Sometime in late 1984 the Surrey, Va., nuclear power plant could find itself in a bind. If workers need to repair its reactor core, they might be stymied by a frustratingly simple fact: There will be no place left at the facility to stash the reactor's highly radioactive fuel assemblies.
Surrey is not alone. By mid-1985, Connecticut's Millstone II plant is expected to share similar difficulties. And as the nation's nuclear plants continue to age, more will soon follow. Shifting spent bundles to other temporary storage sites will take care of part of the problem. But, some day, those too will be filled.
What then? If all goes as planned, by 1998 the United States Department of Energy (DOE) will start to store the overflow in repositories thousands of feet underground. There, out of harm's way (essentially forever), the radioactive or ''hot'' garbage will have a chance to ''cool'' off.
The concept sounds simple. But its execution is far from settled. And if it isn't, the federal government may have to reduce civilian and military nuclear programs drastically.
Scientists are still mulling over what geological material would be the most successful in limiting radiation leaks. At the same time, federal agencies must sort through such unknowns as how close a repository should be to a town, city, or national park, and what effect it might have on the local economy. The goal is to develop site-selection guidelines that will avoid much of the current pioneering guesswork, while speeding the design and placement of future repositories.
All of this is being carried out under a strenuous timetable set by Congress in the 1982 Nuclear Waste Policy Act (NWPA), which President Reagan signed into law in January. From nine sites in six states now being studied, the DOE is to pick three for further consideration by January 1985. Out of those three, one Western site is to be selected by March 1987, when the President is supposed to present a final recommendation to Congress. The same process for a second, presumably Eastern, site is to be carried out by March 1990.
''We want to feel safe enough about those places to trust our grandchildren to them,'' says Harvard University geologist and former Environmental Protection Agency (EPA) consultant Raymond Seiver.
The repositories will have to remain sound for longer than that, however. Radioactive components of nuclear wastes - called radionuclides - can emit intense bursts of lethal gamma radiation for thousands of years. In the case of Plutonium 239, 24,000 years must pass before half of its atoms deteriorate into harmlessness.
That is one reason why construction of a nuclear waste repository poses such an unprecedented engineering problem. Geologists must do more than find a spot that will keep radiation leaks into the outside world well within extremely stiff EPA standards. They also have to find a site that will do so for at least 10,000 years.
''Geologists have been perfectly comfortable telling what's in the ground,'' observes Dr. Seiver of Harvard. ''But now we have to forecast the future.''
Building a storage site carries with it a cascade of unknowns. A repository 2 ,000 to 4,000 feet below ground level would require a 2,000-acre spot to hold 100,000 metric tons of glassified radioactive waste. There are potential rock masses that large in at least half the states. Only two such places are needed to hold more high-level radioactive waste than that generated by all US reactors currently operating or under construction.
But the big challenge is guessing how the rock at such places will behave at depths where it has been little studied under circumstances that, until recently , were rarely considered.
A primary concern is how dry the rock tends to be. This is of extreme importance because ground water, which courses through underground fractures and crevices, must not be contaminated by radioactive waste. In this regard, salt is favored over tuff rock, basalt, or granite. Salt's qualities enable it to seal itself against fractures. Tuff and basalt, on the other hand, tend to be porous. And granite is often fractured.
But what tuff, basalt, and granite lack in density they make up for in their ability to absorb radioactivity. Chemists and geologists are trying to determine how well each type of rock keeps up with moisture creeping through.
''Ultimately, you're never finished,'' notes Kansas Geological Survey director William Hambleton. ''It's an educated guessing game based on experience. There's always more you can do to bring down the odds.''
Indeed, the open-ended nature of this research has left many scientists wondering if the NWPA's timetable is too ambitious. Much of the knowledge underlying any recommendations will be so new, they say, that a certain shake-out period should be allowed to be sure scientists aren't overlooking anything.
But Robert Morgan, interim director of the DOE office charged with overseeing the terms of the NWPA, insists that any recommendation ''will have to satisfy all geological criteria - we are not going to rush to judgment based on a timetable in the act.''
In fact, his office already has let some deadlines slip. By July 7, it was to have completed the guidelines for choosing sites. But they were swamped with more than 2,000 suggestions from scientists and DOE-sponsored public meetings throughout the country after a draft version of the guidelines was circulated in the spring. Now the guidelines are expected to be finished in the fall. Even so, the DOE claims that this setback will not jeopardize the 1998 target date for opening the first repository.
Such delays and uncertainties - par for many scientific endeavors - are not adapting easily to such a politically high-strung issue. Thus, the 1982 act has also provided the framework for noisy battles among lawyers and politicians. Field tests and evaluations from Texas salt domes to ancient lava fields in Washington are carried out in an atmosphere where an announcement of mere interest in a site is almost certain to stir a local furor. The seven salt deposit sites in Louisiana, Mississippi, Texas, and Utah have run into serious opposition.
''Most people simply don't want a repository in their backyard,'' insists Thomas Cotton, a senior policy analyst with the US Office of Technology Assessment. ''The only places it sells easily is on government property.''
Indeed, the other two sites under consideration - a tuff deposit on the Nevada Test Site and a basalt bed at the Hanford, Wash., federal reservation - are on federal land and have run into virtually no opposition.