Science and Industry
THE first chairman (1946 to 1950) of the Atomic Energy Commission, David E. Lilienthal, startled the Joint Congressional Committee on Atomic Energy last spring by declaring that he would not care to live in the vicinity of an atom-fired electric power plant. The present chairman, Dr. Glenn Seaborg. Nobel-Prize-winning chemist, told a press-gathering a few months ago, “I would live next door to the atom. I would not fear having my family residence within the vicinity of a modern power reactor built and operated under our [AEC’s] regulations and controls.”
Mr. Lilienthal’s apprehensions, which he has expounded in addresses, magazine articles, and a book, are shared by many members of the general public. Dr. Seaborg’s confident statement reflects the belief of the AEC and the electric utility industry that nuclear power plants are so sale that consideration can be given to building them where they would be most useful: close to the great urban centers of population.
These conflicting attitudes have clashed on both coasts. In California, plans to build atomic plants in the general vicinity of Los Angeles and San Francisco have raised storms of controversy, still unsettled. In New York, a proposal by Consolidated Edison for a million-kilowatt atomic power plant right in the middle of the city led to vigorous protests from community groups and leaders. Eventually Consolidated Edison withdrew its request for an AEC license to build the plant, ostensibly because its engineers had found that it would cost less to import electricity 1100 miles, from a huge hydroelectric project in Labrador.
Consolidated Edison’s retreat il it is one — is only a lull in flic battle. Atomic power plants, experts say. are beginning to compete in cost with conventional generating stations in areas remote from fossil fuel sources. About a dozen large reactors arc already feeding electricity into American power systems, with some half dozen under way. More atomic power plants will undoubtedly be proposed. The Atomic Energy Commission must approve detailed plans for any proposed reactor and must license it before it can operate. The question of safety has a direct bearing on where these plants are to be located and sometimes on whether they will be built at all.
How much danger?
Certainly there are risks to running an atomic plant, but the fear probably most widely held is largely imaginary. The experts agree that the chances of an atomic plant’s blowing up like an atomic bomb are virtually nonexistent. The core of an atomic bomb is composed almost entirely of fissionable fuel carefully kept divided until the bomb is triggered. Then the mechanism slams the fuel together to create a mass of great density and sufficient size to start an uncontrolled chain reaction practically instantly. In contrast, the core of a power reactor contains fuel only partly fissionable (usually about 2 percent) and barely enough in quantity to maintain a slow reaction.
“It is inconceivable to me that any reactor designed presently for power or research use will behave like an atomic bomb. “ says Prolessor Theos Thompson, director of M.I.T.’s nuclear reactor. “Where then does the hazard exist . . . .? It exists in these fission products which remain stored within the reactor core. ... The safety aims of the designer and the AEC are directed for the most part to insuring that these fission products do not escape from their normal position within the core.”
Several different kinds of reactors are used for power production, but the safety problems are common to all. The reactor core consists of a great number of long cylindrical rods of nuclear fuel — usually a form of uranium arranged in precise patterns that permit a chain reaction to take place. Splitting atoms in the fuel release subatomic particles that hit and split other atoms, the process continuing on a sell-sustaining basis. In this fission process some of the fuel is transformed into energy in the form of beat. The rods are “clad" in metal sheathing that contains the fission products but allows the heat to escape into a cooling material — usually water in the power reactors — in which the rods are immersed. This coolant not only serves to keep the rods from overheating (which might crack open the metal sheaths and allow the radioactive materials to escape) but also moderates the subatomic particles so that they move at the right speed. In a power reactor, the heat absorbed by the coolant is what is used, directly or indirectly, to produce steam to drive a conventional turbine.
Tiny imperfections in the metal cladding may permit small amounts of radioactive materials to leak from the fuel rods into the coolant. Additional amounts form in the coolant or on the structure of the reactor and are taken up by the coolant.
The coolant itself circulates in a closed loop, so that it cannot contaminate anything, but from time to time the radioactive materials are removed from it by a purification process. Most of the solids and liquids are temporarily stored for later removal from the plant. A tiny residue of a few millionths of a gram a day is discharged to a waterway in a waste stream so faintly radioactive that it meets the A EC’s standards for drinking water. Radioactive material in gaseous form, also removed by the purification process, averages a few hundred thousandths of a gram a day. This is released through a tall chimney on a controlled basis to assure atmospheric dispersion that meets the AEC regulations.
Public health experts say that the total amount of radioactivity discharged to the atmosphere from a water-cooled reactor is likely to be less than amounts normally contained in the stack gases of plants powered by fossil fuels.
Protection against accidents
A more serious concern is the possibility of accidental melting or destruction of the reactor core. One cause could be failure of the coolant system, and auxiliary cooling systems are built into the reactor to take over instantly should the primary system fail. Overheating could also be caused by an accidental increase in the chain-reaction rate — in the technician’s language, a “nuclear excursion.”
