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          rH = 3.5 ft bH = 0.5 ft

The temperature distribution, as a function of the seed ratio, is given by equation (8.61). The seed ratio is varied until the temperature at the inner edge of the graphite reflector is reduced below 40000K, the approximate melting temperature of graphite. The effect of the tungsten seed ratio on the graphite temperature is shown in Figure 19. With no seed in the hydrogen, the graphite temperature is 11,3001K. The graphite temperature is reduced as the seed ratio increases, until the desired value of 40001K is obtained with a seed ratio of 0.142. The resulting temperature distribution for this case is shown with the corresponding uranium and hydrogen distributions, in Figure 20. These temperature and density distributions are then used in the iterative calculation to determine the pressure which makes the reactor critical, as described in the first section of this chapter.

        Calculated temperature distributions for centerline temperatures from 20,0000K to 80,0000K are shown in Figure 21. The pressure (in atmospheres) and the seed ratio used in each calculation are shown on the respective curves. For centerline temperatures of T(0) = 20,000'K and 30,0000K, the hydrogen distribution parameters are