OT: How a Nuclear Power Plant Freezes - Saab General Bulletin Board - Saabnet.com
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All of us have probably heard about the challenges being faced by residents and business in Texas regarding no electric power, which apparently has resulted from none of the Texas power generation facilities having been constructed with winterizing features, and Texas having their own power grid fully independent from grids serving neighboring states.
So how does a Nuclear Power Plant freeze?
All power plants generate tremendous amounts of heat. Heat which is necessary to produce massive quantities of super-heated steam needed to spin the turbines and drive the generators. The low quality steam leaving the turbines then needs to be cooled to return it to liquid state water so that it can be pumped then re-heated again to change into super-heated steam and repeat this thermo-cycle.
Massive amounts of cooling water are needed to cool this low quality steam. This cooling water gets warm in the process and must be cooled itself. The plant where I worked had two hyperbolic concrete cooling towers, each 450 feet tall and capable of handling 450,000 gallons per minute of this heated cooling water.
The towers achieve this cooling by admitting fresh air at ground level and passing it horizontally through a vertical cascade of falling heated cooling water. The height and hyperbolic shape of the tower causes a powerful chimney effect which is the sole motive power to suck in the cool air at ground level (actually 0 ft to 45 ft high) and exhaust it more than 400 feet higher.
The outside surface of the towers' 45 foot tall air inlets (which extend around the full circumference of the towers) are continuously wet from the cascading water. During freezing weather these wet surfaces will freeze solid if the tower's defrosting system is not operating. If the exterior freezes solid, no air can enter, the cooling water will remain warm, the power plant's condenser will not be able to phase change the low quality steam to water for pumping back to the reactor to be re-heated to steam again, and the plant will automatically scram.
The defrosting system works by dumping large quantities of the warmest cooling water in a thin falling curtain immediately along the tower perimeter. This defrosting water is delivered to the tower exterior via more than eighty 14-inch diameter pipes, and different sections of the tower are defrosted in groups using a hydraulically operated loose fitting butterfly valve in each pipe. The hydraulic fluid used is heated glycol rather than oil.
So, without a specific defrosting/deicing system to prevent a complete wall of ice being created on the tower perimeter, the tower will cease cooling the warm water and the Power Plant will need to be shut down. The emergency action needed to restore air flow to the towers is to shatter the ice wall by blasting it with hose streams from fire trucks.
Similar situations will exist at all Coal and Gas Power Plants if their cooling towers, regardless of the towers' design, are not equipped with de-icing systems.
->Posting last edited on Tue, 16 Feb 2021 17:40:13.
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