Hello and welcome to PRISM of the past, a weekly series about historical events, people and situations, from the fascinating to the forgotten.

I'm the aluminati, and today we're definitely going to be taking a

look at a topic that's interested me for quite some time. We're going to be

talking about Three Mile Island. However, although we're talking about it today, it's not just

about the island I'm referring to but obviously one of the most serious accidents in

US commercial nuclear power plant operating history. It's a really fascinating history and one that I

thought many of you might like as much as I loved researching it as well, so let's just jump

right into it.

There has been a vigorous debate in this country about the safety of the nation's 72 nuclear

energy power plants.

That debate is likely to be intensified because of what happened early this morning at a nuclear power plant in Pennsylvania.

The U.S. Nuclear Regulation Commission states that the accident began at about 4 a.m. on Wednesday, March 28,

1979, when the plant experienced a failure in the secondary

non-nuclear section of the plant, one or two reactors on the site.

Either a mechanical or electrical failure prevented the main feedwater pumps from sending water to the steam generators that remove heat from the reactor core.

This caused the plant's turbine generator and then the reactor itself to automatically shut down.

Immediately the pressure in the primary system, the nuclear piping portion, began to increase.

In order to control that pressure, the pilot operated relief valve opened. It was located at the top of the pressurizer.

The valve should have closed when the pressure fell to proper levels, but became stuck open.

Instruments in the control room, however, indicated to the plant staff that the valve was closed.

As a result, the plant staff was unaware that cooling water in the form of steam was pouring

out of the stuck open valve.

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