HARRISBURG, Pa.  The reactor at Three Mile Island, site of the nation's worst nuclear accident, shut down Thursday, but radiation was not released and there was no danger to the public, company and federal officials said.
A faulty instrument reading triggered the automatic shutdown, officials said. It was the first shutdown of Unit 1 since 1997, said Ralph DeSantis, a spokesman for the plant's operator, AmerGen Energy Co. LLC.
The unit, which opened in 1974, shut off at 1:35 p.m. and remained down Thursday evening.
"It appears this was an uncomplicated, smooth shutdown,"said Neil Sheehan, a spokesman for the Nuclear Regulatory Commission.
DeSantis said other power plants in the regional electricity grid would ensure that customers experienced no power failures. Workers were investigating, and it was unclear when the reactor would resume operation.
The plant, about 10 miles southeast of Harrisburg, was the site of the nation's worst nuclear accident when a partial meltdown occurred in the Unit 2 reactor in March 1979.
Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Three Mile Island in 1979. A reading taken from a "faulty" instrument panel on the Unit 1 reactor at the Three Mile Island nuclear power plant located near Harrisburg, Pennsylvania has caused the reactor to shut down, but officials say that there is no threat to the public as radiation has not been released into the air. A wrong reading was displayed on a control panel which triggered the reactor to automatically shut itself down.

"It appears this was an uncomplicated, smooth shutdown. The company will need to take a careful and deliberate look at what went wrong," said Nuclear Regularitory Commission spokesman, Neil Sheehan.

A worker at the power plant was injured while the reactor was shutting down, after being scared by steam venting from the reactor, which caused him to fall.

The reactor, which first went operational in 1974, shutdown on Thursday afternoon on the "non-nuclear side of the reactor" at 1:35 p.m. EST and as of the moment remains offline, added Sheehan. This is the first time since 1997 that the reactor has shutdown.

In 1979, the Unit 2 reactor suffered a partial meltdown and has remained offline since the disaster.