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To: ptanner who wrote (55304)	9/14/2001 11:56:33 PM
From: pgerassi	Respond to of 275872

Dear PT: The reason that the core shuts down is that adding water decreases the required beta below that needed for the chain reaction. The high temperatures means increased efficiency. The theoretical efficiency is (high temp - sink temp)/(high temp) all measured in units above absolute zero (Rankine, R (F+460) or Kelvin, K (C+273.15)). Gas turbines have sink temperatures somewhere between 300 to 400K. With a source temperature of about 2300K (just above 2000C), the max theoretical efficiency is 87%. Losses for turbine friction, generator, cooling and compressor probably drop it to between 50% to 70% depending on size, optional waste heat for steam generation and planned longevity. This is higher due to the closed loop system over that normally ascribed to NG fired open loop gas turbines (open loops trade higher sink temperatures for elimination of gas cooling system expense and complexity plus combustion usually requires new air to continue burning which is not a problem for a nuclear thermal source). Steam turbines are limited to about 500C for a high temperature due to the very high pressures required (100atm). Thus, closed loop gas turbines are both far more efficient than steam or open loop gas turbines and smaller than steam turbines. Pete