Enhancement of natural circulation by conduction through a vertical redan in LMRs during total loss of heat sink

A high degree of inherent safety is one of the major features of the latest design concept of advanced liquid metal reactors. A shutdown heat removal system can be designed based on radiative heat transfer among the reactor vessel, guard vessel, and biological shield such that air flow adjacent to the shield provides the ultimate heat sink. Proper sizing can ensure that all of the decay heat can be removed, even in the case of complete loss of normal heat rejection capability. To achieve this goal, the reactor vessel temperature must be high enough to dissipate all the decay heat by means of radiation. A coupled condition is that the temperature at the outlet of the reactor core cannot reach sodium boiling. A most reliable and economical way to satisfy these two criteria is the utilization of a vertical redan. By transmitting heat through the vertical redan from the hot pool into the cold pool, a local natural circulation path will result in the cold pool, which will heat the reactor vessel; simultaneously, a more global natural circulation flow path in the reactor will ensure mass flow rates, which will prevent sodium boiling. To demonstrate this heat removal capability and illustrate the resulting flow pattern inside the vessel, a three-dimensional integral simulation for a generic pool-type reactor has been performed using the multidimensional COMMIX code