Transient studies of hot pools

The limiting transient states are emergency shutdowns or rapid shutdowns. During these transient conditions, the sodium temperature at the core outlet falls rapidly (DT = 130°C at 20°C/s). Moreover, depending on operating choices, the primary flow rate can also vary. When these transients occur, two problems must be examined  

Influence of the core outlet temperature transient. The thermal-hydraulic behaviour of a plenum can be characterized by means of a Richardson number (Ri) constructed with the core outlet temperature difference DT during the transient. In the same way as for steady-state conditions, fully turbulent flow in the model must be ensured by imposing a low Reynolds distortion. 

In SPXl geometry [8.17, 8.48] comparisons (fig. 8.28) made between mock-up test measurements and reactor measurements showed that, by respecting Richardson similitude, antilogous behaviour in the mock-up and the reactor, including within the above core stracture, was observed. 

Above core structures studies. The above core stmcture is another particular zone that must be carefully studied. Placed above the core, it plays an essential role in the thermal-hydraulics of the plenum, but must also be studied from the point of view of its own thermal loading, whether steady or transient. Considering the particularly complex geometry of this component (fig. 8.26), the use of tests remains essential. A large-scale mock-up, able to represent geometric detail very precisely, has to be used in this case. For SPXl [8.17], the GODOMl mock-up (90 deg sector, 1/5 scale) was used, and model and reactor measurements were shown to be very close (fig. 8.29). 

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