Regulating Rod

regulating rod

[′reg·yə‚lād·iŋ ‚räd]
A control rod intended to accomplish rapid, fine, and sometimes continuous adjustment of the reactivity of a nuclear reactor; it usually can move much more rapidly than a shim rod but makes a smaller change in reactivity.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Regulating Rod


a rod that is made of a substance that easily absorbs neutrons and is used to regulate the rate of nuclear fission in a nuclear reactor.

The neutron balance, or reactivity, of the reactor, that is, the ratio between the number of neutrons released and the number of neutrons absorbed during fission per unit time, is controlled by means of a regulating rod. The introduction of a regulating rod into the core results in a decrease in the reactivity and power of the reactor and even in the complete termination of a chain reaction. The removal of a rod from the core results in an increase in the reactor’s reactivity and a corresponding increase in its power. The position of a rod is also varied to compensate for operational changes in the reactivity of a nuclear reactor that result from, for example, a temperature change, a reduction in nuclear fuel, or an increase in the number of fragments of atomic nuclei that absorb neutrons.

Boron, cadmium, and rare earth elements are primarily used in rod manufacturing. Regulating rods are set in motion usually by electric or hydraulic drive. When an emergency shutdown of a chain reaction is needed, a regulating rod is simply released and allowed to fall freely into the reactor core.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The effective multiplication factors, [k.sub.eff], were analyzed for two cases corresponding to the complete withdrawal and the full insertion of control rods (four shim rods and one automatic regulating rod).
The reactor core is controlled by seven control rods: two safety rods (SR), four shim rods (ShR), and one automatic regulating rod (AR).
Other nonfuel lattice cells such as aluminum rod, beryllium rod, and regulating rod were also simulated using the PIJ code.
In the case of full insertion of the four shim rods and the automatic regulating rod, the difference of the [k.sub.eff] values is about 242 pcm.