nuclear powertechnology, burnup is a measure of the neutronirradiation of the fuel. It is normally quoted in megawatt–days per metric tonof uraniummetal or its equivalent (MWd/MTU), or gigawatt–days/MTU (GWd/MT). One GW is 1,000 MW; 1 MW–day is 24,000 kilowatt hours.
The unit GWd/MTU is the (average) thermal output, multiplied by the time of operation, and divided by the mass of fuel involved. This gives a rough measure of the number of
nuclear fissionevents that have taken place within the fuel.
The actual fuel may be uranium,
plutonium, or a mixture of these or of either or both of these with thorium. This fuel content is often referred to as the "heavy metal" to distinguish it from other metals present in the fuel, such as those used for cladding. The heavy metal is typically present as either metal or oxide, but other compounds such as carbides or other salts are possible. Generation II reactors were typically designed to achieve about 40 GWd/MTU. With newer fuel technology, and particularly the use of burnable poisons, these same reactors are now capable of achieving up to 60 GWd/MTU.Some more-advanced reactor designs are expected to achieve over 90 GWd/MT of higher-enriched fuel, and eventually over 200 GWd/MT. [cite web
title= Advanced Nuclear Power Reactors
year= 2008 |month= July |work= Information Papers |publisher=
World Nuclear Association
accessdate= 2008-08-02 ] The Deep Burn Modular Helium Reactor (DB-MHR) might reach 500 GWd/MT of
transuranic elements. [cite web
title= Small Nuclear Power Reactors
year= 2008 |month= July |work= Information Papers |publisher= World Nuclear Association
accessdate= 2008-08-02 ] Complete fission of all heavy metal in a
breeder reactor, not just fissilecontent but also any fissionableor fertile material, would yield around 1,000 GWd/MT.
In a power station, high fuel burnup is desirable for:
* Reducing downtime for refueling
* Reducing the number of fresh nuclear fuel elements required and
spent nuclear fuelelements generated while producing a given amount of energy
* Reducing the potential for diversion of
plutoniumfrom spent fuel for use in nuclear weapons
It is also desirable that burnup should be as uniform as possible both within individual fuel elements and from one element to another within a fuel charge. In reactors with
online refuelling, fuel elements can be repositioned during operation to help achieve this. In reactors without this facility, fine positioning of control rods to balance reactivity within the core, and repositioning of remaining fuel during shutdowns in which only part of the fuel charge is replaced may be used.
nuclear fuel cycles such as are currently in use in much of the world, used fuel elements are buried whole as high level nuclear waste, and the remaining uranium and plutonium content is lost. Higher burnup allows more of the fissile 235U and of the plutonium bred from the 238U to be utilised, reducing the uranium requirements of the fuel cycle.
In once-through nuclear fuel cycles, higher burnup reduces the number of elements that need to be buried. However short-term heat emission, one
deep geological repositorylimiting factor, is predominantly from medium-lived fission products, particularly 137Cs and 90Sr. As there are proportionately more of these in high-burnup fuel, the heat generated by the spent fuel is roughly constant for a given amount of energy generated.
Similarly, in fuel cycles with
nuclear reprocessing, the amount of high-level waste for a given amount of energy generated is not closely related to burnup. High-burnup fuel generates a smaller volume of fuel for reprocessing, but with a higher specific activity.
Burnup is one of the key factors determining the isotopic composition of
spent nuclear fuel, the others being its initial composition and the neutron spectrumof the reactor. Very low fuel burnup is essential for the production of weapons-grade plutoniumfor nuclear weapons, in order to produce plutonium that is predominantly 239Pu with the smallest possible proportion of 240Pu and 242Pu.
One 2003 analysis concludes that "the fuel cycle cost associated with a burnup level of 100 GWd/MTHM is higher than for a burnup of 50 GWd/MTHM. In addition, expenses will be required for the development of fuels capable of sustaining such high levels of irradiation. Under current conditions, the benefits of high burnup (lower spent fuel and plutonium discharge rates, degraded plutonium isotopics) are not rewarded. Hence there is no incentive for nuclear power plant operators to invest in high burnup fuels." [cite web|url=http://dspace.mit.edu/bitstream/handle/1721.1/17027/54495851.pdf|title=Nuclear Fuel Cycles for Mid-Century Deployment|page=81|author=Etienne Parent|publisher=MIT|year=2003]
* [http://mit.edu/canes/research/nfc/modeling.html High Burnup LWR Fuel Modeling and Optimization] at the
* [http://www.inspi.ufl.edu/icapp07/program/abstracts/7177.html Improved Nuclear Fuel Pellet Design and Process to Eliminate the RIM Effect] (abstract) discusses the effect of high burnup at fuel pellet extremities.
* [http://inrwww.fzk.de/students_work/thesis_send.pdf Basic Requirements of High Burn-up fuels in LWRs]
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Burnup — Le burnup est dans les technologies de l énergie nucléaire, le degré d irradiation et d énergie fournie par le combustible nucléaire. Il est exprimé par le ratio megawatt par jour par tonne de combustible. Liens externes Définition du burn up sur … Wikipédia en Français
burnup — urnup n. the amount of fuel used up (as in a nuclear reactor). [WordNet 1.5] … The Collaborative International Dictionary of English
Burnup — См. Глубина выгорания Термины атомной энергетики. Концерн Росэнергоатом, 2010 … Термины атомной энергетики
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