![]() ![]() Steam generators are heat exchangers used to convert feedwater into steam from heat produced in a nuclear reactor core. Water pressure in a closed system tracks water temperature directly as the temperature goes up, pressure goes up. On the other hand the submerged electrical heaters are designed to increase the pressure by evaporation the water in the vessel. The water spray system (relatively cool water – from cold leg) can decrease the pressure in the vessel by condensing the steam on water droplets sprayed in the vessel. Volume of the pressurizer (tens of cubic meters) is filled with water on saturation parameters and steam. Water spray system and electrical heaters system. For these purposes two systems are installed. Pressure in the pressurizer is controlled by varying the temperature of the coolant in the pressurizer. To achieve this, the coolant in the reactor coolant system is maintained at a pressure sufficiently high that boiling does not occur at the coolant temperatures experienced while the plant is operating or in an analyzed transient. The basic design of the pressurized water reactor includes such requirement that the coolant (water) in the reactor coolant system must not boil. Subcooling margin is very important safety parameter of PWRs, since the boiling in the reactor core must be excluded. Temperature in the pressurizer can be maintained at 350 ☌ (662 ☏), which gives a subcooling margin (the difference between the pressurizer temperature and the highest temperature in the reactor core) of 30 ☌. Pressure in the primary circuit of PWRs is maintained by a pressurizer, a separate vessel that is connected to the primary circuit (hot leg) and partially filled with water which is heated to the saturation temperature (boiling point) for the desired pressure by submerged electrical heaters. The exhausted steam is at a pressure well below atmospheric, and is in a partially condensed state (point F), typically of a quality near 90%.Ī pressurizer is a key component of PWRs.Ī pressurizer is a component of a pressurized water reactor. The reheater heats the steam (point D) and then the steam is directed to the low-pressure stage of steam turbine, where expands (point E to F). The steam must be reheated in order to avoid damages that could be caused to blades of steam turbine by low quality steam. In these turbines the high-pressure stage receives steam (this steam is nearly saturated steam – x = 0.995 – point C at the figure) from a steam generator and exhaust it to moisture separator-reheater (point D). Typically most of nuclear power plants operates multi-stage condensing steam turbines. Saturated liquid water, which has no latent heat and therefore 0% quality, will therefore only contain sensible heat. In the case of dry steam (100% quality), it contains 100% of the latent heat available at that pressure. ![]() At constant pressure, an addition of energy does not changes the temperature of the mixture, but the vapor quality and specific volume changes. Between these two states, we talk about vapor-liquid mixture or wet steam (two-phase mixture). On the other hand, when the vapor quality is equal to 1, it is referred to as the saturated vapor state or dry steam (single-phase). When the vapor quality is equal to 0, it is referred to as the saturated liquid state (single-phase). Dry Steam – Saturated Vapor Phase diagram of water.ĭry steam, or saturated steam, is characterized by the vapor quality, which is equal to unity. ![]()
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