Fukushima workers are being doused with highly radioactive water. enenews.com
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Geiger Counter Readings in Seattle, WA on April 10, 2013
Ambient office = 93 nanosieverts per hour
Ambient outside = 67 nanosieverts per hour
Soil exposed to rain = 74 nanosieverts per hour
Banana from QFC = 67 nanosieverts per hour
Tap water = 127 nanosieverts per hour
Filtered water = 111 nanosieverts per hour
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Nuclear Reactors 63 – Nuclear Breeder Reactors 4 – Thermal Breeder Reactors
Recently, I have been focusing on nuclear breeder reactors which can generate more fissile material than they burn. Today I am going to talk about thermal breeder reactors (TBR). These reactors utilize moderated neutrons which have been slowed down by some moderator.
A liquid fluoride thorium reactor design was first researched at the Oak Ridge Laboratory Molten-Salt Reactor Experiment in the 1960s. This design has advantages such as being able to drain its fuel into a catch basin under the reactor where it will cool without danger. It is also is simpler to fuel because precisely machined fuel rods are not necessary. And, there is the possibility of removing some of the fuel mix during operation to be reprocessed. There is interest in some nuclear countries in pursuing this technology.
A pressurized light water thermal breeder reactor was put into operation at the Shippingport Atomic Power Station in Beaver County Pennsylvania. The reactor was testing a design for naval vessels and commercial power generation. It was fueled by pellets that were a mixture of thorium oxide and U-233 oxide. There were three different sections in the reactor that contained thorium. The “seed” area in the core, the “blanket” area surrounding the core and the reflector area around the blanket. U-233 is used as the initial fuel to provide neutrons to the thorium. In the seed area in the core, the percent of U-233 is about five or six percent. In the blanket area, there is about one and one half percent U-233. As the U-233 decays, it emits neutrons some of which are absorbed by the thorium. Then the thorium atom emits electrons and is transmuted into U-233. When the core was taken out after five years of operation, it was found that there was about one and one half percent more fissile material that was originally put into the reactor thereby proving the design for breeding fissile materials.
India has great interest in thermal breeder reactors fuel with thorium. India has chronic power outages and desperately needs more electricity. India has been a nuclear nation for some time and has created over one hundred nuclear warheads. However, India does not have any uranium resources. It does have huge reserves of thorium. If they could deploy thermal breeder reactors that were fueled with thorium and a little U-233, they could get power from the reactors and also breed more U-233 that could be used to fuel additional reactors. Thorium thermal breeder reactors cannot be used to make weapons grade nuclear materials although that is a moot point because India already has nuclear weapons.
Core of the Molten Salt Reactor Experiment:
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Radiation News Round Up for April 9, 2013
In a stunning reversal of disclosure, Japan asks for immediate international assistance to stop radiation leaks into the Pacific. huffingtonpost.com
A worker at the Fukushima nuclear plant accidentally pushed a button turning off power to the four badly damaged reactors yesterday. dailymail.co.uk
Offline inspection finds a potential coolant leak at Palo Verde reactor. nuclearstreet.com
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Geiger Counter Readings in Seattle, WA on April 9, 2013
Ambient office = 84 nanosieverts per hour
Ambient outside = 108 nanosieverts per hour
Soil exposed to rain = 114 nanosieverts per hour
Crimini Mushrooms from Top Foods = 70 nanosieverts per hour
Tap water = 103 nanosieverts per hour
Filtered water = 79 nanosieverts per hour
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Nuclear Reactors 62 – Nuclear Breeder Reactors 3 – Fast Breeder Reactors
Recently, I have been focusing on nuclear breeder reactors which can generate more fissile material than they burn. These reactors can create weapons grade plutonium, generate electrical power and burn nuclear waste. Today I am going to talk about fast breeder reactors (FBR). These reactors utilize unmoderated neutrons which have not been slowed down by some moderator.
Ordinary water is generally not used as a coolant because water slows down neutrons. There have been some new designs which would use supercritical water held at the exact point between liquid water and steam as a coolant for a breeder reactor. An early FBR used mercury for a coolant and plutonium for fuel. It was found that mercury had some serious disadvantages as a coolant. Lead has been used as a coolant in reactors for naval vessels. Currently, big FBRs use molten sodium as a coolant. Molten salts may be used in future FBRs with the light metal fluorides being replaced with heavy metal chlorides. There are also designs that use gases such as helium for a coolant that have garnered some interest.
