Reactor Cores At The Three Mile Island example essay topic

In the mid-1950's, nuclear physicists confidently predicted that nuclear energy would usher in a new age for humanity. The cost of energy would be so low it would be almost too cheap to meter. They predicted that by the year 2000 there would be thousands of commercial reactors producing unlimited amounts of power. Like the horse and buggy, oil and coal would become little more than historical curiosities. With such a bright outlook for the future the engineers and scientists started to get careless. Then on March 28, 1979, an event took place that rocked the nuclear power industry so badly that it has yet to recover.

That event was the partial meltdown of one of the reactor cores at the Three Mile Island nuclear power plant in Londonderry Township, Pennsylvania. The accident at Three Mile Island was a combination of equipment failures, design problems, and human error. It was even more that though it was a complacent attitude that the industry had as a whole as Harold Denton former Nuclear Regulatory Commission official said, We thought the plant was too well designed to have a serious accident. It was kind of like the Titanic. (CNN) It may surprise some people to find out how close we came to a major disaster and the shear amount of problems that occurred. To understand what went wrong you first need to understand how a nuclear power plant works.

At the heart or every plant is it's radioactive core. The core is a nuclear furnace creating heat by the splitting of atoms during a controlled chain reaction. Control rods that are raised and lowered into the core to control the rate the atoms split and there by controlling the amount to heat produced. To slow down the reaction the rods are lowered into the core, to speed it up they are raised or taken out of the core. Surrounding the core is the water in the primary loop.

This water removes the heat generated by the core as it is pumped through the loop. Because the wate in the primary loop comes in contact with the core it becomes radioactive. The heat is then transferred from the water in the primary loop to the water in the secondary loop. The water in the secondary then turns in to steam that steam turns a turbine that is connected to a generator that produces electricity. Pumps move the water through the secondary loop and back to where the heat is exchanged.

Because the water in the secondary loop never comes in contact with the radioactive water in the primary loop it is not radioactive. (PBS) At 4: 00 a.m. on March 28, 1979 the main pumps in the secondary non-nuclear loop of the unit 2 reactor stopped working caused by a slight malfunction. The turbine and then the reactor shut down according to their design. Because water is no longer flowing through the secondary loop, heat is no longer being transferred from the primary loop to the secondary loop. The water temperature and pressure in the reactor raise, this is normal and no cause for alarm. To prevent the pressure from getting too high, a pressure relief valve opens to relieve some of the pressure and water to a drain tank.

(Raso) All according to what was supposed to happen in case of such an event. This is when things start to go wrong. The back up pumps for the secondary loop had had a test run on them 42 hours before the indent. Part of this test included a valve being closed and then reopened at the end of the test.

But this time the valve was not reopened after the test. The valve being closed prevented the backup system from functioning. The plant workers discovered the valve closed in about eight minutes and reopened. Once the valve was open the back up system started to work correctly. Cooling water then flowed into the steam generators. (NRC) This solved one problem but a bigger one existed.

Because the secondary loop was out of commission for about eight minuets the pressure relief valve had to open. The pressure relief valve should have closed after the pressure dropped but it did not. The emergency water injection system had also come on to inject water into the primary loop to prevent a loss of coolant accident. Plant workers were not concerned when this happened because it had come on in the past when there had been no leak. Operators seeing that the water level and pressure are going up turn the emergency water injection off.

In reality the water level was still dropping but since the gauge that the workers saw was reading incorrectly they were unaware of this. Because of design shortcomings the plant operators also did not know that the pressure relief valve was stuck open. Allowing pressure to continue to drop and too much water to escape. Since so much water had escaped and it was no longer under as much pressure and there began to be pockets of steam in the primary loop. When these pockets of steam passed through the pumps it made them shake violently prompting the workers to shut two of the four pumps down. All this time steam is escaping through the pressure relief valve and going in to the drain tank.

Once the drain tank filled a component called a rupture disk broke spilling thousands of gallons of radioactive water in the basement of the containment building. Pumps start to transfer the water from the basement to waste-storage tanks in an auxiliary building, but the water overflowed these tanks and spilled to the floor. Because of the high water temperature some of the gases dissolved in it escaped in to the atmosphere. The water loss due to the stuck pressure relief valve left the core partially uncovered. With no water covering the core it begins to self-destruct raising the radioactivity of the water being drained into the basement. With the core no longer covered the heat it produced turned the steam in to super heated steam.

The now super heated steam reacts with the control rods to produce hydrogen and radioactive gases some of witch escapes through the pressure relief valve. An operator from the next shift comes on and notices that the temperature from the pressure relief valve is very high. He realized that the pressure relief valve is stuck open and closed it, but by this time it had already been stuck open for more than two hours. Now with the pressure relief valve closed water is no longer escaping but the workers still do not know that the water level was low and that the core was uncovered. With the core uncovered more waters boils away creating more heat, more hydrogen, more radioactivity, and more damage to the core. At this point the radiation gets high enough where an alarm sounds and a site emergency is declared.

