Three Mile Island 0 Shares Email Three Mile Island, the Pennsylvania nuclear power plant that was the site of the worst commercial nuclear power accident in the United States 38 years ago, will close in unless it receives a state bailout, parent company Exelon Corp. The state is the second largest producer of nuclear power in the nation, after Illinois, according to the The Associated Press. Here is a brief history of one of the most infamous nuclear power plants in the U. March 28, One of the two reactors at Three Mile Island experienced a mechanical or electrical failure in water pumps that helped cool its core.
The TMI-2 reactor was destroyed. Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents.
It had two pressurized water reactors. It involved a relatively minor malfunction in the secondary cooling circuit which caused the temperature in the primary coolant to rise.
This in turn caused the reactor to shut down automatically. Shut down took about one second. At this point a relief valve failed to close, but instrumentation did not reveal the fact, and so much of the primary coolant drained away that the residual decay heat in the reactor core was not removed.
The core suffered severe damage as a result. The operators were unable to diagnose or respond properly to the unplanned automatic shutdown of the reactor.
Deficient control room instrumentation and inadequate emergency response training proved to be root causes of the accident The chain of events during the Three Mile Island accident Within seconds of the shutdown, the pilot-operated relief valve PORV on the reactor cooling system opened, as it was supposed to.
About 10 seconds later it should have closed.
But it remained open, leaking vital reactor coolant water to the reactor coolant drain tank. The operators believed the relief valve had shut because instruments showed them that a "close" signal was sent to the valve.
However, they did not have an instrument indicating the valve's actual position. Responding to the loss of cooling water, high-pressure injection pumps automatically pushed replacement water into the reactor system.
As water and steam escaped through the relief valve, cooling water surged into the pressuriser, raising the water level in it. The pressuriser is a tank which is part of the primary reactor cooling system, maintaining proper pressure in the system.
The relief valve is located on the pressuriser. In a PWR like TMI-2, water in the primary cooling system around the core is kept under very high pressure to keep it from boiling.
Operators responded by reducing the flow of replacement water. Their training told them that the pressuriser water level was the only dependable indication of the amount of cooling water in the system. Because the pressuriser level was increasing, they thought the reactor system was too full of water.
Their training told them to do all they could to keep the pressuriser from filling with water. If it filled, they could not control pressure in the cooling system and it might rupture.
Steam then formed in the reactor primary cooling system. Pumping a mixture of steam and water caused the reactor cooling pumps to vibrate. Because the severe vibrations could have damaged the pumps and made them unusable, operators shut down the pumps.
This ended forced cooling of the reactor core. The operators still believed the system was nearly full of water because the pressuriser level remained high.
However, as reactor coolant water boiled away, the reactor's fuel core was uncovered and became even hotter. The fuel rods were damaged and released radioactive material into the cooling water. This action stopped the loss of coolant water through the relief valve.
However, superheated steam and gases blocked the flow of water through the core cooling system. Throughout the morning, operators attempted to force more water into the reactor system to condense steam bubbles that they believed were blocking the flow of cooling water.
During the afternoon, operators attempted to decrease the pressure in the reactor system to allow a low pressure cooling system to be used and emergency water supplies to be put into the system.
Cooling restored, radioactive releases to air By late afternoon, operators began high-pressure injection of water into the reactor cooling system to increase pressure and to collapse steam bubbles.
They had condensed steam so that the pump could run without severe vibrations.At 4 a.m. on March 28, , the worst accident in the history of the U.S.
Three Mile Island, the Pennsylvania nuclear power plant that was the site of the worst commercial nuclear power accident in the United States 38 years ago, will close in unless it receives a state bailout, parent company Exelon Corp. said. The Three Mile Island accident occurred on March 28, , in reactor number 2 of Three Mile Island Nuclear Generating Station (TMI-2) in Dauphin County, Pennsylvania, near Harrisburg. It was the most significant accident in . Mar 28, · Watch video · After the Three Mile Island (or TMI) accident, public support for nuclear energy fell from an all-time high of 69 percent in to 46 percent in
nuclear power industry begins when a pressure valve in the Unit-2 reactor at Three Mile Island fails to close. Cooling water, contaminated with radiation, drained from the open valve into adjoining buildings, and the core began to dangerously overheat.
Under the INES, Three Mile Island is classified as Level 5, an accident with wider consequences, whereas both Fukushima and Chernobyl are Level 7, major accidents. The nuclear fuel cycle No discussion of nuclear power is complete without a brief exposition of the nuclear fuel cycle.
May 30, · Three Mile Island Nuclear Power Plant To Shut Down In The Two-Way The company that owns the Three Mile Island nuclear plant, site of the worst nuclear disaster in U.S. history, says the facility will be closed unless the state of Pennsylvania decides to bail it out.
Three Mile Island accident, accident in at the Three Mile Island nuclear power station that was the most serious in the history of the American nuclear power industry.
The Three Mile Island power station was named after the island on which it was situated in the Susquehanna River near Harrisburg, Pa.
Three Mile Island, the Pennsylvania nuclear power plant that was the site of the worst commercial nuclear power accident in the United States 38 years ago, will close in unless it receives a state bailout, parent company Exelon Corp. said. Three Mile Island Accident (March , minor update Jan ) In at Three Mile Island nuclear power plant in USA a cooling malfunction caused part of the core to melt in the #2 reactor.
The TMI-2 reactor was destroyed.