PWR reactors have been designed to avoid the use of contaminated water vapor as is the case in BWR described above. To this end, the water cooling the core, used as usual as the moderator, is kept at high pressure around 150 bar, so you can reach high temperatures without change in status. This, which is on one hand the main advantage of PWR reactors, is also its limitation: the critical temperature of water is equal to 374.13 ° C, and then the primary circuit can operate at maximum temperatures of the order of 320 ° C, in practice this limits the production of steam in the secondary pressure of the order of 70-80 bar , thereby reducing the thermal efficiency of the system. On the other hand, water in contact with the core is a higher pressure than that of a BWR reactor, and therefore more prone to rot in H + and OH - , leading to corrosion problems.
With reference to Figure 4, the operation of a PWR reactor is:
The fuel rods C, even here in the form of tablets partially enriched uranium oxide, are immersed in the moderator M, water , which also serves as a fluid diathermy. Are housed in the same water control rods D used to modulate the emission of neutrons. The water is contained in a tank V . The water is circulated by a pump P1 , and removes heat by contact to the core warm. The circuit, said primary circuit is maintained at a pressure high enough to reach without vaporization temperature to permit heat exchange in the secondary circuit. The secondary circuit
, non-radioactive, consists of a steam generator B where water is circulated, not too active. The exchange between non-contact the water of the primary and secondary generates steam at relatively low pressure, passes into the turbine T coupled to a generator that produces electricity G be placed on the network. From turbine steam passes to the condenser where K is condensed, thus providing water for re-cycle via the pump P2 .
A variation to the classic scheme PWR (Westinghouse) is the WWER reactor, designed in the then USSR , which has a similar pattern to that of Figure 4, differs in larger sizes (up to 1500 MW per reactor ).
Despite the greater inherent security PWR reactor, the only serious incident occurred in graphite-moderated reactors, one of the central U.S. Three Mile Island, had as its protagonist a PWR, technology and Babcock & Wilcox has brought out the issue of quantity significant radioactive material (see item for details).
In Italy you have installed a single central PWR, Westinghouse technology to Trino Vercellese , this too was disbanded following the decision to withdraw from electricity generation by nuclear power. However, the National Energy Plan, developed in the early '80s, as provided for unified design (PUN) of nuclear a PWR of 1000 MW [citation needed ] production of electricity (hence with 4 cooling circuits, instead of 3 Trino). The only site selected for the second one of the new central PUN was Trino (4 units), while no one has ever come to a site selection of the other four plants that had to complete the National Energy Plan.
It 's easy to find on the web reports on the defects and dangers of this plant in particular, just search with a search engine "Krsko nuclear power plant"
We hope that the return fire is true and that the European authorities and the Italian experience not the actual danger!!
