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 us
great pleasure to bring out this special issue on “Natural circulation in
nuclear reactor systems” which assumes special significance in the context of
present energy technology scenarios. Today nuclear energy produces about
15% of total world electricity. However, public
concern about the safety of nuclear plants has resulted in sociopolitical constraints on its use in some countries. Now a
world-wide renewed interest in nuclear energy is evident which is caused
mainly by the following factors: (a) progressively dwindling world reserve of
fossil fuel, (b) a deep-rooted concern about global warming, (c) increasing oil
price, and (d) good performance of current plants. These factors are leading to rising expectations for nuclear energy for the future.
For the
sustenance of this renewed interest, besides fuel resource, a number of
important issues are being addressed leading to the development of advanced
reactor designs as well as fuel cycle technologies. The major issues, which these
advanced reactors and fuel cycle concepts are addressing, include economic
competitiveness, achieving very high level of safety, waste disposal,
environmental effects and proliferation resistance.
An
important feature of several advanced reactors designs is the incorporation of passive
safety systems. The IAEA conference on “The Safety of Nuclear Power: Strategy
for the Future,” convened in 1991, recommended that for new plants “the use of
passive safety features is a desirable method of achieving simplification and
increasing the reliability of the performance of essential safety functions and
should 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 advanced
reactors employ natural circulation as the mode of energy removal underlining the
importance of natural circulation in nuclear reactor design
By definition,
natural circulation is a process in which the fluid motion is driven by a
density gradient and no external source of energy is required. However, the
driving head for natural circulation is low and can be influenced by small
changes in operating conditions. Sometimes the flow is not fully developed and
can be multidimensional in nature. All these have led to the need of thoroughly
understanding the phenomena involved to ensure reliability of natural
circulation systems. This has necessitated dissemination of knowledge in this
complex and important area. This special issue is a timely and very effective
step in this direction.
The papers
in this issue cover most of the important aspects of natural
circulation-modeling and code development, experimental investigations,
development of performance evaluation tools, flow instabilities, safety
analysis, and lastly reliability of natural circulation systems.
This issue
has been a modest effort to bring to the readers an update on a subject of
importance to the reactor designers. We are sure that the readers of this issue
will find the papers of immense value and get provoked to explore further in
this area.
Dilip Saha
John Cleveland