Newspaper: The Patriot
Date: March 29, 1979
Title: Melt-Down Most Feared of Accidents
Author: Associated Press

WASHINGTON (AP)-Cooling systems, such as the one that failed at a nuclear plant near Harrisburg, Pa., Wednesday, are the critical key to safety in nuclear power.

The accident most feared by environmentalists and scientists alike is the breakdown of the elaborate coolant apparatus which keeps nuclear reactors from overheating, erupting, and releasing deadly radiation into the atmosphere.

Less than two weeks ago, the Nuclear Regulatory Commission ordered the shutdown of five large nuclear power plants because of questions about whether their cooling systems could withstand earthquakes.

In the Harrisburg accident, a water pump used to cool the reactor at the Three Mile Island nuclear plant broke down, resulting in the release of some radiated steam into the atmosphere. Authorities said, however, that there were no injuries and the radiation outside was not considered dangerous.

The cooling system is critical in a nuclear plant because of the intense temperatures at which a nuclear reaction occurs. If the nuclear fuel should overheat, it could melt and burn its way through the protective enclosure, ultimately releasing radioactivity to the outside.

Reactor core melt-down would occur at a temperature of about 5,000 degrees Fahrenheit, the approximate melting point for the nuclear fuel.

Normally the operating temperature inside a reactor core is about 500 to 600 degrees Fahrenheit and the cooling water is pressurized at some 1,000 to 2,000 per square inch to prevent it from boiling into steam.

The NRC, however, requires that the primary and emergency cooling systems work well enough to prevent the temperature of any part of the nuclear fuel from ever going beyond 2,200 degrees Fahrenheit, less than half the estimated melting point.

Scientists generally agree that a break in a pipe carrying cooling water is one of the most threatening accidents, risking dispersion of radioactive materials.

To prevent such a catastrophe plants have backup cooling systems, to rush cooling water to the core casing if the primary system fails.