HARRISBURG, Pa., April 3, 1979 (UPI) - Federal officials today cautiously expressed hope that the worst is over in the Three Mile Island nuclear crisis but said the reactor's core appeared to be damaged badly enough that it may have to be scrapped.
A Nuclear Regulatory Commission official said preliminary indications suggest most - and probably all - of the 3,600 metal-covered uranium fuel rods that make up the core were irreparably damaged in the accident that launched the nation's worst nuclear power emergency last week.
Normally, one official said, only one-third of a reactor's core would have to be replaced each year to add new fuel. But at Three Mile Island, he said, the intense heat from the accident appears to have knocked out the entire core.
"The core appears to be damaged to the point it would not be re-usable," the official said.
NRC teams have gradually raised their estimate of core damage as the full dimensions of the Three Mile Island incident unfolded.
The first estimates said only 1% of the core was badly damaged, while estimates Friday said 25 to 50% of the core had been knocked out.
At first officials said some of the fuel rods might have melted. But new analysis led officials to believe the rods might only have split and twisted.
After more than five days on the defensive, engineers said they finally have taken the offensive in subduing the reactor.
They said radiation emissions from the plant this morning measured a maximum 1 millirem about 2 miles from the facility.
Two separate events yesterday - one planned and one a surprise - marked what Nuclear Regulatory Commission experts viewed as the turning point.
First, a large hydrogen bubble within the reactor suddenly and unexpectedly appeared to have shrunk to 6% of its original size for reasons not entirely understood by engineers.
Later, in a planned move, engineers began removing hydrogen gas from the reactor's castle-shaped containment building, a concrete cylinder 120 feet wide and about 230 feet high. Both promised to reduce the risk of potentially catastrophic hydrogen explosions.
"Those two events put us on the offensive," NRC technical specialist Tom Elsasser said early today. "That was when our people started thinking optimistically."
But traces of radiation - from 0.1 millirem to 1.1 millirem per hour at ground level and from 0.1 to 3 millirem at an altitude of 500 feet - still wafted over the Pennsylvania Dutch countryside near Harrisburg. A dental X-ray, by comparison, is about 6 millirem.
Officials estimated that 200,000 people - one-fourth the population of York, Dauphin, Lancaster and Cumberland counties which surround the Susquehanna River plant - had quietly fled the area in an almost invisible voluntary evacuation since Friday.
Federal, state and civil defense officials remained poised for precautionary total evacuation should the situation threaten to get worse.
The Food and Drug Administration in Washington, in cooperation with the Mallinckrodt drug firm of St. Louis, got 250,000 bottles of the anti-radiation solution potassium iodide airlifted to Harrisburg as a precaution against thyroid problems should a major radiation release occur.
Harold Denton, chief Nuclear Regulatory Commission official on the scene, called the apparent change in the size of the reactor bubble a "reason for optimism."
"I think it's certainly safer than it was yesterday (Sunday)," Denton said yesterday. "I think there certainly is reason for optimism."
But Denton said he was taken aback and skeptical about the size of the drop, from 850 cubic feet to 47 cubic feet, and to stay on the safe side he ordered a careful recheck of the calculation before accepting the dramatic decrease as fact.
The good news about the bubble was matched later in the day by the start of "recombiners" - electric furnaces hooked to ports in the containment building to remove hydrogen gas, cook it with a catalyst to add oxygen and turn it from a possibly explosive gas to harmless water.
Those developments were tempered by the first failure of an instrument in the reactor due to radiation exposure.
That failure did no harm because the instrument was not in use. But Denton said he was concerned that others might fail as well, depriving engineers of information about conditions in the reactor.