Saturday, March 28, 2009

Three Mile Island, Thirty Years Later

On March 28th, 1979, beginning at 4 AM, the Three Mile Island nuclear facility in Pennsylvania suffered a partial core meltdown. The U.S. nuclear power industry has only recently begun to recover, based on concerns over global warming.

Ironically, the movie "The China Syndrome," which detailed a cover-up over a near accident at a nuclear power plant had recently opened. It couldn't have been worse timing (for the nuclear industry).

A China Syndrome event is a hypothetical event in which a reactor core melts down, and the molten reactor core breaches the barriers below them and flow downwards through the floor of the containment building, melting their way to China.

Specifically, Unit 2 (TMI‑2) experienced a failure in the secondary, non‑nuclear section of the plant. As the NRC's fact sheet on the incident describes:
The main feedwater pumps stopped running, caused by either a mechanical or electrical failure, which prevented the steam generators from removing heat. First the turbine, then the reactor automatically shut down. Immediately, the pressure in the primary system (the nuclear portion of the plant) began to increase. In order to prevent that pressure from becoming excessive, the pilot-operated relief valve (a valve located at the top of the pressurizer) opened. The valve should have closed when the pressure decreased by a certain amount, but it did not. Signals available to the operator failed to show that the valve was still open. As a result, cooling water poured out of the stuck-open valve and caused the core of the reactor to overheat.

As coolant flowed from the core through the pressurizer, the instruments available to reactor operators provided confusing information. There was no instrument that showed the level of coolant in the core. Instead, the operators judged the level of water in the core by the level in the pressurizer, and since it was high, they assumed that the core was properly covered with coolant. In addition, there was no clear signal that the pilot-operated relief valve was open. As a result, as alarms rang and warning lights flashed, the operators did not realize that the plant was experiencing a loss-of-coolant accident. They took a series of actions that made conditions worse by simply reducing the flow of coolant through the core.

Because adequate cooling was not available, the nuclear fuel overheated to the point at which the zirconium cladding (the long metal tubes which hold the nuclear fuel pellets) ruptured and the fuel pellets began to melt. It was later found that about one-half of the core melted during the early stages of the accident. Although the TMI-2 plant suffered a severe core meltdown, the most dangerous kind of nuclear power accident, it did not produce the worst-case consequences that reactor experts had long feared. In a worst-case accident, the melting of nuclear fuel would lead to a breach of the walls of the containment building and release massive quantities of radiation to the environment. But this did not occur as a result of the Three Mile Island accident.
Right, there were not massive quantities of radiation released. But there was some amount of radiation released.

Granted, this was no Chernobyl. But it did raise red flags about safety in the U.S. nuclear industry.

Now, with global warming an issue on many people's minds, the nuclear industry sees a change for a renaissance.

Twenty percent of America's electricity is generated by nuclear power. Contrast this with France, where over 70% is generated by nuclear energy.

Yet not all are happy with the development, global warming aside.

Dr. Edwin Lyman of the Union of Concerned Scientists, said
"The industry is engaged in an all-out public relations campaign. They're painting nuclear energy as clean-air energy by talking about the fact that it doesn't release pollutants into the atmosphere.

"But the issue really is the potential for a catastrophic accident or a terrorist attack. And this is what the industry does not want to address head on.

"My concern is that as Three Mile Island retreats into the distance, people forget and complacency sets in. That is the biggest danger and the biggest threat to nuclear safety."

1 comment:

Pet Care Rx Reviews said...

They're painting nuclear energy as clean-air energy by talking about the fact that it doesn't release pollutants into the atmosphere.