And in the Russian and British uranium-graphite reactors "have problems with graphite." After three decades of service due to the aggressiveness of the neutron flux on the graphite blocks cracks began to appear. On the stages of development and design of PEM on the occurrence of this problem no one anticipated.
In the UK, the home of the first commercial nuclear power plants are in operation uranium-graphite reactors with a current installed capacity of 16.5 GW. British nuclear power plants private - owned campaign Électricité de France Energy (EDF), which owns and operates seven nuclear power plants, each with two gas-cooled uranium-graphite reactors AGR. Construction of nuclear power stations was a priority and strategic importance for the country. Not surprisingly, the Queen of England, which enjoys absolute respect from his subjects, was present at the commissioning of the first commercial nuclear power plant.
Superior gas-cooled reactor AGR (Advanced gas-cooled reactor) runs on enriched uranium oxide (2,3% U-235). As the carbon dioxide coolant is used under a high pressure. In the pre-reinforced concrete casing is sealed and the reactor core and the steam heat exchangers. It also acts as a constructive reactor. The walls of the shell have different thicknesses - from 3.8 to 6 meters. High-pressure shell made of prestressed concrete, and must be operated at a temperature not exceeding 100 0C. Under normal operating conditions, this is achieved by a system of walls arranged in a casing tube in which cooling water circulates.
At one of the reactors at Hartlepool in the graphite rods (assemblies) were first discovered cracks. Cracks today confirmed and six other reactors AGR: NPP Heysham, Hinkley Point, in Hunterston. Studies show that the cracks in the graphite rods in nuclear power plants Hinkley Point, Hunterston B, Heysham 1, Hartlepool can change the geometry and location of the holes in the graphite rods reactor core.
Resizing graphite rods is due to shrinkage of graphite. When shrinkage of the graphite rods may jam the fuel assemblies, which may lead to termination of fuel assemblies around the circulation of cooling gas, and finally konchno - overheating of the fuel rods, they melt and release the radiation directly to the concrete body surrounding the reactor core. Changing the geometry of the channels of the core, which moves the control rods of the reactor may cause them to jam in the channels, which would create an emergency situation at power plant.
When the reactor is in operation, the interaction of neutrons with the graphite, and this leads to aging, i.e. a change in its physical and mechanical characteristics. Graphite also aging also contributes to thermal cycling and chemical interaction of graphite with carbon dioxide.
When exposed to neutrons are changing properties of graphite rods:· Change in modulus of elasticity - the quantity characterizing the elastic properties of graphite rods.· Change in coefficient of thermal expansion - the size of graphite rods vary with temperature.· Change in thermal conductivity - the ability of graphite rods to the conduction of heat flows through them.· Change in electrical resistance of graphite rods (blocks).· As a result of prolonged exposure to neutron irradiation creep phenomenon occurs graphite rod.
Company Électricité de France Energy issued a statement that the cracking of graphite rods is a consequence of neutron bombardment of graphite, and that it is working to solve the problem of monitoring the state of the graphite in the reactor core. EDF also said that the state of graphite reactors will be monitored every three years. Therefore lifetime Rector plan to limit 35 years. Key decisions regarding further operation of the reactor, taken as a rule, after the periodic shutdown of the reactor and after the assessment of the national body of graphite nuclear safety.
In October 1957 in the UK at the factory on running weapons-grade plutonium from understudied graphite physical problems, namely, the problem of extracting iron accumulated neutron irradiation energy - Wigner energy, there was a fire. Lighted uranium-graphite reactor, and then the use of water to extinguish, there was a major release of radioactive material. Disaster surpassed Britain escaped the catastrophe - the reactor exploded and collapsed, unable to extinguish the fire. This accident was the largest in the history of the country and adequate level 5 danger. And its influence on the environment, it was comparable to the Chernobyl disaster for the USSR.
Électricité de France Energy informs that of the fourteen existing second generation reactors rectors AGR, located in the UK at the plant Dungeness, Hartlepool, Heysham, Hinkley Point, Hunterston, Sizewell and Torness, the last scheduled to close by the end of 2023.
