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Science and Technology of Nuclear InstallationsVolume 2008 2008, Article ID 932319, 1 page


Reactor Engineering Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India

Nuclear Power Technology Development Section, Division of Nuclear Power, International Atomic Energy Agency, Wagramer Strasse 5, P. O. Box 100, 1400 Vienna, Austria

Received 2 April 2008; Accepted 2 April 2008

Copyright © 2008 Dilip Saha and John Cleveland. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

It gives usgreat pleasure to bring out this special issue on “Natural circulation innuclear reactor systems” which assumes special significance in the context ofpresent energy technology scenarios. Today nuclear energy produces about15% of total world electricity. However, publicconcern about the safety of nuclear plants has resulted in sociopolitical constraints on its use in some countries. Now aworld-wide renewed interest in nuclear energy is evident which is causedmainly by the following factors: a progressively dwindling world reserve offossil fuel, b a deep-rooted concern about global warming, c increasing oilprice, and d good performance of current plants. These factors are leading to rising expectations for nuclear energy for the future.

For thesustenance of this renewed interest, besides fuel resource, a number ofimportant issues are being addressed leading to the development of advancedreactor designs as well as fuel cycle technologies. The major issues, which theseadvanced reactors and fuel cycle concepts are addressing, include economiccompetitiveness, achieving very high level of safety, waste disposal,environmental effects and proliferation resistance.

Animportant feature of several advanced reactors designs is the incorporation of passivesafety systems. The IAEA conference on “The Safety of Nuclear Power: Strategyfor the Future,” convened in 1991, recommended that for new plants “the use ofpassive safety features is a desirable method of achieving simplification andincreasing the reliability of the performance of essential safety functions andshould be used wherever appropriate.” Nuclear plant designers select active safety systems, passive safety systems, or combinations considering fulfilment of required safety functions with sufficient reliability, and the impact on plant operation and cost. A number of passive systems incorporated in advancedreactors employ natural circulation as the mode of energy removal underlining theimportance of natural circulation in nuclear reactor design

By definition,natural circulation is a process in which the fluid motion is driven by adensity gradient and no external source of energy is required. However, thedriving head for natural circulation is low and can be influenced by smallchanges in operating conditions. Sometimes the flow is not fully developed andcan be multidimensional in nature. All these have led to the need of thoroughlyunderstanding the phenomena involved to ensure reliability of naturalcirculation systems. This has necessitated dissemination of knowledge in thiscomplex and important area. This special issue is a timely and very effectivestep in this direction.

The papersin this issue cover most of the important aspects of naturalcirculation-modeling and code development, experimental investigations,development of performance evaluation tools, flow instabilities, safetyanalysis, and lastly reliability of natural circulation systems.

This issuehas been a modest effort to bring to the readers an update on a subject ofimportance to the reactor designers. We are sure that the readers of this issuewill find the papers of immense value and get provoked to explore further inthis area.

Dilip SahaJohn Cleveland

Autor: Dilip Saha and John Cleveland



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