Object of the study relates to passive safety systems of cooling, heat removal and thermal protection that operate as independent evaporation-condensation (EC) systems and could maintain required thermal conditions of the technological systems of nuclear power cycle. Reliability of the passive systems is provided by absence of moving parts and by their operation based on physical laws of nature, i.e., without any intervention of staff, power supply, and control signals.

One of the main features of these systems is their ultimate heat transferring ability. There are hydrodynamic limitations of heat transferring ability connected with provision of coolant circulation in vapor-condensate lines of transportation zone that could be combined into two groups: 1) the crises depending upon quantity and distribution of liquid phase; and 2) the crises affected by hydrodynamic interaction of liquid and vapor phases. The authors undertook investigation of various thermophysical factors limiting this ability, determined and analyzed its regularities, which depend upon thermodynamical conditions, transport ability of capillary structures (if any), and the interaction of vapor and liquid flows of HP coolant.

Heat transferring ability of a model of EC system of passive surface cooling and thermal shielding under the conditions of heat supply from radiating surface of reactor simulator to heat pipes as the elements of two-row screen was investigated.

The analysis and calculations made by the authors proved the possibility to create an efficient passive evaporation EC system of surface cooling and thermal shielding of reactor unit. Such a system has a number of advantages as compared with known active safety systems (e.g., autonomy, higher reliability, and operational safety), does not require emergency water resources, compressed air systems, numerous valves, etc.).

The tests were performed at vertical orientation of HP evaporation zone (condensation zone was above evaporation zone) as a part of the double-row screen. The heat pipe was tested at its location in each of two rows and at two options of condensation zone: vertical and inclined in transportation zone at 20° to horizon.

It was found that only insignificant circumferential nonisothermality of heat-pipe surface under steady one-side heat supply in evaporation zone took place. Quite satisfactory agreement of the experimental and predicted values of heat flux transmitted by heat pipes of two-row screen was obtained.

The investigation proved efficiency and reliability of EC system of surface cooling and thermal shielding of the reactor equipment.

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