Editing Convection (section)

===Nuclear reactors===
In a [[nuclear reactor]], natural circulation can be a design criterion. It is achieved by reducing turbulence and friction in the fluid flow (that is, minimizing [[head loss]]), and by providing a way to remove any inoperative pumps from the fluid path. Also, the reactor (as the heat source) must be physically lower than the steam generators or turbines (the heat sink). In this way, natural circulation will ensure that the fluid will continue to flow as long as the reactor is hotter than the heat sink, even when power cannot be supplied to the pumps. Notable examples are the [[S5G reactor|S5G]]
<ref>{{cite web| url=http://www.chinfo.navy.mil/navpalib/cno/n87/history/tech-3.html| publisher=Chief of Naval Operations Submarine Warfare Division| title=Technical Innovations of the Submarine Force| access-date=2006-03-12| url-status=dead| archive-url=https://web.archive.org/web/20060127003651/http://www.chinfo.navy.mil/navpalib/cno/n87/history/tech-3.html| archive-date=2006-01-27}}</ref><ref>{{cite web| url=http://ar.inel.gov/images/pdf/200506/2005061600214ALL.pdf| title=Appendix C, Attachment to NR:IBO-05/023, Evaluation of Naval Reactors Facility Radioactive Waste Disposed of at the Radioactive Waste Management Complex| access-date=2006-03-12| archive-url=https://web.archive.org/web/20120204154809/http://ar.inel.gov/images/pdf/200506/2005061600214ALL.pdf| archive-date=2012-02-04| url-status=dead}}</ref><ref>{{cite book |last1=Jones |first1=Edward Monroe |last2=Roderick |first2=Shawn S. |title=Submarine Torpedo Tactics: An American History |date=4 November 2014 |publisher=McFarland |isbn=978-0-7864-9646-4 |page=153 |url=https://books.google.com/books?id=6F6QBQAAQBAJ |language=en}}</ref>
and [[S8G reactor|S8G]]<ref>{{cite web| url=http://ship.bsu.by/main.asp?id=100092| script-title=ru:Энциклопедия кораблей /Ракетные ПЛ /Огайо| access-date=2006-03-12| language=ru| archive-date=2006-07-14| archive-url=https://web.archive.org/web/20060714151444/http://ship.bsu.by/main.asp?id=100092| url-status=dead}}</ref><ref>{{cite web| url=http://www.submarinesonstamps.co.il/openhist.php?ID=269| title=The Ohio, US Navy's nuclear-powered ballistic missile submarine| access-date=2006-03-12 |archive-url = https://web.archive.org/web/20060720075350/http://www.submarinesonstamps.co.il/openhist.php?ID=269 <!-- Bot retrieved archive --> |archive-date = 2006-07-20}}</ref><ref>{{cite web| url=http://tech.military.com/equipment/viewEquipment.do?eq_id=89213| title=Members-only feature, registration required| access-date=2006-03-12| archive-url=https://web.archive.org/web/20070223130956/http://tech.military.com/equipment/viewEquipment.do?eq_id=89213| archive-date=2007-02-23| url-status=dead}}</ref> [[United States Naval reactor]]s, which were designed to operate at a significant fraction of full power under natural circulation, quieting those propulsion plants. The [[S6G reactor]] cannot operate at power under natural circulation, but can use it to maintain emergency cooling while shut down.

By the nature of natural circulation, fluids do not typically move very fast, but this is not necessarily bad, as high flow rates are not essential to safe and effective reactor operation. In modern design nuclear reactors, flow reversal is almost impossible.  All nuclear reactors, even ones designed to primarily use natural circulation as the main method of fluid circulation, have pumps that can circulate the fluid in the case that natural circulation is not sufficient.