Monday, March 14, 2011

About Radiation from Nuclear Power Plant Explosions

    About Radiation from Nuclear Power Plant Explosions The nations of the world now have more than enough nuclear bombs to kill every person on Earth. The two most powerful nations -- Russia and the United States -- have about 50,000 nuclear weapons between them. What if there were to be a nuclear war? What if terrorists got their hands on nuclear weapons? Or what if nuclear weapons were launched by accident?
    • Nuclear explosions produce radiation. The nuclear radiation harms the cells of the body which can make people sick or even kill them. Illness can strike people years after their exposure to nuclear radiation.
    • One possible type of reactor disaster is known as a meltdown. In such an accident, the fission reaction goes out of control, leading to a nuclear explosion and the emission of great amounts of radiation.
      • In 1979, the cooling system failed at the Three Mile Island nuclear reactor near Harrisburg, Pennsylvania. Radiation leaked, forcing tens of thousands of people to flee. The problem was solved minutes before a total meltdown would have occurred. Fortunately, there were no deaths.
      • In 1986, a much worse disaster struck Russia's Chernobyl nuclear power plant. In this incident, a large amount of radiation escaped from the reactor. Hundreds of thousands of people were exposed to the radiation. Several dozen died within a few days. In the years to come, thousands more may die of cancers induced by the radiation.
    • Nuclear reactors also have waste disposal problems. Reactors produce nuclear waste products which emit dangerous radiation. Because they could kill people who touch them, they cannot be thrown away like ordinary garbage. Currently, many nuclear wastes are stored in special cooling pools at the nuclear reactors.
      • The United States plans to move its nuclear waste to a remote underground dump by the year 2010.
      • In 1957, at a dump site in Russia's Ural Mountains, several hundred miles from Moscow, buried nuclear wastes mysteriously exploded, killing dozens of people.
    • Nuclear reactors only last for about forty to fifty years.
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      Three Mile Island

      One minute past 4 a.m. on Wednesday, March 18, 1979, maintenance workers cleaning sludge from a small pipe blocked the flow of water in the main feedwater system of a reactor at Three Mile Island near Harrisburg, Pennsylvania. The sift foreman heard "loud, thunderous noises, like a couple of freight trains," coming from Unit 2. Loudspeakers broadcast warnings. Since the reactor was still producing heat, it heated the blocked cooling water around its core hot enough to create a pressure surge which popped a relief valve. Three emergency feedwater pumps started up to restore circulation. But the relief valve stuck open, and some 220 gallons of water per minute began flowing out of the reactor vessel. Two valves that normally channeled water from the emergency pumps on the system could have supplied the reactor vessel with enough cooling water to replace the escaping water, but he control-room operators didn't know that the valve was stuck open. Within five minutes after the main feedwater system failed, the reactor, deprived of all normal and emergency sources of cooling water, and no longer able to use its enormous energy to generate electricity, gradually started to tear itself apart. The loss of coolant at the reactor continued for some 16 hours. About a third of the core melted down. Radioactive water flowed through the stuck relief valve into an auxiliary building, where it pooled on the floor. Radioactive gas was released into the atmosphere. An estimated 140,000 people were evacuated from the area. It took a month to stabilize the malfunctioning unit and safely shut it down. The reactor was a total loss and the cleanup required years and cost hundreds of millions of dollars. No one was reported injured and the little radiation that leaked out was quickly dispersed. Although this accident did cost lots of money and time, no one was hurt. Three Mile Island inspired the NRC mandated safety modifications to nuclear plants throughout the United States that averaged $20 million per plant. "It is not an exaggeration to say," Cohen concludes, "that lessons learned from the Three Mile Island accident revolutionized the nuclear power industry."


