to China, some jokers have suggested!).

Needless to say, the nuclear establishment would like to avoid an occurrence of the China syndrome. That’s why all light-water nuclear reactors are equipped with something called the emergency core cooling system (ECCS), the main job of which is to spray the reactor core with water after a LOCA to cool it and prevent a melt-down. Unfortunately, though, both theoretical analyses and limited experimentation with components and models of the ECCS are ambiguous with regard to whether the system would work in a real emergency. (No full-scale test of a complete ECCS has ever been conducted.)

It is important to remember that although the basic idea behind the nuclear reactor is simple, the device itself is complex almost beyond belief. A power reactor contains many thousands of fuel rods, miles of pipes and electrical wiring, and countless valves and other mechanical devices. (To say nothing of the millions of welds, bolts, screws, and other fasteners that hold the whole apparatus together.) This is one reason that evaluating the safety of the overall device is extraordinarily difficult. To do the job right, one must test or otherwise judge the safety of each component alone and in combination with the others.

But there are additional problems, too. It’s enormously difficult, for instance, to determine the likelihood of certain types of human errors or incidents of sabotage. Also, it’s hard to predict the (somewhat novel) behavior of materials subjected to high levels of radioactivity. Then too, there’s the lack of experience that society has had in operating reactors (at present, existing reactors of the type that are now scheduled to go into service have only been in operation a relatively few years).

And a final problem in determining reactor safety — as we shall see in our next column — is the combination of massive incompetence and dishonesty shown by the Atomic Energy Commission and its successor as “overseer of nuclear safety” . . . the Nuclear Regulatory Commission (NRC).

(To be continued)

An overview of nuclear power technology and its relationship to other technologies may be found in Chapter 8 (and other sections) of Ecoscience: Population, Resources, Environment by Paul R. Ehrlich, Anne H. Ehrlich, and John P. Holdren ($19.95 ppd. from, W.H. Freeman, and Company, 660 Market St., San Francisco, California 94104).