Nuclear Power Still Rocked By Three Mile Island. NUCLEAR INDUSTRY

NEXT May, the new World Organization of Nuclear Operators will hold its first meeting in Moscow. This is the latest fruit of the soul-searching efforts that the nuclear power industry has made to upgrade its performance since the Three Mile Island (TMI) accident a decade ago. The lesson of lax safety standards and operator incompetence that the TMI near-tragedy taught was powerfully reinforced by the Soviet Union's real tragedy at Chernobyl in 1985. So the world's atomic power plant operators - not just their governments - are organizing to pool their experience in the hope that this will help all of them run safer, more efficient utilities.

The American nuclear power industry didn't need Chernobyl to spur it on. It already faced a bleak future as utilities canceled new plant orders and an alarmed public seriously questioned whether the country should rely on nuclear power at all.

Now, on the TMI accident's 10th anniversary, industry analysts look at its history and see substantial improvement in safety and performance. But they admit that nuclear power's future remains uncertain.

The accident that began at Three Mile Island Unit 2 10 years ago tomorrow was due more to operator error than to equipment malfunction. The unit had been on line for 11 months. During full-power operation, a reactor core feed-water pump became clogged triggering a reactor shutdown. A pressure relief valve let steam and water escape into a catchment facility. These events were supposed to happen.

But the relief valve remained open for two hours, unnoticed by operators. That was not supposed to happen. Almost a million gallons of coolant water escaped, leaving half the reactor core uncovered.

Retrospective analysis shows that the accident was even more serious than was realized at the time. Ann Marie Cunningham, who served on the staff of the President's Commission on the Accident at Three Mile Island, notes that at least half the core melted. Commenting on this in the April issue of Technology Review, she explains: ``The molten fuel was so hot that it burned through a double-steel inner wall of the reactor containment vessel. The unsolved mystery is why the outer wall did not rupture, allowing a breach of radioactive fuel.''

But the containment did hold. There was little off-site danger. The largest whole body radiation dose anyone off-site would have received was not much more than the annual dose people in the United States get, on average, from medical and dental X-rays.

GPU Nuclear - the TMI operating company - expects to have 99 percent of the mess within the plant cleaned up by the end of this year. That includes evaporating some 2 million gallons of radioactive water according to a plan awaiting Nuclear Regulatory Commission approval. Then the plant will be mothballed for some 30 years until the adjacent Unit 1 is taken out of service. Operators restarted Unit 1, which was not involved in the accident, in 1985. GPU Nuclear wants to carry out the final decommissioning of the site on both units together.

The cleanup has cost nearly $1 billion - some $300 million more than Unit 2's construction price tag. Plant owner General Public Utilities and its customers and insurers are paying a third of that. The Department of Energy plus the states of New Jersey and Pennsylvania, which tax TMI electricity sales, are picking up much of the remaining bill. Japan's nuclear industry is contributing $18 million and sharing any technical information from the cleanup operation. In addition, the Energy Department will pay some $20 million to store the 150 tons of radioactive debris removed from the site.

Today, there are 111 nuclear power plants licensed to operate in 33 states as opposed to 71 plants a decade ago. They supply about 7 percent of US raw energy. But they are the second main source, after coal, of the nation's electricity.

Electricity use has risen 50 percent in the past 15 years and now accounts for 37 percent of all US energy usage. Nuclear power supplies 19.6 percent of that electricity. In six states, it supplies over half the power: Vermont (82 percent), South Carolina (64 percent), Connecticut (61 percent), New Jersey (61 percent), Maine (59 percent), Illinois (57 percent).

The atom has attained this important economic status even though no new plant has been ordered since the TMI accident and many orders outstanding at that time were canceled. The nuclear industry is counting on this status plus what it sees as a coming electricity crunch to revitalize its business.

A recent position paper by the Nuclear Power Oversight Committee, composed of executives of the industry's various trade associations, projects a need for 120 to 220 new large power plants of all types in the 1990s. But as the committee paper itself acknowledges, the nuclear industry must overcome public skepticism and improve its operating performance before new orders for atomic power plants will flow.

Both industry organizations and the Nuclear Regulatory Commission insist that nuclear plant safety and performance has substantially improved. But in day-to-day availability of generating capacity, the US industry is substantially below that of Europe.

The industry blames its rising costs and inefficiencies partly on arbitrary and quixotic state and federal regulation. The Massachusetts Institute of Technology's Nuclear Engineering Department and Energy Laboratory made a comparison of the US with five European countries. It concluded that the Europeans had many problems familiar to American utilities. But they overcame them through cooperation among operators and regulators.

In contrast, a ``highly antagonistic relationship between regulators and utilities'' hampers the US nuclear power industry, the MIT study said. It added that state and local rate-setting agencies often force utilities into short-term cost cutting that compromises their long-term performance.

One of the nuclear power industry's biggest needs, the study said, is for an atmosphere of national consensus concerning its role. This does not mean an uncritical coziness between regulators and utilities.

But there do need to be mechanisms through which all concerned with the industry can agree on what is needed for plants to operate safely and efficiently.