      A far more serious accident occured at Chernobyl, in what was then still the Soviet Union. At the time of the accident--April 26, 1986--the Chernobyl nuclear power station consisted of four operating 1,000 megawatt power reactors sited along the banks of the Pripyat River, about sixty miles north of Kiev in the Ukraine. A fifth reactor was under construction. All the Chernobyl reactors were of a design that the Russians call the RBMK--natural uranium-fueled, water-cooled, and graphite-moderated--a design that American physicist and Nobel laureate Hans Bethe has called "fundamentally faulty, having a built-in instability." Because of the instability, an RMBK reactor that loses its coolant can under certain circumstances increase in reactivity and run progressively faster and hotter rather than shut itself down. Nor were the Chernobyl reactors protected by containment structures like those required for U.S. reactors, though they were shielded with heavy concrete covers. Without question, the accident at Chernobyl was the result of a fatal combination of ignorance and complacency. "As members of a select scientific panel convened immediately after the... accident," writes Nobel laureate Hans Bethe, "my colleagues and I established that the Chernobyl disaster tells us about the deficiencies of the Soviet political and administrative system rather than about problems with nuclear power." Although the problem at Chernobyl was relatively complex, it can basically be summarized as a mismanaged electrical engineering experiment which resulted in the reactor exploding. The explosion was chemical, driven by gases and steam generated by the core runaway, not by nuclear reactions. Flames, sparks, and chunks of burning material wree flying into the air above the unit. These were red-hot pieces of nuclear fuel and graphite. About 50 tons of nuclear fuel evaporated and were released by the explosion into the atmosphere. In addition, about 70 tons were ejected sideways from the periphery of the core. Some 50 tons of nuclear fuel and 800 tons of reactor graphite remained in the reactor vault, where they formed a pit reminiscent of a volcanic crater as the graphite still in the reactor had burned up completely in a few days after the explosion. The resulting radioactive release was equivalent to ten Hiroshimas. In fact, since the Hiroshima bomb was air-burst--no part of the fireball touched the ground--the Chernobyl release polluted the countryside much more than ten Hiroshimas would have. Many people died from the explosion and even more from the effects of the radiation later. Still today, people are dying from the radiation caused by the Chernobyl accident. The estimated total number of deaths will be 16,000.
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Power Plants - Nuclear Accidents