It requires highly enriched plutonium or uranium to fuel a FBR. When an atom of natural U-238 absorbs a neutron, it can emit two electrons and become an atom of Pu-239 which highly fissile. There are moderators in a conventional nuclear reactor for the express purpose of slowing down neutrons to make it more likely that the neutron will trigger the desired fission. Most fast neutron will pass right through atoms of plutonium and uranium without causing fission. FBRs cannot be fueled with natural uranium. Spent fuel from an FBR can be reprocessed and used again to burn up more of the fissile material. Most existing FBRs are fueled with a MOX or mixed oxide fuel with both uranium and plutonium. The Russians are building a lot of FBRs these days and using highly enriched U-235 for fuel. Regular nuclear reactors are fueled with uranium enriched to have about five percent of U-235. FBRs usually have the uranium enriched to more than twenty percent U-235. U-235 decays, creating fission products and emitting two neutron for every decay. In an FBR, these fast neutrons are absorbed by U-238 atoms which emit two electrons and become Pu-239 atoms. These Pu-239 atoms decay, generating fission products and more fast neutrons than U-235. The material that is intended to produce fissile isotopes is either mixed into the fuel or placed in a blanket around the core of the reactors. FBRs generally use neutron absorbing control rods to keep the reactor from going supercritical and melting down.
In 2008, the International Atomic Energy Agency published a report that said that there had been a falling of interest in most nations with atomic technology in the development of FBRs. Only Russia, Japan and France were still proceeding with research on FBRs and that research has been impeded by a lack of qualified personnel. The U.S. has a FBR that is having serious problems. The Japanese cannot seem to get their FBR to work. Only the Russians have embarked on a program to build FBRs for commercial purposes such as breeding nuclear fuel and burning nuclear waste.
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Radiation News Round Up for April 8, 2013
Operators began powering up Exelon’s Oyster Creek nuclear plant in New Jersey Sunday only to shut it down because of a problem with the condenser. nuclearstreet.com
Unless Congress passes a federal budget, the Nuclear Regulatory Commission will run short on cash at some point this week. nuclearstreet.com
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Geiger Counter Readings in Seattle, WA on April 8, 2013
Ambient office = 92 nanosieverts per hour
Ambient outside = 93 nanosieverts per hour
Soil exposed to rain = 79 nanosieverts per hour
Frozen salmon from Costco= 90 nanosieverts per hour
Tap water = 125 nanosieverts per hour
Filtered water = 105 nanosieverts per hour
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Nuclear Reactors 61 – Nuclear Breeder Reactors 2
In my last post, I talked about breeder reactors in general terms. There is renewed interest in this category of reactors which can burn many kinds of fuel and can generate more fissile materials than they consume. Today I will delve a little deeper into the subcategories of breeder reactors.
There are two broad types of breeder reactors. One is designed to burn uranium fuels and transuranics, the radioactive materials heavier than uranium that are created as uranium fuel is burned. The other type is designed to burn thorium and not transuranics. There are many possible designs for breeder reactors. Light water has been used in the past as a coolant but there are designs that would use molten-salt, liquid-metal or other possible coolants.
When fissile materials are created in a operating reactor, there is also a creation of materials that absorb neutrons. This means that in order to take advantage of the breeding of new fissile materials, the spent fuel from the breeder reactor must be reprocessed. The current widely used reprocessing system is called Plutonium Uranium Extraction or PUREX. PUREX is a chemical method for separating pure plutonium or pure uranium for other materials in an ore, spent fuel or nuclear waste. Any country that has an operating PUREX facility can produce pure plutonium for nuclear weapons.
Fast breeder reactors (FBR) are called that because they rely on unmoderated neutrons that are not slowed down in the reactor. This type of breeder reactor is primarily intended to breed fissile plutonium and other transuranics as it burns uranium-235. It can also breed fissile uranium-233 from thorium. Thermal breeder reactors (TBR) on the other hand utilize moderated neutrons to breed fissile uranium-233 from thorium. Unlike the FBR, the TBR reactors cannot breed transuranics from uranium fuel. This is would be important consideration with respect to the proliferation of nuclear weapons. In addition to this benefit of TBRs, they also do not product transuranics which are the hottest, most long lasting and most dangerous components of spent nuclear fuel.
Breeder reactors are being considered for such purposes as the generation of fissile materials for extraction and uses other than fuel, long term stable operation for energy generation or burning of nuclear wastes. The economics of nuclear power is making it less desirable. The existence of huge amounts of nuclear waste and the need for a disposal system makes breeders very desirable. The production of weapons grade plutonium is a threat to the world. So, in sum, while breeder reactors are very desirable for some needs, they can be very dangerous for other reasons. In future posts, I will detail some breeder reactor designs and some problems with currently operating breeder reactors.
