Adobe Acrobat PDF Document -
on 11/26/24 at 2:31 PM
Passive thermal-hydraulic systems are widely used in nuclear reactor safety and design. For example, primary circuits in existing boiling and pressurised water reactors are designed to take advantage of the relative position of the reactor core and heat sinks to remove nuclear decay heat. The use of passive systems that rely on the low driving forces(e.g. compared with forces in systems with active pumps) arising from buoyancy effects may not be sufficient to establish stable flow patterns under expected accident conditions and must be considered and addressed carefully in the design to demonstrate that safety functions can be achieved.
Passive safety features take advantage of natural forces or phenomena such as gravity, pressure differences or natural heat convection, and have been used for many decades. The passive systems of Generation II boiling and pressurised water reactor designs have been widely investigated in the past and have been found to be capable of achieving the required safety functions. Newer Generation III and advanced reactor designs rely more on passive systems in their design and therefore, attention is now being devoted to understanding their capabilities. This report seeks to achieve a common understanding of thermal-hydraulic passive systems and their performance, and not the wider class of passive systems possible in nuclear reactors. The phenomena and mechanisms being considered are those associated with the transient behaviour of single- and two-phase fluids, and not with other possible mechanical, electric, electronic and instrumentation and control (I&C) failures.
