Thirty minutes later, Gary Miller, the TMI Station Manager, became aware of the situation and declared a General Emergency, and at 7:02 a.m. Zewe called the Pennsylvania Emergency Management Agency. Captain Dave, Traffic Reporter for a top-40 radio station in Harrisburg, WKBO, picked up an odd State Police conversation on the CB radio in his car. They were babbling about an emergency at the plant. He called it in to the news director, Mike Pintek, who rang up the Three Mile Island Nuclear Generating Station. The switchboard operator, not knowing what to do with someone wanting to know if the plant was going to explode, switched him to the TMI-2 control room. Pintek connected with the reactor operator who was closest to the phone and got a sense of frantic chaos. The story aired at 8:25 a.m., and the cat, so to speak, was out of the bag.[235]
At this point, although it was not fully realized, the TMI-2 power plant was a total loss. There were several things tried to bring the reactor back to some normal shutdown condition, but all failed. An entirely new set of goals had to be set. The fission products must be kept inside the primary cooling loop and not be allowed to escape into the area surrounding the plant. The public must be informed of the problem and any developments on a timely basis, but not in overly technical terms, causing panic and a mass stampede to get out of Harrisburg. The state and federal emergency services must monitor the landscape for a possible radiation plume and be prepared to relocate anyone under threat of harmful radiation exposure.
By 9:00 a.m. the radiation counter in the ceiling of the containment building was reading 6,000 rads per hour, indicating that not only had the coolant escaped through the overfilled drain tank, but that the fuel pins were no longer containing the fuel.[236] Hot fuel had lost its zirconium cladding and had dissolved in the steam, sending fission products out of the primary loop. The sealed containment building, made of concrete and steel five feet thick, was a solid blockage between the wet, steamy radioactive waste and the outside world.[237] It held throughout the danger period of the accident, and still stands today.
The uranium-oxide fuel in the reactor, laid bare of any effective cooling, reached temperatures as high as 5,000 degrees Fahrenheit. Normal temperature with the reactor running at full power was 600 degrees Fahrenheit. Nothing approaching this had ever happened in a full-sized, billion-watt power reactor, and the core temperature was way outside the range of the control instrumentation.
The operating crew, supplemented now by a mass of experts from the factory and the NRC, could only guess what was happening. By the time the NRC showed up, at 10:30 a.m., radiation had started to leak into the control room, and everybody had to wear a respirator to keep from breathing radioactive dust.
At the elevated temperature, the zirconium alloy fuel pins and supporting structure not only melted, they reacted chemically with the steam left in the reactor vessel, making zirconium oxide. This chemical action stripped the oxygen out of the water, making hydrogen gas. At first, the hydrogen escaped with the steam and floated to the top of the containment structure, but when the block valve was closed, it was sealed tightly in the reactor vessel. There were things wrong with the B&W reactor, but vessel integrity was not one of them. With the block valve closed, nothing could escape the reactor. The hydrogen, imprisoned in the vessel, floated to the top, formed a bubble, and exerted gas pressure on the structure. The bubble grew to a highly compressed 1,000 cubic feet, and by Thursday, March 29, it was 20,000 cubic feet.
This situation caused a great deal of anxiety in the control room. There was fear that the hydrogen pressure could either break open the 9-inch-thick, stainless-steel-lined reactor vessel, or it could explode, or both.[238] Furthermore, the fuel, now molten and dripping into the bottom of the vessel, could melt through it. Either scenario would contaminate the area downwind, as far as 10 miles. On Friday evening, March 30, at 8:23 P.M., the Associated Press had gotten wind of the worries about hydrogen exploding in the reactor, and they issued an urgent advisory to the public.[239] Two thirds of the people around Harrisburg who heard this announcement interpreted it as a warning of an impending massive nuclear explosion, a “hydrogen bomb,” and 42,000 left town as quickly as was possible. The next day on the TV show Saturday Night Live, the venerable comedy team of Bob & Ray announced a contest to name a new capital of Pennsylvania. By Sunday, 135,000 people, or 20 percent of everybody who lived within 20 miles of the plant, had voluntarily evacuated.
