Patent Number: 039752330
Section: summary

The present invention relates to neutronic reactors, and to neutron absorbing control elements for neutronic reactors. Structures capable of neutronic reactions produce either converging or diverging reactions, that is, the neutron flux density within the structures either increases or decreases with the passage of time. Structures which converge will not sustain a neutronic chain reaction, the reaction merely dying out as a result of the absorption of neutrons in the structure and leakage from the structure. However, a diverging neutronic chain reaction is self-sustaining and will increase exponentially as long as the structure remains physically unchanged. One of the methods used in the art to control diverging neutronic chain reactions is to insert an adjustable neutron absorbing element into the structure. Fermi et al. U.S. Patent No. 2,708,656, dated May 17, 1955, discloses neutronic reactors controlled by means of neutron absorbing elements positionable within the mass of the reactor structure. Neutronic reactors are generally provided with a radiation and particle shield disposed thereabout in order to protect operating personnel from injurious radiations emanating from the reactor. If a control element is to be positionable within the structure of the reactor, it is generally necessary that the control element pierce the shield surrounding the active portion of the reactor. However, apertures in the shield provide a pathway of escape for neutrons and other radiations and often necessitate additional shielding for the reactor. Hence, it is an object of the present invention to provide a neutronic reactor with neutron absorbing elements for controlling the reaction which pierce the shield of the reactor and minimize the amount of neutrons and other radiations escaping from the apertures in the shield. Most neutronic reactors which are controlled by neutron absorbing elements, are provided with at least two types of neutron absorbing elements. The neutron absorbing elements are often in rod form and are designated "safety rods" and "control rods". Both types of control elements are constructed of neutron absorbing materials and are intended to retard the neutronic chain reaction, but the "control rods" are positionable to provide control for small variations in neutron flux density within the reactor, and the "safety rods" are positionable to control large changes in the neutron flux density within the reactor, or solely for the purpose of starting and stopping the reactor. The present invention is also directed to providing "safety rods" which minimize the escape of radiations through the apertures in the radiation shield, although it may be utilized with "control rods" also.