Physical factors of a low-power medical reactor.

Abstract

Relatively low-power, homogeneous, solid-fuel reactors became available for training and familiarization during the year 1957. These reactors were intended for the training of scientific and engineering students, in a program of reactor technology being supported by the U. S. Atomic Energy Commission (A.E.C.). A type offered by the Aerojet-General Nucleonics Laboratories of San Ramon, Calif., the AGN-201, stimulated the interest of staff members of the Isotope Branch of the U. S. Naval Hospital, Bethesda, Md. The reactor was investigated and, when it was found to be intrinsically safe for operation in proximity to a hospital, the process of licensure and procurement was initiated. The AGN-201 (Fig. 1) was designed to operate at 0.1 watt and, with the exception of the control console, was a unit package, including the shielding. In order to furnish medically useful isotopes, a minimum requirement of 3 and perhaps 5 watts of power was thought desirable. This higher power level, when authorized by the A.E.C., required some modifications of the 0.1-watt model. These modifications, chiefly reflected in the levels of instrumentation and increase in bulk shielding, were readily accomplished by the manufacturers. The reactor, for which a twenty-year license has been issued to the U. S. Naval Hospital (Bethesda), is an integrated part of the isotope branch of the Radiology Service of the hospital. In addition to x-ray therapy, an extensive radioisotope service for both diagnosis and treatment is maintained. A nuclear casualty evaluation facility is under consideration. The reactor is expected to augment all of these. The reactor is installed in a 21 × 21 × 21-foot air-conditioned concrete “block-house” type of building. With the console, it occupies most of the square footage of the building. “Cat-walks,” graphite column, and building services occupy the cubic footage. To utilize the reactor products, a radiochemical laboratory is located in the adjacent building with access to the reactor room through an interlocking door. Conventional chemical laboratories and radionuclide counting and assay rooms are also in the adjoining building, as is the office and health physics section. The characteristics of the reactor, reported by Biehl et al. (1) are as shown below. It must be noted, however, that Biehl's paper dealt with the 0.1-watt reactor and that power and flux levels have been adjusted for the 5-watt level at which we are licensed to operate. The reactor with these characteristics (Fig. 2) is a unit fabricated with three concentrically located waterproof metal tanks. The core tank is the inner tank of aluminum, containing the uranium core or fuel and is small and located in the reactor center. The larger tank containing the reflector and gamma shield, entirely encapsulates the core tank; this is known as the reactor tank.