This thermodynamic process of turning heat into work is also known as the Rankine Cycle, or more colloquially as the steam cycle, which can be considered a practical Carnot cycle but using a pump to return the fluid as liquid to the heat source. The function of the condenser is to condense exhaust steam from the steam turbine by losing the latent heat of vaporisation to the cooling water or possibly air passing through the condenser.
The temperature of the condensate determines the pressure in that side of the condenser. This pressure is called the turbine backpressure and is usually a partial vacuum. Decreasing the condensate temperature will result in a lowering of the turbine backpressure which will increase the thermal efficiency of the turbine. A typical condenser consists of tubes within a shell or casing. There may be primary and secondary circuits, as in pressurized water reactors PWRs and two or three other types.
In this case the primary circuit simply conveys the heat from reactor core to steam generators, and the water in it remains liquid at high pressure. In a boiling water reactor and one other type, the water boils in or near the core. What is said in the body of the paper refers to the latter situation or the secondary circuit, where there are two.
This has a major influence on reactor engineering. A more detailed treatment of different primary coolants is in the Nuclear Power Reactors paper. With latent heat of vaporization 2. This would amount to 77 or 67 megalitres per day respectively for a MWe plant if all cooling were evaporative only. Other calculated figures for higher efficiencies: ultrasupercritical steam cycle USC using cooling towers would need about 1.
The DOE report critiqued below shows 2. Other US sources quote 1. About 0. The new Medupi plant will use it and be the largest dry-cooled plant in the world MWe. Kendal in South Africa uses indirect dry cooling system.
Dry cooling is apparently also used in Iran and Europe. Over such plants are operating world-wide. One stream of development for Generation IV nuclear reactors involves supercritical water-cooled designs. Supercritical fluids are those above the thermodynamic critical point, defined as the highest temperature and pressure at which gas and liquid phases can co-exist in equilibrium, as a homogenous fluid. They have properties between those of gas and liquid.
For water the critical point is at C and 22 MPa, giving it a "steam" density one third that of the liquid so that it can drive a turbine in a similar way to normal steam. In the UK all nuclear plants are on the coast and total transmission losses in the system are 1.
Cooling Power Plants Updated September The amount of cooling required by any steam-cycle power plant of a given size is determined by its thermal efficiency.
It has essentially nothing to do with whether it is fuelled by coal, gas or uranium. However, currently operating nuclear plants often do have slightly lower thermal efficiency than coal counterparts of similar age, and coal plants discharge some waste heat with combustion gases, whereas nuclear plants rely on water.
Nuclear power plants have greater flexibility in location than coal-fired plants due to fuel logistics, giving them more potential for their siting to be determined by cooling considerations. The most common types of nuclear power plants use water for cooling in two ways: To convey heat from the reactor core to the steam turbines.
To remove and dump surplus heat from this steam circuit. Steam cycle heat transfer For the purpose of heat transfer from the core, the water is circulated continuously in a closed loop steam cycle and hardly any is lost b. Decay heat in fuel at Fukushima Daiichi reactors 2. Cooling to condense the steam and discharge surplus heat The second function for water in such a power plant is to cool the system so as to condense the low-pressure steam and recycle it.
This cooling function to condense the steam may be done in one of three ways: Direct or "once-through" cooling. If the power plant is next to the sea, a big river, or large inland water body it may be done simply by running a large amount of water through the condensers in a single pass and discharging it back into the sea, lake or river a few degrees warmer and without much loss from the amount withdrawn. The water may be salt or fresh. Some small amount of evaporation will occur off site due to the water being a few degrees warmer.
Recirculating or indirect cooling. If the power plant does not have access to abundant water, cooling may be done by passing the steam through the condenser and then using a cooling tower, where an updraught of air through water droplets cools the water. Sometimes an on-site pond or canal may be sufficient for cooling the water. Normally the cooling is chiefly through evaporation, with simple heat transfer to the air being of less significance.
This is the main type of recirculating or indirect cooling. Dry cooling. A few power plants are cooled simply by air, without relying on the physics of evaporation.
