China General Nuclear (CGN) announced today that it has signed memoranda of understanding with Czech engineering companies to cooperate in nuclear energy. world-nuclear-news.org
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Geiger Readings for Mar 31, 2016
Ambient office = 52 nanosieverts per hourAmbient outside = 107 nanosieverts per hourSoil exposed to rain water = 121 nanosieverts per hourMango from Central Market = 66 nanosieverts per hourTap water = 78 nanosieverts per hourFiltered water = 58 nanosieverts per hour -
Nuclear Weapons 195 – Terrorist Scenarios Involving Nuclear Materials
I have been blogging lately about concerns that terrorists may have been targeting the nuclear power plants in Belgium. There has been speculation that they were planning an attack but that they changed targets because the authorities were rounding up members of their network in the aftermath of the Paris attack last November. People who worked at nuclear power plants have left and gone to Syria to join ISIS. There are terrorist surveillance tapes of an official at a nuclear isotope production facility in Belgium. A security guard has been killed and his key card was taken. There have been reported attempts by ISIS and Al Qaeda to buy nuclear materials in Moldavia which has become a center for the smuggling of nuclear materials.
The first concern is that terrorist could infiltrate or attack a nuclear power plant with the intention of causing major damage that would result in the release of radioactive materials into the environment. This would require specialized knowledge of the security and the technology of a nuclear power plant. The nuclear official under surveillance, the murdered security guard or the Belgian nuclear workers that joined ISIS could have potentially supplied the needed expertise for an attack on a Belgian power plant. The Fukushima nuclear disaster is an example of the havoc that can be wrought by a major accident at a nuclear power plant. There are over four hundred operational nuclear power plants around the world that could make tempting targets for terrorists.
Another big concern is the possibility of terrorists getting their hands on radioactive materials that could be combined with conventional explosives to create what is called a “dirty” bomb. The dispersal of radioactive materials over a wide area by a dirty bomb would poison people living there and be very hard to clean up. The disruption and cost would be great. The Belgian government sent armed troops to the four Belgian nuclear power plants before the recent attack on the airport and subway in Brussels. However, there are many other places where terrorists could obtain nuclear materials for a dirty bomb. Research reactors, hospitals, construction sites, and other places make use of radioactive materials for a variety of purposes. None of these enjoy the same level of security as a nuclear power plant. It is estimated that there are tens of thousands of radiological sources located in more than 100 countries around the world that could provide terrorists with materials to make a dirty bomb. In 2013 and 2014 alone, there were three hundred and twenty five reported incidents of radioactive materials being lost or stolen or improperly secured in some way.
The possibility of terrorists getting their hands on an actual nuclear bomb is the most frightening of terrorist nuclear scenarios. First of all, it is very difficult to enrich uranium to weapons grade. Huge production facilities are required. So that makes it unlikely that terrorists could actually produce the highly enriched uranium (HEU) needed for a bomb. So the next question is how difficult it would it be for terrorist to steal or purchase the HEU they would need? There are large quantities of HEU in stockpiles around the world with varying degrees of security. The International Atomic Energy Agency has reported that between 1993 and 2014 there were thirteen reported case of the “illegal possession, sale, or movement” of HEU. All of these incidents involved less than two pounds of HEU which is far less than the amount needed to make a bomb. As I mentioned above, there is a traffic in nuclear materials in such places as Moldavia and it is unknown whether or not there have been successful transactions involving substantial amounts of HEU. Even with the possession of enough HEU, the construction of a working nuclear bomb is not simple and requires expertise, equipment and facilities. While this possibility is remote, it is not impossible and there are terrorist organizations who wish to accomplish it.
Simple nuclear bomb design:
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Geiger Readings for Mar 30, 2016
Ambient office = 39 nanosieverts per hourAmbient outside = 46 nanosieverts per hourSoil exposed to rain water = 52 nanosieverts per hourAvocado from Central Market = 92 nanosieverts per hourTap water = 105 nanosieverts per hourFiltered water = 94 nanosieverts per hour -
Nuclear Reactors 349 – MIT Researchers Working On Improving Zirconium Cladding For Nuclear Fuel Rods
Recently, I blogged about new developments for materials used in the construction of nuclear reactors. Stainless steel used in reactor containment vessels becomes brittle from neutron bombardment over time which makes it weak. A new type of alloy called “high-entropy” which contains equal parts of five or more metals is being studied as a possible replacement for the stainless steel used in containment vessels because it is more resistant to embrittlement. Other researchers are working on replacing materials used in other components of reactors.
Fuel rods used in nuclear reactors are long thin cylinders stuffed with enriched uranium pellets. The rods are coated with a zirconium alloy such as Zircaloy-4. This is referred to as cladding. In the conditions inside a nuclear reactor, a thin layer of zirconium oxide forms on the outside of the zirconium cladding on the fuel rods. This thin oxide layer provides some protection for the cladding against the high temperatures and moisture inside the reactor.
