A STUDY OF THE NUCLEAR AND PHYSICAL PROPERTIES OF THE ORNL GRAPHITE REACTOR SHIELD

A study of the nuclear and physical properties of the concrete shield of the ORNL Graphite Reactor was performed both to determine the radiation attenuation characteristics of the shield and to discover any effects of a long- term (12-year) irradiation. In the experiment neutron and gamma radiation measurements were made in a 4 5/8-in.-diam. hole in the shield as the hole was drilled in increments of 1 or 1/2 ft. Concrete plugs were always placed behind the detectors to simulate a homegeneous shield. The average relaxation length for gamma rays in the barytes-haydite concrete, of which most of the shield is made, was found to be approximately 13.8 cm, increasing gradually from 13.0 cm at a shield thickness of 2 ft to 14.8 cm at a shield thickness of 5 ft. The fast- neutron relaxation length in the barytes-haydite concrete varied from 10.0 cm to 10.8 cm, the avernge being approximately 10.2 cm. Measurements of the streaming of radiation through the hole were also made. The concrete dust collected from the drillings was used to determine the chemical composition, water content, density, compressive strength and raalicactivity of the shield at the various depths. The temperatare gradient through tbe shield wasmore » also measured. This investigation showed that the chemical properties and density of the shield have not changed appreciably since a simikar investigation in 1948, but its compressive strength is lower (~ 40% near the reflector-shield interface). (auth)« less