At the same time, the various emergency holding tanks in the containment building and the auxiliary building were reaching maximum capacity. By Thursday night, March 29, the low-level waste-water tank, containing minimally contaminated water from the toilets, drains, showers, and laundry had reached its capacity of 40,000 gallons. The plant workers did what they always did under this condition. They opened a valve and let it drain slowly into the Susquehanna. There was nothing illegal or even unusual about dumping the water tank, except under these frantic conditions of alert and anxiety. When the Governor of Pennsylvania, Richard Thornburgh, got wind of this in Harrisburg, he hit the ceiling and forbade any further release of anything radioactive. That was unfortunate, because anything that could have been disposed of that had a small enough radiation load to be safe for disposal, would have to wind up on the floor of the auxiliary building, and this made things more complicated than they had to be.
There was no governor’s mandate that could stop the other radiation release, which was the gaseous fission products. The iodine-131 mainly bonded to the inside of the containment building, and although at the peak concentration there were 64 million curies of iodine in the reactor core, the amount that escaped was barely detectable. On the other hand, a great deal of xenon escaped, and that was 13 million curies.[240] That is a lot of radiation, and if it were any other fission product, there would have been long-term evacuation and contamination cleanup in an area ten miles long and a mile wide in an east-northeasterly direction from the plant, or in the direction that the wind was blowing. Xenon, however, is different. Its body burden is practically zero, because human metabolism has no use for a noble element that cannot chemically bond with anything, and so it is not able to bond to our biological bodies and cause us harm. It just floats in the atmosphere, decaying into non-radioactive cesium-133 over 52 days. One can breathe it in but will most likely breathe it back out without experiencing a radiation release in the lungs.
235
After his short conversation with a reactor operator, Pintek called Blain Fabian, Communications Director at Med Ed, and eventually got a prepared statement for his radio announcement: “The nuclear reactor at Three Mile Island Unit Two was shut down as prescribed when a malfunction related to a feed-water pump occurred about 4:00 a.m. Wednesday [March 28]. The entire unit was systematically shut down and will be out of service for about a week while equipment is checked and repairs made.” The announcement proved to be wildly optimistic.
236
The radiation dose rate was correctly measured in rads and not rem, because there was not a human being in the containment building. A rad is simply the radiation dose that causes 0.01 joule of energy to be absorbed per kilogram of matter. To be expressed in rem or sieverts, the dose must be multiplied by a factor that depends upon the type of radiation and its effect on an average-sized man.
237
Commercial PWR power stations at the time were built with containment structures that could withstand a direct hit from a jet airliner, which was the worst accident that an engineer could think of. This was long before the 9-11-2001 terrorist attack in New York City, in which two airliners were used to take down two skyscrapers.
238
The level of concern about the strength of the reactor vessel and a hypothetical hydrogen explosion shows the extent of technical hysteria in the control room. To explode, hydrogen must have a similar volume of free oxygen, and there was zero oxygen in the vessel. If there had been, then the hot zirconium would have scavenged it away. Moreover, every water-cooled power reactor has passive hydrogen recombiners built into the primary cooling loop. A catalyst, usually platinum, is used to recombine hydrogen and oxygen back into water after it has been broken down in the severe radiation environment of controlled fission. The reactor vessel for the B&W 177FA was designed to handle 2,500 pounds per square inch of internal pressure, and the hydrogen pressure never approached this value.
239
There was a hydrogen explosion at TMI-2, but nobody knew about it until much later, when data recordings were analyzed. Hydrogen entrapped at the concave ceiling of the containment building was set off by a spark and combined explosively with the air in the building. In the control room it was felt as a big thump, but nobody was certain what it meant. The containment building, which is quite robust, was not affected. I have mixed feelings about AP’s announcement. I am all for telling the public what is going on, as this very book attests, but to let them leap to the conclusion that it would be a thermonuclear explosion was criminal.
240
For the sake of simplicity, I have limited this account to Xe-133. Actually, fission makes 18 xenon nuclides, from Xe-129 to Xe-146. Most have half-lives of seconds, and they never make it out of the fuel. Xe-135 is sometimes measured in reactor off-gas, but it has a half-life of only 9.1 hours. Three of these nuclides are not even radioactive. Xe-133 is probably the culprit in all radiation measurements outside the TMI power plant.