السبت، 30 يوليو 2011

مشاهدة فيلم صرخة نملة dvd اون لاين وجزء واحد وسريع التحميل

مشاهدة فيلم  صرخة نملة dvd اون لاين وجزء واحد وسريع التحميل

In January 2006 the President announced that the Atomic Energy Commission (CEA)* was to embark upon designing a prototype Generation IV reactor to be operating in 2020, bringing forward the timeline for this by some five years. France has been pursuing three Gen IV technologies: gas-cooled fast reactor, sodium-cooled fast reactor, and very high temperature reactor (gas-cooled). While Areva has been working on the last two types, the main interest in the very high temperature reactors has been in the USA, as well as South Africa and China. CEA interest in the fast reactors is on the basis that they will produce less waste and will better exploit uranium resources, including the 220,000 tonnes of depleted uranium and some reprocessed uranium stockpiled in France.
*  Now the Commission of Atomic and Alternative Energy 
If the CEA embarks on the sodium-cooled design, there is plenty of experience to draw on - Phenix and Superphenix - and they could go straight to a demonstration plant - the main innovations would be dispensing with the breeding blanket around the core and substituting gas for water as the intermediate coolant. A gas-cooled fast reactor would be entirely new and would require a small prototype as first step - the form of its fuel would need to be unique. Neither would operate at a high enough temperature for hydrogen production, but still CEA would participate in very high temperature R&D with the USA and east Asia.
In December 2006 the government's Atomic Energy Committee decided to proceed with a Generation IV sodium-cooled fast reactor prototype whose design features are to be decided by 2012 and the start up aimed for 2020. A new generation of sodium-cooled fast reactor with innovations intended to improve the competitiveness and the safety of this reactor type is the reference approach for this prototype. A gas-cooled fast reactor design is to be developed in parallel as an alternative option. The prototype will also have the mission of demonstrating advanced recycling modes intended to improve the ultimate high-level and long-lived waste to be disposed of. The objective is to have one type of competitive fast reactor technology ready for industrial deployment in France and for export after 2035-2040. The prototype, possibly built near Phenix at Marcoule, will be 250 to 800 MWe and is expected to cost about EUR 1.5 to 2 billion and come on line in 2020. The project will be led by the CEA. 

Load-following with PWR nuclear plants

Normally base-load generating plants, with high capital cost and low operating cost, are run continuously, since this is the most economic mode.  But also it is technically the simplest way, since nuclear and coal-fired plants cannot readily alter power output, compared with gas or hydro plants.  The high reliance on nuclear power in France thus poses some technical challenges, since the reactors collectively need to be used in load-following mode.  (Since electricity cannot be stored, generation output must exactly equal to consumption at all times.  Any change in demand or generation of electricity at a given point on the transmission network has an instant impact on the entire system.  This means the system must constantly adapt to satisfy the balance between supply and demand.)
RTE, a subsidiary of EdF, is responsible for operating, maintaining and developing the French electricity transmission network.  France has the biggest grid network in Europe, made up of some 100,000 km of high and extra high voltage lines, and 44 cross-border lines, including a DC link to UK.  Electricity is transmitted regionally at 400 and 225 kilovolts.  Frequency and voltage are controlled from the national control centre, but dispatching of capacity is done regionally.  Due to its central geographical position, RTE is a crucial entity in the European electricity market and a critical operator in maintaining its reliability.
All France's nuclear capacity is from PWR units.  There are two ways of varying the power output from a PWR: control rods, and boron addition to the primary cooling water.  Using normal control rods to reduce power means that there is a portion of the core where neutrons are being absorbed rather than creating fission, and if this is maintained it creates an imbalance in the fuel, with the lower part of the fuel assemblies being more reactive that the upper parts.  Adding boron to the water diminishes the reactivity uniformly, but to reverse the effect the water has to be treated to remove the boron, which is slow and costly, and it creates a radioactive waste.
So to minimise these impacts for the last 25 years EdF has used in each PWR reactor some less absorptive "grey" control rods which weigh less from a neutronic point of view than ordinary control rods and they allow sustained variation in power output.  This means that RTE can depend on flexible load following from the nuclear fleet to contribute to regulation in these three respects:

1. Primary power regulation for system stability (when frequency varies, power must be automatically adjusted by the turbine),
2. Secondary power regulation related to trading contracts,
3. Adjusting power in response to demand (decrease from 100% during the day, down to 50% or less during the night, etc.)
PWR plants are very flexible at the beginning of their cycle, with fresh fuel and high reserve reactivity.  But when the fuel cycle is around 65% through these reactors are less flexible, and they take a rapidly diminishing part in the third, load-following, aspect above.  When they are 90% through the fuel cycle, they only take part in frequency regulation, and essentially no power variation is allowed (unless necessary for safety).  So at the very end of the cycle, they are run at steady power output and do not regulate or load-follow until the next refueling outage.  RTE has continuous oversight of all French plants and determines which plants adjust output in relation to the three considerations above, and by how much.

RTE's real-time picture of the whole French system
 operating in response to load and against predicted demand shows the total of all inputs.  This includes the hydro contribution at peak times, but it is apparent that in a coordinated system the nuclear fleet is capable of a degree of load following, even though the capability of individual units to follow load may be limited.
Plants being built today, eg according to European Utilities' Requirements (EUR), have load-following capacity fully built in.
Fuel cycle - front end
France uses some 12,400 tonnes of uranium oxide concentrate (10,500 tonnes of U) per year for its electricity generation. Much of this comes from Areva in Canada (4500 tU/yr) and Niger (3200 tU/yr) together with other imports, principally from Australia, Kazakhstan and Russia, mostly under long-term contracts.
Beyond this, it is self-sufficient and has conversion, enrichment, uranium fuel fabrication and MOX fuel fabrication plants operational (together with reprocessing and a waste management program). Most fuel cycle activities are carried out by Areva NC.
Conversion: 
Uranium concentrates are converted to hexafluoride at the 14,000 t/yr Comurhex Malvesi and Pierrelatte plants in the Rhone Valley, which commenced operation in 1959.  Current production is at 13,000 t/yr UF6. At Malvesi near Moussan uranium oxide concentrate is converted to UF4 powder, and this is sent on to Pierrelatte to produce UF6. About 40% of production is on toll basis or exported.
Comurhex also converts reprocessed uranium.

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