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Technology Stocks : Advanced Micro Devices - Moderated (AMD) -- Ignore unavailable to you. Want to Upgrade?

To: dale_laroy who wrote (55490)	9/16/2001 2:13:39 AM
From: hmaly	Respond to of 275872

Dale Re...I am quite certain that, while the coolant in a heavy water reactor might not be able to moderate the neutrons alone, it is needed to at least "finish the job". Thus, a coolant loss will lead to an automatic shutdown. <<<<< From Candu's site http://www.ieee.ca/millennium/candu/candu_about.html The moderator operates at low pressure and temperature, completely separate from the primary heat transport coolant circuit, providing a huge body of water capable of absorbing excess heat if a major accident should occur. Among other safety features in CANDU power plants are the emergency core cooling system and the containment system. In the event of a loss-of-coolant accident, the reactor safety systems will shut down the reactor, isolate the defective primary heat transport coolant circuit, and assure a supply of cooling water over the fuel. Multiple containment consists of several systems and structures that provide sealed barriers around nuclear components to prevent the release of radioactivity. CANDU's many safety systems are the embodiment of a world leading defence-in-depth design philosophy.<<<<<< As you can see, a loss of coolant requires a supply of cooling water to keep the core from melting, which isn't necessary in pebble bed reactors, as it is physically impossible for the fuel to go over 3000 degrees without any coolant, and the ceramic vessel is designed to withstand 6000 degrees. Thus pebble bed reactors require no safety coolant systems.