This may involve cooling towers with a closed circuit, or high forced draft air flow through a finned assembly like a car radiator. Recirculating or indirect wet cooling Where a power plant does not have abundant water, it can discharge surplus heat to the air using recirculating water systems which mostly use the physics of evaporation. They are used in large nuclear and coal-fired plants in Europe, eastern USA, Australia, and South Africa Mechanical draft cooling towers have large axial flow fans in a timber and plastic structure.
Dry cooling Where access to water is even more restricted, or environmental and aesthetic considerations are prioritised, dry cooling techniques may be chosen for conventional reactors. Environmental and social aspects of cooling Each of the different methods of cooling entails their own set of local environmental and social impacts and is subject to regulation. Future implications of cooling requirements for nuclear power Fresh water is a valuable resource in most parts of the world.
APPENDIX: Comment on US reports It is evident that apart from heat discharged with combustion gases from a coal-burning plant and any difference in thermal efficiency which affects the amount of heat to be dumped in the cooling system, there is no real difference in the amount of water used for cooling nuclear power plants, relative to coal-fired plants of the same size.
Cooling water requirements for each type of plant were calculated from NETL data and are tabulated as follows for "model" plants' consumption of fresh water: Coal, once-through, subcritical, wet FGD 0. Czech Republic.
There are a total of six mechanical draft cooling towers — each one seven stories tall — at Catawba Nuclear Station, which is located on Lake Wylie in South Carolina. In this type of tower, the warm water is circulated inside each tower and over structures that create droplets of water. At the same time, large fans draw the warm, moist air out the top of the cooling tower, lowering the temperature of the water more than 20 degrees. The cooler water then returns to the plant and condenses steam back into water in the condenser and the entire cycle is repeated.
When warm water circulates from the plant back to the cooling tower, it is sprayed through the hollow core of the tower onto a grid in the center of the tower. Cool air flows up through the tower's hollow center and passes the warm falling water. So what are some of the misconceptions surrounding cooling towers?
One of the most common is that the "cloud" leaving the top of a cooling tower — which is often visible from miles away and can create a trail up to two miles long from taller towers — is smoke. It is, of course, clean water vapor that results from the cooling process. It contains no pollutants, and it is not radioactive — the nuclear process takes place inside a secure containment building, not the cooling tower.
They found that on-site surface stability during the time of the storm generation was shown to be stable, making it difficult for a surface-based plume to initiate convection, or the rising of air.
After different water is transformed into steam in a heat exchanger, it flows through a set of turbines that are attached to a steam generator, which creates energy. It then travels through a condenser, which converts it back to liquid form.
The condenser acts as a reverse heat exchanger and cools the steam into water. The condenser takes in cold water and generates hot water. The cooling tower transforms the hot water back to cold water. Because there are three contained water cycles, the primary which reacts directly with the fuel assemblies, secondary, which cools the primary, and tertiary, which cools the secondary the water used in the condenser is not radioactive and can be released into the environment through cooling towers.
This entire process is shown in Fig. The tower has fans that pump air into the bottom of the hyperboloid shaped structure and pumps air out of the top as well.
This creates a fairly strong upward airflow. As this water falls it is cooled by the upward airflow. Some power plants, usually located on lakes or rivers, use cooling towers as a method of cooling the circulating water the third non-radioactive cycle that has been heated in the condenser. During colder months and fish non-spawning periods, the discharge from the condenser may be directed to the river. Recirculation of the water back to the inlet to the condenser occurs during certain fish sensitive times of the year e.
It is important to note that the heat transferred in a condenser may heat the circulating water as much as 40 degrees Fahrenheit F. In some cases, power plants may have restrictions that prevent discharging water to the river at more than 90 degrees F. In other cases, they may have limits of no more than 5 degrees F difference between intake and discharge averaged over a 24 hour period.
When Cooling Towers are used, plant efficiency usually drops. One reason is that the Cooling Tower pumps and fans, if used consume a lot of power.
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