A lot of desalination in the Middle East and North Africa already uses waste heat from oil- and gas-fired power plants, and in future a number of countries are expecting to use nuclear power for this cogeneration role.
See also Nuclear Desalination information paper. 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. However, some US studies quote a significant difference between coal and nuclear plants, this evidently being related to the unstated thermal efficiency of selected examples.
The studies exclude nuclear plants on the coast, which employ salt water for cooling. It uses some "typical" figures for water withdrawal and consumption which show marked differences between coal and nuclear, without giving the source of these or explaining their magnitude. It focuses on freshwater only, and ignores plants with seawater cooling. Its conclusions are presented on a regional basis in the light of projected increased generations and likely changes in generation technology such as from coal to combined cycle gas.
The and reports are both based on examples in public data and EPRI databases that provide cooling water usage and heat rejection information for multiple facilities.
The numbers provided in these reports and the bar chart above are broadly representative of the water use requirements. Other reports on estimating fresh water needs are from the US Department of Energy's National Energy Technology Laboratory, in , with a update, and a more general one in The first two look out to and use five cooling scenarios applied to regional projections for additions and retirements. However, coal plants are assumed to need flue gas desulfurization FGD , which usually increases water use.
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:. The figures are puzzling in that supercritical coal should use significantly less than less-efficient subcritical coal-fired plants, and for recirculating use of cooling towers the large difference between subcritical coal and nuclear is unexplained. Clearly there are significant variables which are not accounted for though they must surely be relevant to NETL's projections.
This is a lot more than that of the figures in the subcritical coal-fired diagram with FGD Fig - 1. In explanation the text says: "Nuclear plants have a higher cooling tower load relative to net power generation. This is because the steam conditions are limited by metal brittleness effects from the nuclear reactor thereby reducing efficiency. At theoretical full efficiency and considering only the vapour phase this is known as the Carnot cycle.
The Carnot efficiency of a system refers to the difference between input and output heat levels and is more generally referred to as thermal efficiency. 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. Water would be it, essentially. The reserve tanks at a reactor contain the same grade of water in terms of purity and chemical composition that are normally used in the core. It is possible, if you have a situation where you have exhausted that source of coolant to introduce, quote—unquote, regular water.
That will do the job of cooling. Why do nuclear power plants need electricity to be cooled? Nuclear reactors are net positive in terms of supporting the grid. They produce much more electricity than they need to run their systems. As a basic design feature in the U. That's by design, because you don't want to end up in a situation where a problem at the plant cuts off its own power source.
Therefore, the primary means of power for a plant in order for it to run is electricity from the grid. As a general matter, for U. What kinds of events could knock out a diesel generator? You always have the possibility of just plain old failure.
That's why you have multiple diesels at a plant for redundancy's sake. It can be the case that diesel itself is running properly but the distribution system, the buses or the cabling could be misaligned to the point where the diesel detects that its power is not being accepted by the plant. It's not going to run if it's trying to generate power and that power's not going anywhere. When we say a diesel fails, it's not always a problem with the diesel [itself].
How long does it take to cool down a reactor? There are design specific variables there. The easiest way to answer that question is that NRC regulatory requirements for emergency power supplies is that they be available on the order of a month. You can render a plant in an acceptable condition within a few hours. In this case, decay heat is removed through the secondary system. For RCS cooldown to Hot Standby mode , steam generators usually dissipates heat directly to the main condenser or via the atmospheric steam dump system.
In this operational mode a some of reactor coolant pumps RCPs must be in operation. Proper loop flow and desired loop temperatures are maintained with these RCPs until the residual heat removal system RHRS is in service. If the plant is to remain in this condition for some period of time, SDM must be maintained including xenon transients by changes in boron concentration. If the shutdown period will be lengthy or involves functions requiring cooldown of the reactor e.
The methods for actually conducting cooldown of the reactor vary depending on plant design, but in all cases limitations are imposed on the maximum rate at which the reactor systems may be cooled.
These limits are provided to reduce the stress applied to system materials, thereby reducing the possibility of stress induced failure. During this cooldown, the system pressure decreases as steam generator steam pressure decreases. SDM must be maintained also in this case, therefore boration is initiated to bring the boron concentration to the cold shutdown value.
Reactor coolant pumps are run only as needed to assure uniform loops and reactor pressure vessel cooldown and to provide spray for pressurizer cooldown. When the RCS pressure is lower than the residual heat removal RHR system design pressure , this system is used for further cooldown, depressurization and long term reactor cooling.
To accomplish RHR heat removal, RHR heat exchangers transfer heat to the component cooling water or service water system, which then transports heat to the ultimate heat sink UHS. The same way we do in the U. Several spent-fuel-rod pools also lost electric power, shutting down pumps. Water in the cooling pools stopped circulating and began to boil off or leak out. As the water level fell, the spent fuel rods were exposed, and their temperatures soared.
Several began to melt down, releasing extremely high levels of radiation into the air. Could that happen in the U. The U. All told, there are 71, tons of spent fuel rods at U. Is there a threat of terrorism?
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