Newspaper: The Evening Sentinel

Date: April 3, 1979

Title: Confused? The Crisis Explained…

Author: Dennis O'Brien


Here is what happened, and what's now happening, at the Three Mile Island nuclear generating station:

Last Wednesday, at 4 a.m., a leak sprung in the cooling system of the nuclear reactor.

The cooling system, a series of pipes that circulate water near the reactor, is necessary to keep the reactor from getting too hot during the process of nuclear fission. (Nuclear fission is simply the splitting of uranium atoms in the reactor, which produces heat.)

Under normal conditions, a small amount of water is continually broken down into hydrogen and oxygen. The gases rise to the top of the steel reactor capsule and are pumped out, ignited and combined back into water in a device known as a "hydrogen recombiner."

WHEN THE LEAK sprung, however, the temperature inside the reactor grew hotter than its normal 240 degrees and an emergency cooling system automatically began to circulate water near the reactor, which is a tubular structure 15 feet wide and 40 feet high.

The reactor, encased in a steel and concrete vessel that's 138 feet wide and 202 feet high, is currently at 280 degrees, according to officials of Metropolitan Edison, which owns a major share of the plant.

For a reason that's still unknown-either through human error or mechanical failure-this secondary cooling system apparently shut down.

This lead to an explosion from hydrogen gas collecting inside the nuclear reactor.

THE EXPLOSION, which meant that an undetermined amount of radioactive gases escaped into the air, occurred at 2 p.m. Thursday, 34 hours after the initial leak was discovered.

Harold Denton, a top ranking official with the Nuclear Regulatory Commission, said that it was not until 9 a.m. Friday that the NRC was informed of the hydrogen blast, which is what led to last week's order to prepare for an evacuation.

So for those two days hydrogen gas was forming at dangerously high levels inside the reactor.

The hydrogen explosion led to the formation Saturday of a potentially lethal bubble of hydrogen gas-which is now the major cause for concern among NRC and Met Ed officials.

What has the NRC and utility officials worried is how to get rid of the hydrogen bubble and keep the temperature in the reactor down at the same time.

To get rid of it they have to reduce pressure inside the reactor, but they are not sure of the safest way to do that.

If the temperature inside the reactor is not kept down, the uranium could get so hot that it would melt through the floor of the reactor and containment level.

Scientists differ on what a meltdown at Three Mile Island would mean.

Some say the molten mass would disperse through the ground just below the reactor with the radioactive gases floating right back up into the reactor, where it would be safely shielded.

But another possibility is that the mass would hold together and melt down through the earth below the reactor creating a "China syndrome" effect (this catchphrase was coined in the belief such a molten core would, hypothetically, continue melting through the earth eventually reaching the other side of the world, or China). Radioactive gases would be sent through the earth's surface at various, unpredictable points and would be disseminated through underground water supplies.

BUT RIGHT NOW NRC and utility officials agree that a meltdown is not the immediate danger. For a meltdown the temperature of the uranium inside the reactor must reach 5,000 degrees, according to MetEd officials.

THE BUBBLE is trapped near the top of the reactor. To reduce its size some of the hydrogen, which is in solution in the water around the uranium, is being pumped through a one-inch line into a nearby pressurizer.

The pressurizer is normally used to check levels of water and gaseous materials in the reactor.
As the hydrogen in solution and other materials are removed from the reactor, pressure is being reduced, shrinking the size of the bubble, officials say.

From the pressurizer, the hydrogen in solution is being vented into a pipe to another storage tank in the containment vessel.

The hydrogen in solution in that storage tank, which is highly radioactive, will be transported off-site in the near future, according to Thomas Elasser, a nuclear physicist for the NRC.

Officials are currently optimistic, claiming a reduction in the risk of danger from the bubble.
Uranium is currently 500 degrees.

The main concern is still the bubble, which officials say is slowly diminishing in size.

If the bubble, which is now estimated at roughly 50 cubic feet, were pure hydrogen it would be harmless. But there are also minimal amounts of oxygen present.

If the mixture of gases reaches the right combination-five percent oxygen and four to six percent hydrogen, the hydrogen will burn.

If the hydrogen reaches seven percent, it may explode.

Scientists are not sure how much hydrogen is inside the bubble, but one NRC official estimated it could be as high as six percent.

Denton said Sunday that if the bubble were left untouched, the oxygen and hydrogen levels will reach the explosive stage in five or six days.

After that the bubble may explode at any time.

NRC and Met Ed officials agree, therefore, that it's vital that the bubble be dissipated.