Since the Three Mile Island (TMI) emergency four years ago, much progress has been made in controlling the potentially dangerous genie of nuclear power production.
Federal regulations now require larger, better trained staffs in nuclear power plant control rooms. Reactor instrument panels are easier to read. Safety devices have been redesigned.
But implementation of many post-TMI safety suggestions has fallen far behind schedule - as the current struggle over a New York reactor's evacuation plan points out. And, when it comes to regulating nuclear power, the United States government still hasn't decided how safe is safe enough.
''In the absence of a clearly conceived (policy),'' writes William Wood in a new American Enterprise Institute study on nuclear regulation, ''the safety goal becomes 'just a little safer than it was.' ''
This ensures that nuclear regulation will be fraught with ''indecision, delay , and redundancy,'' according to Mr. Wood.
The Three Mile Island accident was the nuclear industry's darkest moment. Six different groups, from a presidential commission to congressional committees, investigated the incident. Eventually the Nuclear Regulatory Commission (NRC) produced the TMI Action Plan - a list of 347 recommendations for improving reactor safety all across the country.
According to NRC documents, 192 of these changes were completely put in place by the beginning of this year. Action on 125 isn't yet finished, and 30 are ''inactive.''
Utilities spent at least $25 million per nuclear plant to implement these suggestions, say industry officials.
Advisers with scientific training are now on constant duty at all nuclear power plants, for instance. Instruments that measure water level inside the reactor building are being installed in control rooms.
''Changes made so far follow up on 98 percent of the lessons we learned'' at TMI, says Robert Szalay, a vice-president of the Atomic Industrial Forum.
But critics claim this safety effort has been undermined by industry foot-dragging and NRC laxity. Indeed, action on some of the unimplemented safety suggestions is more than one year behind schedule.
Originally, all nuclear plants were supposed to install cooling system vents operable from inside the control room by January 1981. The NRC then moved the deadline to July 1982. The vents still aren't installed and the NRC has yet to set another date for finishing the task.
The NRC, after the Three Mile incident, also ordered state and local governments with nuclear plants in their area to develop plans for evacuating residents in an emergency. Of the 53 US nuclear plants, only 16 have formally approved plans. One - Indian Point, N.Y. - is so far behind schedule that the NRC last month threatened to close it down.
''We're a long way from where the authors of the TMI Action Plan thought we'd be at this time,'' says Steven Sholley, a member of the Union of Concerned Scientists, a nuclear watchdog group.
Critics also say the action plan doesn't address many important safety issues , such as the increasing brittleness of aging reactors, and the corrosion of pipes in many plants.
But, as other observers point out, the US government's nuclear regulators are hampered by not having an explicit answer to a bedeviling question: When it comes to nuclear power, how much safety do we want to pay for?
One reason the Indian Point plant was not shut down, despite its problems, was economic. Its owners would have been forced to pay large sums of money for replacement power from other utilities.
''I cannot ignore the economic costs of a shutdown,'' said NRC chairman Nunzio J. Palladino, when announcing the commission's decision to keep the plant open.
Congress has stayed aloof from decisions concerning the cost-effectiveness of nuclear regulations. It has fallen to the NRC to make those tough choices, on an ad hoc, case-by-case basis, points out William Wood in his new study, ''Nuclear Safety.''
As a result, licensing of new plants is a tedious process. Nuclear safety research and development proceeds without clear goals. The regulation of nuclear safety, ''an extraordinarily difficult job under the best of circumstances,'' is made far more difficult, writes Mr. Wood.
The NRC has made a start toward setting explicit safety goals. A statement on the acceptable level of risk to the public from nuclear power is in the first stages of a two-year review. Among other things, the statement says a nuclear power plant should be about as dangerous as a coal-fired one, and that the likelihood of a major reactor accident should be less than one in 10,000 per year of operation.
Many critics of nuclear power attack the premise of setting a generally acceptable level of nuclear risk. There is no such thing as an ''acceptable'' risk, they say, when the consequences of a mistake are so severe.
The safety goals are a ''placebo,'' argues Virginia Witt, publications head at the Nuclear Information and Resource Center. ''After all, it's not like you're talking about your chances of being in a plane crash.''
The NRC and the administration are also attempting to speed up decisions on the safety of nuclear plants by streamlining licensing procedures. Two license reform bills are currently being considered by Congress. Both would cut steps out of the current licensing process; both would allow quick approval of standardized reactor designs. The two bills would also try to limit the amount of ''backfitting'' - safety modifications in already-operating nuclear plants - required of utilities.