3 January 1961
The world's first nuclear-related fatalities occurred following a reactor explosion at the National Reactor Testing Station in Idaho Falls, Idaho. Three technicians, were killed, with radioactivity "largely confined" (words of John A. McCone, Director of the Atomic Energy Commission) to the reactor building. The men were killed as they moved fuel rods in a "routine" preparation for the reactor start-up. One technician was blown to the ceiling of the containment dome and impaled on a control rod. His body remained there until it was taken down six days later. The men were so heavily exposed to radiation that their hands had to be buried separately with other radioactive waste, and their bodies were interred in lead coffins. Another incident three weeks later (on 25 January) resulted in a release of radiation into the atmosphere.24 July 1964
Robert Peabody, 37, died at the United Nuclear Corp. fuel facility in Charlestown, Rhode Island, when liquid uranium he was pouring went critical, starting a reaction that exposed him to a lethal dose of radiation.
19 November 1971
The water storage space at the Northern States Power Company's reactor in Monticello, Minnesota filled to capacity and spilled over, dumping about 50,000 gallons of radioactive waste water into the Mississippi River. Some was taken into the St. Paul water system.
March 1972
Senator Mike Gravel of Alaska submitted to the Congressional Record facts surrounding a routine check in a nuclear power plant which indicated abnormal radioactivity in the building's water system. Radioactivity was confirmed in the plant drinking fountain. Apparently there was an inappropriate cross-connection between a 3,000 gallon radioactive tank and the water system.
27 July 1972
Two workers at the Surry Unit 2 facility in Virginia were fatally scalded after a routine valve adjustment led to a steam release in a gap in a vent line. [See also 
9 December 1986]
28 May 1974
The Atomic Energy Commission reported that 861 "abnormal events" had occurred in 1973 in the nation's 42 operative nuclear power plants. Twelve involved the release of radioactivity "above permissible levels."
22 March 1975
A technician checking for air leaks with a lighted candle caused $100 million in damage when insulation caught fire at the Browns Ferry reactor in Decatur, Alabama. The fire burned out electrical controls, lowering the cooling water to dangerous levels, before the plant could be shut down.
28 March 1979
A major accident at the Three Mile Island nuclear plant near Middletown, Pennsylvania. At 4:00 a.m. a series of human and mechanical failures nearly triggered a nuclear disaster. By 8:00 a.m., after cooling water was lost and temperatures soared above 5,000 degrees, the top portion of the reactor's 150-ton core melted. Contaminated coolant water escaped into a nearby building, releasing radioactive gasses, leading as many as 200,000 people to flee the region. Despite claims by the nuclear industry that "no one died at Three Mile Island," a study by Dr. Ernest J. Sternglass, professor of radiation physics at the University of Pittsburgh, showed that the accident led to a minimum of 430 infant deaths.
The Critical Mass Energy Project of Public Citizen, Inc. reported that there were 4,060 mishaps and 140 serious events at nuclear power plants in 1981, up from 3,804 mishaps and 104 serious events the previous year.
11 February 1981
An Auxiliary Unit Operator, working his first day on the new job without proper training, inadvertently opened a valve which led to the contamination of eight men by 110,000 gallons of radioactive coolant sprayed into the containment building of the Tennessee Valley Authority's Sequoyah I plant in Tennessee.
July 1981
A flood of low-level radioactive wastewater in the sub-basement at Nine Mile Point's Unit 1 (in New York state) caused approximately 150 55-gallon drums of high-level waste to overturn, some of which released their highly radioactive contents. Some 50,000 gallons of low-level radioactive water were subsequently dumped into Lake Ontario to make room for the cleanup. The discharge was reported to the Nuclear Regulatory Commission, but the sub-basement contamination was not. A report leaked to the press 8 years later resulted in a study which found that high levels of radiation persisted in the still flooded facility.
The Critical Mass Energy Project of Public Citizen, Inc. reported that 84,322 power plant workers were exposed to radiation in 1982, up from 82,183 the previous year.
25 January 1982
A steam generator pipe broke at the Rochester Gas & Electric Company's Ginna plant near Rochester, New York. Fifteen thousand gallons of radioactive coolant spilled onto the plant floor, and small amounts of radioactive steam escaped into the air.
15-16 January 1983
Nearly 208,000 gallons of water with low-level radioactive contamination was accidentally dumped into the Tennesee River at the Browns Ferry power plant.
25 February 1983
A catastrophe at the Salem 1 reactor in New Jersey was averted by just 90 seconds when the plant was shut down manually, following the failure of automatic shutdown systems to act properly. The same automatic systems had failed to respond in an incident three days before, and other problems plagued this plant as well, such as a 3,000 gallon leak of radioactive water in June 1981 at the Salem 2 reactor, a 23,000 gallon leak of "mildly" radioactive water (which splashed onto 16 workers) in February 1982, and radioactive gas leaks in March 1981 and September 1982 from Salem 1.
9 December 1986
A feedwater pipe ruptured at the Surry Unit 2 facility in Virginia, causing 8 workers to be scalded by a release of hot water and steam. Four of the workers later died from their injuries. In addition, water from the sprinkler systems caused a malfunction of the security system, preventing personnel from entering the facility. This was the second time that an incident at the Surry 2 unit resulted in fatal injuries due to scalding [see also 
27 July 1972].
It was reported that there were 2,810 accidents in U.S. commercial nuclear power plants in 1987, down slightly from the 2,836 accidents reported in 1986, according to a report issued by the Critical Mass Energy Project of Public Citizen, Inc.
28 May 1993
The Nuclear Regulatory Commission released a warning to the operators of 34 nuclear reactors around the country that the instruments used to measure levels of water in the reactor could give false readings during routine shutdowns and fail to detect important leaks. The problem was first bought to light by an engineer at Northeast Utilities in Connecticut who had been harassed for raising safety questions. The flawed instruments at boiling-water reactors designed by General Electric utilize pipes which were prone to being blocked by gas bubbles; a failure to detect falling water levels could have resulted, potentially leading to a meltdown.
15 February 2000
New York's Indian Point II power plant vented a small amount of radioactive steam when a an aging steam generator ruptured. The Nuclear Regulatory Commission initially reported that no radioactive material was released, but later changed their report to say that there wasa leak, but not of a sufficient amount to threaten public safety.
6 March 2002
Workers discovered a foot-long cavity eaten into the reactor vessel head at the Davis-Besse nuclear plant in Ohio. Borated water had corroded the metal to a 3/16 inch stainless steel liner which held back over 80,000 gallons of highly pressurized radioactive water. In April 2005 the Nuclear Regulatory Commission proposed fining plant owner First Energy 5.4 million dollars for their failure to uncover the problem sooner (similar problems plaguing other plants were already known within the industry), and also proposed banning System Engineer Andrew Siemaszko from working in the industry for five years due to his falsifying reactor vessel logs. As of this writing the fine and suspension were under appeal.
Nov 2005
High tritium levels, the result of leaking pipes, were discovered to have contaminated groundwater immediately adjacent to the Braidwood Generating Station in Braceville, Illinois.

Major Nuclear Power Plant Accidents

December 12, 1952

A partial meltdown of a reactor's uranium core at the Chalk River plant near Ottawa, Canada, resulted after the accidental removal of four control rods. Although millions of gallons of radioactive water poured into the reactor, there were no injuries.

October 1957

Fire destroyed the core of a plutonium-producing reactor at Britain's Windscale nuclear complex - since renamed Sellafield - sending clouds of radioactivity into the atmosphere. An official report said the leaked radiation could have caused dozens of cancer deaths in the vicinity of Liverpool.

Winter 1957-'58

A serious accident occurred during the winter of 1957-58 near the town of Kyshtym in the Urals. A Russian scientist who first reported the disaster estimated that hundreds died from radiation sickness.

