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Meltdown-Proof Nuclear Reactors (molten salt reactors) Get a Safety Check in Europe
http://www.technologyreview.com/news/540991/meltdown-proof-nuclear-reactors-get-a-safety-check-in-europe/[font face=Serif][font size=5]Meltdown-Proof Nuclear Reactors Get a Safety Check in Europe[/font]
[font size=4]Researchers say they could build a prototype of a molten salt reactor, a safer, cleaner nuclear power option, in 10 years.[/font]
By Richard Martin on September 4, 2015
[font size=3]For years nuclear scientists have talked about a revival of molten salt reactors, which are powered by a liquid fuel rather than solid fuel rods, that will help spark the long-awaited “nuclear renaissance.” Recent developments indicate that this alternative nuclear power technology is finally making gradual progress toward commercialization.
…
First built and tested in the 1960s, at Oak Ridge National Laboratory, molten salt reactors would be the first genuinely new technology for nuclear power generation to reach the market in the last three decades. Producing zero carbon, they use a radioactive solution that blends nuclear fuel with a liquid salt. They can run on uranium, but are also ideally suited for thorium, an alternative nuclear fuel that is cleaner, safer, and more abundant than uranium.
Molten salt reactors also offer inherent safety advantages: because the fuel is liquid, it expands when heated, thus slowing the rate of nuclear reactions and making the reactor self-governing. And they’re built like bathtubs, with a drain in the bottom that’s blocked by a “freeze plug.” If anything goes wrong, the freeze plug melts and the reactor core drains into a shielded underground container. They can operate as producers of thermal power or as “burner” reactors that consume nuclear waste from conventional reactors.
…
The project represents “the first step towards large scale validation and demonstration of the technology,” says Jan-Leen Kloosterman, a professor of nuclear physics at TU Delft and the lead researcher on Samofar. “Hopefully the results will also lead to much more commitment from the large nuclear industry.”
…[/font][/font]
[font size=4]Researchers say they could build a prototype of a molten salt reactor, a safer, cleaner nuclear power option, in 10 years.[/font]
By Richard Martin on September 4, 2015
[font size=3]For years nuclear scientists have talked about a revival of molten salt reactors, which are powered by a liquid fuel rather than solid fuel rods, that will help spark the long-awaited “nuclear renaissance.” Recent developments indicate that this alternative nuclear power technology is finally making gradual progress toward commercialization.
…
First built and tested in the 1960s, at Oak Ridge National Laboratory, molten salt reactors would be the first genuinely new technology for nuclear power generation to reach the market in the last three decades. Producing zero carbon, they use a radioactive solution that blends nuclear fuel with a liquid salt. They can run on uranium, but are also ideally suited for thorium, an alternative nuclear fuel that is cleaner, safer, and more abundant than uranium.
Molten salt reactors also offer inherent safety advantages: because the fuel is liquid, it expands when heated, thus slowing the rate of nuclear reactions and making the reactor self-governing. And they’re built like bathtubs, with a drain in the bottom that’s blocked by a “freeze plug.” If anything goes wrong, the freeze plug melts and the reactor core drains into a shielded underground container. They can operate as producers of thermal power or as “burner” reactors that consume nuclear waste from conventional reactors.
…
The project represents “the first step towards large scale validation and demonstration of the technology,” says Jan-Leen Kloosterman, a professor of nuclear physics at TU Delft and the lead researcher on Samofar. “Hopefully the results will also lead to much more commitment from the large nuclear industry.”
…[/font][/font]
What would a “meltdown” be in a reactor whose fuel is “molten” by design?
11 replies
= new reply since forum marked as read
= new reply since forum marked as read
Or are we talking about "cold fission"? 
