Now for Operation Teakettle

A long, arduous cooldown at Three Mile Island

At 9:34 one evening last week, technicians at the big nuclear plant in Wiscasset, Me., felt the floor vibrate under their feet. A minor earthquake had struck. It measured only 4.0 on the Richter scale and did no damage to the plant or much of anything else in New England. But the temblor must have caused shudders of delight in Washington. For once the Nuclear Regulatory Commission had guessed right. Maine Yankee was one of five power plants on the East Coast, not known for its seismic risks, that it had ordered temporarily shut down last month --only two weeks before the Three Mile Island nightmare. Reason: to check their ability to stand up to a major earthquake.

As the NRC investigators continued their post-mortem on the Pennsylvania accident, an advisory panel recommended installation of expensive new monitoring instruments at all 43 of the U.S.'s pressurized-water reactors--the type in use at Three Mile Island. The NRC also heard a complaint from a nuclear analyst for the Tennessee Valley Authority that the reactor's builder, Babcock & Wilcox, had brushed off his warning of a "serious" design problem. Perhaps of greatest immediate import, officials conceded that it may take several more weeks, possibly months, to achieve a "cold shutdown" of the crippled reactor, meaning bringing it down to the minimum possible temperature. Said NRC Operations Boss Harold Denton: "I don't think we ought to commit ourselves to any more timetables--only safety."

During routine maintenance or refueling of a nuke, lowering a reactor's normal operating temperatures of about 315DEG C (600DEG F) is as simple as the binary code of the computer that does most of the work. Control rods are automatically dropped into the fuel core, which in effect douses its nuclear fires by stopping the fissioning of uranium atoms. Within several hours the temperature drops to 140DEG C (280DEG F). Then fresh coolant water is pumped through the reactor's heat exchanger (or steam generator) until the reactor's temperature dwindles to a still warm 65DEG C (150DEG F)-about as "cold" as an operational reactor ever gets. It all takes about a day.

But there is nothing ordinary any more about Three Mile Island's Unit 2. For one thing, the collection of pumps and machinery called the residual heat removal system, essential to the final temperature drop, is not "canned." In nuclear-engineering jargon, that means it is not designed to handle coolant as radioactive as Three Mile Island's. If the elaborate plumbing system were turned on, it would flush contaminated water through pipes and into the plant's auxiliary building, from which it could leak into the atmosphere. The technicians also point out that the pumps themselves produce heat, and could increase water pressure, cause vibrations or otherwise disturb the reactor's touchy, damaged core. As Robert Bernero, the NRC's on-site decommissioning expert, told TIME Correspondent Peter Stoler: "When you've got a napping tiger, you don't want to rattle its cage."

Not rattling that cage is proving more difficult than anyone anticipated. But the NRC and its newly recruited experts from almost all over the nuclear map think they finally have a "non-textbook" solution that may succeed. For starters, they have settled on a series of complex, interlocking steps, some of which have already been initiated:

> Continual degassing of the bubbly water in the reactor's primary cooling system. Objective: to remove any lingering, potentially explosive hydrogen and reduce water pressure within the reactor.

> Testing pumps to see if they will circulate coolant through the reactor's steam generator, which creates the steam that normally powers the electricity-producing turbogenerator.

> Modifying the plant's entire cooling apparatus so engineers will have five back-up systems (vs. two normally) for quick mobilization should new trouble develop.

But these steps, which should bring the reactor temperature down to around 93DEG C (200DEG F), are only a prelude to the grand finale: a kind of exercise in Yankee ingenuity that the engineers are calling natural circulation. It is an apt name and involves elements of physics taught in grade school. Bypassing the residual heat removal system, the heat will be transported out of the core by free convection-the principle at work when hot water circulates in a simmering teakettle.

To initiate this elegantly simple remedy, the entire secondary loop will be pumped "solid" with water rather than its usual complement of steam and water. Then the primary loop's pumps will be shut off. And lo, what might be called Operation Teakettle will start. Hot water will rise through convection in the reactor's core, and be carried off by a leg of the radioactive-tight primary loop that is already blueprinted as the "hot leg." The water's destination: the steam generator, where it will transfer (exchange, in engineering parlance) much of its heat to the water now flowing in the separated secondary loop. Presumably only low-level radioactivity will be passed on, and so, in a sense, the heat passing out of the system will not be accompanied by any dangerous cargo. Meanwhile, the water from the core, having yielded its heat--and thereby become denser and heavier--will flow down and out of the generator into the primary loop's "cold leg." That will carry the water back into the hot reactor, where the water will be re heated, expanded and able to carry off still more heat in a steady repeat of the cycle.

Every degree will be a battle. Even under the best of circumstances, Operation Teakettle will take at least five days to lower the core temperature the final 28DEG C. But the NRC team is determined not to hurry the process with pumps or other heavy-duty machinery. All in all, the technicians at Three Mile Island are cautiously optimistic. But even after cooldown, their job will not be done. They must still purge the stricken and perhaps permanently wrecked plant of its overburden of frighteningly dangerous radioactivity, a process that could easily go on for months. Then they must figure out a way to dispose of tons of unprecedented high-level nuclear waste left by the nightmare. Even Yankee ingenuity has not come up with a solution to that one yet.

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