January 3, 1961

Three technicians died at a U.S. plant in Idaho Falls in an accident at an experimental reactor.

July 4, 1961

The captain and seven crew members died when radiation spread through the Soviet Union's first nuclear-powered submarine. A pipe in the control system of one of the two reactors had ruptured.

October 5, 1966

The core of an experimental reactor near Detroit, Mich., melted partially when a sodium cooling system failed.

January 21, 1969

A coolant malfunction from an experimental underground reactor at Lucens Vad, Switzerland, releases a large amount of radiation into a cave, which was then sealed.

December 7, 1975

At the Lubmin nuclear power complex on the Baltic coast in the former East Germany, a short-circuit caused by an electrician's mistake started a fire. Some news reports said there was almost a meltdown of the reactor core.

March 28, 1979

Near Harrisburg, Pennsylvania, America's worst nuclear accident occurred. A partial meltdown of one of the reactors forced the evacuation of the residents after radioactive gas escaped into the atmosphere.

February 11, 1981

Eight workers are contaminated when more than 100,000 gallons of radioactive coolant fluid leaks into the contaminant building of the Tennessee Valley Authority's Sequoyah 1 plant in Tennessee.

April 25, 1981

Officials said around 45 workers were exposed to radioactivity during repairs to a plant at Tsuruga, Japan.

April 26, 1986

The world's worst nuclear accident occurred after an explosion and fire at the Chernobyl nuclear power plant. It released radiation over much of Europe. Thirty-one people died iin the immediate aftermath of the explosion. Hundreds of thousands of residents were moved from the area and a similar number are belived to have suffered from the effects of radiation exposure.

March 24, 1992

At the Sosnovy Bor station near St. Petersburg, Russia, radioactive iodine escaped into the atmosphere. A loss of pressure in a reactor channel was the source of the accident.

November 1992

In France's most serious nuclear accident, three workers were contaminated after entering a nuclear particle accelerator in Forbach without protective clothing. Executives were jailed in 1993 for failing to take proper safety measures.

November 1995

Japan's Monju prototype fast-breeder nuclear reactor leaked two to three tons of sodium from the reactor's secondary cooling system.

March 1997

The state-run Power Reactor and Nuclear Fuel Development Corporation reprocessing plant at Tokaimura, Japan, contaminated at least 35 workers with minor radiation after a fire and explosion occurred.

September 30, 1999

Another accident at the uranium processing plant at Tokaimura, Japan, plant exposed fifty-five workers to radiation. More than 300,000 people living near the plant were ordered to stay indoors. Workers had been mixing uranium with nitric acid to make nuclear fuel, but had used too much uranium and set off the accidental uncontrolled reaction.

Office of Nuclear Energy

The Office of Nuclear Energy (NE) is working with its partners to demonstrate the commercial-scale production of hydrogen using heat from a nuclear energy system by 2017. In addition to the emission-free electricity currently produced by nuclear reactors, some advanced nuclear reactor designs operate at very high temperatures, making them well suited for promising new thermally-driven hydrogen production processes. These advanced reactors, now being developed by the Generation IV Nuclear Energy Systems Initiative (Gen IV), could provide the low-cost heat necessary for these processes to economically produce hydrogen.
NE established the Nuclear Hydrogen Initiative to further the development of nuclear-based hydrogen production processes. The Nuclear Hydrogen Initiative will research and develop the following technologies that use nuclear reactors to produce hydrogen.
  • Thermochemical water-splitting cycles (TC): Research conducted under the Department'sNuclear Energy Research Initiative (NERI) indicates strong potential for the use of thermochemical water splitting processes to produce hydrogen. Thermochemical cycles are a series of chemical reactions that convert water to hydrogen and oxygen using chemical catalysts at high temperatures. These processes offer the potential for high efficiency hydrogen production at large-scale production rates, but the technology is relatively immature.
  • High-temperature electrolysis (HTE): HTE, or steam electrolysis as it is also called, uses electricity to produce hydrogen from steam, instead of liquid water. This method promises higher efficiencies than standard electrolysis, which is employed commercially today. The new high-temperature design involves many technical challenges, including the development of high-temperature materials and membranes.
  • Reactor/Hydrogen Production Process Interface: The interface between the nuclear reactor and the hydrogen production system involves potentially long heat transfer paths at elevated temperatures, heat exchangers that are subject to both elevated temperature and corrosive chemical environments, new safety and regulatory issues, and supporting systems for chemical processes and hydrogen and oxygen storage.

    1 comment:

    Radiation shielding said...

    Thank you very much for your informative knowledge. and thanks for your special report about accident in japan.