It’s right there in the name… “Meltdown”
http://www.nrc.gov/about-nrc/emerg-preparedness/faq.html#5b
[font face=Serif]…
[font size=4]What is a "meltdown"? Can a meltdown be prevented?[/font]
[font size=3]A nuclear reactor is fueled with many thousands of ceramic uranium pellets located within 12-foot long metal fuel rods. As the reactor performs its intended function (uranium atoms fission, releasing heat energy, generating steam for electrical power production) many of the uranium atoms are converted into new atoms which are highly energetic and highly radioactive. Under normal conditions these highly radioactive "fission products" remain safely within the confines of the metal fuel rod. During a severe malfunction, it is possible that the energy released by the fission products could be sufficient enough to damage the metal fuel rod, and even melt the ceramic fuel pellet itself.
Fuel pellet melting is a significant concern because it indicates that multiple protection systems and radiation barriers have failed and that other systems and barriers are about to be challenged. Accidents of this magnitude are classified at the highest severity level (general emergency).
A meltdown is prevented by ensuring that sufficient cooling water is always available to remove fission product heat from the reactor. Multiple water systems, pumps, and flow paths are maintained to ensure that water will always be available for this purpose. But in case all these precautions fail, the emergency response organization must always be ready.
…[/font][/font]
[font size=4]What is a "meltdown"? Can a meltdown be prevented?[/font]
[font size=3]A nuclear reactor is fueled with many thousands of ceramic uranium pellets located within 12-foot long metal fuel rods. As the reactor performs its intended function (uranium atoms fission, releasing heat energy, generating steam for electrical power production) many of the uranium atoms are converted into new atoms which are highly energetic and highly radioactive. Under normal conditions these highly radioactive "fission products" remain safely within the confines of the metal fuel rod. During a severe malfunction, it is possible that the energy released by the fission products could be sufficient enough to damage the metal fuel rod, and even melt the ceramic fuel pellet itself.
Fuel pellet melting is a significant concern because it indicates that multiple protection systems and radiation barriers have failed and that other systems and barriers are about to be challenged. Accidents of this magnitude are classified at the highest severity level (general emergency).
A meltdown is prevented by ensuring that sufficient cooling water is always available to remove fission product heat from the reactor. Multiple water systems, pumps, and flow paths are maintained to ensure that water will always be available for this purpose. But in case all these precautions fail, the emergency response organization must always be ready.
…[/font][/font]
http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html
[font face=Serif][font size=5]Backgrounder on the Three Mile Island Accident[/font]
[font size=3]For three days beginning on March 28, 1979, a series of mechanical, electrical, and human failures led to a severe meltdown of the reactor core at the Three Mile Island Nuclear Power Plant.[/font]
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[font size=3]The Three Mile Island Unit 2 (TMI-2) reactor, near Middletown, Pa., partially melted down on March 28, 1979. This was the most serious accident in U.S. commercial nuclear power plant operating history, although its small radioactive releases had no detectable health effects on plant workers or the public. Its aftermath brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. It also caused the NRC to tighten and heighten its regulatory oversight. All of these changes significantly enhanced U.S. reactor safety.
A combination of equipment malfunctions, design-related problems and worker errors led to TMI-2's partial meltdown and very small off-site releases of radioactivity.
…
Without the proper water flow, the nuclear fuel overheated to the point at which the zirconium cladding (the long metal tubes that hold the nuclear fuel pellets) ruptured and the fuel pellets began to melt. It was later found that about half of the core melted during the early stages of the accident. Although TMI-2 suffered a severe core meltdown, the most dangerous kind of nuclear power accident, consequences outside the plant were minimal. Unlike the Chernobyl and Fukushima accidents, TMI-2's containment building remained intact and held almost all of the accident's radioactive material.
Federal and state authorities were initially concerned about the small releases of radioactive gases that were measured off-site by the late morning of March 28 and even more concerned about the potential threat that the reactor posed to the surrounding population. They did not know that the core had melted, but they immediately took steps to try to gain control of the reactor and ensure adequate cooling to the core. The NRC's regional office in King of Prussia, Pa., was notified at 7:45 a.m. on March 28. By 8 a.m., NRC Headquarters in Washington, D.C., was alerted and the NRC Operations Center in Bethesda, Md., was activated. The regional office promptly dispatched the first team of inspectors to the site and other agencies, such as the Department of Energy and the Environmental Protection Agency, also mobilized their response teams. Helicopters hired by TMI's owner, General Public Utilities Nuclear, and the Department of Energy were sampling radioactivity in the atmosphere above the plant by midday. A team from the Brookhaven National Laboratory was also sent to assist in radiation monitoring. At 9:15 a.m., the White House was notified and at 11 a.m., all non-essential personnel were ordered off the plant's premises.
