The Future Of Nuclear Technology Energy Planners Study Potential Safety Features

May 13, 1986|By David L. Chandler, Boston Globe

The next generation of nuclear power plants in this country -- assuming there is one -- will likely differ in several important respects from the kind of plants built in the past.

For a variety of reasons, the nuclear industry in the United States has been moribund since long before the Chernobyl accident, with no new orders for commercial power plants booked since 1973. If it is to have a future, nuclear industry planners say, significant design changes must be made.

One example would be smaller plants built from standardized, factory- assembled modules, which would be expected to have a significant advantage in cost, reliability and construction times. They would also simplify the regulatory process, compared with the current situation in which every plant is essentially custom-built.

Perhaps the most important change needed, some nuclear engineers have suggested, is in the safety systems that are supposed to prevent damage to the core of nuclear fuel if something goes wrong. Present safety systems are among the most complex and expensive parts of nuclear plants, and, as Three Mile Island demonstrated, they are not foolproof.

The most promising suggestions for a new generation of nuclear plants, according to nuclear engineer Richard K. Lester of Massachusetts Institute of Technology, are designs that include ``inherently safe`` systems. In theory, most of their safety features depend on basic physical principles integral to the design and require no action on the part of the plant operators.

In a Swedish design called the Process Inherent Ultimately Safe (PIUS), the entire reactor core assembly is submerged in a deep pool of water laced with neutron-absorbing boron. Should the cooling-water system fail, natural convection currents would immediately draw water from the pool into the core, stopping the reaction. The huge pool would also provide enough cooling, even without outside circulation, to allow several days to fix the problem.

Other designs include a German system in which spherical ``pebbles`` of graphite containing the nuclear fuel are cooled by inert helium gas. The use of helium instead of water as a coolant eliminates the danger of water breaking down, under heat and pressure, to produce explosive hydrogen -- something that reports suggest may have occurred at Chernobyl.

Also, in the German system, the physical structure of the fuel elements is designed so that if the coolant is lost and temperatures rise in the core, the nuclear reaction becomes less efficient -- a self-extinguishing system.

Incorporating some form of passive cooling systems could improve the safety of nuclear plants and possibly lower their costs by simplifying the design.

But critics point out that some safety issues would remain, including the need to store and disposing of spent nuclear fuel. And while a design such as PIUS would eliminate the requirement for instant, correct responses from operators to ensure safety, it would not eliminate the need for other safety systems. If the passive cooling worked as expected, the core would be protected for some days, but eventually the cooling system would have to be restored for the reactor to remain safe.

And even advocates of such systems acknowledge that passive cooling systems are a long way from commercial availability. Even if a national policy decision were made today to pursue such research intensively -- an unlikely event in the post-Chernobyl climate -- it would be 15 to 20 years before construction could begin on a commercial plant of such design, according to Lester.

For the near future, at least, some analysts now say the most important technological advances to affect the electrical power industry may be ones that have nothing to do with nuclear power: new generating systems such as solar cells or fuel cells powered by natural gas or coal slurries, and efficient new appliances and distribution systems that could lower the demand for electricity.

By reducing the need for electricty or providing low-cost, small-scale alternatives to the present huge, centralized power plants, such developments could significantly reduce -- some say even eliminate -- the need for more new nuclear plants.

Recent studies, such as one by Princeton University professor Robert Williams, suggest that by using energy more efficiently, the United States -- and the world as a whole -- could substantially increase economic production and improve living conditions with little or no increase in energy generation.

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