For about a year after the accident at Three Mile Island, even minor issues of nuclear safety commanded instant public attention. The recommendations of the Kemeny Commission, the Rogovin Commission and numerous congressional and Nuclear Regulatory Commission task forces were widely read and discussed. But when the krypton gas at Three Mile Island was finally safetly vented and clean-up of the damaged reactor began, interest evaporated.

Since then, back in its familiar shadoes outside the glare of public scrutiny, the NRC has made at least one decision suggesting in has succumbed to the pressures to get the nuclear industry moving again even before safety problems brought to light by Three Mile Island are solved. The controversial decision involves an operating license for a reactor in Tennessee called Sequoyah-1, whose containment is so thin that it could not have withstood the pressures that were actually generated at Three Mile Island.

Nuclear reactors are surrounded by a huge containment vessel designed to keep the radioactivity inside in all circumstances short of a full-scale core meltdown. During the 1960s, competition led the companies that sell reactors to look for ways to lessen the expense of these enormous shells. At the time, the only thing thought likely to break open a containment was steam pressure caused by a failure in the reactor's cooling system. Therefore, the thinking went, if ways could be devised to remove steam, the containments did not need to be nearly so strong and so expensive. Both General Electric and Westinghouse cameup with such designs.

The catch is that no one anticipated what actually took place at Three Mile Island when the metal cladding that protects the nuclear fuel reacted with water, producing large amounts not of steam, but of hydrogen. Before Three Mile Island, the NRC thought that this oxidation reaction might affect 1 percent of the metal. Allowing a conservative margin of safety, its design criteria therefore specified that reactors must be able to withstand 5 percent oxidation. But at Three Mile Island somewhere between 30 percent and 60 percent of the metal was oxidized.

The NRC staff's estimate, based on recent calculations by the reactor's designer, is that, though designed to meet only the 5 percent criterion, the Sequoyah containment could withstand pressures caused by up to 25 percent oxidation, still below the lowest possible estimate for Three Mile Island. Yet the NRC staff recommended, and the commission has now granted, a license to begin operating the plant.

The Sequoyah reactor does contain a system of burners to remove hydrogen, but the system is new, controversial and completely untested. Serious doubts have been raised by independent experts that it will work. Incredibly, the NRC has also decided not to change the criterion that requires plant designers to plan for only 5 percent metal oxidation.

The justification for these decisions is that the technical fixes introduced since Three Mile Island make a repeat of that accident such a low probability as not to be "credible." The NRC and the nuclear industry can and have spent years arguing about what constitutes a credible accident scenario. But in the words of Victor Gilinsky, the only commissioner to oppose the grating of Sequoyah's license, "whatever 'credible' means, if it happened last year it's credible."

Gilinsky isn't the only one to question the Sequoyah decision. The Nuclear Safety Oversight Committee, appointed by President Carter on the recommendation of the Kemeny Commission, raised the issue in its first report to the president. Arguing that the NRC has reverted to a "business-as-usual mind-set" in grating licenses based solely on the expectation that Three Mile Island could not happen again, the committee concluded: "We do not share such judgment; any system should presumptively be at least good enough to deal with accidents that have actually occurred." The committee's report is still secret: the White House has neither responded to nor released the text.

Sequoyah-1 is not the only thin-shelled reactor. Two other Westinghouse reactors of the same design are already operating. The question has not even been raised whether their operating licenses should be suspended until a reliable system to prevent the accumulation of hydrogen is developed. Seven other reactors of this type are in some stage of construction, as are 20 more General Electric plants of a similar design.

The Sequoyah decision reeks of the kind of thinking that led to Three Mile Island in the first place. During the endless debates of the past 20 years over unsolved safety issues, industry would argue that its engineers' calculations were "conservative," that safety margins had already been allowed for and, if the numbers still didn't work, that the postulated accident was extremely unlikely in the first place -- hardly reason enough to deny a license to a plant on which so much money had already been spent.

The NRC would respond by deciding that the problem was not a problem because it was just too unlikely to happen. Many of those things happened at Three Mile Island. Now, precisely the same arguments are being made about Sequoyah, and the still unsolved hydrogen issue has been dealt with by ruling out the likelihood that Three Mile Island, or a similar sequence of unanticipated events, will happen again.

For a while it seemed as though Three Mile Island was a blessing in disguise. The shock would force the industry and the NRC to clean up their act without a single life having been lost. Sequoyah and its 29 thin-shelled relatives force the question whether Three Mile Island taught any lasting lessons.