Heatup paths heat transfers

Our heatup path calculations assume that there is no transfer of heat between gas and reactor walls or between gas and catalyst. The result is, therefore, an adiabatic heatup path. 

For the analyses assuming no operator actions, at the onset of core heatup, the Figure 2 nodalization was replaced by a more detailed representation in all calculations except those associated with Case 2. The more detailed noda-1ization provides the flow paths needed to represent hot leg countercurrent natural circulation. This nodalization was never used in Case 2, which was performed to evaluate conditions with minimum ex-vessel heat transfer, or in the intentional depressurization calculations, where the continued flow to the pressurizer PORV prevented hot leg countercurrent natural circulation patterns from developing. Hot leg countercurrent natural circulation becomes possible after saturated liquid in the hot legs drains to the vessel and/or flashes. 

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See also in sourсe #XX -- [ ]

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