Burnup

By the term is understood in burnup of nuclear energy technology, the amount of thermal energy generated per unit mass in a fuel assembly. The burn is usually expressed in gigawatt - days per metric ton of heavy metal ( GWd / t SM). Besides are FIMA (English: Fission by initial metal atom ) and FIFA (English: fissile nuclear fission per initial ), usually given as a percentage, use: Would a fuel of 3.3 % 235U and 238U 96.7 % as many divisions take place, such as 235U atoms were initially present, the burn would be 3.3% or 100% FIMA FIFA. An indication in FIFA is particularly suitable to compare Brennstoffabbrände different initial enrichment degree.

The current release of burn is also a measure of how much fuel has been consumed. The consumption comes from the fact that the concentration of fissile 235U nuclei decreases over time by nuclear fissions in the fuel more and more. A portion of the concentration decrease is compensated by the formation of fissile 239Pu. In short, through the fission of 235U nuclei of the stock is consumed in U235 in the fuel - " he burns down ." In addition, also the formation of decomposition products affect the reactivity of the reactor core. Here, in particular, the cleavage products of importance that have a high capture cross section for neutrons. To be mentioned in this context, especially the noble gas xenon and the metal samarium.

Today, in light water reactors average burnup of about 40-55 GWd / t SM are achieved from Swiss plant Spitzenabbrände individual elements up to 105 GWd / t SM are occupied. The fuel manufacturers strive for pressurized water reactors using modified, hochabbrandfähiger fuel an increase in the average burnup to 75 GWd / t to SM. Even higher burn-ups can be reached at present in high-temperature reactors and breeder reactors. In Magnox reactors and in the Canadian Candu reactors, the discharge burn are expressed in GWd / t due to the lower initial enrichment, naturally, lower, in the unity FIFA especially in Candu reactors but higher than in conventional reactors.

The research hopes that new reactor design greatly increased erosion rates up to 500 GWd / t SM.

Swell

  • Reactor Technology
  • Nuclear fuel technology
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