Advanced Pressurized Water Reactor
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Advanced Pressurized Water Reactor is a type of nuclear reactor which is an improved version of existing Pressurized Water Reactor types.
In this design the safety systems mainly apply passive protection, which yield such high degree of safety that there is no need for the usual diesel generators, which provide the equipment with power in the case of a loss of electrical supply. They require little intervention, which reduces the chance of human error and other failures. Safety enhancement is also achieved by using modern, reliable devices. The probability of failures is even more decreased by applying the concept of diversity: several and different type of systems are used and thus the effect of potential intrinsic failures can be avoided.
In a standard PWR design, cooling requires elaborate pumps, while in an APWR it can be handled by simple gravity flow with natural convection — cool water enters the bottom of the reactor, which heats it, causing it to rise because warm water is less dense. This process sets up a natural circulation driven only by gravity. Unlike pumps which can fail and are driven by electric power which may not always be available, gravity never stops working. This is what makes this design inherently safer. It is referred to "passive stability," since no active measures by operators or by mechanical or electrical control systems are required.
The design is less expensive to build partly due to the fact that it uses existing and proven technology. The expense is also reduced by rationalizing technology, which means decreasing not only the amount of pipes, wires, and valves necessary, but reducing a number of other components, and therefore reducing cost. Standardization and type-related licencing will also help reduce the time and cost of construction.
[edit] AP1000
The AP1000 is a proposed passively safe pressurized water reactor designed and manufactured by Westinghouse Electric Company for nuclear power plants. This is considered a Generation III+ design. Each reactor is designed to generate over 1000-megawatts-electric (1117 to 1154 per Westinghouse).
The AP1000 is an enlarged version of an earlier, lower-output proposed design, the AP600. However, the AP600 design failed to attract customers. This is primarily because the construction cost per megawatt output made the cost of power generation uncompetitive, particularly in the economic climate of lower natural gas prices in the 1990s. The AP1000 builds on the research for that plant, with the economies of scale of a larger plant reducing the cost per megawatt output.
In January 2006, the Nuclear Regulatory Commission approved the final design certification for the AP1000. This means two things: (1) prospective builders can apply for a combined Construction and Operating License (COL) before construction starts, whose validity is conditional upon the plant being built as designed, and (2) each AP1000 will be virtually identical.
Probabilistic risk assessment was used in the design of the plants. This enabled minimization of risks, and calculation of the overall safety of the plant. (The Nuclear Regulatory Commission is preparing a new safety study - these plants will be orders of magnitude safer than the last, overly pessimistic study, NUREG-1150.)
The AP1000 will be manufactured in modules designed for rail or barge shipment. This will allow constructing many modules in parallel, and the plant is designed to have fuel load 36 months after concrete is first poured. This construction period is considerably shorter than earlier generation designs, and if achieved in practice will greatly decrease the overall capital cost of the plant. Such reductions would make the design much more economically competitive against other power sources than previous generation nuclear plants.
Two AP1000s are slated for Cherokee County, South Carolina, and one or two for the Bellefonte Nuclear Generating Station in Alabama.