The UK government in October 2013 has allowed the company to build on the EDF Hinkley Point nuclear power plant to replace the uranium-graphite blocks two modern pressurized water reactor with a capacity of 1,600 megawatts - EPR-1600 the French company AREVA NP.
UK National Authority security ONR constantly monitors the graphite NPPs by university research centers. In 2004, it was formed by an independent advisory committee composed of scientists and other recognized experts in the field of nuclear technology using graphite.
In Russia, the home of the first nuclear power plants are in operation uranium-graphite reactors with a current installed capacity of 11 GW. All RBMK (high-power channel reactor - graphite-water boiling type reactor) operating in the European part of Russia on the three nuclear power plants - Leningrad, Kursk and Smolensk. Frankly. that grafitovodnye reactors (LWGR - light water graphite reactor) - it was forced and unsuccessful hybrid, combining a variety of design solutions for the peaceful use of nuclear energy. Existing power plants of this type today were only in Russian.
Reactors RMBK-1000 is not provided as AGR reactors concrete hard protective shell, which in the case of the accident could keep the emission of radiation. Due to lack of containment zone of radioactive contamination at the Chernobyl nuclear power plant has spread to hundreds of kilometers.
State Corporation Rosatom said that it will take action to extend to 45 years lifetime Russian RBMK-1000 reactors built during the Soviet period. Then the designers and engineers believed that the operation of these reactors should be terminated after 30 years. However, the first unit of SELA to date has worked for 40 years.
Leningrad NPP was the flagship of the Soviet nuclear power industry. She was the epitome of a real political will "electrification of the whole country", which proclaimed their time s founders of the USSR. Due to the presence of cracks in the graphite stack core first unit SELA was stopped. It was found to change the geometry of the graphite stack.
"Rosenergoatom" set the task to develop a technology fix graphite assemblies. In the reactor core, large-scale studies have been conducted state graphite stack and technological channels, namely;
· Integrity graphite blocks and determining the strength and physical properties of graphite· Values telescopic coupling paths· The quantities of gas gap "technology channel - graphite block"· The values of curvature technological channels and channel control and protection system (CPS)· Determination of strength elements of the metal reactor· Determination of strength of zirconium tubes technological channels.
These studies were important for assessing the condition of the core of the first block of SELA and to develop engineering solutions that could be applied in similar reactors because be expected of the same problems and ten other RBMK, three of which are mounted on the SELA, four - and three of the Kursk - Smolensk stations.
In 2013 was made a costly program of deep modernization of the reactor core of the first block of SELA. According to the program to restore the resource characteristics of the unit, replaced dismantled and restored more than 300 fuel channels in the core. The studies and reports submitted by national supervisory authorities allowed - Rostehnadzoru - decide about the fate of the first SELA.
Rostehnadzor eventually issued a new license for the further operation of the first unit of SELA. However, the intention of Rosatom extend for 15 years in addition to the design life, the work of the old block SELA not equipped with protective sheath and having a single channel control and protection, frankly, is not called the "enthusiastic" the residents of St. Petersburg and Leningrad region.
Impossible today to decommission the "problem" of RBMK-1000 reactors in the European part of Russia, as the construction of new safer water-cooled pressurized reactors VVER-1200 NPP-2 and -2 NVNPP delayed, and at the sites of the Kursk and Smolensk NPP can say, has not yet started. Leningrad NPP-1 was planned to finish construction in 2014 - 2015, but judging by the pace of construction, real term input of the first block of SELA -2 commercial operation, apparently, will be in 2018 - the year of the final decommissioning of the first block of NPP-1.
What is happening in the world with uranium-graphite reactors-
In Britain decommissioned 11 'NPPs with gas cooled uranium-graphite reactors of the first generation Magnox. Today there is only one block from the Magnox reactor at the plant Wylfa, which is owned by Magnox Ltd. Reactor number 2 at the Wylfa nuclear power plant stopped working in 2012. Reactor number 1 of this station will be shut down in 2014. In addition, the reactors were shut down type Magnox, which were exported to the NPP T
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