As water molecules in the coolant are broken down by the conditions in the reactor, the hydrogen released can enter nearby metals such as the zirconium cladding, interacting with them chemically. This reaction can reduce the ductility of the metal which is a measure of the ability of the metal to withstand mechanical stress before it breaks. This can result in cracks forming in the metal and cause a breakdown of the metal.
Researchers at MIT hope to be able to influence the migration of hydrogen into the fuel rod cladding by modifying the oxide layer. The first step is gaining a better understanding of exactly how hydrogen dissolves in the oxide layer. Once this understanding has been gained, it may be possible to predict how changes to the oxide layer might be able to reduce the entry of hydrogen in the first place or perhaps to expel hydrogen as a gas after the it has entered the cladding.
Other materials can be added to the zirconium oxide to change its properties in a process called doping. Some dopants such as chromium can reduce the ability of the hydrogen to dissolve in the oxide layer. Other dopants including niobium can release electrons which combine with the hydrogen to form hydrogen gas that is then expelled from the oxide layer. A great deal of research is still needed to find the correct proportions of dopants that need to be added to the oxide layer and to develop industrial methods of adding the dopants. This will probably consist of adding the dopants to the zirconium used for cladding. Then, when the surface of the cladding oxidizes, the dopants will be incorporated into the oxide layer.
Oxide layers form on a lot of different metals when subjected to high temperatures and moisture. The development of techniques for improving fuel rod cladding should be applicable to a wide range of other metallic components with many different uses. Possible applications include improving alloys used in fossil fuel plants, pipelines, fuel cells, bridges.
Photomicrograph of an oxide layer on zircaloy-4 cladding:
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Radiation News Roundup Mar 29, 2016
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Geiger Readings for Mar 29, 2016
Ambient office = 88 nanosieverts per hourAmbient outside = 143 nanosieverts per hourSoil exposed to rain water = 143 nanosieverts per hourOrange bell pepper from Central Market = 121 nanosieverts per hourTap water = 72 nanosieverts per hourFiltered water = 59 nanosieverts per hour -
Nuclear Reactors 348 – The Necessity for Shutting Down and Decommissioning Old Nuclear Power Reactors
One big concern I have with respect to nuclear power is the question of lifespan. Usually, nuclear reactors are licensed for a forty year lifespan. With many existing reactors having been built in the 1970s, their original projected life spans have ended or are ending soon. Nuclear power plants are such a huge investment and generate so much electricity that there is a serious reluctance on the part of energy consumers and power plant owners to retire them when the original license period runs out. These days there is also the problem of climate change and the need for low carbon energy sources such as nuclear power. This results in a push to relicense power reactors for an additional twenty years which has been done frequently. Aside from questions of commercial viability which may result in a request for subsidies from governments, the wisdom of widespread relicensing has been challenged.
Nuclear reactor pressure vessels deteriorate over a forty year lifespan as constant neutron bombardment dislodges atoms for the crystalline matrix of the steel alloy and tiny cracks form which weakens the vessel. Critics of relicensing say that this fact overshadows all other considerations and all old reactors should be shut down and decommissioned after forty years of operation.
Following the Fukushima nuclear disaster in March of 2011, there was a worldwide movement to learn important lessons from the disaster and to apply those lessons to making all existing nuclear power reactors more safe to operate. Many new regulations were passed by various governments and nuclear power reactors were carefully inspected to see what improvements would be necessary to meet the new requirements. In some cases, such as the Ikata nuclear power station in Japan, it was decided that the cost of the required changes to the reactor would be prohibitive and that it made more sense to shut down the reactor permanently.
Another major concern about keeping old power reactors operating for extended life spans has to do with knowledge and expertise. Although there are major designs that are shared among groups of nuclear power reactors, every power reactor is customized to some degree. The longer a particular nuclear power plant has been in operation, the more difficult it is to find engineers who are familiar with the specific details of design and operation of that particular plant. In addition, the older a power plant and the design of its reactors, the more difficult and expensive it is to upgrade that plant to modern standards.
One of the difficulties with decommissioning old nuclear power plants has to do with the cost. In addition, there is the problem of disposing of the spent fuel and current fuel at the plant as well as all of the contaminated materials and equipment. Shutting down and decommissioning nuclear power plants will have a serious impact on electricity supply and regional economics in the area around the plant but in view of the safety problems associated with old nuclear power reactors, decommissioning is a critical necessity and it must be dealt with. Extending the lifespan of an old reactor increases the possibility of serious accidents and just postpones the economic reckoning. With economic difficulties mounting in many parts of the world, if decommissioning is delayed, there may not be sufficient funds to accomplish it and the reactors may be shut down and fenced off. This can result in serious problems about safety and security as time passes.