The water in the primary loop in now 350 times its normal level of radioactivity. As the radioactivity increases a general emergency is declared. The high heat being generated by the core prompts some to think that the core is at least partially uncovered. Realizing that the core is indeed uncovered the plant operators once again turn the emergency water injection system. The plants operators once again turn on the pumps for the primary loop this starts the water circulating again.

By doing this the cores temperature is finally brought back into line. For the most part the crisis was over. However there was still a hydrogen bubble above the reactor core. The concern was that as pressure decreased the bubble would expand blocking the cooling water. If that were to happen the heat could rise again causing the hydrogen to explode. This was later proved to be impossible because there was not enough oxygen to support such a reaction.

The hydrogen bubble was reduced over the next few days degassing the pressurizer and controlling the air and water pressure. (NRC) Later a remote controlled camera was sent in to the reactor to see how much damage was done. What the work men saw was that no meltdown had occurred in the classic sense, meaning that the reactor did not melt through the steel containment reactor vessel or the or the floor of the containment building. However a good amount of the fuel did in fact melt or disintegrate altogether.

Their have been many studies done to see what if any effect the radiation that was released had on people's health. The resounding answer has been very little if any. Estimates are that the average dose to about two million people in the area was only about one millirem. To put this in to context, exposure from a full set of chest x-rays is about six millirem. (NRC) The amount of radiation the community was exposed to be quite small. Still many questions were raised about the effects of the radiation had on the things surrounding the site.

Groups monitoring the area took thousands of environmental samples. These groups did find that very low levels of radionuclides that were caused by the gasses released during the accident. Nevertheless several well-respected organizations have concluded that in spite of the damage done to the reactor most of the radiation was contained. The crisis at Three Mile Island did have an interesting effect on the community's mental health though. After the Three Mile Island event the community had a transient but pounced demoralizing effect on TMI vicinity residents. Continued demoralization of Three Mile Island Nuclear Station employees.

And continuing problems of trust among both groups that stem directly from the accident. (Diamond) A lot of the stress on the residents was from disagreements on weather the family should leave or stay. Most of the stress and mental problems that were caused by this event went away with time. Unfortunately the industry did not get away as easily as residents did. The public's opinion of nuclear power was so badly hurt it may never again be hailed as the power source for the future. This was partly if not mostly the medias fault.

The Los Angeles Times said that reporters knew shocking little about nuclear power and compounded their ignorance by focusing too narrowly on worst-case scenario questions. (Raso) Walter Cronkite said on his March 30th nightly broadcast We are faced with the remote but very real possibility of a nuclear meltdown at the Three Mile Island atomic-power plant. The danger faced by man for tampering with natural forces, a theme familiar from the myths of Prometheus to the story of Frankenstein, moved a step closer to fact from fancy through the day. (Qty. in Raso) This was not entirely false; there was a problem at the reactor but the situation was not nearly as grim as Mr. Cronkite made it sound.

It did not help that a fictional movie called The China Syndrome that was about a meltdown was released that month either. Fueled by the media and antinuclear activists that had flew to the area to tell people that it was unsafe to be there and that they should leave their homes and stay elsewhere publics fear grew. Because of that fear peoples attitudes shifted to the not in my back yard attitude of today. Before Three Mile Island 70% of people supported nuclear power, it has since slipped to only 43% in 1997. (Donn) Since the accident the nuclear power industry has been stagnant at best. No new reactors have been ordered in the United States in the past twenty-two years.

New plants have opened since Three Mile Island but they had all been planed before the incident. Virtually on one in the industry can imagine building a plant in the foreseeable future. (Raso) Further more many reactors that were supposed to be built have come under so much political and environmental fire that they will never open. An example of this is Shoreham plant; it was a 5.5 billion plant built in Long Island. Because of fears it never opened, and it is only one of about 65 that have been canceled. With 111 plants operating in the U.S. nuclear provides about twenty percent of the nations power second only to coal.

The licenses of fifty-six reactors run out in the next twenty years only two have applied for new licenses. Officials admit that many will close long before their in licenses run out. This is due in large part to the sky rocketing cost of clean up. Like the owners of San Onore 1, which shut down in 1992, they have decided to take it out of cold storage and dismantle it quickly before it gets more expensive to do so.

The estimated cost to dismantle the small 450-megawatt reactor is 460 million over seven years. As these plants close for one reason or another the country need to find another source for power. Other renewable such as wind and solar power have been slow coming at best. The incident Three Mile Island was the worst nuclear accident in U.S. history, but it was far from the worst in the world. At Three Mile Island the fail safe system worked.

The power station switched itself off. There was a scare but no disaster. (Raso) It was however a disaster for the power industry. By damaging the publics trust of nuclear energy it has all but halted the progress of this technology. In some European countries nuclear power provides nearly four times the power that it does in America. As Jeff Donn put it Maybe nuclear power was fundamentally flawed; Steeped in danger and, as environmentalists sometimes suggest, the most expensive way ever devised to boil water.

Maybe nuclear plants are too big and centralized to thrive in an ere of smaller is better (Donn) The truest testament to what happened to the nuclear power industry may be the fact that Amer Gen has offered to buy Three Mile Island's remaining working reactor for 100 million, it cost 400 million to build.