Reactor Shielding Research Articles

The problem of the use of organic compounds as moderators in nuclear reactors

1. Replacement of water by organic liquids in water-water reactors did not lead to an essential increase in the critical volume of the reactor. A slight increase in the volume of the active zone occurred due to the escape of neutrons from the reactor. 2. The neutron age in organic liquids increased more slowly than the concentration of hydrogen nuclei in them fell. 3. Due to the presence of carbon in the organic liquids, the value of the neutron ager in them was much less than in water (at the same concentration of hydrogen nuclei). This property of organic liquids of the isoamyl alcohol type offers prospects of their use in biological shields of small nuclear reactors. 4. To obtain more accurate results, comparative experiments on reactors with organic moderators are best carried out on less enriched uranium.

Design and Performance of Field-Defining Apertures for Neutron Capture Therapy

The purpose of this report is to present some of the special radiological problems which arise when a nuclear reactor or atomic pile is used in medical research and experimental radiation therapy. While there are many and various ways in which this new tool can be used, the principal emphasis here will be toward the means and the devices which are utilized in order to control the energy spectrum of the external neutron stream and to direct it selectively to the treatment site. It has become possible to investigate these problems under practical conditions of use now that a nuclear reactor has been built expressly for and as an integral part of a Medical Research Center (1). Figure 1 shows the general external aspect of the Medical Research Center at Brookhaven National Laboratory, with the reactor housed in the cylindrical building in the background. The initial exploratory phase of its operation has turned up the acute problem of extracting from the machine the kinds and the numbers of neutrons required for experimental therapy, and the concurrent problem of keeping the gamma-ray contamination down to an acceptable level. Except for some pertinent details of power level and neutron fluxes, the nuclear engineering aspects of the machine are not related here. The emphasis is instead placed on the machine as a device for studies on man and the diseases of man. Its design began with the establishing of criteria for the treatment situation in terms of human convenience as well as of radiation. The beginning point was the patient and a suitable radiation exposure room around him. The neutron aperture was stipulated to be at the appropriate location and to have the desired flow of neutrons controlled by a shutter. The situation is thus entirely medical in nature; the reactor was designed to provide the factors demanded. Other conveniences were, of course, included, and flexibility of application was built in at every possible point. Other kinds of investigation are planned and still others—as yet not imagined—must surely present themselves. The reactor will run typically at a power of 1,000,000 watts (1 megawatt). Performance of the reactor has actually been satisfactory in terms of its internal and operational characteristics. Its pattern of control, heat transfer, and other engineering attributes have been good enough that permission has been granted to run at power levels up to 3 megawatts. For the typical operating condition at the 1-MW power level, central core flux figures are greater than 1013 n/cm.2·sec., as predicted. On the other hand, the primary reason for building this reactor is to use streams of neutrons external to the reactor shield. To provide for this, the design includes specialized shielding components to minimize the delivery distance. The channel combines elements arranged for best neutron optics, planned from studies made during the criticality experiments.

Nuclear Engineering Monographs

Nuclear Engineering Monographs No. 1, Elementary Nuclear Physics. By W. K. Mansfield. Pp. viii + 60. 10s. 6d. net. No. 2, Nuclear Reactor Theory. By J. J. Syrett. Pp. viii + 80. 12s. 6d. net. No. 3, Reactor Heat Transfer. By W. B. Hall. Pp. viii + 68. 10s. 6d. net. No. 4, Nuclear Reactor Shielding. By J. R. Harrison. Pp. viii + 68. 10s. 6d. net. No. 5, Nuclear Reactor Control and Instrumentation. By J. H. Bowen and E. F. O. Masters. Pp. x + 78. 12s. 6d. net. No. 6, Steam Cycles for Nuclear Power Plant. By W. R. Wootton. Pp. vii + 66. 10s. 6d. net. (London: Temple Press, Ltd., 1958.)

Intermediate Energy Neutron Leakage Through Iron

Neutron leakage through a reactor shield composed primarily of iron is discussed. This is of interest whenever the hydrogen content of a shield is reduced either by design requirements or thermal deterioration. Work done at several sites on individual aspects of the problem is combined to present an over-all description of the neutron streaming. In general there are two different phenomena involved, each determined by the geometry. In the case of a long thin streaming path, such as a structural member penetrating the shield, the leakage consists of neutrons which have suffered no collisions. These neutrons will have energies corresponding to energies at which the iron total cross section is small. Iron has several antiresonances in the interval 25 to 100 kev, with the largest dip apparently at 25 kev, so most of the neutron leakage will be at these energies. The other case involves the attenuation of neutrons by large slabs of iron with little or no hydrogen (or other good moderator) present. The 25 kev neutrons are still present, but they are augmented by a large number of neutrons of energy between thermal and 1 Mev. These neutrons may have collided elastically many times but with only a small energy loss each time. Above 1 Mev, inelastic scattering suppresses the leakage, and below a few volts, absorption removes the neutrons.

Cryostat for Reactor Irradiation

A cryostat for continuously bathing samples in liquid nitrogen or other heat transfer liquids during nuclear reactor irradiation has been constructed and successfully operated. The samples to be irradiated at low temperature are immersed in the heat transfer fluid which is high-purity liquified nitrogen circulating in a closed system at a pressure greater than that of the atmosphere. The liquid is kept below its boiling point throughout its cycle by use of a heat exchanger located outside the reactor shield. The heat exchanger is cooled by commercial liquid nitrogen boiling at atmospheric pressure. Since oxygen and water vapor from the air cannot enter the closed pressurized system, no chemical explosions inside the nuclear reactor have occurred. Baths at other temperatures may be obtained by substituting suitable liquids for the high-purity nitrogen heat transfer fluid and by keeping the heat exchanger at the desired temperature.

Reactor Shielding

Abstract The problems attendant upon shielding of reactors are described briefly. The sources of radiation and their relative importance are enumerated. The interaction processes for gamma rays and neutrons are described; some discussion is given of their relative importance. The need for thermal shields in a reactor is described. Common biological shield materials are enumerated with their relative advantages and disadvantages. Some current shield designs are illustrated.

原子炉しゃ弊用コンクリート

原子炉しゃ弊用コンクリート

BOOK REVIEWS AND NOTICES

Book Reviewed in this article:REACTOR SHIELDING DESIGN MANUAL Edited by Theodore Rockwell, IIIENGINEERING DRAWING AND GEOMETRY By Randolph P. Hoelscher and Clifford H. Springer Published in 1956 by John Wiley and Sons, Inc.Reviewed by Assistant Professor John W. NeilNAVAL BOILERS By Robert F. LathamSHIPS, MACHINERY and MOSSBACKS by Vice‐Admiral Harold J. Bowen, USN (Ret.)GAS TURBINES AND JET PROPULSION By G. Geoffrey Smiths

原子炉におけるしゃ弊について

原子炉におけるしゃ弊について

Materials Testing Reactor

The materials testing reactor, designed to produce a flow of intense neutron radiation, is now in operation at the National Reactor Testing Station, according to L. E. Johnston, manager of the Idaho Operations Office of the Atomic Energy Commission. While the reactor operates primarily on thermal neutrons, it also can produce neutrons of higher energies, thus providing a means for determining the effects of radiation of different intensities on materials considered for use in the structures, cooling systems, and shields of new reactors. An enriched uranium reactor, it uses water circulating at high velocity as a coolant. Excavation for the reactor was started at the station in May 1950 and on March 31st of this year it became critical.