…
Within a short time, chemical reactions in the melting fuel created a large hydrogen bubble in the dome of the pressure vessel, the container that holds the reactor core. NRC officials worried the hydrogen bubble might burn or even explode and rupture the pressure vessel. In that event, the core would fall into the containment building and perhaps cause a breach of containment. The hydrogen bubble was a source of intense scrutiny and great anxiety, both among government authorities and the population, throughout the day on Saturday, March 31. The crisis ended when experts determined on Sunday, April 1, that the bubble could not burn or explode because of the absence of oxygen in the pressure vessel. Further, by that time, the utility had succeeded in greatly reducing the size of the bubble.
…[/font][/font]
[font size=3]For three days beginning on March 28, 1979, a series of mechanical, electrical, and human failures led to a severe meltdown of the reactor core at the Three Mile Island Nuclear Power Plant.[/font]
…
[font size=3]The Three Mile Island Unit 2 (TMI-2) reactor, near Middletown, Pa., partially melted down on March 28, 1979. This was the most serious accident in U.S. commercial nuclear power plant operating history, although its small radioactive releases had no detectable health effects on plant workers or the public. Its aftermath brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. It also caused the NRC to tighten and heighten its regulatory oversight. All of these changes significantly enhanced U.S. reactor safety.
A combination of equipment malfunctions, design-related problems and worker errors led to TMI-2's partial meltdown and very small off-site releases of radioactivity.
…
Without the proper water flow, the nuclear fuel overheated to the point at which the zirconium cladding (the long metal tubes that hold the nuclear fuel pellets) ruptured and the fuel pellets began to melt. It was later found that about half of the core melted during the early stages of the accident. Although TMI-2 suffered a severe core meltdown, the most dangerous kind of nuclear power accident, consequences outside the plant were minimal. Unlike the Chernobyl and Fukushima accidents, TMI-2's containment building remained intact and held almost all of the accident's radioactive material.
Federal and state authorities were initially concerned about the small releases of radioactive gases that were measured off-site by the late morning of March 28 and even more concerned about the potential threat that the reactor posed to the surrounding population. They did not know that the core had melted, but they immediately took steps to try to gain control of the reactor and ensure adequate cooling to the core. The NRC's regional office in King of Prussia, Pa., was notified at 7:45 a.m. on March 28. By 8 a.m., NRC Headquarters in Washington, D.C., was alerted and the NRC Operations Center in Bethesda, Md., was activated. The regional office promptly dispatched the first team of inspectors to the site and other agencies, such as the Department of Energy and the Environmental Protection Agency, also mobilized their response teams. Helicopters hired by TMI's owner, General Public Utilities Nuclear, and the Department of Energy were sampling radioactivity in the atmosphere above the plant by midday. A team from the Brookhaven National Laboratory was also sent to assist in radiation monitoring. At 9:15 a.m., the White House was notified and at 11 a.m., all non-essential personnel were ordered off the plant's premises.
…
Within a short time, chemical reactions in the melting fuel created a large hydrogen bubble in the dome of the pressure vessel, the container that holds the reactor core. NRC officials worried the hydrogen bubble might burn or even explode and rupture the pressure vessel. In that event, the core would fall into the containment building and perhaps cause a breach of containment. The hydrogen bubble was a source of intense scrutiny and great anxiety, both among government authorities and the population, throughout the day on Saturday, March 31. The crisis ended when experts determined on Sunday, April 1, that the bubble could not burn or explode because of the absence of oxygen in the pressure vessel. Further, by that time, the utility had succeeded in greatly reducing the size of the bubble.
…[/font][/font]