Those who regulate the nuclear power industry have an informal safety ranking of the nation's reactors, and many are or were lower on the list than Three Mile Island 2.

TMI 2 had a rather run-of-the-mill reputation during the year it had operated after its nuclear fuel was fired up in March 1978, according to several industry sources. "The gossip was that it wasn't operating too badly," said Harold D. Thornburg, director of the NRC's division of reactor construction inspection.

Thornburg heads a project trying to produce a formal evaluating procedure for the NRC to use, but he has asked that his midsummer deadline be extended in the wake of the Three Mile Island near-disaster.

"There's a story we should have seen at Three Mile Island", he said. "We have to do a lot of thinking on how you can see it."

Transcripts of a closed NRC meeting April 5, one week after the accident began at the Pennysylvania plant, show that while the commissioners had been frustrated in getting information out of Metropolitan Edison Co., they had much less confidence in some other reactor sites.

The Davis-Besse plant at Oak Harbor, Ohio, for example, run by Toledo Edison Co., had already been shut down while persistent safety problems were checked. The commissioners had no intention of opening it back up.

"If we did have a rating system of A, B, C, we would not put Davis-Besse 'C' on this scale," said John G. Davis, NRC's acting director of the office of inspection and enforcement, at the April 5 meeting. "It should be a better plant."

The regulators were discussing a recent problem with the main water pumping system at Davis-Besse similar to the one that started the March 28 near-disaster at Three Mile Island. Both plants were built by the Baboock & Wilcox Co. of Lynchburg, Va.

Norman Moseley of Davis' staff told the NRC during the meeting that his regional office had been about to begin a "full-blown enforcement meeting" with Davis-Besse officials because "the problems were not being properly handled."

A similar series of meetings had already taken place at another plant that one Washington engineer described as "a real turkey". the Zion 1 plant just north of Chicago on Lake Michigan, run by Commonwealth Edison Co.

At Davis-Besse, the intention was "to move in the direction that we had moved in the past in Zion, whereby we would identify specific problems and there would be frequent meetings between [NRC officials] and the management on-site," said Moseley.

Discussing later the best way to ensure full-time NRC supervision of all the Babcock & Wilcox plants, NRC Chairman Joseph Hendrie expressed confidence in the Oconee 1, 2 and 3 plants near Greenville, S.C. run by Duke Power Co.

"I'm inclined to have less concern about Oconee, because without...remembering any of the operating history, I just have a sense that they would have to have a little tighter operating shop," he said.

An early attempt to bring some uniformity to these gut feelings resulted ina two-inch-thick report last November that attempted to rank the 51 plants operating in 1975 in some kind of A, B and C categories.

Three Mile Island 1, which had been operating since 1974, was ranked "B", or average, in all the categories, the same final ranking received by the Oconee units, the Calvert Cliffs plant in Maryland and two-thirds of the rest of the 51 plants. Zion and Surry 1 and 2 near Newport News, Va., were among the 10 plants rated "C" or below average.

Notes from individual site inspectors, however, collected in an appendix to the report, were prophetic:

"The licensing of [Three Mile Island] Unit 2 in October 1977 will have an impact on the site/corporate staffs. In all probability the safety may become worse over the year due to this increased workload."