distribution was undertaken by developing a separate code [4] that incorporates several general assumptions. One assumption is that the core is in a state of vacuum immediately following the postulated primary loop rupture. The vacuum permits only one form of heat transfer to occur, radiative heat transfer. The other assumption is that the radial power profile of the core is flat. It is also assumed that the pore size distribution in the wick is uniform enough to support an isothermal temperature. Each fuel bundle can therefore be treated as a thermally isolated body. The core power and the decay heat levels are evaluated [3] by constructing a one group neutron point kinetics model and a two group decay heat model. Point kinetics is used for power prediction seconds after the reactor scram while the decay heat model is used for power prediction on the order of hours. The heat transfer model was developed by accounting for the radiative exchange that occurs between pins in a single fuel bundle. This simplifies the problem significantly since a fuel bundle has a large number of planes of symmetry. Figure 4 represents a section of a fuel bundle. The dashed lines represent lines of symmetry and the pins that have the same shading pattern can be considered as symmetrical doubles. The lines of symmetry provide a method of reducing the total number of pins that have to be included in the computational scheme. A fuel bundle in this problem has 69 pins which were reduced to nine by symmetrical elimination. The fuel bundle temperature profile is shown in Fig. 5. The model takes into consideration surface characteristics and geometry. The plots were generated by assuming that the temperature of the fuel in the core prior to the rupture was 1350 K and that each fuel pin generates 2193 W. Pore size was designed such that the wick temperature was maintained at 1350 K. From Fig. 5, it can be seen that the maximum temperature that was reached by the fuel pins was significantly lower than the clad melting temperatures. Maximum temperature that was reached is approximately 1725 K, while the melting temperature of the clad is about 2000 K. Comparing this with the fuel temperature of 2900 K
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