A built-in protection against this is the nature of uranium itself: an increase in the temperature of the fuel element results in a slowing down of the fission process, which tends to shut down the entire system automatically. Overheating makes the coolant water less dense, and this also tends to slow the fission process. Thus the system is by nature selfregulating. Should the “excursion” take place, however, despite these natural obstacles, control rods are propelled into the reactor automatically, placing barriers between the fuel elements and halting the fission process. Presumably there could be an accidental release of fission products within the core despite the safeguards. If the core greatly overheats at such a time, it could transform the coolant into high-pressure steam that would expand with explosive force. This force would be of an entirely different order of magnitude from even the smallest nuclear blast: the danger would not be in the explosion itself but in the radioactive products it might expel.
But if this should happen, there are a number of sturdy barriers between the core and the outer world. The first is the reactor vessel containing the core and the coolant, a heavy-walled steel vessel capable of retaining operating pressures. A second barrier is the reactor shielding, a concrete wall surrounding the pressure vessel to protect operating personnel. Outside of everything is a vapor container — in many plants a huge steel ball that engulfs the entire system and allows for any escaping steam to expand and lose its force.
The extent of this protective system is a major factor in AEC decisions on reactor locations. The commission’s experts figure roughly that a 500,000-kilowatt atomic power plant with conventional protection should be no closer than 13.7 miles to a center of 25,000 people or more. The distance can be reduced as protection is increased.
Consolidated Edison planned elaborate extra safeguards for the New York plant. Instead of the ball-like vapor container, the outer barrier was to be a sandwich of two feet of porous concrete between two leakproof steel walls. The concrete filling was designed as a partial vacuum, its air pumped back inside the steel lining, so that anything that got past the inner steel wall could not pass the concrete. Outside this trap, the plans called for five and one half feet of crashproof concrete reinforced with two-inch steel bars. Whether the AEC would have regarded the extra safeguards as sufficient is not known.
The safety record
What has been the safety record of atomic plants to date? Professor Thompson points out that in the entire American atomic-energy program, there have been only five fatalities due to radiation or accidents involving reactors: two in early wartime experiments with fuel assemblies at Los Alamos, the other three at the AEC’s test-reactor station in Idaho in January, 1961. in neither case was there any danger to the public.
The problem of reactor safety is under continuing AEG study. Special projects try to find out what happens when an “excursion” takes place. An AEG safety expert said recently that the Idaho test reactors had undergone two thousand induced excursions and in every case the reactor had shut down. Another project is investigating the results of core “melt down" following failure of the coolant system.
T here has been criticism of the AEC for allowing power reactors to be built before these tests are completed. One answer is that these programs are designed to find out if some safety regulations are overcautious: the experts feel that they have leaned over backward to be on the safe side and may be requiring unnecessary costly design features. Twentieth-century life, say the backers of atomic power, in essence, is a matter of calculated risks. We accept an unknown amount of health and property damage resulting from air pollution by internal-combustionengine fumes and the burning of fossil fuels. In contrast, the life expectancy of a man living next to an atomic plant is estimated to be shortened by about six hours.
Double-decker railroads
A 300-mph ground-transportation system that would transform the right-of-way into hundreds of miles of ribbon city is suggested as a substitute for Britain’s much criticized railroads. This radical proposal comes from a successful aircraft designer, Frederick G. Miles, head of his own group of engineering companies, writing in the British weekly The New Scientist.
Miles would use the existing tracks to transport materials to build his system on a top-heavy, many-layered ramp on stilts, leaving the present railroad in operation until the replacement is complete. A mobile factory astride the rails would mix and pour concrete, raise the molds, and roll down the tracks, leaving a trail of freshly built ramp behind it, under which trains could run on the old tracks as long as they were needed. On the first ramp above the ground, freight would be carried in automated wheeled trains at 150 mph, propelled by a linear induction motor. The train would pull itself along the rails with a series of electromagnetic coils: in effect, train and rails would be the two elements of an electric motor that is stretched out horizontally instead of being arranged for rotary motion. The ramp would widen at intervals to support factory buildings, with tunnel connections for cargo loading.
Passenger trains, also propelled by linear induction motors, would operate on a separate level, floating on air cushions, with neither wheels nor tracks. (A metal strip along the “floatway” would provide the fixed element of the induction motor.) With high acceleration and a speed of 300 mph, a five-mile trip would take about 90 seconds.
The next layer would be a highspeed motor road, and higher still, a pedestrian level. Superstructures spaced at intervals above the layered roadways would be designed for apartments, recreation, shops, and offices. Miles says that his system would not only run trains faster but would give the railroads extra profits from rental of air rights to overhead structures. Locating the factories on top of the freight line would cut use of highway trucks, while ribbon suburbs built along the tracks would enable suburbanites to get into town and city centers in minutes.