In dit hoofdstuk vindt u enige aantekeningen bij een gangbare U-centrale (LWR)
- Beschrijving van het algemene schema
- – Aan de linkerkant het reactor-gebouw met extra binnenmantel
- * In de paarse kring het reactor-vat , met in het roodbruin het circuit van de koelvloeistof , die
- * de nucleaire hitte onder verhoogde druk naar de groene warmtewisselaar wordt gepompt , waar
- * water onder druk tot stoom wordt verhit (blauw circuit)
- – De stoom expandeert in de turbine die de generator aandrijft
- * De elektra wordt via een hoogspanningstransformator aan het net geleverd ;
- * de afgewerkte stoom wordt in de condensor (lichtroze) afgekoeld tot het weer water is (groen) ;
- * waarna dit water door een pomp (blauw) weer op druk wordt gebracht en naar de groene warmtewisselaar gevoerd
- – De condensatie warmte wordt uit de condensor (lichtroze) afgevoerd naar de omgeving
- * verlies-energie >150% in verhouding tot de geleverde elektra
- – De blauwe pomp wordt aangedreven met 1…2% van de opgewekte elektra
- Er bestaan diverse types kern-reactor (LWR , PWR, BWR , etc).
[N.06b] geeft hierover nadere uitleg samen met de bijbehorende , iets afwijkende schema’s voor reactor en reactor-circuit
– LWR komt het meest voor
- Citaten uit [N.06b]:
- “If graphite or heavy water is used as moderator, it is possible to run a power reactor on natural instead of enriched uranium. Natural uranium has the same elemental composition as when it was mined (0.7% U-235, over 99.2% U-238), enriched uranium has had the proportion of the fissile isotope (U-235) increased by a process called enrichment, commonly to 3.5 – 5.0%. In this case the moderator can be ordinary water, and such reactors are collectively called Light Water Reactors (LWR). Because the light water absorbs neutrons as well as slowing them, it is less efficient as a moderator than heavy water or graphite.
- During operation, some of the U-238 is changed to plutonium, and Pu-239 ends up providing about one third of the energy from the fuel.
- In most reactors the fuel is ceramic uranium oxide (UO2 with a melting point of 2800°C) and most is enriched. The fuel pellets (usually about 1 cm diameter and 1.5 cm long) are typically arranged in a long zirconium alloy (zircaloy) tube to form a fuel rod, the zirconium being hard, corrosion-resistant and transparent to neutrons.* Numerous rods form a fuel assembly, which is an open lattice and can be lifted into and out of the reactor core. In the most common reactors these are about 4 metres long. A BWR (BoilingWaterReactor) fuel assembly may be about 320 kg, a PWR (PressurizedWaterReactor) one 655 kg, in which case they hold 183 kg uranium and 460 kgU respectively. In both, about 100 kg of zircaloy is involved.
- * Zirconium is an important mineral for nuclear power, where it finds its main use. It is therefore subject to controls on trading. It is normally contaminated with hafnium, a neutron absorber, so very pure ‘nuclear grade’ Zr is used to make the zircaloy, which is about 98% Zr plus about 1.5% tin, also iron, chromium and sometimes nickel to enhance its strength “
- “Nuclear plant reactor power outputs are quoted in three ways:
- – Thermal MWt, which depends on the design of the actual nuclear reactor itself, and relates to the quantity and quality of the steam it produces.
- – Gross electrical MWe, which indicates the power produced by the attached steam turbine and generator, and also takes into account the ambient temperature for the condenser circuit (cooler means more electric power, warmer means less). Rated gross power assumes certain conditions with both.
- – Net electrical MWe, which is the power available to be sent out from the plant to the grid, after deducting the electrical power needed to run the reactor (cooling and feedwater pumps, etc.) and the rest of the plant. “
- “In World Nuclear Association papers and figures and World Nuclear News items, generally net MWe is used for operating plants, and gross MWe for those under construction or planned/proposed.”
- “The relationship between these is expressed in two ways:
- – Thermal efficiency %, the ratio of gross MWe to thermal MW. This relates to the difference in temperature between the steam from the reactor and the cooling water. It is often 33-37%.
- – Net efficiency %, the ratio of net MWe achieved to thermal MW. This is a little lower, and allows for plant usage.
- In World Nuclear Association papers and figures and World Nuclear News items, generally net MWe is used for operating plants, and gross MWe for those under construction or planned/proposed. ”